JP5765573B2 - Method for detecting deterioration of exhaust gas purification catalyst and exhaust gas purification device - Google Patents

Description

  The present invention relates to a method for detecting deterioration of an exhaust gas purification catalyst and an exhaust gas purification device that implements the deterioration detection method.

Exhaust gas discharged from an internal combustion engine such as an automobile contains harmful components such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NO _x ). In general, an exhaust gas purification catalyst for removing these harmful components from the exhaust gas is disposed in the exhaust passage of the internal combustion engine. As the exhaust gas purification catalyst, a three-way catalyst that simultaneously performs the oxidation of CO and HC and the reduction of NO _x is preferably used. As such a three-way catalyst, a noble metal catalyst such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported on a porous carrier generally made of a metal oxide such as alumina (Al ₂ O ₃ ). Are widely known. Such a three-way catalyst has a particularly high catalytic function when the air-fuel ratio (A / F) of the mixed gas supplied to the internal combustion engine is set in the vicinity of the stoichiometric air-fuel ratio (Stoichi: A / F = 14.7). Can be demonstrated.

However, it is difficult to keep the air-fuel ratio of the mixed gas actually supplied to the internal combustion engine in the vicinity of the stoichiometric range, and the air-fuel ratio of the mixed gas becomes excessive (rich: A / F <14.7) depending on the driving conditions of the automobile. Or oxygen excess (lean: A / F> 14.7). Therefore, in recent years, an OSC material having a so-called oxygen storage capacity (OSC) that stores oxygen when the mixed gas becomes lean and releases the stored oxygen when the mixed gas becomes rich is used. An exhaust gas purification catalyst is used which is contained in a carrier and supported on the three-way catalyst on a carrier containing the OSC material. When the exhaust gas when the mixed gas is lean is supplied to the exhaust gas purification catalyst including the OSC material as the carrier, oxygen in the exhaust gas is absorbed by the OSC material, and NO _{x in} the exhaust gas is reduced. On the other hand, when the exhaust gas is supplied when the mixed gas is rich, oxygen stored in the OSC material is released, and CO and HC in the exhaust gas are oxidized.

  As described above, the OSC material contributes to the purification of harmful components by the exhaust gas purification catalyst, and the decrease in the oxygen storage capacity of the OSC material greatly affects the exhaust gas purification capability of the exhaust gas purification catalyst. Therefore, in the exhaust gas purification apparatus using the exhaust gas purification catalyst containing the OSC material, a deterioration detection method for detecting the oxygen storage capacity of the OSC material is carried out, and the oxygen storage of the OSC material obtained based on the method is performed. Performance is used as a guideline for replacing the exhaust gas purification catalyst.

  For example, Patent Literature 1 discloses a catalyst deterioration detection device that calculates the oxygen storage capacity of an exhaust gas purification catalyst and detects deterioration of the catalyst with higher accuracy. In such a catalyst deterioration detection device, the air-fuel ratio of the mixed gas supplied to the internal combustion engine is forcibly controlled to be lean (hereinafter referred to as “forced lean control”), and the amount of oxygen absorbed by the exhaust gas purification catalyst is detected. Then, the air-fuel ratio of the mixed gas supplied to the internal combustion engine is forcibly controlled to be rich (hereinafter referred to as “forced rich control”), and the amount of oxygen released from the exhaust gas purification catalyst is detected. Then, an oxygen storage amount of the exhaust gas purification catalyst is calculated based on the oxygen release amount and the oxygen absorption amount, and it is determined whether or not the exhaust gas purification catalyst is deteriorated based on the oxygen storage amount.

JP 2008-8158 A

  By the way, in recent years, development of a low precious metal exhaust gas purification catalyst in which the amount of the precious metal catalyst used is reduced has been promoted for the purpose of reducing the manufacturing cost and stably supplying the material. As a result of various studies on the low precious metal exhaust gas purification catalyst, the present inventor has a problem that it becomes difficult to accurately perform the deterioration detection method of the exhaust gas purification catalyst when the low precious metal exhaust gas purification catalyst is used. I found. The reason for this will be described below.

  When exhaust gas in a case where the air-fuel ratio is lean is supplied to an exhaust gas purification catalyst containing a precious metal catalyst at a normal ratio, most of the oxygen contained in the exhaust gas is absorbed by the exhaust gas purification catalyst. This is because the noble metal catalyst functions as an intermediary when the OSC material absorbs oxygen. Therefore, in an ordinary exhaust gas purification catalyst, even if the exhaust gas when the air-fuel ratio is lean is supplied to the exhaust gas purification catalyst, oxygen is hardly detected downstream of the exhaust gas purification catalyst. In other words, when forced lean control is performed on a normal exhaust gas purification catalyst, oxygen is not detected downstream of the exhaust gas purification catalyst until the OSC material becomes saturated, and the exhaust gas purification catalyst when the OSC material becomes saturated. The oxygen concentration in the downstream rises at a stretch (abruptly leans to the lean side) (see FIG. 7A). In the conventional degradation detection method, forced lean control is terminated when an abrupt change in oxygen concentration downstream of the exhaust gas purification catalyst occurs, and oxygen absorbed by the exhaust gas purification catalyst while the forced lean control is being executed. Was detected as the oxygen absorption amount, and the oxygen storage capacity of the OSC material was calculated based on the detected oxygen absorption amount.

  However, in the low precious metal exhaust gas purification catalyst, since the content of the precious metal catalyst that mediates oxygen absorption is small, the efficiency of oxygen absorption into the OSC material decreases. In this case, the amount of oxygen supplied to the exhaust gas purification catalyst exceeds the oxygen absorption efficiency, and although the OSC material has not reached saturation, oxygen flows out to the downstream side, and the oxygen concentration on the downstream side of the exhaust gas purification catalyst gradually increases. (The change from the lean side to the rich side becomes gradual) (see FIG. 7B). As described above, in the conventional deterioration detection method, the forced lean control is terminated when the air-fuel ratio downstream of the catalyst suddenly leans. Therefore, if the air-fuel ratio downstream of the catalyst changes gradually, the forced lean control is performed. It cannot be terminated at an accurate timing, and the amount of oxygen absorbed during the forced lean control cannot be accurately detected.

  As a solution to the above-mentioned problem, for example, a method of setting a threshold value for the amount of change in oxygen concentration to a low value can be cited. However, since it becomes easy to be affected by the noise included when detecting the oxygen concentration, it is difficult to say that the problems that occur when using the low precious metal exhaust gas purification catalyst can be sufficiently solved.

  The present invention has been created to solve the above-mentioned problems, and even when a low precious metal exhaust gas purification catalyst is used, forced lean control can be terminated at an appropriate timing, thereby reducing the exhaust gas purification catalyst. It is an object of the present invention to provide a method capable of accurately detecting, and an exhaust gas purification apparatus capable of suitably implementing the deterioration detection method.

In order to achieve the above object, the present invention provides a method for detecting deterioration of an exhaust gas purifying catalyst having the following configuration. That is, the deterioration detection method according to the present invention is configured by forming a catalyst layer including a noble metal catalyst and a carrier containing an OSC material having oxygen storage capacity on a base material, and the mixed gas is an internal combustion engine. This is a method for detecting deterioration of an exhaust gas purification catalyst that purifies exhaust gas generated by being burned in an engine. The degradation detection method disclosed here is:
When the exhaust gas downstream of the exhaust gas purification catalyst is an air-fuel ratio lean or stoichiometric exhaust gas, the air-fuel ratio of the mixed gas is forcibly changed until the exhaust gas downstream of the exhaust gas purification catalyst becomes an air-fuel ratio rich exhaust gas. Rich control;
Detecting an oxygen release amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in the forced rich control;
When the exhaust gas downstream of the exhaust gas purification catalyst is an air-fuel ratio rich exhaust gas, the exhaust gas downstream of the exhaust gas purification catalyst is supplied to the internal combustion engine until it becomes an air-fuel ratio lean exhaust gas or an air-fuel ratio stoichiometric exhaust gas. Forcing the air-fuel ratio of the mixed gas to be lean or stoichiometrically controlled;
Detecting an oxygen absorption amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in the forced lean control;
Calculating the oxygen storage capacity of the exhaust gas purifying catalyst based on the oxygen release amount and / or the oxygen absorption amount;
Is included. Furthermore, the degradation detection method disclosed here is:
Setting the content of the noble metal catalyst to 2 g or less per liter of the exhaust gas purification catalyst;
Using a barium compound as an additive to the carrier containing the OSC material;
The air-fuel ratio of the mixed gas in the forced rich control is controlled to A / F <14.7, and the air-fuel ratio of the mixed gas in the forced lean control is within a range of A / F = 14.7 ± 0.05. The oxygen storage capacity of the exhaust gas purification catalyst is compared with a predetermined threshold value, and it is determined that the exhaust gas purification catalyst has deteriorated when the oxygen storage capacity falls below the predetermined threshold value. about;
Is further included.

  Note that the “air-fuel ratio rich exhaust gas” refers to an exhaust gas exhausted from an internal combustion engine when a mixed gas having a rich air-fuel ratio (A / F <14.7) is burned in the internal combustion engine. It refers to exhaust gas having an air-fuel ratio equivalent to the fuel ratio. Similarly, “exhaust gas of air-fuel ratio stoichiometric” refers to exhaust gas having an air-fuel ratio similar to the air-fuel ratio of exhaust gas discharged from the internal combustion engine when the mixed gas of which the air-fuel ratio is stoichiometric is burned. The “air-fuel ratio lean exhaust gas” refers to an exhaust gas having an air-fuel ratio similar to the air-fuel ratio of the exhaust gas discharged from the internal combustion engine when a mixed gas having a lean air-fuel ratio is burned. The numerical value (A / F = x) defined as “exhaust gas air-fuel ratio” indicates the air-fuel ratio of exhaust gas discharged when the mixed gas having the numerical value of the air-fuel ratio is burned. This is a technical matter that can be clearly and easily understood by those skilled in the art. For convenience of explanation, in the following description of the present specification, the “air-fuel ratio rich exhaust gas” is referred to as “rich exhaust gas”, the “air-fuel ratio stoichiometric exhaust gas” is referred to as “stoichiometric exhaust gas”, and “air-fuel ratio lean exhaust gas”. It is abbreviated as “lean exhaust gas” as appropriate.

