JP2002256856A - Device for detecting deterioration of exhaust emission control catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the deterioration condition of an exhaust emission control catalyst with a high degree of accuracy regardless of the type thereof in a deterioration detecting device therefor. SOLUTION: An O2 sensor 27 is installed on an exhaust pipe 21 at the downstream side of a three-way conversion catalyst 22, and a deterioration judgment value is preset by storing the reference output value of the O2 sensor 27 in the normal state of the three-way conversion catalyst 22 when an exhaust gas is in a reduction atmosphere. When the sensor output value of the O2 sensor 27 is more than the above judgment value, it is judged that the three-way conversion catalyst 22 deteriorates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting deterioration of an exhaust gas purifying catalyst provided in an exhaust system of an internal combustion engine and having at least an oxidizing function.

[0002]

2. Description of the Related Art Recently, in addition to a three-way catalyst and an oxidation catalyst having a noble metal such as platinum (Pt) as an exhaust purification catalyst having an oxidation function, NOx in exhaust gas is stored or adsorbed during operation at a lean air-fuel ratio. (Hereinafter simply referred to as occlusion), and a storage-type NOx catalyst (NO) for reducing and purifying NOx occluded during operation at a stoichiometric air-fuel ratio or a rich air-fuel ratio.
(A catalyst having an oxidizing function because it has the property of oxidizing NO to NO ₂ and occluding it) has been put to practical use. If such a catalyst is deteriorated and its exhaust purification ability is reduced, it is necessary to make the driver aware by turning on the engine check lamp on the instrument panel, etc., and to take measures such as replacing the catalyst at a maintenance shop or the like. is there.

As a technique for detecting such a state of deterioration of the exhaust purification catalyst, for example, there is a technique disclosed in Japanese Patent Application Laid-Open No. Hei 3-74540. The "air-fuel ratio control apparatus for an internal combustion engine" disclosed in Japanese is, O ₂ provided on the upstream side of the catalyst
Together to correct the fuel supply amount for feedback controlling the air-fuel ratio to the stoichiometric air-fuel ratio based on the output of the sensor, monitoring the output of the linear O ₂ sensor disposed downstream of the catalyst, given the output from the stoichiometric air-fuel ratio If the difference is not less than the value, the deterioration of the catalyst is determined.

[0004]

However, in this conventional "air-fuel ratio control device for an internal combustion engine", even if the oxygen concentration on the upstream side of the catalyst is changed around the stoichiometric air-fuel ratio by feedback control, the catalyst operates normally. In this case, the oxygen concentration on the downstream side does not fluctuate greatly, but when the catalyst is deteriorated, the oxygen concentration on the downstream side of the catalyst fluctuates greatly following the change in the oxygen concentration on the upstream side. This phenomenon is due to the oxygen storage function of the catalyst.In a state where the sufficient oxygen storage function is maintained, oxygen is adsorbed in an oxidizing atmosphere and released in a reducing atmosphere. Oxygen storage function causes little change in downstream oxygen concentration.However, if the catalyst deteriorates and the oxygen storage function decreases, the oxygen adsorption and release reactions decrease. Fluctuates greatly.

That is, in this prior art, the deterioration of the catalyst is indirectly determined by detecting the deterioration of the oxygen storage function of the catalyst mainly due to the deterioration of additives such as ceria. However, this oxygen storage function only assists the purifying action by the catalyst, so that there is a problem that it is not possible to accurately judge the decrease of the purifying reaction by the catalyst.

[0006] Some of the various catalysts hardly have the oxygen storage function, and therefore, it is impossible to judge the deterioration of the catalyst. For example, in a three-way catalyst disposed in an exhaust passage close to an engine, in order to prevent CO as a reducing agent from being oxidized when a storage-type NOx catalyst provided downstream thereof is reduced. In addition, the content of additives such as ceria is suppressed or removed so that the oxygen storage function is reduced. Therefore, there is a problem that an appropriate deterioration determination cannot be performed for such a three-way catalyst having no oxygen storage function.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a device for detecting deterioration of an exhaust purification catalyst capable of detecting a deterioration state with high accuracy regardless of the type of catalyst.

