JPH1181994A - Diagnosing device for catalyst for purifying exhaust gas from internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure in a short time the condition of a catalyst for purifying exhaust gas. SOLUTION: A supply volume of trace substance (HC) is calculated in accordance with an engine operating condition upon catalyst diagnosing terms being satisfied, and the trace substance (HC) is fed in a pulse-like manner to ternary catalyst 23 form an HC supply nozzle 15 upstream of the ternary catalyst 23. After initiation of supply of the trace substance, a density of the trace substance in exhaust gas downstream of NOx catalyst 13, is detected by a NOx density sensor 19, and an HC adsorbing quantity (poisoning degree) of the NOx catalyst 13 is estimated from a relationship between the supply volume of the trance substance and the density of the trace substance. After diagnosis of the catalyst, the supply volume of HC as a reductant fed to the NOx catalyst 13 is compensated and obtained in accordance with an HC adsorbing quantity of the NOx catalyst 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device for an exhaust gas purifying catalyst of an internal combustion engine for diagnosing the state of the exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art As exhaust gas purifying catalysts for automobiles, three-way catalysts used for gasoline engine vehicles and NOx catalysts used for diesel engine vehicles are known. The three-way catalyst is used for reducing gas components (C
The exhaust gas is purified by causing an oxidation-reduction reaction between the oxidizing gas components (O ₂ , NOx) and the oxidizing gas components (O ₂ , NOx). Further, in a diesel engine using a NOx catalyst, the amount of HC necessary for purifying NOx in the exhaust gas is not contained in the exhaust gas.
Is added to reduce and purify NOx in exhaust gas with HC.

[0003] The exhaust gas purification performance of these catalysts may be reduced depending on the actual use conditions. Specifically, in the three-way catalyst, the active metal coated on the surface gradually agglomerates due to the heat of the exhaust gas to reduce the surface area, thereby causing catalyst deterioration. Further, in the NOx catalyst, the NOx purification performance is reduced because HC is gradually adsorbed on the catalyst surface and the surface area is reduced. Conventionally, several methods have been implemented or proposed in order to grasp the state of deterioration of the catalyst.

For example, in Japanese Patent Application Laid-Open No. 9-4437,
A method for estimating the amount of HC adsorbed on the catalyst by estimating the amount of HC adsorbed and desorbed from the time of engine start to grasp the amount of HC adsorbed on the catalyst and tracking these values has been proposed. I have.

[0005]

However, since the technique disclosed in the above publication is an indirect method of integrating and estimating past adsorption and desorption information, errors accumulate in the middle of the estimation and the estimation is performed. The amount of adsorption and the actual amount of adsorption may be significantly different.

Incidentally, there is a method in which the catalyst is removed from an automobile, and all or a part of the catalyst is used as a sample, and various physical or chemical analysis techniques are used. Among them, Kodansha Scientific Catalyst Course (Catalysis Society of Japan) Basic Edition 3 “Characterization of solid catalyst” published by Kodansha
On page 160, there is a method called the pulse method. In this method, the operation of supplying the reducing gas to the catalyst in a pulsed manner is repeated until the amount of adsorption of the catalyst becomes saturated, and the amount of adsorption of the catalyst is measured.

However, in order to use this method, it is necessary to remove the catalyst from the automobile, so that it is impossible to measure the amount of catalyst adsorbed during running. In addition, since the gas supply is repeated until the catalyst is in a saturated adsorption state, not only does it take a long time to measure, but also when the catalyst becomes in a saturated adsorption state,
It is not easy to recover the catalyst.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and therefore has as its object to directly and accurately measure the state of a catalyst during a vehicle operation in a short time and to purify the catalyst by measurement. It is an object of the present invention to provide an apparatus for diagnosing an exhaust gas purifying catalyst of an internal combustion engine, which can avoid a decrease in performance.