  In the deterioration detection method having the above configuration, a barium compound is used as an additive to the carrier containing the OSC material, and the air-fuel ratio of the mixed gas in the forced lean control is set to a value within the range of 14.7 ± 0.05. It is characterized by control. The barium compound has a characteristic of exhibiting high oxygen absorption ability when weak lean exhaust gas (A / F = 14.7 ± 0.05) is supplied. For this reason, the oxygen absorption rate reduced by using the low noble metal exhaust gas purification catalyst with a noble metal usage amount of 2 g / L or less can be compensated by the characteristics of the barium compound. Therefore, according to the deterioration detection method of the above configuration, even when a low precious metal exhaust gas purification catalyst is used, oxygen is prevented from flowing out downstream of the exhaust gas purification catalyst during forced lean control, and forced lean control is performed at an appropriate timing. Can be terminated. Therefore, the oxygen storage capacity of the exhaust gas purification catalyst can be calculated based on the accurate oxygen rapid flow rate, and the deterioration of the exhaust gas purification catalyst can be detected based on the calculated oxygen storage capacity.

In a preferred aspect of the deterioration detection method disclosed herein, in the calculation of the oxygen storage capacity, the oxygen storage capacity of the exhaust gas purification catalyst is calculated based only on the oxygen absorption amount.
As described above, when a weak lean exhaust gas is supplied to an exhaust gas purification catalyst in which a barium compound is added to a carrier containing an OSC material (hereinafter referred to as “Ba-added exhaust gas purification catalyst” as appropriate), the oxygen absorption amount of the exhaust gas purification catalyst is reduced. improves. However, the oxygen absorption amount of the Ba-added exhaust gas purification catalyst is improved when the weak lean exhaust gas is supplied because oxygen is absorbed in the barium compound, and the oxygen storage amount in the OSC material is not improved. . For this reason, the supply of weak lean exhaust gas having a low oxygen concentration may reduce the amount of oxygen absorbed by the OSC material and reduce the amount of released oxygen. Accordingly, when weak lean exhaust gas is supplied to the Ba-added exhaust gas purification catalyst, the deterioration of the exhaust gas purification catalyst can be detected more accurately by calculating the oxygen storage capacity based only on the oxygen absorption amount.

In a preferred aspect of the degradation detection method disclosed herein, barium acetate is used as the barium compound.
The exhaust gas purification catalyst to which barium acetate is added has a larger amount of oxygen absorption when the weak lean exhaust gas is supplied than the exhaust gas purification catalyst to which other barium compounds are added. Therefore, by using barium acetate as the barium compound, the oxygen storage capacity of the exhaust gas purification catalyst can be calculated more accurately.

In a preferred embodiment of the degradation detection method disclosed herein, at least palladium and rhodium are used as the noble metal catalyst.
The three-way catalyst containing palladium and rhodium as a noble metal catalyst can exhibit a high catalytic effect in an exhaust gas purification catalyst having a high oxygen storage capacity.

In a preferable aspect of the degradation detection method disclosed herein, a ceria-zirconia composite oxide is used as the OSC material.
Ceria-zirconia composite oxide has a high oxygen storage capacity and is suitable as an OSC material.

In a preferred aspect of the deterioration detection method disclosed herein, the amount of barium compound added is set to 5 to 10 parts by mass with respect to 100 parts by mass of the OSC material.
When the addition amount of the barium compound is 5 parts by mass or less, there is a possibility that a suitable oxygen absorption amount cannot be obtained even if weak lean exhaust gas is supplied. On the other hand, when the addition amount of the barium compound is 10 parts by mass or more, the surface of the support or the noble metal catalyst is covered with the barium compound, and the catalytic function of the exhaust gas purification catalyst may be lowered. Therefore, by setting the addition amount of the barium compound within the above numerical range, a suitable oxygen absorption amount can be obtained at the time of weak lean exhaust gas supply, and the catalytic function of the exhaust gas purification catalyst can be maintained in a high state. Can do.

In a preferred aspect of the degradation detection method disclosed herein, the catalyst layer includes an OSC region made of a carrier containing the OSC material and a non-OSC region made of a carrier made of a carrier material other than the OSC material. It is characterized by having.
According to the deterioration detection method having the above-described configuration, the non-OSC region including the carrier containing the carrier material other than the OSC material is provided. As the carrier material used for such a non-OSC region, it is not necessary to consider the oxygen storage capacity, and a carrier material having a large specific surface area can be selected. Thereby, an exhaust gas purification catalyst having a higher catalytic function can be obtained. As the carrier material having a large specific surface area, for example, at least one of complex oxides mainly composed of aluminum oxide (alumina), zirconium oxide (zirconia), and silicon oxide (silica) can be preferably used.

Moreover, in the aspect in which the said catalyst layer is provided with the said OSC area | region and the said non-OSC area | region, the addition amount of the said barium compound to the said OSC area | region is 5 mass parts-10 mass parts with respect to 100 mass parts of said OSC materials. More preferably, the amount of the barium compound added to the non-OSC region is set to 10 to 15 parts by mass with respect to 100 parts by mass of the carrier material other than the OSC material.
In the deterioration detection method having the above configuration, since the barium compound is also added to the non-OSC region, the oxygen absorption amount in forced lean control (weak lean exhaust gas supply) can be further improved. Moreover, the barium compound at this time is good to set to 10-15 mass parts for the same reason as the case where the addition amount of the barium compound to the said OSC area | region is set.

Moreover, this invention provides the exhaust gas purification apparatus which is provided in the exhaust system of the said internal combustion engine as another side surface, and purifies the exhaust gas discharged | emitted from this internal combustion engine. This exhaust gas purification device
An exhaust gas purification catalyst which is disposed in the exhaust system and is configured by forming a catalyst layer including a noble metal catalyst and a support containing an OSC material having an oxygen storage capacity on a substrate;
A catalyst downstream sensor that is disposed downstream of the exhaust gas purification catalyst in the exhaust system and detects an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst;
A control unit that transmits the exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst detected by the catalyst downstream sensor, and adjusts the air-fuel ratio of the mixed gas supplied to the internal combustion engine based on the transmitted exhaust gas air-fuel ratio When,
It has. Furthermore, the control unit of the exhaust gas purification device disclosed herein is:
When the air-fuel ratio lean or stoichiometric exhaust gas is detected in the catalyst downstream sensor, the air-fuel ratio of the mixed gas is controlled to be rich until the air-fuel ratio rich exhaust gas is detected in the catalyst downstream sensor. To do;
In the forced rich control, detecting an oxygen release amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio detected by the catalyst downstream sensor;
When the air-fuel ratio rich exhaust gas is detected by the catalyst downstream sensor, the air-fuel ratio of the mixed gas is forcibly made lean or stoichiometric until the air-fuel ratio lean or stoichiometric exhaust gas is detected by the catalyst downstream sensor. To control;
Detecting the oxygen absorption amount of the exhaust gas purification catalyst based on the exhaust gas air-fuel ratio detected by the catalyst downstream sensor in the forced lean control;
Calculating the oxygen storage capacity of the exhaust gas purifying catalyst based on the oxygen release amount and / or the oxygen absorption amount;
Is configured to run. And the exhaust gas purification device disclosed here is
The precious metal catalyst is contained at a rate of 2 g or less per 1 L of the capacity of the exhaust gas purification catalyst;
A barium compound is added to the carrier containing the OSC material;
The control unit controls the air-fuel ratio of the mixed gas in the forced rich control to A / F <14.7, and the air-fuel ratio of the mixed gas in the forced lean control is A / F = 14.7 ± 0. The control unit compares the oxygen storage capacity of the exhaust gas purification catalyst with a predetermined threshold value, and the exhaust gas when the oxygen storage capacity falls below the predetermined threshold value. Determining that the purification catalyst has deteriorated;
Is further included.

  The exhaust gas purifying apparatus having the above configuration can suitably implement the above-described deterioration detection method. That is, the exhaust gas purifying apparatus having the above configuration can accurately detect the deterioration of the exhaust gas purifying catalyst, and therefore can be suitably used for a vehicle (for example, an automobile) in which the exhaust gas purifying catalyst is continuously used during traveling.

The figure which showed typically the exhaust gas purification apparatus which concerns on one Embodiment of this invention. The figure which showed typically the exhaust gas purification catalyst of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. The figure which expanded and expanded the cross-sectional structure of the exhaust gas purification catalyst of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. The flowchart which showed an example of the deterioration detection method which concerns on this invention. The graph which showed the oxygen absorption amount of each sample produced in the Example. The graph which showed the oxygen release amount of each sample produced in the Example. The figure which illustrated the air fuel ratio in the downstream of a low noble metal exhaust gas purification catalyst (A) and a normal exhaust gas purification catalyst (B).

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the field.

<Exhaust gas purification device>
Here, first, an exhaust gas purification apparatus according to an embodiment of the present invention will be described. The exhaust gas purifying apparatus disclosed here is provided in an exhaust system of an internal combustion engine. Hereinafter, an internal combustion engine and an exhaust gas purification apparatus will be described with reference to FIG. FIG. 1 is a diagram schematically showing an internal combustion engine 1 and an exhaust gas purification device 100 provided in an exhaust system of the internal combustion engine 1.

A. Internal combustion engine An internal combustion engine is supplied with a mixed gas containing oxygen and fuel gas. The internal combustion engine burns the mixed gas and converts the combustion energy into mechanical energy. At this time, the mixed gas after combustion becomes exhaust gas and is discharged to an exhaust system described later. The internal combustion engine 1 having the configuration shown in FIG. 1 includes a plurality of combustion chambers 2 and a fuel injection valve 3 that injects fuel into each of the combustion chambers 2. Each fuel injection valve 3 is connected to a common rail 22 via a fuel supply pipe 21. The common rail 22 is connected to the fuel tank 24 via the fuel pump 23. The fuel pump 23 supplies the fuel in the fuel tank 24 to the combustion chamber 2 through the common rail 22, the fuel supply pipe 21, and the fuel injection valve 3. The configuration of the fuel pump 23 does not particularly limit the present invention. For example, an electronically controlled fuel pump having a variable discharge amount can be used.