[0008]

In order to achieve the above object, in the exhaust gas purifying catalyst deterioration detecting device according to the present invention, an exhaust gas purifying catalyst having at least an oxidizing ability is provided in an exhaust passage of an internal combustion engine. The storage means stores the reference output of the oxygen concentration sensor when the exhaust gas purifying catalyst is normal in the predetermined operation state, and the deterioration determination means stores the output of the oxygen concentration sensor and the reference output in the predetermined operation state. Are compared to determine the deterioration of the exhaust purification catalyst.

Therefore, in the oxygen concentration sensor, in general, a phenomenon occurs in which the sensor output characteristic shifts to the low oxygen concentration side with respect to the actual oxygen concentration in the presence of hydrogen. Since an exhaust purification catalyst having at least an oxidizing ability is provided, if the exhaust purification catalyst is normal, the oxygen concentration sensor supplies an oxidation target component, for example,
Since no hydrogen arrives, no shift phenomenon occurs in the sensor output characteristics. On the other hand, when the oxidation ability of the exhaust purification catalyst is reduced, many components to be oxidized reach the oxygen concentration sensor, and this shift phenomenon occurs. Therefore, the reference output of the oxygen concentration sensor when the exhaust gas purification catalyst is normal in the predetermined operation state is stored, and when the output of the oxygen concentration sensor is compared with this reference output in the predetermined operation state, the exhaust gas purification catalyst is deteriorated. Can be determined. This makes it possible to accurately detect a decrease in the oxidizing ability of the catalyst, which is directly related to the exhaust purification ability of the exhaust purification catalyst, and to accurately determine the deterioration of the catalyst. In addition, accurate determination of deterioration of the exhaust gas purification catalyst is possible even with a single oxygen concentration sensor, and the configuration for determining deterioration can be simplified. Further, since deterioration is not detected by detecting a decrease in the oxygen storage capacity of the exhaust purification catalyst, the deterioration can be effectively detected even for an exhaust purification catalyst having almost no oxygen storage capacity.

In a preferred embodiment, the predetermined operating condition is that the deterioration determination is performed when the exhaust gas flowing into the exhaust purification catalyst is in a stoichiometric or reducing atmosphere, for example, in a specific operating condition in which the concentration of hydrogen in the exhaust gas is high. Thus, catalyst deterioration can be accurately determined.

[0011]

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

FIG. 1 is a schematic configuration of an exhaust gas purifying apparatus for an internal combustion engine to which an exhaust gas purifying catalyst deterioration detecting apparatus according to an embodiment of the present invention is applied, FIG. 2 is a sectional view of a main part of an O ₂ sensor, and FIG. FIG. 4 is a flowchart showing deterioration detection control by the exhaust gas purification catalyst deterioration detection device according to the embodiment, and FIG. 4 is a graph showing the output voltage of the O ₂ sensor with respect to the air-fuel ratio.

The internal combustion engine (hereinafter referred to as an engine) of the present embodiment is, for example, in a fuel injection mode (operation mode).
The in-cylinder injection type spark ignition type in-line four-cylinder gasoline engine capable of performing fuel injection in the intake stroke (intake stroke injection mode) or fuel injection in the compression stroke (compression stroke injection mode). The in-cylinder injection type engine 11 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). Operation) can be realized, and in particular, in the compression stroke injection mode, operation at an ultra lean air-fuel ratio is possible.

In the present embodiment, as shown in FIG.
An electromagnetic fuel injection valve 14 is attached to a cylinder head 12 of the engine 11 together with an ignition plug 13 for each cylinder, and the fuel injection valve 14 enables direct injection of fuel into a combustion chamber 15. . This fuel injection valve 14
Is connected to a fuel supply device (fuel pump) via a fuel pipe (not shown). The fuel in the fuel tank is supplied at a high fuel pressure, and the fuel is directed from the fuel injection valve 14 into the combustion chamber 15. Inject at a predetermined fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the fuel pump and the valve opening time (fuel injection time) of the fuel injection valve 14.