[0009]

In order to achieve the above object, a diagnostic device for an exhaust gas purifying catalyst for an internal combustion engine according to the present invention is provided. After the trace substance is supplied and the concentration of the trace substance passing through the catalyst is detected by the trace substance concentration detection means, the relationship between the trace substance supply amount by the trace substance supply means and the detection value of the trace substance concentration detection means Then, the state of the catalyst is diagnosed by the catalyst diagnosis means (claim 1). That is, as the purification ability of the catalyst increases, the amount of the trace substance adsorbed or reacted inside the catalyst increases, and the concentration of the trace substance passing through the catalyst decreases. From this relationship, the state of the catalyst can be directly and accurately diagnosed in a short time from the relationship between the supply amount of the trace substance and the concentration of the trace substance passing through the catalyst. In addition, the diagnosis of the catalyst state can be performed during the operation of the vehicle while the catalyst is mounted on the vehicle, and it is not necessary to bring the catalyst into a saturated adsorption state, so that a reduction in the purification performance of the catalyst can be avoided. .

When the present invention is applied to a diesel engine, a NOx catalyst is used as a catalyst, and a hydrocarbon (HC) is used as a trace substance.
The HC adsorption amount of the Ox catalyst may be estimated. That is, when a large amount of HC is adsorbed on the NOx catalyst, the H
The NOx catalyst is poisoned by C and becomes difficult to recover to the original state, and the NOx purification performance is significantly reduced.
Therefore, the poisoning state of the NOx catalyst and the NOx purification performance can be evaluated by estimating the hydrocarbon adsorption amount of the NOx catalyst.

In this case, during normal operation other than the time of catalyst diagnosis, NOx is supplied from the trace material supply means.
HC may be supplied to the catalyst as a NOx reducing agent. By doing so, the trace substance supply means can be
It can also be used as HC supply means for supplying HC to the NOx catalyst, and the configuration can be simplified.

On the other hand, when the present invention is applied to a gasoline engine, carbon monoxide (CO) is used as a trace substance and the amount of adsorbed carbon monoxide on the catalyst is estimated to determine the activity of the catalyst. The surface area of the metal may be estimated. In other words, the active metal coated on the surface of the catalyst, such as platinum, rhodium, palladium and other noble metal surfaces, has the property that CO is adsorbed equivalently,
The deterioration of the catalyst occurs when the active metal gradually aggregates due to the heat of the exhaust gas and the surface area decreases. Therefore, by estimating the amount of adsorbed carbon monoxide on the catalyst, the surface area of the active metal of the catalyst can be estimated, and the degree of deterioration of the catalyst can be evaluated from the surface area of the active metal.

According to a fifth aspect of the present invention, the diagnostic condition determining means for determining the catalyst diagnostic condition includes: when detecting that the internal combustion engine is in a steady operation state from the operation state of the internal combustion engine;
An operation command signal may be output to the trace material supply means assuming that the catalyst diagnosis condition has been satisfied. In this manner, when the internal combustion engine is in a steady operation state, the diagnosis of the catalyst is executed, so that a stable diagnosis of the catalyst can be performed. However, according to the present invention, as the catalyst diagnosis conditions, besides that the internal combustion engine is in a steady operation state, for example, that the temperature of the catalyst has risen to the activation temperature and that the operation region is within a predetermined range (when the engine speed is It may be appropriately added that the temperature is within a predetermined range, the intake pipe pressure is within a predetermined range, and that the cooling water temperature is equal to or higher than a predetermined temperature.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment (1)] FIG. 1 shows an embodiment (1) in which the present invention is applied to an exhaust gas purification system for a diesel engine.
This will be described with reference to FIGS. First, the configuration of the entire system will be described with reference to FIG. A NOx catalyst 13 that reduces and purifies NOx in exhaust gas is provided in the exhaust pipe 12 (exhaust gas passage) of a diesel engine 11 that is an internal combustion engine. The NOx catalyst 13 has platinum, which is an active metal, supported on a kind of porous zeolite. In the NOx catalyst 13, NOx in exhaust gas reacts with hydrocarbon (HC) as a reducing agent. Be purified. An exhaust gas temperature sensor 14 that detects the temperature of exhaust gas flowing into the NOx catalyst 13 is installed at the inlet of the NOx catalyst 13 to evaluate the catalyst temperature. Note that the exhaust gas temperature sensor 14 may be installed at the outlet of the NOx catalyst 13, and in this case, the catalyst temperature can be evaluated from the temperature of the exhaust gas flowing out of the NOx catalyst 13.