  An intake manifold 4 and an exhaust manifold 5 communicate with the combustion chamber 2. In the following description, a system that is provided upstream of the intake manifold 4 and supplies air (oxygen) to the internal combustion engine 1 is referred to as an “intake system”, and is provided downstream of the exhaust manifold 5. A system that exhausts the exhaust gas generated in step 1 to the outside is referred to as an “exhaust system”. The intake system and the exhaust system are connected to each other via the exhaust gas recirculation passage 18 so that the exhaust gas discharged to the exhaust system can be supplied again into the combustion chamber 2. An electronically controlled control valve 19 is disposed in the exhaust gas recirculation passage 18, and the exhaust gas to be recirculated can be adjusted by opening and closing the control valve 19. A cooling device 20 for cooling the gas flowing in the exhaust gas recirculation passage 18 is disposed around the exhaust gas recirculation passage 18.

A-1. Intake System The intake system of the internal combustion engine 1 will be described. An intake duct 6 is connected to an intake manifold 5 that communicates the internal combustion engine 1 with an intake system. The intake duct 6 is connected to a compressor 7a of an exhaust turbocharger 7, and an air cleaner 9 is connected to the compressor 7a. The air cleaner 9 is provided with an intake air temperature sensor 9a for detecting the temperature (intake air temperature) of air taken from the outside of the internal combustion engine. An air flow meter 8 is disposed downstream of the air cleaner 9 (internal combustion engine 1 side). The air flow meter 8 is a sensor that detects an intake air amount Ga supplied to the intake duct 6. A throttle valve 10 is provided further downstream of the air flow meter 8 in the intake duct 6. The amount of air supplied to the internal combustion engine 1 can be adjusted by opening and closing the throttle valve 10. In addition, a throttle sensor (not shown) for detecting the opening degree of the throttle valve 10 may be disposed in the vicinity of the throttle valve 10. A cooling device 11 for cooling the air flowing through the intake duct 6 is preferably disposed around the intake duct 6.

A-2. Exhaust System Next, the exhaust system of the internal combustion engine 1 will be described. An exhaust manifold 5 that allows the internal combustion engine 1 to communicate with an exhaust system is connected to an exhaust turbine 7 b of an exhaust turbocharger 7. An exhaust passage 12 through which exhaust gas flows is connected to the exhaust turbine 7b. The exhaust system (for example, the exhaust manifold 5) may be provided with an exhaust system fuel injection valve 13 that injects the fuel F into the exhaust gas. The exhaust system fuel injection valve 13 can adjust the air-fuel ratio (A / F) of exhaust gas supplied to an exhaust gas purification catalyst 40 described later by injecting fuel F into the exhaust gas.

B. Exhaust gas purification device The exhaust gas purification device disclosed here is provided in the exhaust system of the internal combustion engine. The exhaust gas purification apparatus includes an exhaust gas purification catalyst, a catalyst downstream sensor, and a control unit, and includes harmful components (for example, carbon monoxide (CO), hydrocarbon (HC), nitrogen, etc.) contained in the exhaust gas discharged from the internal combustion engine. Oxide (NO _x )) is purified. The exhaust gas purification apparatus 100 having the configuration shown in FIG. 1 also includes a catalyst upstream sensor 14.

C. Exhaust gas purification catalyst The exhaust gas purification catalyst is disposed in an exhaust system of an internal combustion engine. In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the exhaust gas purification catalyst 40 is disposed in the exhaust passage 12 of the exhaust system.
This exhaust gas purification catalyst is configured by forming a catalyst layer on a substrate, and removes harmful components contained in the exhaust gas by the catalytic function of the catalyst layer. The details of such an exhaust gas purification catalyst will be described with reference to FIGS. FIG. 2 is a perspective view schematically showing the exhaust gas purification catalyst 40, and FIG. 3 is an enlarged view schematically showing an example of a cross-sectional configuration of the exhaust gas purification catalyst 40.

C-1. Substrate As the substrate of the exhaust gas purification catalyst disclosed herein, the same substrate as that of a conventionally known exhaust gas purification catalyst can be used. For example, the base material is preferably made of a heat resistant material having a porous structure. Examples of the heat-resistant material include cordierite, silicon carbide (silicon carbide: SiC), heat-resistant metal such as aluminum titanate, silicon nitride, and stainless steel, and alloys thereof. The substrate preferably has a honeycomb structure, a foam shape, a pellet shape, or the like. In addition, cylindrical shape, elliptic cylinder shape, polygonal cylinder shape etc. can be employ | adopted for the external shape of the whole base material. In the exhaust gas purification catalyst 40 having the configuration shown in FIG. 2, a cylindrical member having a honeycomb structure is employed as the base material 42. The honeycomb-structured substrate 42 has a plurality of flow paths 48 along the cylinder axis direction (the direction of the arrow in FIG. 2), which is the direction in which the exhaust gas flows. Moreover, the capacity | capacitance (volume of the flow path 48 in the base material 42) of the base material 42 is 0.1L or more (preferably 0.5L or more), 5L or less (preferably 3L or less, more preferably 2L or less). It is good to be.

C-2. Catalyst layer In the exhaust gas purification catalyst disclosed herein, a catalyst layer is formed on the substrate. The catalyst layer includes a noble metal catalyst and a support. In the exhaust gas purification catalyst 40 having the configuration shown in FIG. 3, the catalyst layer 43 is formed on the surface of the base material 42. The exhaust gas supplied to the exhaust gas purification catalyst 40 flows in the flow path 48 of the base material 42 and contacts the catalyst layer 43 to remove harmful components. For example, CO and HC contained in the exhaust gas are oxidized by the catalyst layer 43 and converted (purified) into water (H ₂ O), carbon dioxide (CO ₂ ), and the like, and NO _x is reduced by the catalyst layer 43 and nitrogen (N ₂ ) Is converted (purified).
The catalyst layer includes a noble metal catalyst and a carrier supporting the noble metal catalyst. In the exhaust gas purifying catalyst disclosed herein, the carrier contains an OSC material, and a barium compound is added to the carrier containing the OSC material (hereinafter referred to as “OSC carrier”). Hereinafter, materials contained in the catalyst layer will be described.

C-2-1. Noble metal catalyst The noble metal catalyst contained in the catalyst layer only needs to have a catalytic function against harmful components contained in the exhaust gas, and noble metal particles composed of various noble metal elements can be used. As a metal that can be used for the noble metal catalyst, for example, any metal included in the platinum group, or an alloy mainly composed of any metal included in the platinum group can be preferably used. Examples of the metal contained in the platinum group include platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os).
It is more preferable that a three-way catalyst containing at least palladium and rhodium is used as the noble metal catalyst. Three-way catalyst can be stoichiometric exhaust gas when supplied to purify CO in the exhaust gas, HC, and NO _x simultaneously. Furthermore, such a three-way catalyst can exhibit a high catalytic effect in an exhaust gas purification catalyst having a high oxygen storage capacity. The three-way catalyst may contain other catalytic metals (for example, platinum) of palladium and rhodium.

  Moreover, the exhaust gas purification catalyst of the exhaust gas purification apparatus disclosed here is a low noble metal exhaust gas purification catalyst having a lower content of noble metal catalyst than the conventional exhaust gas purification catalyst. Specifically, in the exhaust gas purification catalyst disclosed herein, the precious metal catalyst is 2 g or less (for example, 0.5 g to 2.0 g, preferably 0) per liter of the capacity of the exhaust gas purification catalyst (volume of the base material). 0.5 g to 1.0 g). The content of the noble metal catalyst in a general exhaust gas purification catalyst is set to be larger than 2.0 g and less than 10 g per liter of the exhaust gas purification catalyst, and the exhaust gas purification disclosed here In the catalyst, the content of the noble metal catalyst is greatly reduced as compared with the conventional exhaust gas purification catalyst. Therefore, in the exhaust gas purifying apparatus disclosed here, the content of the noble metal catalyst is reduced, thereby contributing to the reduction of manufacturing costs and the stable supply of materials.

C-2-2. Support The catalyst layer is formed by supporting a noble metal catalyst on a support. The catalyst layer of the exhaust gas purification catalyst disclosed herein includes a carrier (OSC carrier) containing an OSC material having an oxygen storage capacity. The OSC carrier may be composed of only the OSC material, or may contain another carrier material (non-OSC material).

C-2-2-1. OSC material The OSC material contained in the OSC carrier has an oxygen storage capability of absorbing oxygen when lean exhaust gas is supplied and releasing the absorbed oxygen when rich exhaust gas is supplied. Examples of such OSC materials include cerium oxide (ceria: CeO ₂ ) and composite oxides containing the ceria (eg, ceria-zirconia composite oxide (CeO ₂ —ZrO ₂ composite oxide)). Among the OSC materials described above, the ceria-zirconia composite oxide is particularly preferably used because it has a high oxygen storage capacity and is relatively inexpensive. The mixing ratio of ceria and zirconia in this ceria-zirconia composite oxide is CeO ₂ / ZrO ₂ = 0.25 to 0.75 (preferably about 0.3 to 0.6, more preferably about 0.5). There should be.

The shape (outer shape) of the OSC material is not particularly limited, but it is more preferable that the OSC material has a shape that can constitute an OSC carrier having a large specific surface area. For example, the specific surface area of the OSC carrier (specific surface area measured by the BET method; hereinafter the same) is preferably 20 m ² / g or more and 80 m ² / g or less, and more preferably 40 m ² / g or more and 60 m ² / g or less. As a specific shape of the OSC material suitable for realizing the OSC carrier having such a specific surface area, a powder form (particulate form) may be mentioned. In order to realize an OSC carrier having a more suitable specific surface area, the average particle size of the powdered OSC material may be set to 5 nm to 20 nm, preferably 7 nm to 12 nm. When the average particle size of the OSC material particles is too large (or the specific surface area is too small), the dispersibility of the noble metal tends to be lowered when the noble metal catalyst is supported on the OSC carrier, and the purification performance of the catalyst is lowered. Therefore, it is not preferable. Further, when the particle size of the particles constituting the OSC carrier is too small (or the specific surface area is too large), the heat resistance of the OSC carrier itself is lowered, and the heat resistance characteristics of the catalyst are lowered, which is not preferable.

C-2-2-2. Other carrier materials (non-OSC materials)
In the exhaust gas purification catalyst disclosed herein, the OSC carrier may contain a carrier material (non-OSC material) other than the OSC material. As such a non-OSC material, a porous metal oxide having excellent heat resistance is preferably used. For example, aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ), silicon oxide (silica: SiO ₂ ), or two or three kinds of these metal oxides are the main components. A composite oxide or the like is preferable. Among these, alumina and zirconia satisfy particularly preferable conditions for the above-mentioned carrier material and are particularly preferable because they are inexpensive. OSC carriers containing these non-OSC materials are preferable because they have a large specific surface area and can be produced at low cost.