An intake port is formed in the cylinder head 12 in a substantially upright direction for each cylinder, and one end of an intake manifold 16 is connected to communicate with each intake port. A drive-by-wire (DBW) type electric throttle valve 17 is connected to the other end of the intake manifold 16, and an accelerator pedal (not shown) is provided with an accelerator opening sensor for detecting the accelerator opening θth. Also, the cylinder head 12 has
An exhaust port is formed in a substantially horizontal direction for each cylinder,
Exhaust manifold 1 so that it communicates with each exhaust port
9 are connected to each other.

The engine 11 is provided with a crank angle sensor 20 for detecting a crank angle, and the crank angle sensor 20 can detect an engine rotation speed Ne. The above-described in-cylinder injection engine 1
1 is already known, and the details of its configuration will not be described here.

The exhaust manifold 1 of the engine 11
An exhaust pipe (exhaust passage) 21 is connected to 9, and a muffler (not shown) is connected to the exhaust pipe 21 via a small three-way catalyst 22 and an exhaust purification catalyst device 23 close to the engine 11. . In the portion of the exhaust pipe 21 between the proximity three-way catalyst 22 and the exhaust purification catalyst device 23, the exhaust gas temperature is located immediately upstream of the exhaust purification catalyst device 23, that is, immediately upstream of the storage NOx catalyst 25 described later. Is provided.

The close three-way catalyst 22 is heated by the exhaust gas at the time of cold start of the engine 11 to be activated early, and when the exhaust air-fuel ratio is close to the stoichiometric air-fuel ratio, harmful substances (HC) , CO, NOx), and platinum (Pt) and rhodium (R) as noble metals.
h) and the like. The proximity three-way catalyst 22 is connected to the storage NOx catalyst 2 provided on the downstream side.
In order to prevent CO as a reducing agent from being oxidized during the emission reduction of 5, the content of additives such as ceria is suppressed so that the oxygen storage function is reduced.

The exhaust gas purifying catalyst device 23 has a NOx reduction function of storing NOx in exhaust gas when the exhaust air-fuel ratio is lean, and when the exhaust air-fuel ratio is near the stoichiometric air-fuel ratio. In order to have a three-way function of purifying harmful substances (HC, CO, NOx), the three-way catalyst 26 has two catalysts, that is, a storage type NOx catalyst 25 and a three-way catalyst 26. Is disposed downstream of the storage NOx catalyst 25. This three-way catalyst 26 is a storage type N
When the stored NOx is released from the Ox catalyst 25, the storage NOx catalyst 25 itself also serves to reduce NOx that could not be reduced.

The exhaust gas purifying catalyst device 23 has a function of a three-way catalyst in which the storage NOx catalyst 25 reduces NOx and oxidizes HC and CO (hereinafter, referred to as a three-way function).
If the storage NOx catalyst 25
Alternatively, the storage NOx catalyst and the three-way catalyst may be integrated. The storage type NOx catalyst 25 has a reduction function of temporarily storing NOx in an oxidizing atmosphere (NOx reduction function) and releasing NOx in a reducing atmosphere where CO is mainly present to reduce it to N ₂ (nitrogen) or the like. It is. Specifically, the storage NOx catalyst 25 is configured as a catalyst having platinum (Pt), palladium (Pd), or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage material. Has been adopted.

An O ₂ sensor (oxygen concentration sensor) 27 is provided downstream of the proximity three-way catalyst 22. The O ₂ sensor 27 detects the oxygen concentration in the exhaust gas, and is configured to output a small voltage value when the amount of oxygen is large. In other words, the output characteristics of the O ₂ sensor 27 are such that the oxygen is almost not present,
HC, greatly rich air-fuel ratio atmosphere H ₂ or the like there are many, toggle characteristics stoichiometric atmosphere, and is set smaller than a lean air-fuel ratio atmosphere of the oxygen-excess state. The O ₂ sensor 27 detects the oxygen concentration of the exhaust gas discharged from the engine 11 and is used when performing feedback control of the air-fuel ratio to the stoichiometric air-fuel ratio.