The NOx catalyst 13 in the exhaust pipe 12
Upstream of the HC supply nozzle 15 that supplies fuel such as light oil as a trace substance to the NOx catalyst 13 at the time of catalyst diagnosis.
(Trace substance supply means) is provided. This HC
At the time of normal operation other than the time of catalyst diagnosis, the supply nozzle 15
It is also used as HC supply means for supplying HC (fuel) as a NOx reducing agent to the NOx catalyst 13. Fuel pumped by an injection pump 16 from a fuel tank (not shown) is supplied to the HC supply nozzle 15. The amount of HC injected from the HC supply nozzle 15 is determined by the engine control circuit 17.
Is controlled by

On the other hand, at the outlet of the NOx catalyst 13, NO
x Sampling pipe 18 for detecting HC concentration (concentration of trace substance) in exhaust gas flowing out of catalyst 13
Is connected to the tip of the sampling pipe 18.
A concentration sensor 19 (trace substance concentration detecting means) is provided. The output signal of the HC concentration sensor 19 is input to the engine control circuit 17.

The engine control circuit 17 is mainly composed of a microcomputer, and supplies fuel to each cylinder of the diesel engine 11 based on the output of various sensors for detecting engine operating conditions, such as an engine speed sensor (not shown). Control the injection volume. The engine control circuit 17 executes the catalyst diagnosis / control program shown in FIG. 2 stored in a ROM (storage medium), so that the NOx catalyst 13
Is estimated, and the HC supply amount is controlled so that the HC adsorption amount of the NOx catalyst 13 does not exceed a preset poisoning limit value.

Hereinafter, the processing contents of the catalyst diagnosis / control program of FIG. 2 will be described. When the processing of this program is started, first, in step 101, in order to detect an engine operating condition, the engine speed Ne, the accelerator opening Ac, N
The exhaust gas temperature Tex at the inlet of the Ox catalyst 13 is read. Thereafter, in step 102, it is determined whether the catalyst diagnosis condition is satisfied. Here, the catalyst diagnosis condition is that the engine operation state does not change, for example, in the past 2 seconds or more (it is a steady operation state). If this condition is not satisfied, the catalyst diagnosis processing of steps 103 to 107 is not executed, The process proceeds to step 108 described later.

On the other hand, when the catalyst diagnosis condition is satisfied (at the time of steady operation), the process proceeds from step 102 to step 103, where the trace substance (HC) is determined according to the engine operating state.
Is calculated. This calculation uses, for example, a trace substance supply amount map (not shown) preset using the engine speed Ne as a parameter.

Here, the supply amount of the trace substance is determined based on the following criteria. The upper limit of the supply amount of the trace substance is 50% of the HC saturated adsorption amount (poisoning limit value) of the NOx catalyst 13, and preferably 10% or less. This is for minimizing the increase in the amount of HC adsorbed by the NOx catalyst 13. In order for the concentration of the trace substance in the exhaust gas flowing out of the NOx catalyst 13 to be accurately detected by the HC concentration sensor 19, the concentration of the trace substance should be at least one digit higher than the detection accuracy of the HC concentration sensor 19. To However, in order to keep the deterioration of the exhaust emission below the allowable range, the concentration of the trace substance is set to a concentration of 10000 ppm or less. The supply amount of the trace material is changed according to the engine speed, and the emission amount discharged per unit time is, for example, 5%.
% Is desirably the upper limit.

An example satisfying the above conditions is shown in FIGS. FIG. 3 shows that the trace substance concentration is set to be lower as the trace substance supply time becomes longer. In consideration of the detection accuracy of the HC concentration sensor 19, the upper limit of the trace substance supply time is desirably 1 sec. On the other hand, FIG. 4 shows that the trace substance supply speed (mol / sec) can be set higher as the engine speed increases. This is because the exhaust gas amount increases as the engine speed increases.