C-2-3. As described above, the exhaust gas purifying apparatus disclosed herein is characterized in that a barium (Ba) compound is added to the OSC carrier. As this barium compound, it exhibits high oxygen absorption ability when exposed to weak lean exhaust gas in the vicinity of A / F = 14.7 (for example, A / F = 14.7 ± 0.05), and an exhaust gas purification catalyst. What can improve the oxygen absorption amount of the whole is used. Examples of such barium compounds include barium acetate ((CH ₃ COO) ₂ Ba), barium sulfate (BaSO ₄ ), barium nitrate ((BaNO ₃ ) ₂ ), and barium oxalate (BaC ₂ O ₄ .2H ₂ O). Etc. Among these, barium acetate is preferable because it can exhibit particularly high oxygen absorption ability when exposed to weak lean exhaust gas.
Moreover, it is preferable that content of the said barium compound is set to 5 mass parts-10 mass parts (preferably 6 mass parts-8 mass parts) with respect to 100 mass parts of OSC materials contained in an OSC support | carrier. When the addition amount of the barium compound is 5 parts by mass or less, there is a possibility that a suitable oxygen absorption amount cannot be obtained even if weak lean exhaust gas is supplied. On the other hand, when the addition amount of the barium compound is 10 parts by mass or more, the catalytic function of the exhaust gas purification catalyst may be deteriorated by covering the surface of the support or the noble metal catalyst with the barium compound. Therefore, by setting the addition amount of the barium compound within the above numerical range, it is possible to obtain an oxygen absorption amount suitable for supplying weak lean exhaust gas, and an exhaust gas purification catalyst maintained in a high catalytic function state. Can be produced. As will be described in detail later, the barium compound is more preferably added to the OSC support in a solution state.

  The barium compound also has an effect of suppressing HC poisoning of Pd, which is a noble metal catalyst. Therefore, when Pd is used as the noble metal catalyst, since the barium compound is added to the OSC carrier, the deterioration of Pd due to HC poisoning can be prevented, and the catalytic function of the gas purification catalyst can be maintained in a high state.

  Although this invention is not limited, the method of adding a barium compound to an OSC support | carrier can be performed in the following procedures, for example. First, a barium solution in which a barium compound (for example, barium acetate) is dissolved in a solvent (for example, water) is prepared. This barium aqueous solution is added to the slurry in which the OSC material is dispersed, stirred, and then dried. An OSC carrier to which a barium compound is added is obtained by maintaining the obtained powder under a high temperature (for example, about 400 ° C. to 600 ° C.) condition for a predetermined time. In this way, by adding the barium compound in water and adding it in the form of a solution, the barium compound can be uniformly dispersed throughout the OSC carrier as compared with the case where it is added in a granular form. Further, the addition of the barium compound as described above may be performed before the noble metal catalyst is supported on the OSC support, or may be performed after the noble metal catalyst is supported on the OSC support. Preferably, the barium compound is added after the noble metal catalyst is supported. As a result, the respective materials are uniformly dispersed, and the exhaust gas purification ability of the exhaust gas purification catalyst can be more suitably exhibited.

C-2-4. Other Additives Other materials (typically inorganic oxides) may be added to the OSC carrier as subcomponents. As materials that can be added to the OSC carrier, rare earth elements such as lanthanum (La) and yttrium (Y), alkaline earth elements such as calcium, and other transition metal elements can be used. Among these, rare earth elements such as lanthanum and yttrium are preferably used as stabilizers because they can improve the specific surface area at high temperatures without impairing the catalytic function. Further, the content ratio of these subcomponents is more preferably set to 10 to 20 parts by mass (for example, 5 parts by mass each of lanthanum and yttrium) with respect to 100 parts by mass of OSC material.

C-2-5. Non-OSC Region The catalyst layer of the exhaust gas purification catalyst may be divided into a plurality of regions, and each region may be composed of a different material. In this case, it is only necessary that at least one of the divided areas is constituted by the OSC carrier.
As an example of an aspect in which the catalyst layer is divided into a plurality of regions, the catalyst layer includes an OSC region made of the OSC carrier and a non-OSC region made of a carrier (non-OSC carrier) made of a non-OSC material. The embodiment is mentioned. When such an embodiment is adopted, the carrier material used for the non-OSC region does not need to consider oxygen storage capacity, and a carrier material having a large specific surface area can be selected. Thereby, an exhaust gas purification catalyst having a higher catalytic function can be obtained. Specifically, as the constituent material of the non-OSC carrier, a material as described in the above section “C-2-2-2. Other carrier material (non-OSC material)” can be preferably used. Among these, aluminum oxide (alumina), zirconium oxide (zirconia), silicon oxide (silica), and the like are preferable. Further, like the OSC support, the non-OSC support preferably contains a stabilizer (rare earth elements such as lanthanum and yttrium).

  In addition, a barium compound may be added to the non-OSC carrier constituting the non-OSC region. In this case, the oxygen absorption amount in forced lean control (weak lean exhaust gas supply) can be further improved. Moreover, the barium compound at this time is good to set to 10-15 mass parts for the same reason as the case where the addition amount of the barium compound to the said OSC area | region is set.

An example of the exhaust gas purification catalyst in which the catalyst layer includes an OSC region and a non-OSC region is schematically shown in FIG. In the exhaust gas purification catalyst 40 having the configuration shown in FIG. 3, a catalyst layer 43 including an OSC region 44 and a non-OSC region 45 is formed on a base material 42. The catalyst layer 43 in the OSC region 44 is composed of an OSC carrier, and a barium compound is added to the OSC carrier. On the other hand, the catalyst layer 43 in the non-OSC region 45 is composed of a non-OSC carrier.
In the case where the OSC region and the non-OSC region are provided, the positions of the OSC region and the non-OSC region may be adjusted so that the exhaust gas contacts the OSC region before the non-OSC region. As a result, oxygen in the exhaust gas can be preferentially absorbed in the OSC region, so that the exhaust gas purification catalyst as a whole can exhibit high oxygen absorption ability. In the exhaust gas purification catalyst 40 having the configuration shown in FIG. 3, the OSC region 44 is formed on the upstream side in the flow path 48 of the exhaust gas purification catalyst 40 (upstream side in the flow direction of the exhaust gas). An OSC region 45 is formed. As a result, the exhaust gas supplied to the exhaust gas purification catalyst 40 comes into contact with the OSC region 44 before the non-OSC region 45.

  The exhaust gas purification catalyst of the exhaust gas purification device disclosed here has been described above. Next, another configuration provided in the exhaust gas purification device disclosed herein will be described.

D. Catalyst Downstream Sensor In the exhaust gas purification device disclosed herein, a catalyst downstream sensor is disposed downstream of the exhaust gas purification catalyst in the exhaust system. In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the catalyst downstream sensor 15 is disposed downstream of the exhaust gas purification catalyst 40 in the exhaust passage 12.
The catalyst downstream sensor only needs to be able to detect the exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst, and its specific configuration does not particularly limit the present invention. For example, an oxygen sensor that detects the oxygen concentration in the exhaust gas can be used as the catalyst downstream sensor. As an example of such an oxygen sensor, there is a 0V-1V oxygen sensor that generates a potential of 1V when contacting rich exhaust gas and generates a potential of 0V when contacting exhaust gas. When such a 0V-1V oxygen sensor is used, a change in the air-fuel ratio of the exhaust gas downstream of the exhaust gas purification catalyst can be detected based on the detected potential change. Another example of the catalyst downstream sensor is an A / F sensor (air-fuel ratio sensor). The A / F sensor detects the oxygen concentration in the exhaust gas and detects the exhaust gas air-fuel ratio based on the oxygen concentration.

E. Catalyst upstream sensor The exhaust gas purification apparatus disclosed herein may include a catalyst upstream sensor upstream of the exhaust gas purification catalyst in the exhaust system. In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the catalyst upstream sensor 14 is disposed upstream of the exhaust gas purification catalyst 40 in the exhaust passage 12.
This catalyst upstream sensor can detect the exhaust gas air-fuel ratio upstream of the exhaust gas purification catalyst. The air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 can be estimated by introducing the exhaust gas air-fuel ratio upstream of the exhaust gas purification catalyst detected by the catalyst upstream sensor into a predetermined calculation formula. For example, the control unit described later causes the exhaust gas air-fuel ratio upstream of the exhaust gas purification catalyst detected by the catalyst upstream sensor to be transmitted to the control unit described later, and the control unit supplies the internal combustion engine based on the exhaust gas air-fuel ratio upstream of the catalyst. The air-fuel ratio of the mixed gas is calculated.

F. Control unit (ECU)
Next, a control unit (ECU) of the exhaust gas purification device disclosed herein will be described. The control unit is mainly composed of a digital computer and functions as a control device in the operation of the internal combustion engine and the exhaust gas purification device. The control unit includes, for example, a ROM that is a read-only storage device, a RAM that is a readable / writable storage device, and a CPU that performs arbitrary calculations and determinations.
The control unit 30 having the configuration shown in FIG. 1 is provided with an input port, and is electrically connected to sensors installed in each part of the internal combustion engine 1 and the exhaust gas purification catalyst 40. As a result, information detected by each sensor is transmitted as electrical signals to the ROM, RAM, and CPU via the input port. The control unit 30 is also provided with an output port. The control unit 30 is connected to each part of the internal combustion engine 1 through the output port, and controls the operation of each member by transmitting a control signal.

  The control unit can estimate the air-fuel ratio (A / F) of the mixed gas burned in the internal combustion engine 1 based on the oxygen concentration of the exhaust gas upstream of the exhaust gas purification catalyst detected by the catalyst upstream sensor. Further, the control unit 30 determines whether the exhaust gas that has passed through the exhaust gas purification catalyst 40 is rich exhaust gas or lean exhaust gas based on the oxygen concentration of the exhaust gas downstream of the exhaust gas purification catalyst 40 detected by the catalyst downstream sensor 15. Can be detected.