Further, an input / output device and a storage device (ROM, R
AM, nonvolatile RAM, etc.), central processing unit (CPU),
An ECU (Electronic Control Unit) 28 having a timer counter and the like is provided, and the ECU 28 performs comprehensive control of the exhaust gas purification apparatus of the present embodiment including the engine 11. That is, on the input side of the ECU 28,
Various sensors such as the high-temperature sensor 24 and the O ₂ sensor 27 described above are connected, and detection information from these sensors is input. On the other hand, the output side of the ECU 28 is connected to the above-described ignition plug 13 and the fuel injection valve 14 via an ignition coil.
For example, the optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information from the various sensors are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 14 at an appropriate timing, and ignition is performed by the spark plug 13 at an appropriate timing.

Actually, the ECU 28 calculates the target in-cylinder pressure corresponding to the engine load, that is, the target average pressure, based on the accelerator opening information θth from the accelerator opening sensor (not shown) and the engine speed information Ne from the crank angle sensor 20. The effective pressure Pe is determined, and the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine speed information Ne. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both low, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases, or When the rotation speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected during the intake stroke.

The target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A / F
Is determined based on Further, from the exhaust gas temperature information detected by the high temperature sensor 24, the catalyst temperature Tcat is estimated. Specifically, the high-temperature sensor 24 and the storage NOx catalyst 25
In order to correct an error caused by being arranged at least a little apart from each other, a temperature difference map is set in advance by an experiment or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne. The catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Therefore, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment thus configured, the exhaust gas purifying catalyst device 23 is used.
In the NOx storage catalyst 25, NOx in the exhaust gas is stored as nitrate in an atmosphere with an excessively high oxygen concentration as in the super-lean combustion operation in the lean mode to purify the exhaust gas. On the other hand, in an atmosphere with a reduced oxygen concentration, the storage type N
The nitrate stored in the Ox catalyst 25 reacts with the CO in the exhaust to generate carbonate and release NOx. Accordingly, as the storage of NOx in the storage NOx catalyst 25 proceeds, CO is supplied by lowering the oxygen concentration by, for example, enriching the air-fuel ratio or performing additional fuel injection.
The function is regenerated by releasing NOx from the x catalyst 25 (N
Ox purge).

The fuel contains a sulfur (S) component, which reacts with oxygen to form a sulfur oxide (S).
Ox), and this SOx is stored in the storage NOx catalyst as sulfate instead of NOx instead of nitrate, and the NOx purification efficiency of the catalyst decreases. Storage NOx
Since the sulfate stored in the catalyst is more stable than the nitrate, when the amount of SOx stored in the NOx catalyst 25 advances, the storage type N
The function of the storage NOx catalyst 25 is regenerated by temporarily enriching the air-fuel ratio while releasing the SOx with the Ox catalyst kept at a high temperature (SOx purge).

On the other hand, the three-way catalyst 22, which purifies harmful substances (HC, CO, NOx) in the exhaust gas, deteriorates with time or deteriorates when the temperature of the catalyst becomes high. Sometimes. Therefore, it is necessary to improve the exhaust gas characteristics by performing the combustion control of the internal combustion engine according to the processing capacity while grasping the processing capacity of the three-way catalyst 22 that changes with time.

Therefore, in the present embodiment, the aforementioned
Thus, O downstream of the three-way catalyst 22 _TwoArrange sensor 27
And this O_TwoThe exhaust gas is detected based on the oxygen concentration detected by the sensor 27.
In a reducing (rich or stoichiometric) atmosphere (specified operating conditions
State), and the ECU 28 determines at this time
O in the normal state of the source catalyst 22_TwoReference output of sensor 27
The value (reference oxygen concentration) is stored (storage means) and the predetermined operation is performed.
In the rolled state, O_TwoThe output value detected by the sensor 27 (acid
Element density) and this reference output value,
The deterioration of the medium 22 is determined (deterioration determination means).
You.