After calculating the supply amount (supply time, supply speed) of the trace substance based on the above criteria, step 104
Then, the HC supply nozzle 15 is driven to trace the trace substance (HC) in a pulsed manner as shown in FIG.
To supply. Then, in the next step 105, the concentration of the trace substance in the exhaust gas downstream of the NOx catalyst 13 after the start of the supply of the trace substance is detected by the HC concentration sensor 19. An example of the change in the trace substance concentration at this time is shown in FIG. The detection time of the trace substance concentration is set to be longer than the supply time of the trace substance, and is set such that the change in the trace substance concentration after the end of the supply of the trace substance can be detected to the end.

After the end of the detection of the trace substance concentration, the routine proceeds to step 106, where it is determined whether or not the engine speed has changed during the detection. If the engine speed has changed, the exhaust gas amount changes and the NOx catalyst Since the poisoning state (HC adsorption amount) of No. 13 cannot be accurately estimated, the process proceeds to step 108 without estimating the poisoning state.

On the other hand, during the detection of the trace substance concentration,
If the engine speed has not changed, step 1
In step 07, the amount of HC adsorbed by the NOx catalyst 13 (poisoned state) is determined from the relationship between the trace substance supply amount and the trace substance concentration.
Is estimated. For this estimation, for example, the detected value of the trace substance concentration is integrated, and based on the integrated value and the engine speed (the amount of exhaust gas), the amount of the trace substance that has passed through the NOx catalyst 13 is estimated, and the amount of the trace substance is estimated. The HC adsorption amount of the NOx catalyst 13 is estimated from the ratio of the slip amount to the supply amount. In other words, it is estimated that the larger the ratio of the amount of trace material that passes through, the larger the amount of HC adsorbed by the NOx catalyst 13 (the poisoning is advanced). This step 10
The processing of 7 plays a role as catalyst diagnosis means in the claims.

Thereafter, the routine proceeds to step 108, where HC supplied as a reducing agent to the NOx catalyst 13 after the catalyst diagnosis is completed.
Is calculated as follows. First, a basic HC supply amount is calculated from a map or the like in accordance with the exhaust gas temperature Tex (catalyst temperature) and the engine speed Ne, and the basic HC supply amount is calculated based on the HC of the NOx catalyst 13 estimated in step 107.
The HC supply amount is obtained by making a correction according to the adsorption amount. As a result, as the HC adsorption amount of the NOx catalyst 13 increases, the HC
The supply amount is set small to prevent the HC adsorption amount of the NOx catalyst 13 from exceeding a poisoning limit value that cannot be recovered.
If “No” in step 102 or “Yes” in step 106, the current HC adsorption amount is not estimated. In these cases, the latest HC adsorption amount estimated in the previous process is used. Using the amount, the basic HC
The supply amount is corrected to determine the HC supply amount.

In the embodiment (1) described above, the trace substance is supplied to the NOx catalyst 13 when the catalyst diagnosis condition is satisfied during the operation of the vehicle, and the concentration of the trace substance passing through the NOx catalyst 13 is detected. The NOx catalyst 1 was determined based on the relationship between the supply amount of the trace substance and the detected value of the trace substance concentration.
Since the HC adsorption amount (poisoned state) of the NOx catalyst 13 is estimated in comparison with the conventional case where the HC adsorption amount of the catalyst is indirectly estimated from the past operation state as in the conventional case. The amount can be directly and accurately estimated in a short time. In addition, the HC adsorption amount can be estimated while the vehicle is operating with the NOx catalyst 13 mounted on the vehicle, and it is not necessary to bring the NOx catalyst 13 into a saturated adsorption state. A reduction in purification performance can be avoided.