Further, as described above, the control unit can adjust the air-fuel ratio of the mixed gas supplied to the internal combustion engine based on the detection result of the catalyst downstream sensor and / or the catalyst upstream sensor.
In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the control unit 30 determines the mixed gas supplied to the internal combustion engine 1 based on the exhaust gas air-fuel ratio detected by the catalyst downstream sensor 15 and / or the catalyst upstream sensor 14. Calculate the air-fuel ratio. Then, a control signal is created based on the calculated air-fuel ratio and the target air-fuel ratio, and the control signal is transmitted to each member of the internal combustion engine 1. For example, the control unit 30 is electrically connected to the fuel pump 23 and the fuel injection valve 3, and is supplied to the internal combustion engine 1 by controlling the operation of the fuel pump 23 and the opening / closing timing of the fuel injection valve 3. The fuel to be adjusted can be adjusted. On the other hand, the control unit 30 is also connected to a throttle valve 10 provided in the intake duct 6 in the intake system, and controls the opening / closing timing of the throttle valve 10 to control the amount of air supplied to the internal combustion engine 1. Can be adjusted. The control unit 30 adjusts the fuel supply amount by the control of the fuel pump 23 and the fuel injection valve 3 and the air supply amount by the control of the throttle valve 10 to adjust the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1. Adjust.
When the internal combustion engine 1 is operating normally, the control unit 30 adjusts the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 to the vicinity of stoichiometric (A / F = 14.7). When the air-fuel ratio of the mixed gas is adjusted in the vicinity of the stoichiometric ratio, the fuel combustion efficiency in the internal combustion engine 1 is the best, and the exhaust gas purification function in the exhaust gas purification catalyst 40 is most suitably exhibited.

<Catalyst deterioration detection method>
As described above, when the internal combustion engine is operating normally, the control unit adjusts the air-fuel ratio of the mixed gas to near the stoichiometric ratio. On the other hand, the control unit of the exhaust gas purification apparatus disclosed herein includes a forced rich control for forcibly adjusting the air-fuel ratio of the mixed gas to the rich side in order to detect deterioration of the exhaust gas purification catalyst, and an air-fuel ratio of the mixed gas. Forcibly lean control that forcibly adjusts to the lean side can be executed. Hereinafter, a deterioration detection method including the forced rich control and the forced lean control will be described.

  The degradation detection methods disclosed herein include “a. Forced rich control”, “b. Oxygen release amount detection”, “c. Forced lean control”, “d. Oxygen absorption amount detection”, “e. The deterioration of the exhaust gas purification catalyst is detected by performing “calculation” and “f. Deterioration determination”. Moreover, the control part of the exhaust gas purification apparatus disclosed here is comprised so that each above-mentioned control can be implemented. Hereinafter, details of each control described above will be described.

a. Forced rich control In forced rich control, the air-fuel ratio of the mixed gas is controlled to be rich, and rich exhaust gas is supplied to the exhaust gas purification catalyst. In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, when the forced rich control is executed, a forced rich control signal is created in the control unit 30, and the forced rich control signal is used as the fuel pump 23, the fuel injection valve 3, the throttle valve. 10 is transmitted. The fuel pump 23 that has received the forced rich control signal increases the fuel supplied from the fuel tank 24 to the fuel injection valve 3. And the opening degree of the fuel injection valve 3 becomes large, and the fuel supplied into the fuel chamber 2 increases. On the other hand, by receiving the forced rich control signal, the opening degree of the throttle valve 10 is reduced, and the amount of air supplied into the fuel chamber 2 is reduced. As a result, the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 becomes rich (excess fuel).
The air-fuel ratio of the mixed gas in the forced rich control is A / F <14.7 (for example, 13.0 <A / F <14.7, preferably 13.5 <A / F <14.7). A value within the range (for example, A / F = 14.0) may be set. By performing forced rich control at an air-fuel ratio within such a numerical range, the amount of oxygen released from the exhaust gas purification catalyst can be suitably detected.

The forced rich control is executed until the exhaust gas downstream of the exhaust gas purification catalyst becomes rich exhaust gas when the exhaust gas downstream of the exhaust gas purification catalyst is lean exhaust gas or stoichiometric exhaust gas. Specifically, the start condition of forced rich control is that lean exhaust gas (or stoichiometric exhaust gas) is detected downstream of the exhaust gas purification catalyst (for example, after the end of forced lean control described later). In this case, lean exhaust gas (or stoichiometric exhaust gas) containing oxygen is supplied to the exhaust gas purification catalyst, and the exhaust gas downstream of the exhaust gas purification catalyst is lean exhaust gas or stoichiometric exhaust gas. That is, forced rich control is performed when lean exhaust gas containing oxygen is supplied to the exhaust gas purification catalyst, but the oxygen is not absorbed by the exhaust gas purification catalyst and is flowing downstream (maximum oxygen storage state). Be started.
When forced rich control starts, oxygen stored in the exhaust gas purification catalyst is released, and oxygen flows out downstream of the exhaust gas purification catalyst (lean exhaust gas and stoichiometric exhaust gas are detected by the catalyst downstream sensor). Thereafter, when the forced rich control is continued, almost all of the oxygen stored in the exhaust gas purification catalyst is released (the exhaust gas purification catalyst enters the minimum oxygen storage state). At this time, oxygen is not detected downstream of the exhaust gas purification catalyst (rich exhaust gas is detected). In this case, the control unit ends the forced rich control.
In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the oxygen concentration of the exhaust gas detected by the catalyst downstream sensor 15 is sent to the control unit 30 during execution of forced rich control. For example, when a 0V-1V oxygen sensor is used as the catalyst downstream sensor 15, the catalyst downstream sensor 15 in the forced rich control detects a potential in the vicinity of 0V (lean exhaust gas is detected). When the exhaust gas purification catalyst 40 enters the minimum oxygen storage state, a potential around 1 V is detected by the sensor (rich exhaust gas is detected). When the potential difference generated in the catalyst downstream sensor 15 at this time exceeds a predetermined threshold (that is, when the exhaust gas downstream of the exhaust gas purification catalyst 40 is suddenly leaned to the rich side), the control unit 30 performs the exhaust gas purification catalyst 40. Is determined to have reached the minimum oxygen storage state, and the forced rich control is terminated.

b. Oxygen release amount detection In the exhaust gas purification device disclosed herein, the oxygen release amount of the exhaust gas purification catalyst is detected based on the exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in forced rich control. Specifically, the control unit detects the amount of oxygen released from the exhaust gas purification catalyst between the start and end of forced rich control as the oxygen release amount. As described above, forced rich control starts when the exhaust gas purification catalyst reaches the maximum oxygen storage state, and forced rich control ends when the exhaust gas purification catalyst enters the minimum oxygen storage state. Oxygen released until the oxygen storage state is detected as an oxygen release amount.
In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, it is based on the time from when the forced rich control is started to when the exhaust gas downstream of the exhaust gas purification catalyst 40 suddenly leans to the rich side (continuation time of forced rich control). Thus, the oxygen release amount can be calculated. Specifically, by substituting the duration of the forced rich control into a calculation formula set in advance in the control unit 30, the integrated value (oxygen release amount) of oxygen released during the duration of the forced rich control is obtained. Can be calculated. In addition, the duration of the forced rich control (the time when the exhaust gas purifying catalyst releases oxygen) itself can be used as a parameter indicating the oxygen release amount.

c. On the other hand, in the deterioration detection method disclosed here, the oxygen absorption amount of the exhaust gas purification catalyst is detected by performing forced lean control.
In the forced lean control, the air-fuel ratio of the mixed gas is forcibly controlled to be lean, and the lean exhaust gas is supplied to the exhaust gas purification catalyst. In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, when forced lean control is executed, a forced lean control signal is created in the control unit 30, and the forced lean control signal is used as the fuel pump 23, fuel injection valve 3, throttle valve. 10 is transmitted. The fuel pump 23 that has received the forced lean control signal reduces the fuel supplied from the fuel tank 24 to the fuel injection valve 3. And the opening degree of the fuel injection valve 3 becomes small, and the fuel supplied into the fuel chamber 2 decreases. On the other hand, by receiving the forced lean control signal, the opening degree of the throttle valve 10 is increased, and the amount of air supplied into the fuel chamber 2 is increased. As a result, the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 becomes lean (excess oxygen).

  In the deterioration detection method disclosed herein, the air-fuel ratio of the mixed gas in the forced lean control is within the range of A / F = 14.7 ± 0.05 (typically A / F = 14.7). It is characterized by controlling to the value of. As described above, the exhaust gas purification catalyst includes a barium compound in the OSC carrier, and the barium compound absorbs high oxygen when a weak lean exhaust gas of A / F = 14.7 ± 0.05 is supplied. Demonstrate the ability. That is, even if it is a low noble metal exhaust gas purification catalyst having a noble metal catalyst content of 2 g or less per liter of the exhaust gas purification catalyst, a suitable oxygen absorption rate can be exhibited as a whole exhaust gas purification catalyst.