That is, in general, the O ₂ sensor 27 measures the amount of oxygen contained in the exhaust gas. However, during operation of the engine 11 at the stoichiometric or rich air-fuel ratio,
Hydrogen other than oxygen is present in the exhaust gas. Since hydrogen has a smaller molecule than oxygen and has a higher diffusion speed in the electrode protection layer of the O ₂ sensor 27, hydrogen reaches the electrode protection layer more quickly than oxygen, and the output characteristics of the O ₂ sensor 27 are oxygen-diluted ( (Low oxygen), that is, the output value increases. However, if the three-way catalyst 22 having an oxidizing ability is provided on the upstream side of the O ₂ sensor 27, the three-way catalyst 22 can normally function as an exhaust gas (a component to be oxidized such as hydrogen).
, The hydrogen does not reach the O ₂ sensor 27, so that the sensor output characteristic does not shift to the oxygen-lean side.

On the other hand, with the passage of time,
When the oxidizing ability of the medium 22 decreases, O _TwoMany for sensor 27
Of hydrogen arrives, and the sensor output characteristics
A phenomenon occurs in which the output value shifts to the thin side, that is, the output value increases.
I do. Therefore, as described above,
O when the three-way catalyst 22 is normal_TwoThe reference output value of the sensor 27
Remember the smell of reducing atmosphere during engine operation
And O_TwoCompare the output value of sensor 27 with this reference output value
Then, it is possible to determine whether the three-way catalyst 22 is deteriorated.
Wear.

Here, the structure of the O ₂ sensor 27 will be described in detail. As shown in FIG. 2, the O ₂ sensor 27 has a cup-shaped detection element 32 mounted inside a housing 31, and an element cover 33 mounted around the detection element 32. The detection element 32 includes a zirconia solid electrolyte 34.
The inside electrode (atmosphere side Pt electrode) 35 is attached inside the
An outer electrode (exhaust-side electrode) 36 is mounted on the outside, and an electrode protection layer (coating of ceramic or the like) 37 is provided outside the outer electrode 36. Therefore, a high oxygen concentration atmosphere is introduced into the inner electrode 35, and the electrode protection layer 3
When an exhaust gas having a low oxygen concentration is introduced to the zirconia 7, the zirconia fixed electrolyte 34 generates an electromotive force according to the oxygen concentration difference between the inner and outer surfaces, and the oxygen concentration is detected based on the electromotive force. , The hydrogen is attached to the electrode protection layer 37 to detect an oxygen concentration shifted to a side where the electromotive force increases, that is, a low oxygen side.

Here, the control by the deterioration detecting device for the exhaust purification catalyst of this embodiment will be described in detail with reference to the flowchart shown in FIG. Before executing the deterioration determination process of the three-way catalyst 22, the reference output value (reference oxygen concentration) of the O ₂ sensor 27 when the three-way catalyst 22 is normal in the reducing atmosphere.
Is stored, and the three-way catalyst 22 is stored in accordance with the reference output value.
A determination value for performing the deterioration determination of is set. In this case, the determination value may be set as a map of the target A / F.

As shown in FIG. 3, first, at step S1, the output value of the O ₂ sensor 27 is read, and at step S2
Then, it is determined whether the air-fuel ratio is a stoichiometric or rich air-fuel ratio. The determination of the air-fuel ratio is performed based on the output value detected by the O ₂ sensor 27, that is, the oxygen concentration. If the air-fuel ratio of the exhaust gas is in an oxidizing (lean) atmosphere, the routine returns as it is. If there is, the process proceeds to step S3.

[0034] It is determined whether this step S3, it is preset determination value or more sensor output value of the O ₂ sensor 27 in accordance with the target air-fuel ratio of the engine. That is, as described above, the exhaust gas discharged from the engine 11 contains a reducing agent such as hydrogen together with oxygen at a stoichiometric or rich air-fuel ratio. However, O ₂ sensor 2
Since the three-way catalyst 22 is provided on the upstream side of FIG.
As shown in the figure, hydrogen is oxidized by the three-way catalyst 22,
The O ₂ sensor 27 generates an appropriate electromotive force (reference output value) and can accurately detect the oxygen concentration. Therefore, in step S3, if the sensor output value of the O ₂ sensor 27 is not equal to or greater than the determination value, it is determined that the three-way catalyst 22 has not deteriorated, and the routine returns.