In the above embodiment (1), the catalyst diagnosis process of step 103 and later is executed during the steady operation as the catalyst diagnosis condition for the steady operation. As a diagnosis condition, the catalyst diagnosis processing after step 103 may be executed during the idling operation. Of course, it goes without saying that other conditions such as exhaust gas temperature (catalyst temperature) may be added as catalyst diagnosis conditions.

In the embodiment (1), the HC supply nozzle 15 is provided in the exhaust pipe 12 as a means (trace substance supply means) for supplying HC (trace substance) to the NOx catalyst 13. Alternatively, a small amount of fuel may be injected by post-injection from the fuel injection nozzle and supplied to the NOx catalyst 13 in an expansion stroke after the fuel is injected from the fuel injection nozzle to the engine. Alternatively, the HC supply nozzle 15 is used only when the trace material is supplied, and NO
The supply of the reducing agent to the x catalyst 13 may be performed by post-injection.

In the above embodiment (1), fuel (light oil) is used as the HC (trace substance) supplied to the NOx catalyst 13. However, liquid HC such as kerosene or gaseous HC such as propane is used. It may be used.

[Embodiment (2)] An embodiment (2) in which the present invention is applied to an exhaust gas purifying system for a gasoline engine will be described below with reference to FIGS. First, FIG.
The configuration of the entire system will be described based on the above. Exhaust pipe 22 (exhaust gas passage) of gasoline engine 21 which is an internal combustion engine
Is provided with a three-way catalyst 23 for simultaneously purifying CO, HC and NOx in the exhaust gas. On the upstream side of the three-way catalyst 23 in the exhaust pipe 22, a CO supply nozzle 24 (trace material supply means) for supplying CO (carbon monoxide) as a trace material to the three-way catalyst 23 at the time of catalyst diagnosis is provided. I have. The CO supply nozzle 24 is supplied with CO from a CO storage tank 25.

On the other hand, a sampling pipe 26 for detecting the CO concentration (concentration of trace substance) in the exhaust gas flowing out of the three-way catalyst 23 is connected to the outlet of the three-way catalyst 23. A CO concentration sensor 27 (trace substance concentration detecting means) is provided at the tip. The output signal of the CO concentration sensor 27 is input to the engine control circuit 28.

The engine control circuit 28 is mainly composed of a microcomputer, and performs fuel injection control and ignition timing control based on outputs of various sensors for detecting engine operating conditions, such as an engine speed sensor (not shown). .

The engine control circuit 28 also functions as catalyst diagnosis means. When the catalyst diagnosis conditions are satisfied (for example, during steady operation or idling operation), the engine control circuit 28 performs the above-described steps 103 to 105 in FIG. The same processing is performed. That is, after the supply amount of the trace substance (CO) is calculated according to the engine operating state, the CO supply nozzle 24 is driven to supply the trace substance (CO) to the three-way catalyst 23 in a pulse form as shown in FIG. At the same time, after starting the supply of the trace substance, the trace substance concentration in the exhaust gas downstream of the three-way catalyst 23 is detected by the CO concentration sensor 27. An example of the change in the trace substance concentration at this time is shown in FIG. The detection time of the trace substance concentration is set to be longer than the supply time of the trace substance, and is set such that the change in the trace substance concentration after the end of the supply of the trace substance can be detected to the end.

After the detection of the trace substance concentration is completed, the CO adsorption amount of the three-way catalyst 23 is estimated from the relationship between the trace substance supply amount and the trace substance concentration, and the surface area (degree of deterioration) of the active metal of the three-way catalyst 23 is determined. Is estimated. For this estimation, for example, the detected value of the trace substance concentration is integrated, and the three-way catalyst 2 is integrated based on the integrated value and the engine speed (exhaust gas amount).
The amount of trace material passing through 3 is estimated, and the amount of CO adsorbed on the three-way catalyst 23 is estimated from the ratio of the amount of trace material supplied to the amount of trace material supplied.

By doing so, the gasoline engine 21
In the exhaust gas purification system described above, the surface area (degree of deterioration) of the active metal of the three-way catalyst 23 can be directly and accurately estimated in a short time.