The forced lean control is executed until the exhaust gas downstream of the exhaust gas purification catalyst becomes lean exhaust gas or stoichiometric exhaust gas when the exhaust gas downstream of the exhaust gas purification catalyst is rich exhaust gas. Specifically, the start condition of the forced lean control is that rich exhaust gas is detected downstream of the exhaust gas purification catalyst (for example, after the forced rich control ends). In this case, rich exhaust gas with a low oxygen ratio (or no oxygen) is supplied to the exhaust gas purification catalyst, and exhaust gas downstream of the exhaust gas purification catalyst is rich exhaust gas. In other words, forced lean control is started when oxygen is released from the exhaust gas purification catalyst in a state where oxygen is not released from the exhaust gas purification catalyst (minimum oxygen storage state).
When forced lean control starts, oxygen is absorbed by the exhaust gas purification catalyst. As described above, in the deterioration detection method disclosed herein, the exhaust gas generated from the mixed gas of A / F = 14.7 ± 0.05 is supplied to the exhaust gas purification catalyst, and the exhaust gas purification catalyst contains a barium compound. Therefore, oxygen in the lean exhaust gas is absorbed by the exhaust gas purification catalyst at a suitable oxygen absorption rate. For this reason, oxygen does not flow downstream of the exhaust gas purification catalyst, and rich exhaust gas is detected by the catalyst downstream sensor. Thereafter, if the forced lean control is continued, the exhaust gas purification catalyst cannot absorb oxygen (the exhaust gas purification catalyst is in the maximum oxygen storage state). At this time, oxygen flows out downstream of the exhaust gas purification catalyst, and lean exhaust gas is detected. When the lean exhaust gas is detected downstream of the exhaust gas purification catalyst, the control unit ends the forced lean control.
In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the oxygen concentration of the exhaust gas detected by the catalyst downstream sensor 15 is sent to the control unit 30 while the forced lean control is being performed. For example, when a 0V-1V oxygen sensor is used as the catalyst downstream sensor 15, a potential in the vicinity of 1V is detected by the sensor while the rich rich control is being executed (rich exhaust gas is detected). When the exhaust gas purification catalyst 40 is in the maximum oxygen storage state, a potential around 0 V is detected by the sensor (lean exhaust gas is detected). When the potential difference generated in the catalyst downstream sensor 15 at this time exceeds a predetermined threshold (that is, when the exhaust gas downstream of the exhaust gas purification catalyst 40 suddenly leans to the lean side), the control unit 30 performs the exhaust gas purification catalyst 40. Is determined to have reached the maximum oxygen storage state, and the forced lean control is terminated.

d. Oxygen Absorption Amount Detection In the exhaust gas purification device disclosed herein, the oxygen absorption amount of the exhaust gas purification catalyst is detected based on the exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in forced lean control. Specifically, the control unit detects the amount of oxygen absorbed by the exhaust gas purification catalyst from the start to the end of forced lean control as an oxygen absorption amount. As described above, forced lean control starts when the exhaust gas purification catalyst enters the minimum oxygen storage state, and forced lean control ends when the exhaust gas purification catalyst reaches the maximum oxygen storage state. Oxygen absorbed until the oxygen storage state is detected as an oxygen absorption amount.
In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, it is based on the time from when the forced lean control starts to when the exhaust gas downstream of the exhaust gas purification catalyst 40 suddenly leans to the lean side (continuation time of forced lean control). Thus, the amount of oxygen absorbed can be calculated. Specifically, by substituting the continuation time of the forced lean control into a calculation formula set in advance in the control unit 30, the integrated value (oxygen release amount) of oxygen absorbed during the continuation time of the forced lean control is obtained. Can be calculated. Note that the duration of the forced lean control (the time when the exhaust gas purifying catalyst releases oxygen) itself may be used as a parameter indicating the oxygen absorption amount.

e. Oxygen storage capacity calculation In the oxygen storage capacity calculation, the oxygen storage capacity of the exhaust gas purification catalyst is calculated based on the oxygen release amount and / or the oxygen absorption amount. That is, the oxygen storage capacity of the exhaust gas purification catalyst may be calculated based on both the oxygen release amount detected by performing the forced rich control and the oxygen absorption amount detected by performing the forced lean control. It may be calculated based on only one of them. For example, when calculating the oxygen storage capacity from both the oxygen release amount and the oxygen absorption amount, an average value of the absolute values may be obtained. On the other hand, when calculating the oxygen storage capacity from either the oxygen release amount or the oxygen absorption amount, the detected oxygen release amount (or oxygen absorption amount) itself may be regarded as the oxygen storage capacity, and forced lean control and An average value of a plurality of oxygen release amounts (or oxygen absorption amounts) obtained by repeating the forced rich control a plurality of times may be regarded as the oxygen storage capacity.

  In the oxygen storage capacity calculation, it is more preferable to calculate the oxygen storage capacity based only on the oxygen absorption amount. As described above, when weak lean exhaust gas is supplied to the Ba-added exhaust gas purification catalyst, the oxygen absorption amount (oxygen absorption rate) of the exhaust gas purification catalyst is improved. However, the improvement in the oxygen absorption amount is because oxygen is absorbed in the barium compound, and the oxygen storage amount of the OSC carrier is not improved. In the deterioration detection method disclosed here, since the weak lean exhaust gas having a low oxygen concentration is supplied, the amount of oxygen stored in the OSC carrier itself is small, and the amount of oxygen released is the amount of released oxygen. The amount tends to decrease. Therefore, the deterioration of the exhaust gas purification catalyst can be detected more accurately by calculating the oxygen storage capacity based only on the oxygen absorption amount.

f. Degradation Determination In the degradation detection method disclosed herein, after performing the “e. Oxygen storage capacity calculation”, “degradation determination” is performed to determine whether or not the exhaust gas purification catalyst is degraded. Specifically, the control unit compares the calculated oxygen storage capacity with a predetermined threshold value. An arbitrary value can be set as the threshold value for the oxygen storage capacity in consideration of the functions of the exhaust gas purification catalyst and the internal combustion engine, the regulations of the country in which the exhaust gas purification catalyst is used, and the like. Furthermore, it is more preferable that the threshold value is appropriately changed based on the results of various preliminary tests. The control unit determines that the exhaust gas purification catalyst is deteriorated when the oxygen storage capacity falls below a predetermined threshold, and the exhaust gas purification catalyst is not deteriorated when the oxygen storage capacity exceeds the predetermined threshold.

  The deterioration detection method disclosed here has been described above. In this deterioration detection method, a barium compound is used as an additive to the OSC carrier, and the air-fuel ratio of the mixed gas in forced lean control is controlled to a value within the range of A / F = 14.7 ± 0.05. . The exhaust gas purifying catalyst to which the barium compound is added is supplied with exhaust gas having a weak lean (in other words, near stoichiometric) A / F = 14.7 vicinity (for example, A / F = 14.7 ± 0.05). High oxygen absorption capacity when exposed. Thus, even in a so-called low noble metal exhaust gas purification catalyst having a noble metal catalyst content of 2.0 g or less per liter of the exhaust gas purification catalyst, oxygen in the exhaust gas supplied during forced lean control can be sufficiently absorbed, It is possible to prevent oxygen from flowing out to the downstream side when the purification catalyst is not in the maximum oxygen storage state. For this reason, when the exhaust gas purification catalyst is in the maximum oxygen storage state, the exhaust gas downstream of the exhaust gas purification catalyst suddenly leans to the lean side, and it becomes easy to end forced lean control at an appropriate timing. Thereby, since an accurate oxygen absorption amount can be detected, it is possible to execute the deterioration determination of the exhaust gas purification catalyst based on the oxygen storage capacity calculated from the accurate oxygen absorption amount.

Here, the reason why the oxygen absorption ability is improved when weak lean exhaust gas is supplied to the Ba-added exhaust gas purification catalyst has not been clarified in detail at present. However, as a result of the investigation by the present inventor, it has been found that a higher concentration of NO _x is detected downstream of the exhaust gas purification catalyst during forced rich control than when a normal exhaust gas purification catalyst is used. From this, it is estimated that the improvement of the oxygen absorption capacity by supplying weak lean exhaust gas to the Ba-added exhaust gas purification catalyst is due to the NO _x adsorption effect by the barium compound.

  The exhaust gas control device and the degradation detection method disclosed here have been described above. Next, a specific example of the deterioration detection method disclosed herein will be described with reference to the flowchart shown in FIG. The deterioration detection method of the configuration shown in FIG. 4 includes “1. Each control start determination (S10)”, “2. Forced lean control (S20 to S24)”, “3. Oxygen absorption amount detection (S30)”, “4 Each control end determination (S40) "," 5. Forced rich control (S50 to S54) "," 6. Oxygen release amount detection (S60) "," 7. Oxygen storage amount (OSC) calculation (S70) ", The process of “8. Degradation determination (S80 to S84)” is included. Hereinafter, each process will be described.

1. Each control start determination In the deterioration detection method shown in FIG. 4, before starting the forced lean control or the forced rich control, a determination process (S10) for selecting a control process to be started is performed. Specifically, in this determination process, it is determined whether or not the exhaust gas detected by the catalyst downstream sensor 15 is rich exhaust gas (A / F <14.7). At this time, if rich exhaust gas is detected in the catalyst downstream sensor 15 (S10 is YES), the control unit 30 advances the control process to step S20 and starts forced lean control. On the other hand, when the lean exhaust gas is detected in the catalyst downstream sensor 15 (S10 is NO), the control unit 30 advances the control process to step S50 and starts forced rich control.
In step S10, it may be determined whether the exhaust gas detected by the catalyst downstream sensor 15 is lean exhaust gas (A / F> 14.7). Even in this case, it is possible to determine whether the exhaust gas is lean exhaust gas or rich exhaust gas, and to select one of the control processes based on the determination result.
For convenience of explanation, the following describes a case where step S10 is YES and forced lean control (S20 to S24) is started first, but forced lean control (S20 to S24) and forced rich control (S50 to S54). Which of these is performed first does not limit the present invention.

2. Forced lean control (S20-S24)
When the control start determination S10 is YES and the forced lean control starts, first, the forced lean control flag is turned on in the control unit 30 (S20). Then, the control unit 30 controls the fuel pump 23, the fuel injection valve 3, and the throttle valve 10 to supply the internal combustion engine 1 with the mixed gas whose air-fuel ratio is adjusted to be lean (S22). In the deterioration detection method disclosed herein, the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 in the forced lean control is adjusted to a value of A / F = 14.7 ± 0.05.

  While the forced lean control is being executed, the control unit 30 repeatedly determines whether or not lean exhaust gas (A / F> 14.7) is detected by the catalyst downstream sensor 15 (S24). That is, while oxygen does not flow downstream of the exhaust gas purification catalyst 40 and rich exhaust gas is detected by the catalyst downstream sensor 15, the control unit 30 sets the determination result in step S 24 to NO, and lean exhaust gas is detected by the catalyst downstream sensor 15. The same determination process is repeated until it is detected. When oxygen flows out downstream of the exhaust gas purification catalyst 40 and lean exhaust gas is detected by the catalyst downstream sensor 15, the control unit 30 sets the determination result in step S24 to YES, ends forced lean control, and absorbs oxygen. The amount detection (S30) is started.

3. Oxygen absorption detection (S30)
In step S30, the amount of oxygen absorbed by the exhaust gas purification catalyst 40 is detected based on the oxygen concentration detected by the catalyst downstream sensor 15 while the forced lean control (S20 to S24) is being performed. As described above, this oxygen absorption amount can be calculated based on the duration of the forced lean control (the time during which oxygen is not detected by the catalyst downstream sensor 15). The oxygen absorption amount calculated here is stored in the control unit 30.

4). End determination of each control (S40)
When the detection of the oxygen absorption amount ends, the control process proceeds to each control end determination (S40). In step S40, the control unit 30 determines whether both the forced lean control flag and the forced rich control flag are ON. In the description here, the forced lean control flag is ON because the control process has passed through step S20, but the forced rich control flag is not ON. In this case, the control unit 30 returns the control process to “1. Control process start determination S10”, with the determination in step S40 being NO.
As described in step S24, the condition for terminating the forced lean control is that the exhaust gas (A / F> 14.7) is detected by the catalyst downstream sensor 15, and thus the control process is performed in this state. When returning to S10, the determination result is always NO. That is, when the forced lean control is executed in the first control process, the forced rich control is executed in the next control process, and vice versa.

5. Force rich control (S50-S54)
When the control start determination S10 is NO and forced rich control is started, first, the forced rich control flag is turned ON in the control unit 30 (S50). Then, the control unit 30 controls the fuel pump 23, the fuel injection valve 3, and the throttle valve 10 to supply the internal combustion engine 1 with the mixed gas whose air-fuel ratio is adjusted to be rich (A / F <14.7). (S52).

While the forced rich control is being executed, the control unit 30 repeatedly determines whether or not the rich exhaust gas (A / F <14.7) is detected by the catalyst downstream sensor 15 (S54). That is, while oxygen flows out downstream of the exhaust gas purification catalyst 40 and lean exhaust gas is detected by the catalyst downstream sensor 15, the control unit 30 sets the determination result in step S 54 to NO, and rich exhaust gas is detected by the catalyst downstream sensor 15. The same determination process is repeated until it is done. When oxygen does not flow out downstream of the exhaust gas purification catalyst 40 and rich exhaust gas is detected by the catalyst downstream sensor 15, the control unit 30 sets the determination result in step S54 to YES, ends forced rich control, and releases oxygen. The amount detection (S60) is started.
And the process proceeds to a step (S60) for detecting the amount of released oxygen.

6). Oxygen release amount detection (S60)
In step S60, the amount of oxygen released from the exhaust gas purification catalyst 40 is detected based on the oxygen concentration detected by the catalyst downstream sensor 15 while the forced rich control (S50 to S54) is being performed. As described above, this oxygen release amount can be calculated based on the duration of the forced rich control (the time during which oxygen was detected in the catalyst downstream sensor 15). When step S60 ends, the control unit 30 stores the calculated oxygen release amount, and advances the control process to “4. End determination of each control (S40)” again.

When the control process proceeds to steps S20 and S50 and the control unit 30 proceeds to the control end determination (S40) in a state where both the forced lean control flag and the forced rich control flag are ON, the control unit 30 performs the forced lean control. It is determined that both the control and the forced rich control are finished, and the control process is advanced to the calculation of the oxygen storage capacity (S70).
Here, the fact that both the forced lean control and the forced rich control flags are set to ON (the forced lean control and the forced rich control are executed once) is set as an end condition. Execution of both (or any) forced lean control and forced rich control a plurality of times may be set as an end condition. In this case, a plurality of oxygen absorption amounts (and / or oxygen release amounts) are obtained, and the oxygen storage capacity can be calculated based on the plurality of data, so that more accurate deterioration detection can be performed.
Further, in this step S40, it is only necessary to set at least that the forced lean control flag is ON as an end condition. Even if the forced rich control is not performed, the oxygen storage capacity is calculated (S70). It is also possible to set a condition for proceeding to.

7). Oxygen storage amount (OSC) calculation (S70)
In step S70, the oxygen storage amount (OSC) of the exhaust gas purification catalyst 40 is calculated based on the oxygen absorption amount and / or the oxygen release amount stored in the control unit 30. For example, when calculating the OSC based on the oxygen absorption amount and the oxygen release amount, an average value of absolute values of these parameters is obtained. Further, when any one of the parameters is adopted, the detected parameter can be regarded as the OSC as it is. Further, when the control process of forced lean control and forced rich control is executed a plurality of times, the average of the absolute values of the parameters obtained in each control process can be obtained as the OSC. After calculating the OSC as described above, the control unit 30 advances the control process to “8. Degradation determination (S80)”.

8). Degradation determination (S80 to S84)
Here, the OSC calculated in “7. Oxygen storage amount (OSC) calculation” is compared with a predetermined threshold (T _OSC ). Then, when the OSC falls below the threshold value (T _OSC ) (OSC <T _OSC ), the control unit 30 determines that the exhaust gas purification catalyst 40 has deteriorated (YES in S80), and advances the control process to step S82. The exhaust gas purification catalyst 40 is notified that it has deteriorated. On the other hand, when the OSC exceeds the threshold value (T _OSC ) (OSC> T _OSC ), the control unit 30 determines that the exhaust gas purification catalyst 40 is normal (NO in S80), advances the control process to step S84, and sets the exhaust gas. Notifying that the purification catalyst 40 is normal.

  The preferred embodiments of the present invention have been described above. Note that switching between forced lean control and forced rich control in the above-described degradation detection method is not only a method for detecting degradation of the exhaust gas purification catalyst, but also various internal combustion engines that require switching between other forced lean control and forced rich control. It can also be applied to the driving method.

  Next, examples relating to the present invention will be described. However, the examples described below are not intended to limit the present invention.

<Example 1: Preparation of sample>
In this example, three types of metal exhaust gas purification catalysts (samples 1 to 3) having different constituent materials were produced. Details of each sample will be described below.

(Sample 1)
Here, as sample 1, an exhaust gas purification catalyst having an OSC region composed of an OSC carrier and a non-OSC region composed of a non-OSC carrier, and barium acetate, which is a barium compound, is added to the OSC region. Produced. The exhaust gas purification catalyst produced here is a low noble metal exhaust gas purification catalyst having a noble metal catalyst content of 2.0 g or less per 1 L of the base material volume. The base material of the exhaust gas purification catalyst used here is a cylindrical honeycomb base material having a base length of 105 mm and a capacity of 0.9 L. In the following description of the material composition, what is described as (g / L) indicates the amount contained in the base material capacity of 1 L.
First, a dispersion was prepared by suspending 85 g / L of alumina (Al ₂ O ₃ ) powder in a nitric Pd chemical containing 1.0 g / L of palladium (Pd). The dispersion is 65 g / L of ceria-zirconia composite oxide (CeO ₂ / ZrO ₂ = 0.49) as an OSC material, and 5 g of barium acetate ((CH ₃ COO) ₂ Ba) as a barium compound. / L, 5 g / L of alumina as a binder was dispersed to obtain an OSC region slurry. The OSC region slurry was dried at 120 ° C. for 30 minutes and then calcined at 500 ° C. for 2 hours to obtain a catalyst material for the OSC region.
On the other hand, a dispersion liquid was prepared by suspending 65 g / L zirconia (ZrO ₂ ) powder in a nitric acid-based Rh chemical solution containing 0.2 g / L rhodium (Rh). Then, 25 g / L of lanthanum (La) -added alumina, which is a material for non-OSC carrier, and 5 g / L of alumina, which is a binder, were dispersed in the dispersion to obtain a slurry for non-OSC region. This non-OSC region slurry was dried at 120 ° C. for 30 minutes, and further calcined at 500 ° C. for 2 hours to obtain a non-OSC region catalyst material.

Next, the catalyst material for the OSC region was dispersed in an acidic aqueous solution to prepare a slurry. And the area | region of 20% (namely, about 21 mm) of the base material full length from one end of the said cylindrical honeycomb base material was immersed in the slurry which disperse | distributed the catalyst material for OSC area | regions. Then, the substrate is pulled up from the slurry, dried at 20 ° C. for 30 minutes, and further fired at 500 ° C. for 2 hours, so that 20% of the total length of the substrate from one end of the tubular honeycomb substrate The OSC region was formed up to this site.
Thereafter, the catalyst material for the non-OSC region was dispersed in an acidic aqueous solution to prepare a slurry. Then, an area of 80% (that is, about 84 mm) of the entire length of the base material from the other end of the cylindrical honeycomb base material (the end opposite to the end where the OSC region is formed) is used for the non-OSC region. It was immersed in the slurry in which the catalyst material was dispersed. Then, the base material is pulled up from the slurry, dried under a temperature condition of 20 ° C. for 30 minutes, and further fired at a temperature condition of 500 ° C. for 2 hours. Non-OSC regions were formed up to% sites.
The exhaust gas purifying catalyst obtained as described above is hereinafter referred to as Sample 1.

(Sample 2)
Sample 2 was prepared in the same procedure as Sample 1 except that barium sulfate (BaSO ₄ ) was used as the barium compound.

(Sample 3)
Sample 3 was prepared in the same procedure as Sample 1 except that no barium compound was added to the OSC region.

<Example 2: Endurance test>
In this example, samples 1 to 3 prepared in Example 1 were attached to an exhaust system of a V8 engine that is an internal combustion engine, and durability tests on samples 1 to 3 were performed. At this time, the OSC region was disposed on the upstream side with respect to the direction in which the exhaust gas flows, and the non-OSC region was disposed on the downstream side. Then, the V8 engine was operated, and the exhaust gas at 1000 ° C. was continuously supplied to Samples 1 to 3 for 50 hours.

<Example 3: OSC evaluation>
After the durability test, each sample was removed from the V8 engine and attached to the exhaust system of the L4 engine. Moreover, the catalyst downstream sensor (0V-1V oxygen sensor) was attached to the downstream of each sample. Also at this time, the OSC region was arranged on the upstream side, and the non-OSC region was arranged on the downstream side. Then, the air-fuel ratio of the mixed gas supplied to the L4 engine was changed as in Conditions 1 to 5 described in Table 1 below. Specifically, in Condition 1, after performing forced lean control with A / F = 15.1, forced rich control with A / F = 14.1 was performed. In condition 2, the air-fuel ratio in forced lean control was changed to A / F = 15.0. In condition 3, the air-fuel ratio for forced lean control was changed to A / F = 14.9. In condition 4, the air-fuel ratio in forced lean control was changed to A / F = 14.8. In condition 5, the air-fuel ratio in forced lean control was changed to A / F = 14.7. Note that the air-fuel ratios of forced rich control in Conditions 2 to 5 were all set to A / F = 14.1.
And the oxygen absorption amount of each sample was detected during the forced lean control of the above conditions 1 to 5, and the oxygen release amount of each sample was detected by forced rich control. The oxygen absorption amount of each sample obtained in this way is shown in FIG. 5, and the oxygen release amount is shown in FIG.

As shown in FIG. 5, in samples 1 and 2 in which a barium compound is added to the OSC carrier, the forced lean control is performed under conditions 4 and 5 where the air-fuel ratio (A / F) of the mixed gas is 14.8 or less. The amount of oxygen absorbed was improved. That is, when a mixed gas whose air-fuel ratio is adjusted to be slightly lean (A / F <14.8, particularly A / F = 14.7) is supplied to an exhaust gas purification catalyst in which a barium compound is added to an OSC carrier, high oxygen absorption is achieved. It was found that the ability was demonstrated. Therefore, even if a low precious metal exhaust gas purification catalyst is used by using an exhaust gas purification catalyst in which a barium compound is added to the OSC carrier and adjusting the air-fuel ratio of the mixed gas during forced lean control to a weak lean, forced lean It is understood that the control can be terminated at an appropriate timing.
Among samples 1 and 2, sample 1 using barium acetate as the barium compound exhibited a higher oxygen absorption capacity. From this, it was found that barium acetate is suitable as the barium compound added to the OSC carrier.

  On the other hand, as shown in FIG. 6, in any sample, the amount of oxygen released during forced rich control decreased as the mixed gas during forced lean control was adjusted to the weak lean side. Therefore, when the gas mixture under forced lean control is adjusted to weak lean, the oxygen release amount during execution of forced rich control decreases, so the oxygen storage capacity is based only on the amount of oxygen absorbed during forced lean control. It is understood that a more accurate value can be obtained by calculating.

  According to the deterioration detection method and the exhaust gas purification device disclosed herein, even when a low precious metal exhaust gas purification catalyst is used, oxygen is prevented from flowing out downstream of the exhaust gas purification catalyst during the forced lean control. Switching to forced rich control can be executed at an appropriate timing. As a result, the oxygen storage capacity of the exhaust gas purification catalyst can be accurately calculated, and the deterioration of the exhaust gas purification catalyst can be accurately detected based on the calculated oxygen storage capacity. That is, the present invention is an important technology for solving the problems of low precious metal exhaust gas purification catalysts aimed at cost reduction and the stable supply of materials, and for practical application of low precious metal exhaust gas purification catalysts. It greatly contributes to.

1 Internal combustion engine
2 Combustion chamber 3 Fuel injection valve 4 Intake manifold 5 Exhaust manifold 6 Intake duct 7 Exhaust turbocharger 7a Compressor 8 Air flow meter 9 Air cleaner 9a Intake temperature sensor 10 Throttle valve 11 Cooling device 12 Exhaust passage 13 Exhaust fuel injection valve 14 Catalyst upstream sensor 15 Catalyst Downstream Sensor 18 Exhaust Gas Recirculation Passage 20 EGR Cooling Device 21 Fuel Supply Pipe 22 Common Rail 23 Fuel Pump 24 Fuel Tank 30 Control Unit (ECU: Engine Control Unit)
40 exhaust gas purification catalyst 42 base material 43 catalyst layer 44 OSC region 45 non-OSC region 48 flow path 100 exhaust gas purification device

Claims (18)

A catalyst layer comprising a noble metal catalyst and a carrier containing an OSC material having an oxygen storage capacity is formed on a base material, and purifies exhaust gas generated by combustion of a mixed gas in an internal combustion engine. A method for detecting deterioration of an exhaust gas purifying catalyst,
When the exhaust gas downstream of the exhaust gas purification catalyst is an air-fuel ratio lean or stoichiometric exhaust gas, the air-fuel ratio of the mixed gas is forcibly set until the exhaust gas downstream of the exhaust gas purification catalyst becomes an air-fuel ratio rich exhaust gas. Rich control;
Detecting an oxygen release amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in the forced rich control;
When the exhaust gas downstream of the exhaust gas purification catalyst is an air-fuel ratio rich exhaust gas, the mixed gas supplied to the internal combustion engine is exhausted until the exhaust gas downstream of the exhaust gas purification catalyst becomes an air-fuel ratio lean or stoichiometric exhaust gas. Forcing the air-fuel ratio to be lean or stoichiometric;
Detecting an oxygen absorption amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst in the forced lean control;
Calculating the oxygen storage capacity of the exhaust gas purifying catalyst based on the oxygen release amount and / or the oxygen absorption amount;
Including
here,
Setting the content of the noble metal catalyst to 2 g or less per liter of the capacity of the exhaust gas purification catalyst;
Using a barium compound as an additive to the carrier containing the OSC material;
The air-fuel ratio of the mixed gas in the forced rich control is controlled to 13.0 <A / F ≦ 14.1, and the air-fuel ratio of the mixed gas in the forced lean control is A / F = 14.7 ± 0.05. The oxygen storage capacity of the exhaust gas purification catalyst is compared with a predetermined threshold value, and the exhaust gas purification catalyst deteriorates when the oxygen storage capacity falls below the predetermined threshold value. Determining that
A method for detecting deterioration of an exhaust gas purification catalyst, further comprising:   The deterioration detection method according to claim 1, wherein, in calculating the oxygen storage capacity, the oxygen storage capacity of the exhaust gas purification catalyst is calculated based only on the oxygen absorption amount.   The deterioration detection method according to claim 1, wherein barium acetate is used as the barium compound.   The deterioration detection method according to claim 1, wherein at least palladium and rhodium are used as the noble metal catalyst.   The degradation detection method according to claim 1, wherein a ceria-zirconia composite oxide is used as the OSC material.   The deterioration detection method according to claim 1, wherein an addition amount of the barium compound is set to 5 to 10 parts by mass with respect to 100 parts by mass of the OSC material.   The said catalyst layer is equipped with the OSC area | region which consists of a support | carrier containing the said OSC material, and the non-OSC area | region which consists of a support | carrier comprised with support | carrier materials other than the said OSC material, The 1-6 characterized by the above-mentioned. The deterioration detection method according to any one of the above.   The deterioration detection method according to claim 7, wherein at least one of complex oxides mainly composed of aluminum oxide, zirconium oxide, and silicon oxide is used as a carrier material other than the OSC material. The amount of the barium compound added to the OSC region is set to 5 to 10 parts by mass with respect to 100 parts by mass of the OSC material,
The amount of the barium compound added to the non-OSC region is set to 10 to 15 parts by mass with respect to 100 parts by mass of the carrier material other than the OSC material. Degradation detection method. An exhaust gas purification apparatus for purifying the exhaust gas, provided in an exhaust system of an internal combustion engine that is supplied with a mixed gas containing oxygen and fuel gas and exhausts the exhaust gas to the exhaust system by burning the mixed gas ,
An exhaust gas purification catalyst which is disposed in the exhaust system and is configured by forming a catalyst layer including a noble metal catalyst and a support containing an OSC material having an oxygen storage capacity on a substrate;
A catalyst downstream sensor that is disposed downstream of the exhaust gas purification catalyst in the exhaust system, and that detects an exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst;
A control unit that transmits the exhaust gas air-fuel ratio downstream of the exhaust gas purification catalyst detected by the catalyst downstream sensor, and adjusts the air-fuel ratio of the mixed gas supplied to the internal combustion engine based on the transmitted exhaust gas air-fuel ratio When,
With
The controller is
When the air-fuel ratio lean or stoichiometric exhaust gas is detected in the catalyst downstream sensor, the air-fuel ratio of the mixed gas is controlled to be rich until the air-fuel ratio rich exhaust gas is detected in the catalyst downstream sensor. To do;
In the forced rich control, detecting an oxygen release amount of the exhaust gas purification catalyst based on an exhaust gas air-fuel ratio detected by the catalyst downstream sensor;
When the air-fuel ratio rich exhaust gas is detected by the catalyst downstream sensor, the air-fuel ratio of the mixed gas is forcibly made lean or stoichiometric until the air-fuel ratio lean or stoichiometric exhaust gas is detected by the catalyst downstream sensor. To control;
Detecting the oxygen absorption amount of the exhaust gas purification catalyst based on the exhaust gas air-fuel ratio detected by the catalyst downstream sensor in the forced lean control;
Calculating the oxygen storage capacity of the exhaust gas purifying catalyst based on the oxygen release amount and / or the oxygen absorption amount;
Is configured to run,
Here, the precious metal catalyst is included in a ratio of 2 g or less per 1 L of the capacity of the exhaust gas purification catalyst;
A barium compound is added to the carrier containing the OSC material;
The control unit controls the air-fuel ratio of the mixed gas in the forced rich control to 13.0 <A / F ≦ 14.1 , and sets the air-fuel ratio of the mixed gas in the forced lean control to A / F = 14.1 . The control unit compares the oxygen storage capacity of the exhaust gas purifying catalyst with a predetermined threshold value, and the oxygen storage capacity falls below the predetermined threshold value. Determining that the exhaust gas purification catalyst is deteriorated in the case;
An exhaust gas purifying apparatus, further comprising:   The exhaust gas purification apparatus according to claim 10, wherein the control unit is configured to calculate an oxygen storage capacity of the exhaust gas purification catalyst based only on the oxygen absorption amount.   The exhaust gas purifying apparatus according to claim 10 or 11, wherein barium acetate is added as the barium compound to the carrier containing the OSC material.   The exhaust gas purifying apparatus according to any one of claims 10 to 12, wherein the noble metal catalyst contains at least palladium and rhodium.   The exhaust gas purification apparatus according to any one of claims 10 to 13, wherein the OSC material is a ceria-zirconia composite oxide.   The carrier containing the OSC material, wherein the barium compound is added at a ratio of 5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the OSC material. The exhaust gas purifying apparatus according to claim 1.   The said catalyst layer is provided with the OSC area | region which consists of a support | carrier containing the said OSC material, and the non-OSC area | region which consists of a support | carrier comprised with support | carrier materials other than the said OSC material, The any one of Claims 10-15. The exhaust gas purification apparatus according to 1.   The exhaust gas purifying apparatus according to claim 16, wherein the carrier material other than the OSC material includes at least one of complex oxides mainly composed of aluminum oxide, zirconium oxide, and silicon oxide. The barium compound is included in the OSC region at a ratio of 5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the OSC material.
The non-OSC region includes the barium compound at a ratio of 10 parts by mass to 15 parts by mass with respect to 100 parts by mass of a carrier material other than the OSC material. The exhaust gas purification apparatus as described.

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