However, if the three-way catalyst 22 deteriorates, hydrogen cannot be oxidized, and the hydrogen that has passed through the three-way catalyst 22 reaches the O ₂ sensor 27. At this time, in the O ₂ sensor 27, hydrogen adheres to the electrode protection layer earlier than oxygen, so that an appropriate electromotive force cannot be generated, and the oxygen concentration shifts to a lean side (electromotive force increases). Therefore, step S
In step 3, if the sensor output value of the O ₂ sensor 27 is equal to or larger than the determination value, the deterioration of the three-way catalyst 22 is determined in step S4, and the engine check lamp 29 on the dashboard is turned on in step S5. To make the driver aware. As a result, the driver can take measures such as replacing the deteriorated catalyst at a maintenance shop or the like.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to this embodiment, the O ₂ sensor 27 is provided in the exhaust pipe 21 at the downstream side by the three-way catalyst 22, and the exhaust gas is supplied to the three-way catalyst 22 in a reducing atmosphere. The reference output value (reference oxygen concentration) of the O ₂ sensor 27 in the normal state is stored and a deterioration determination value is set. If the sensor output value of the O ₂ sensor 27 becomes equal to or greater than the determination value, the three-way catalyst The engine check lamp 29 is turned on so that the driver can recognize the deterioration. Thus, based on the change in the output value of the O ₂ sensor 27 downstream of the three-way catalyst 22, it is possible to accurately determine a decrease in the exhaust gas purification capability of the three-way catalyst 22.

In the embodiment described above, the three-way catalyst 2
The deterioration determination of No. 2 was performed when the air-fuel ratio was at the stoichiometric or rich air-fuel ratio. However, the deterioration determination of the three-way catalyst 22 can be performed in an operating state in which hydrogen is generated. An oxidizing atmosphere having a lean air-fuel ratio may be used. Further, when the engine 11 is started, the combustion is in an incomplete combustion state, hydrogen is easily generated, and the sensor output characteristic of the O ₂ sensor 27 shifts to the oxygen-lean side. A determination may be made.

In each of the above-described embodiments, the oxygen concentration of the exhaust gas is detected by providing the O ₂ sensor 27 downstream of the three-way catalyst 22, but a linear A / F sensor is used instead of the O ₂ sensor. You may. Also, O ₂ output value of the exhaust gas sensor 27 has detected ternary reference output value of the O ₂ sensor 27 in the normal catalyst 22 (reference oxygen concentration) the ternary by comparing the judgment value set from the catalyst 22 Is determined, the deterioration of the three-way catalyst 22 may be determined based on the difference or ratio between the output value of the O ₂ sensor 27 and the reference output value.

The reference output value (reference oxygen concentration) of the O ₂ sensor 27 when the three-way catalyst 22 is normal may be experimentally obtained in advance. In the short mileage where 22 has not yet deteriorated,
The output value of the O ₂ sensor 27 may be stored for each predetermined operation state and for each predetermined A / F, and this may be used as a reference output value. By using such a method of learning the reference output value during traveling, it is possible to eliminate the influence of variations in the individual engines and sensors.

Further, in each of the above embodiments, the three-way catalyst 2
The deterioration of the three-way catalyst 22 is determined based on the oxygen concentration of the exhaust gas by providing an O ₂ sensor 27 downstream of the two-way catalyst 2, but regardless of the three-way catalyst 22, platinum (Pt), palladium (P
d), rhodium (Rh), iridium (Ir), etc., can be used as long as the catalyst has an oxidizing ability, for example, an oxidation catalyst, a storage NOx catalyst, and an adsorption type N2.
The deterioration can be properly determined by applying to an Ox catalyst, a selective reduction type NOx catalyst, or the like. In addition, the deterioration determination is performed for the three-way catalyst 22 having no oxygen storage function due to an additive such as ceria. However, it is needless to say that this additive is added to a catalyst having an oxygen storage function. You can also.

In each of the above embodiments, the oxygen concentration of the exhaust gas detected by the O ₂ sensor 27 is used for the feedback control of the air-fuel ratio. However, the air-fuel ratio control does not use the output value of the O ₂ sensor. The ECU 29 may appropriately perform forced modulation by duty control or the like so that the output of the O ₂ sensor downstream of the three-way catalyst 22 becomes a predetermined value.
At the same time as setting the center air-fuel ratio to the optimum value, the amplitude and frequency of the modulation can be arbitrarily set to the optimum values. In this case, if the response by the O ₂ sensor on the downstream side of the three-way catalyst 22 is insufficient, another sensor may be provided upstream of the three-way catalyst 22 for air-fuel ratio control.