As a catalyst for purifying exhaust gas, an oxidation catalyst may be used instead of the three-way catalyst.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire system showing an embodiment (1) in which the present invention is applied to an exhaust gas purification system for a diesel engine.

FIG. 2 is a flowchart showing a processing flow of a catalyst diagnosis / control program.

FIG. 3 is a diagram showing a relationship between a trace substance (HC) supply time and a trace substance concentration in exhaust gas.

FIG. 4 is a diagram showing a relationship between a trace material (HC) supply speed and an engine speed;

FIG. 5 is a timing chart showing an example of a trace substance (HC) supply operation;

FIG. 6 is a timing chart showing an example of a change in trace substance concentration when a trace substance (HC) is supplied.

FIG. 7 is a schematic configuration diagram of an entire system showing an embodiment (2) in which the present invention is applied to an exhaust gas purification system for a gasoline engine.

FIG. 8 is a timing chart showing an example of a trace substance (CO) supply operation.

FIG. 9 is a timing chart showing an example of a change in trace substance concentration when a trace substance (CO) is supplied.

[Explanation of symbols]

11: diesel engine (internal combustion engine), 12: exhaust pipe (exhaust gas passage), 13: NOx catalyst, 15: HC supply nozzle (trace substance supply means), 17: engine control circuit (catalyst diagnosis means), 19: HC concentration Sensor (trace substance concentration detecting means), 21: gasoline engine (internal combustion engine), 22: exhaust pipe (exhaust gas passage), 23: three-way catalyst,
24 ... CO supply nozzle (trace substance supply means), 25
... CO storage tank, 27 ... CO concentration sensor (trace substance concentration detection means), 28 ... engine control circuit (catalyst diagnosis means).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naohisa Oyama 14 Iwatani, Shimowasumi-cho, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Inside the corporation

Claims (5)

[Claims] An apparatus for diagnosing an exhaust gas purifying catalyst for an internal combustion engine, which diagnoses a state of an exhaust gas purifying catalyst provided in an exhaust gas passage of the internal combustion engine, wherein the catalyst is diagnosed when a catalyst diagnosing condition is satisfied during vehicle operation. A trace substance supply means for supplying a reducing or oxidizing trace substance from an upstream side, and a trace substance concentration detecting means provided at a downstream side of the catalyst and detecting a concentration of the trace substance passing through the catalyst. Exhaust gas of an internal combustion engine, comprising: catalyst diagnosing means for diagnosing a state of the catalyst from a relationship between a trace substance supply amount by the trace substance supply means and a detection value of the trace substance concentration detecting means. Diagnosis device for purification catalyst. 2. The internal combustion engine is a diesel engine, the catalyst is a NOx catalyst for reducing and purifying nitrogen oxides in exhaust gas, and the trace material supply means is configured to convert hydrocarbons as the trace material into the NOx catalyst. The catalyst diagnosing device for an exhaust gas purifying catalyst for an internal combustion engine according to claim 1, wherein the catalyst diagnosing means includes means for estimating a hydrocarbon adsorption amount of the NOx catalyst. 3. The internal combustion engine according to claim 2, wherein the trace material supply unit supplies a hydrocarbon as a nitrogen oxide reducing agent to the NOx catalyst during a normal operation other than a catalyst diagnosis. Diagnostic device for exhaust gas purification catalyst. 4. The internal combustion engine is a gasoline engine, the trace substance supply means supplies carbon monoxide as the trace substance to the catalyst, and the catalyst diagnosis means determines a carbon monoxide adsorption amount of the catalyst. The diagnostic device for an exhaust gas purifying catalyst for an internal combustion engine according to claim 1, further comprising a unit for estimating the surface area of the active metal of the catalyst. 5. A diagnostic condition for outputting an operation command signal to said trace material supply means on the assumption that said catalyst diagnostic condition has been satisfied when detecting that said internal combustion engine is in a steady operation state from an operation state of said internal combustion engine. The diagnostic device for an exhaust gas purifying catalyst for an internal combustion engine according to any one of claims 1 to 4, further comprising a determination unit.