In each of the above embodiments, the engine is not limited to the in-cylinder injection type engine as in the above embodiment, but may be an intake pipe injection type lean burn engine or a non-lean burn engine. Well, it can be applied to diesel engines.

[0043]

As described above in detail, according to the exhaust gas purifying catalyst deterioration detecting apparatus of the present invention,
An oxygen concentration sensor is provided downstream of the exhaust gas purification catalyst, the storage means stores a reference output of the oxygen concentration sensor when the exhaust gas purification catalyst is normal in a predetermined operation state, and the deterioration determination means outputs the output of the oxygen concentration sensor in the predetermined operation state. Is compared with the reference output to determine the deterioration of the exhaust gas purification catalyst. If the exhaust gas purification catalyst is normal, the sensor output characteristic shifts to the low oxygen concentration side without hydrogen reaching the oxygen concentration sensor. However, when the oxidizing ability of the exhaust gas purification catalyst is reduced, a large amount of hydrogen reaches the oxygen concentration sensor and shifts. Therefore, the output of the oxygen concentration sensor and the reference output of the oxygen concentration sensor when the exhaust gas purification catalyst is normal in a predetermined operation state. The deterioration of the exhaust gas purifying catalyst can be determined by comparing the exhaust gas purifying catalyst with the exhaust gas purifying catalyst. By better detecting it can be determined accurately the deterioration of the catalyst. In addition, accurate deterioration determination of the exhaust gas purification catalyst can be performed even with a single oxygen concentration sensor, and the configuration for the deterioration determination can be simplified.
Further, since deterioration is not detected by detecting a decrease in the oxygen storage capacity of the exhaust purification catalyst, the deterioration can be effectively detected even for an exhaust purification catalyst having almost no oxygen storage capacity.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine to which an exhaust gas purification catalyst deterioration detection device according to an embodiment of the present invention is applied.

FIG. 2 is a sectional view of a main part of an O ₂ sensor.

FIG. 3 is a flowchart illustrating deterioration detection control performed by the exhaust gas purification catalyst deterioration detection device according to the embodiment.

FIG. 4 is a graph showing an output voltage of an O ₂ sensor with respect to an air-fuel ratio.

[Explanation of symbols]

Reference Signs List 11 engine 21 exhaust pipe (exhaust passage) 22 three-way catalyst (exhaust gas purifying catalyst) 23 exhaust gas purifying catalyst device 25 storage type NOx catalyst 27 O ₂ sensor (oxygen concentration sensor) 28 electronic control unit, ECU (deterioration determining means) 29 engine Check lamp

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00 368 B01D 53/36 101B 101Z F-term (Reference) 3G084 AA03 AA04 BA09 BA24 DA27 EA04 EB06 EB08 EB12 EB17 FA10 FA26 FA27 FA29 FA33 FA38 3G091 AA12 AA17 AB02 AB03 AB06 AB09 BA33 DB10 EA00 EA01 EA07 EA17 EA18 EA34 FB11 FB12 GB02Y GB03Y GB05W GB06W HA37 3G301 HA01 HA04 HA06 HA15 JB09 JB10 NB02 PD02 PD02 NC02 PD02 4D048 AA06 AA13 AA18 AB01 AB02 AB05 AB07 CC32 CC46 CD06 CD08 DA02 DA20 EA04

Claims (1)

[Claims] An exhaust purification catalyst provided in an exhaust passage of an internal combustion engine and having at least an oxidizing ability; an oxygen concentration sensor provided in the exhaust passage located downstream of the exhaust purification catalyst; Storage means for storing a reference output of the oxygen concentration sensor when the exhaust gas purification catalyst is normal, and comparing the output of the oxygen concentration sensor with the reference output in the predetermined operating state to determine the deterioration of the exhaust gas purification catalyst. A deterioration detecting device for an exhaust gas purifying catalyst, comprising: