WO2011027470A1

WO2011027470A1 - Exhaust purification device for internal combustion engine

Info

Publication number: WO2011027470A1
Application number: PCT/JP2009/065555
Authority: WO
Inventors: 大月寛; 祖父江優一; 浅沼孝充
Original assignee: トヨタ自動車株式会社
Priority date: 2009-09-01
Filing date: 2009-09-01
Publication date: 2011-03-10

Abstract

An exhaust purification device for an internal combustion engine, which comprises an NOx storage reduction catalyst arranged within an engine exhaust passage and an SOx holding member arranged in the upstream of the NOx storage reduction catalyst within the engine exhaust passage. The SOx holding member is composed of a particulate catalyst carrier (48) supporting a catalyst metal, and a binder which is composed of a material different from that of the catalyst carrier (48) and binds catalyst carriers (48) together. The volume of at least either of the catalyst carrier (48) or the binder is expanded by being modified into a sulfate by adsorbing SOx contained in the exhaust gas, so that the bond between a sulfatized catalyst carrier (48a) and the binder is released. As a result, the sulfatized catalyst carrier (48a) is detached as a separate particle.

Description

Exhaust gas purification device for internal combustion engine

The present invention relates to an exhaust purification device for an internal combustion engine.

Examples of exhaust gases of internal combustion engines such as diesel engines and gasoline engines include carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NO _x ), and particulate matter (PM). Contains ingredients. An exhaust gas purification device is attached to the internal combustion engine to purify these components.
As one of the methods for removing nitrogen oxides, it has been proposed that a NO _X storage reduction catalyst be disposed in the engine exhaust passage. The NO _X storage reduction catalyst holds NO _X when the air-fuel ratio of the exhaust gas is lean. When the holding amount of the NO _X reaches the allowable value, by the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio, the held NO _X is released. The released NO _X is reduced to N ₂ by a reducing agent such as carbon monoxide contained in the exhaust gas.
In JP 2002-21538 discloses, was added potassium as _the NO _X storage agent of the NO _X occluding and reducing catalyst, the catalyst system is disclosed in which a three-way catalyst downstream of the NO _X occluding and reducing catalyst. In this catalyst device, an alkali metal capturing means carrying phosphorus is provided between the NO _X storage reduction catalyst and the three-way catalyst. It is disclosed that potassium evaporated from the NO _X storage reduction catalyst is captured by an alkali metal trapping means to prevent potassium from reaching the downstream three-way catalyst.
Patent In 2006-346525 discloses a three-way catalyst is arranged downstream of the NO _X occluding and reducing catalyst, adding a storage agent and alkaline stabilizer to the catalyst layer of the NO _X occluding and reducing catalyst, the catalyst layer of the three-way catalyst Discloses an exhaust emission control device for an internal combustion engine in which palladium and an alkali trapping agent are added to the lower layer, and platinum and rhodium are added to the upper layer. This exhaust purification device is disclosed as being able to prevent the exhaust purification performance of the three-way catalyst from being reduced by the storage agent.

JP 2002-21538 A JP 2006-346525 A

The exhaust gas of the internal combustion engine may contain sulfur oxide (SO _x ). The NO _X storage reduction catalyst holds SO _X simultaneously with holding NO _X. When SO _X is held, the amount of NO _X that can be held decreases. Thus, so-called sulfur poisoning occurs in the NO _X storage reduction catalyst. The NO _X occluding and reducing catalyst in order to prevent the SO _X is held, on the upstream side of the NO _X occluding and reducing catalyst, it is possible to arrange the stored SO _X material that holds the SO _X. For SO _X is removed from the exhaust gas by stored SO _X material, it is possible to avoid sulfur poisoning of the NO _X occluding and reducing catalyst.
However, or the remaining amount is less capable of holding SO _X of stored SO _X material, if the stored SO _X material is or hot, there is a case where SO _X flows out from the stored SO _X material. SO _X flowing out from the stored SO _X material flows into _the NO _X storage reduction catalyst is held in the NO _X occluding and reducing catalyst. As described above, there is a problem that sulfur poisoning of the NO _X storage reduction catalyst may occur even when the SO _X holding material is arranged in the engine exhaust passage.
An object of the present invention is to provide an exhaust purification device for an internal combustion engine that suppresses the outflow of SO _X from the SO _X holding material.

An exhaust gas purification apparatus for an internal combustion engine according to a first aspect of the present invention is disposed in an engine exhaust passage, retains NO _X contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio is disposed in the stoichiometric air-fuel ratio or the _the NO _X storage reduction catalyst to release the NO _X held and becomes rich, the upstream side of the engine exhaust passage of the NO _X occluding and reducing catalyst, SO _X holding material for holding the SO _X With. The SO _X holding material includes a particulate catalyst carrier that supports a catalyst metal, and a binder that is formed of a material different from that of the catalyst carrier and bonds the catalyst carriers together. At least one of the catalyst carrier and the binding material absorbs SO _X contained in the exhaust gas and is reformed to sulfate, whereby the volume expands and the bond between the catalyst carrier and the binding material is released. The catalyst carrier is detached in the form of particles. With this configuration, the outflow of SO _X from the SO _X holding material can be suppressed.
In the above invention, the catalyst carrier is formed of a material that expands in volume when SO _X is occluded and reformed to sulfate, and the binder is made of a material that does not change when SO _X flows. It is preferable that the material is formed of a material whose volume is not changed when _X is occluded and modified into a sulfate. With this configuration, the catalyst carrier that occludes SO _X can be more reliably desorbed.
The exhaust gas purification apparatus for an internal combustion engine according to the second aspect of the present invention is disposed in the engine exhaust passage, holds NO _X contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and controls the inflowing exhaust gas. air-fuel ratio is arranged to the stoichiometric air-fuel ratio or the _the NO _X storage reduction catalyst to release the NO _X held and becomes rich, the upstream side of the engine exhaust passage of the NO _X occluding and reducing catalyst, SO _X holding material for holding the SO _X With. The SO _X holding material is formed of a particulate catalyst carrier supporting a catalyst metal, a material different from the catalyst carrier, an auxiliary particle having an average particle size smaller than that of the catalyst carrier, and a material substantially the same as the auxiliary particle, And a catalyst carrier that is supported by the auxiliary particles. The catalyst carrier occludes SO _X contained in the exhaust gas and is reformed to sulfate, whereby the volume expands, the support of the catalyst carrier by the auxiliary particles is released, and the catalyst carrier is detached in the form of particles. With this configuration, the outflow of SO _X from the SO _X holding material can be suppressed.
In the above invention, the binder and the auxiliary particles have a decomposition temperature at which the sulfate decomposes when SO _X is occluded to become a sulfate, and the desorption that raises the temperature of the SO _X holding material above the decomposition temperature. By performing the promotion control, it is preferable that the sulfate is decomposed to reduce the volume of the binder and the auxiliary particles, and the support of the catalyst carrier by the auxiliary particles is released. With this configuration, the catalyst carrier that occludes SO _X can be more reliably desorbed.
In the above invention, the collection filter is disposed in the engine exhaust passage downstream of the NO _X storage reduction catalyst and collects desorbed particles including the catalyst carrier desorbed from the SO _X holding material. When the amount of collected desorbed particles becomes larger than a predetermined allowable value, it is preferable to prohibit desorption promotion control. With this configuration, it is possible to avoid the ability of the collection filter to be remarkably reduced or the collection filter to be unusable.
In the above invention, the SO _X holding material has a catalyst carrier arranged in layers on the surface of the substrate, estimates the thickness of the catalyst carrier layer, and uses the thickness of the catalyst carrier layer to calculate the integrated SO of the SO _X holding material. It is preferable to calculate the _X retention amount. With this configuration, the SO _X holding material can be managed.
In the above invention, the collection filter is disposed in the engine exhaust passage downstream of the NO _X storage reduction catalyst and collects desorbed particles including the catalyst carrier desorbed from the SO _X holding material. After releasing SO _X from the collected desorbed particles, NO _X contained in the exhaust gas is preferably held by the desorbed particles. With this configuration, the desorbed particles can be used as a NO _X storage reduction catalyst.
In the above invention, based on the amount of desorbed particles collected by the collection filter, an allowable value by which the desorbed particles can hold NO _X is estimated, and the NO _X retention amount of the desorbed particles exceeds the allowable value. In this case, it is preferable to perform NO _X release control for releasing the NO _X held in the desorbed particles by making the air-fuel ratio of the exhaust gas flowing into the collection filter the stoichiometric air-fuel ratio or rich.
In the above invention, when almost all of the particulate catalyst carrier contained in the SO _X holding material is desorbed, SO _X contained in the exhaust gas is held in the NO _X storage reduction catalyst. When the temperature of the NO _X storage reduction catalyst is raised to a temperature at which SO _X can be released and SO _X release control is performed to make the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst the stoichiometric air-fuel ratio or rich , based on the amount of desorbed particles trapped in the trapping filter, it is preferable to determine at least one of the air-fuel ratio of the exhaust gas flowing into the temperature and _the NO _X storage reduction catalyst of the NO _X occluding and reducing catalyst. With this configuration, the sulfur poisoning recovery process of the NO _X storage reduction catalyst can be performed efficiently.

According to the present invention, it is possible to provide an exhaust purifying apparatus for suppressing internal combustion engine the flow of SO _X from the stored SO _X material.

1 is a schematic overall view of an internal combustion engine in a first embodiment. It is a schematic cross-sectional view of the NO _X occluding and reducing catalyst. It is a schematic sectional drawing of a SO _X trap catalyst. It is an expansion schematic sectional drawing explaining the coupling | bonding state of the catalyst support | carrier of a SO _X trap catalyst. FIG. 3 is a first enlarged schematic cross-sectional view illustrating desorption of the catalyst carrier of the SO _X trap catalyst. It is a 2nd expansion schematic sectional drawing explaining detachment | desorption of the catalyst support | carrier of a SO _X trap catalyst. FIG. 6 is a third enlarged schematic cross-sectional view illustrating desorption of the catalyst carrier of the SO _X trap catalyst. 2 is an enlarged schematic cross-sectional view of a SO _X trap catalyst of a first comparative example in Embodiment 1. FIG. 6 is a graph illustrating the relationship between the SO _X retention amount and the SO _X release amount of the SO _X trap catalyst of the first comparative example in the first embodiment. 6 is an enlarged schematic cross-sectional view when the catalyst carrier of the SO _X trap catalyst of the second comparative example in Embodiment 1 is desorbed. FIG. FIG. 3 is an explanatory diagram of a first step of the method for producing the SO _X trap catalyst in the first embodiment. FIG. 5 is an explanatory diagram of a second step of the method for producing the SO _X trap catalyst in the first embodiment. 2 is a schematic view of an apparatus for detecting the thickness of a SO _X trap catalyst coating layer in Embodiment 1. FIG. 6 is a graph for explaining a relationship between an accumulated SO _X retention amount and a thickness of a coat layer in an SO _X trap catalyst. It is a graph explaining the relationship between the accumulated usage amount of fuel and the accumulated SO _X retention amount in the SO _X trap catalyst. FIG. 3 is a first enlarged schematic cross-sectional view of a SO _X trap catalyst in a second embodiment. FIG. 5 is a second enlarged schematic cross-sectional view of a SO _X trap catalyst in a second embodiment. 10 is a flowchart for determining whether or not to perform desorption promotion control in the second embodiment. It is a map of SO _X amount per unit time discharged from the engine body. 10 is a time chart for explaining desorption promotion control in the second embodiment. It is explanatory drawing of the injection pattern of the fuel at the time of normal driving | operation. It is explanatory drawing of the injection pattern when raising the temperature of the exhaust gas discharged | emitted from an engine main body. FIG. 5 is a schematic diagram of an internal combustion engine in a third embodiment. 10 is a time chart of first operational control in the third embodiment. 10 is a time chart of second operational control in the third embodiment. Is a map of the NO _X amount per unit discharged time from the engine body. It is explanatory drawing of the injection pattern when reducing the air fuel ratio of the exhaust gas discharged | emitted from an engine main body. 12 is a time chart of third operational control in the third embodiment. It is a graph illustrating the operation range of the operating region and the SO _X release control in _the NO _X storage reduction catalyst.

Embodiment 1
With reference to FIG. 1 to FIG. 15, the exhaust gas purification apparatus for an internal combustion engine in the first embodiment will be described. The internal combustion engine in the present embodiment is arranged in a vehicle. In the present embodiment, a compression ignition type diesel engine attached to an automobile will be described as an example.
FIG. 1 shows an overall view of an internal combustion engine in the present embodiment. The internal combustion engine includes an engine body 1. The internal combustion engine also includes an exhaust purification device that purifies the exhaust gas. The engine body 1 includes a combustion chamber 2 as each cylinder, an electronically controlled fuel injection valve 3 for injecting fuel into each combustion chamber 2, an intake manifold 4, and an exhaust manifold 5.
The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6. Further, a cooling device 11 for cooling the intake air flowing through the intake duct 6 is disposed in the middle of the intake duct 6. In the embodiment shown in FIG. 1, engine cooling water is guided to the cooling device 11. The intake air is cooled by the engine cooling water.
The exhaust manifold 5 is connected to the inlet of the turbine 7b of the exhaust turbocharger 7. The exhaust gas purification apparatus in the present embodiment is NO_XAn occlusion reduction catalyst (NSR) 17 is provided. In addition, the exhaust emission control device in the present embodiment is provided with SO contained in the exhaust gas._XSO to remove_XSO as holding material_X A trap catalyst 14 is provided. SO_XThe trap catalyst 14 is NO_XIt is disposed in the engine exhaust passage upstream of the storage reduction catalyst 17. SO_XThe trap catalyst 14 is connected to the outlet of the turbine 7b through the exhaust pipe 12. NO_XIn the engine exhaust passage downstream of the storage reduction catalyst 17, a particulate filter 16 is disposed as a collection filter that collects particulate matter in the exhaust gas. An oxidation catalyst 13 is disposed in the engine exhaust passage downstream of the particulate filter 16.
An EGR passage 18 is disposed between the exhaust manifold 5 and the intake manifold 4 in order to perform exhaust gas recirculation (EGR). An electronically controlled EGR control valve 19 is disposed in the EGR passage 18. A cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed in the middle of the EGR passage 18. In the embodiment shown in FIG. 1, engine cooling water is introduced into the cooling device 20. The EGR gas is cooled by the engine cooling water.
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 a fuel tank 24 via an electronically controlled variable discharge amount fuel pump 23. The fuel stored in the fuel tank 24 is supplied into the common rail 22 by the fuel pump 23. The fuel supplied into the common rail 22 is supplied to the fuel injection valve 3 through each fuel supply pipe 21.
The electronic control unit 30 is composed of a digital computer. The electronic control unit 30 in the present embodiment functions as a control device for the exhaust purification device. The electronic control unit 30 includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36 that are connected to each other by a bidirectional bus 31.
ROM 32 is a read-only storage device. The ROM 32 stores in advance information such as a map necessary for control. The CPU 34 can perform arbitrary calculations and determinations. The RAM 33 is a readable / writable storage device. The RAM 33 can store information such as an operation history and can temporarily store calculation results.
NO_XDownstream of the occlusion reduction catalyst 17 is NO._X A temperature sensor 26 for detecting the temperature of the storage reduction catalyst 17 is disposed. A temperature sensor 27 for detecting the temperature of the oxidation catalyst 13 or the particulate filter 16 is disposed downstream of the oxidation catalyst 13. A differential pressure sensor 28 for detecting the differential pressure across the particulate filter 16 is attached to the particulate filter 16. The output signals of the

temperature sensors

26 and 27, the differential pressure sensor 28, and the intake air amount detector 8 are input to the input port 35 via the corresponding AD converters 37, respectively.
A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. From the output of the crank angle sensor 42, the rotational speed of the engine body 1 can be detected.
On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the EGR control valve 19, and the fuel pump 23 through corresponding drive circuits 38. Thus, the fuel injection valve 3 and the throttle valve 10 are controlled by the electronic control unit 30.
The oxidation catalyst 13 is a catalyst having oxidation ability. The oxidation catalyst 13 includes, for example, a base having a partition extending in the exhaust gas flow direction. The substrate is formed in a honeycomb structure, for example. The base is accommodated in, for example, a cylindrical case. On the surface of the substrate, a coat layer as a catalyst support layer is formed of, for example, porous oxide powder. The coat layer carries a catalyst metal formed of a noble metal such as platinum (Pt), rhodium (Rd), or palladium (Pd). Carbon monoxide or unburned hydrocarbons contained in the exhaust gas are oxidized by an oxidation catalyst and converted into water, carbon dioxide, or the like.
The particulate filter 16 is a filter that removes particulate matter (particulates) such as carbon fine particles and sulfate contained in the exhaust gas. The particulate filter has, for example, a honeycomb structure and a plurality of flow paths extending in the gas flow direction. In the plurality of channels, the channels whose downstream ends are sealed and the channels whose upstream ends are sealed are alternately formed. The partition walls of the flow path are formed of a porous material such as cordierite. Particulate matter is trapped when the exhaust gas passes through the partition wall.
The particulate matter is collected on the particulate filter 16 and oxidized. The particulate matter gradually deposited on the particulate filter 16 is oxidized and removed by raising the temperature to, for example, about 600 ° C. in an atmosphere containing excess air.
Figure 2 shows NO_XThe expansion schematic sectional drawing of an occlusion reduction catalyst is shown. NO_XThe storage reduction catalyst 17 is NO contained in the exhaust gas discharged from the engine body 1._XIs temporarily held and held NO_XN when releasing₂It is a catalyst that converts to The term “retention” in the present invention includes the meanings of “adsorption”, “absorption” and “occlusion”.
NO_XThe storage reduction catalyst 17 has a catalyst carrier 45 made of, for example, aluminum oxide supported on a base. A catalyst metal 46 formed of a noble metal is dispersed and supported on the surface of the catalyst carrier 45. NO on the surface of the catalyst carrier 45_XA layer of absorbent 47 is formed. As the catalyst metal 46, for example, platinum Pt is used. NO_XThe components constituting the absorbent 47 were selected from, for example, alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one is used. In this embodiment, NO_XBarium Ba is used as a component constituting the absorbent 47.
In the present invention, the ratio of the exhaust gas air and fuel (hydrocarbon) supplied to the engine intake passage, combustion chamber, or engine exhaust passage is referred to as the air-fuel ratio (A / F) of the exhaust gas. When the air-fuel ratio of the exhaust gas is lean (when larger than the stoichiometric air-fuel ratio), NO contained in the exhaust gas is oxidized on the catalyst metal 46 and NO.₂become. NO₂Is nitrate ion NO₃ ⁻NO in the form of_XThe absorbent 47 is occluded. On the other hand, when the air-fuel ratio of the exhaust gas is rich or when it becomes the stoichiometric air-fuel ratio, NO_XNitrate ion NO stored in absorbent 47₃ ⁻Is NO₂NO in the form of_XReleased from the absorbent 47. NO released_XN is due to unburned hydrocarbons or carbon monoxide contained in the exhaust gas.₂Reduced to
Continue driving and NO_XNO for storage reduction catalyst_XIs accumulated, NO_XThe stoichiometric or rich air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is made NO._XNO from the storage reduction catalyst_XNO to release_XRelease control can be performed.
For the above example, NO_XHowever, it is not limited to this form._XThe storage reduction catalyst can be NO in any form._XIt does not matter if it holds. For example, NO on the catalyst carrier_XMay be adsorbed.
Figure 3 shows the SO in this embodiment._XThe enlarged schematic sectional drawing of a trap catalyst is shown. SO_XSO as holding material_XThe trap catalyst 14 is SO contained in the exhaust gas discharged from the engine body 1._XIt is formed to hold. SO in this embodiment_XThe trap catalyst 14 is NO_XThe structure is similar to that of the storage reduction catalyst 17.
SO_XThe trap catalyst 14 has a catalyst carrier 48 supported on a substrate. A catalyst metal 49 is dispersed and supported on the surface of the catalyst carrier 48. The surface of the catalyst carrier 48 is SO._XAn absorbent 50 is disposed. The catalyst metal 49 in the present embodiment is made of noble metal platinum Pt. As the catalyst metal 49, a base metal such as iron Fe may be used in addition to a noble metal such as platinum or silver. SO_XThe components constituting the absorbent 50 were selected from, for example, alkali metals such as potassium K, sodium Na, cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one is used. In the present embodiment, SO_XBarium Ba is used as a component constituting the absorbent 50.
SO contained in exhaust gas₂Is SO_XWhen it flows into the trap catalyst 14, it is oxidized at the catalyst metal 49 and SO.₃become. This SO₃Is SO_XAbsorbed in the absorbent 50, for example sulfate BaSO₄Is generated. Thus, SO_XThe trap catalyst 14 contains SO contained in the exhaust gas._XCan be captured and captured SO_XSO_XThe absorbent 50 can be occluded. SO_XThe holding material is not limited to this form._XIf it can hold.
SO in this embodiment_XThe trap catalyst 14 is SO_XBesides NO_XHold. SO_XNO stored in absorbent 50_XIs NO_XNO of storage reduction catalyst 17_XIt is released at the same time as the release control. That is, by making the air-fuel ratio of exhaust gas the stoichiometric air-fuel ratio or rich, SO_XNO from trap catalyst_XIs released. NO released_XIs N₂Reduced to However, sulfate BaSO₄Is stable, NO_XEven with controlled release, SO_XIs SO_XIt remains on the trap catalyst. Thus, SO_XThe trap catalyst is the SO gas from the exhaust gas._XCan be removed. SO_XIf the use of the trap catalyst is continued, the SO_XThe holding amount increases.
On the other hand, NO_XSO for storage reduction catalyst_XNO flows, NO_XSO as absorbent_XIs retained. SO_XIs retained as sulfate. SO_XBecause of its stable sulfate, NO_XEven with controlled release, SO_XAccumulates without being released. For this reason, NO_XSO for storage reduction catalyst_XNO flows, NO_XThis results in sulfur poisoning that reduces the amount of carbon that can be retained.
SO in the engine exhaust passage_XBy arranging the holding material, SO contained in the exhaust gas_XCan be removed. NO_XSO upstream of the storage reduction catalyst_XBy placing the holding material, NO_XSO for storage reduction catalyst_XCan be prevented from flowing in. That is, NO_XSulfur poisoning of the storage reduction catalyst can be suppressed. NO_XNO with high storage reduction catalyst_XThe purification rate can be maintained.
Figure 4 shows the SO in this embodiment._XThe enlarged schematic sectional drawing of a trap catalyst is shown. On the surface of the substrate 52 formed of cordierite or the like, a coat layer 53 as a catalyst support layer is formed. The coat layer 53 includes a catalyst carrier 48. The catalyst carrier 48 in the present embodiment is formed in a particle shape. Catalytic metal 49 and SO_XThe absorbent 50 is disposed on the surface of the catalyst carrier 48. The catalyst carriers 48 are connected to each other by a binding material 51. Further, the catalyst carrier 48 is bonded to the substrate 52 by a bonding material 51.
SO in this embodiment_XIn the trap catalyst, the catalyst carrier 48 and the binding material 51 are formed of different materials. The catalyst carrier 48 is SO_XIt is made of a substance that occludes and becomes sulfate. The binder 51 is made of SO._XIt is formed of a substance that is difficult to chemically change when compared with the catalyst carrier 48. In the present embodiment, the catalyst carrier 48 is made of magnesium oxide MgO. The binder 51 is made of silicon dioxide SiO.₂It is formed by.
Figure 5 shows SO_XThe 1st expansion schematic sectional drawing explaining detachment | desorption of the catalyst support | carrier of a trap catalyst is shown. SO contained in exhaust gas_XIs SO_XWhen flowing into the trap catalyst 14, the SO_XIs SO supported on the catalyst carrier 48._XIt is held in the absorbent 50. Further, the SO in the present embodiment_XIn the trap catalyst, the catalyst carrier 48 itself is SO._XHold. Catalyst carrier 48 is SO_XBy maintaining the MgO as the oxide to the MgSO as the sulfate.₄To be modified. The volume is expanded by the oxide catalyst carrier 48 becoming the sulfate catalyst carrier 48a. That is, the volume of the sulfate catalyst carrier 48 a is larger than the volume of the oxide catalyst carrier 48. On the other hand, the binder 51 is made of silicon dioxide SiO.₂Therefore, it is not in the form of sulfate, but is in an oxide state. That is, the binder 51 is made of SO._XIt does not change even if it touches. For this reason, distortion occurs at the interface between the catalyst carrier 48 and the binder 51.
Figure 6 shows SO_XThe 2nd expansion schematic sectional drawing explaining detachment | desorption of the catalyst support | carrier of a trap catalyst is shown. The catalyst carrier 48 becomes a sulfate in order from the surface of the coat layer 53. The catalyst carrier 48 a that has become a sulfate is released from the bond with the binder 51 due to distortion at the interface with the binder 51. The catalyst carrier 48 a that has become sulfate is detached from the coat layer 53 and scattered as indicated by an arrow 201. The catalyst carrier 48a is detached in the form of particles. In the present embodiment, each of the catalyst carriers 48a is detached individually. Catalyst support 48a in the form of sulfate and SO_XThe absorbent 50 includes SO._XIs held. As described above, the catalyst carrier 48a is made of SO._XIs detached from the coat layer 53 while maintaining
In the present invention, at least a catalyst carrier is included, and SO_XParticles desorbed from the coating layer of the trap catalyst are called desorbed particles. The desorbed particles in the present embodiment are catalyst carrier 48a, SO_XAn absorbent 50 and catalytic metal 49 are included.
Referring to Fig. 1, SO_XThe desorbed particles including the catalyst carrier 48a flowing out from the trap catalyst 14 are NO._XIt flows into the storage reduction catalyst 17. However, the SO retained on the desorbed particles_XIs in a stable state because it is already in the sulfate form. For this reason, the desorbed particles are NO_XNO does not react with the NOx storage reduction catalyst 17_XIt passes through the storage reduction catalyst 17. In particular, NO_XNO of storage reduction catalyst 17_XThe absorbent 47 can pass through without reacting. The desorbed particles are collected by the particulate filter 16. Like this, NO_XThe storage reduction catalyst 17 has SO_XCan be avoided.
Figure 7 shows SO_XThe 3rd expansion schematic sectional drawing explaining detachment | desorption of the catalyst support | carrier of a trap catalyst is shown. SO of this embodiment_XThe trap catalyst is SO_XThe amount of the catalyst carrier 48 gradually decreases because the catalyst carrier 48a holding the catalyst is desorbed. SO contained in exhaust gas_XThe removal of is continued until all the catalyst carriers 48 are scattered as desorbed particles.
FIG. 8 shows the SO of the first comparative example in the present embodiment._XThe enlarged schematic sectional drawing of a trap catalyst is shown. SO of the first comparative example_XIn the trap catalyst, the catalyst carrier 48 and the binding material 51 are formed of the same material. For example, the binder 51 and the catalyst carrier 48 are made of silicon dioxide SiO.₂It is formed with. SO of the first comparative example_XFor trap catalysts, SO_XEven if the catalyst flows in, the catalyst carrier 48 and the binding material 51 remain oxides instead of sulfates. SO_XIs supported on the catalyst carrier 48._XOccluded by absorbent. The catalyst carrier 48 and the binder 51 are made of SO._XDoes not expand even if it flows in. For this reason, the coupling | bonding of the catalyst support 48 and the binder 51 is maintained.
SO of the first comparative example_XContinue to use the trap catalyst, SO_XSO of trap catalyst_XIf the holding amount increases, SO_XThe basicity of the trap catalyst is weakened. SO_XSO in trap catalyst_XThe holding power is reduced. For this reason, in a predetermined operation state, as indicated by an arrow 202, the SO_XA sulfur component may flow out of the trap catalyst. For example, SO_XWhen the exhaust gas flowing into the trap catalyst is in a high temperature state or the exhaust gas has a low air-fuel ratio, the SO_XThe sulfur component held in the trap catalyst may flow out.
Fig. 9 shows the SO of the first comparative example._XSO in trap catalyst_XHolding amount and SO_XSO released from the trap catalyst_XThe graph explaining the relationship with quantity is shown. FIG. 9 shows SO in a state where the temperature of the exhaust gas is high and the air-fuel ratio of the exhaust gas is low._XIndicates the amount released.
SO_XImmediately after the start of use of the trap catalyst, SO_XSO is low due to low holding amount_XIs not released. SO_XIf the holding amount is small, SO_XSO released from the trap catalyst_XSO rather than quantity_XSO retained in the trap catalyst_XBecause of the large amount, SO_XSO from trap catalyst_XWill not leak. However, the use continues and SO_XWhen the holding amount increases, SO_XSO released from the trap catalyst_XThe amount is SO_XSO retained in the trap catalyst_XMore than the amount. For this reason, SO_XSO from trap catalyst_XLeaks. Like this, SO_XSO in trap catalyst_XAs the holding amount increases, SO_XThe amount of release increases.
Referring to Fig. 8, SO_XThe sulfur component stored in the absorbent is H which is a sulfide.₂SO which is S or oxide₂SO in the form_XReleased from the trap catalyst. H₂The sulfur component released in the form of S is a stable SO in a short time._XTo change. SO_XSO discharged from the trap catalyst_XIs NO_XIt is held in the occlusion reduction catalyst 17. For this reason, NO_XSulfur poisoning appears in the occlusion reduction catalyst 17.
Referring to FIG. 6, the SO in the present embodiment_XThe trap catalyst is SO_XThe catalyst carrier 48a holding the air scatters on the exhaust gas flow as desorbed particles. SO_XThe catalyst carrier 48a holding the_XExcluded from the trap catalyst. SO_XOn the surface of the trap catalyst coating layer 53, SO_XA catalyst carrier 48 having a small holding amount is arranged. Or SO_XThe basicity of the entire trap catalyst can be maintained high.
For this purpose, SO_XSO from trap catalyst_XCan be suppressed. Or high SO_XSO2 from exhaust gas while maintaining removal efficiency_XCan be removed. Thus, the SO in the present embodiment_XThe trap catalyst is used until the catalyst carrier is completely scattered, that is, SO_XIntegrated SO of trap catalyst_XHigh SO until the holding amount reaches saturation_XThe removal rate can be maintained.
In the present embodiment, the desorbed particles including the catalyst carrier desorbed from the coat layer are collected by the particulate filter 16. The differential pressure across the particulate filter 16 increases. The particulate filter 16 is a SO_XEven when all the catalyst carriers 48 included in the trap catalyst 14 flow in, it is preferable that the front-rear differential pressure is less than a predetermined allowable value. When the differential pressure across the particulate filter 16 exceeds an allowable value, the performance may be significantly degraded or may not be usable. Therefore, in order to prevent the differential pressure across the particulate filter 16 from exceeding the allowable value, the SO_XThe amount of the catalyst carrier 48 of the trap catalyst 14 or the capacity of the particulate filter 16 is preferably set.
Also, in this embodiment, SO_XThe desorbed particles desorbed from the trap catalyst are collected by the particulate filter. However, the present invention is not limited to this configuration, and the particulate filter may not be disposed in the engine exhaust passage.
In the present embodiment, the catalyst carrier 48 and the binding material 51 are formed of different materials. The binder 51 is made of SO._XThe catalyst carrier 48 is formed of a material that does not change even if the catalyst flows in._XIt is made of a material that becomes sulfate by flowing in and expands in volume. With this configuration, SO_XThe catalyst carrier 48 that holds can be removed.
When the catalyst carrier 48 and the binding material 51 are formed of the same material, SO_XEven if the catalyst carrier 48 expands by occlusion of the catalyst, the catalyst carrier 48 and the binding material 51 expand to the same extent, so that the catalyst carrier 48 is hardly detached. Since the catalyst carrier 48 and the binder 51 are formed of different materials, the catalyst carrier 48 can be easily detached.
In the present embodiment, the catalyst carrier 48 becomes a sulfate and the binding material 51 remains an oxide and remains unchanged. However, the present invention is not limited to this, and at least one of the catalyst carrier 48 and the binding material 51 is exhausted. SO contained in gas_XIt is only necessary that the volume of the catalyst carrier 48 and the binding material 51 is released by occlusion and reforming to sulfate to release the volume. For example, both the catalyst carrier 48 and the binding material 51 are sulfates, and the catalyst carrier 48 is formed so that the interface between the catalyst carrier 48 and the binding material 51 is distorted due to the difference in volume between them. It does not matter.
Table 1 shows physical property values of aluminum oxide, magnesium oxide, and silicon dioxide that can be used as the material of the catalyst carrier or the binder.

From the molecular weight and density listed in Table 1 above, aluminum oxide Al₂O₃And aluminum sulfate Al₂(SO₄)₃The volume per mole of can be calculated. Comparing the calculated volumes, it can be seen that the volume increases approximately five times by changing from aluminum oxide to aluminum sulfate. Magnesium oxide MgO to magnesium sulfate MgSO₄It can be seen that the volume is increased approximately four times. Thus, the volume expands greatly.
The catalyst carrier can be easily detached by combining a material having a large volume such as magnesium oxide and a material that is not modified such as silicon dioxide. That is, one of the catalyst carrier and the binder is SO_XIs formed of a material whose volume is changed by inflow, and the other is SO._XIt is preferable that the material is made of a material that does not change in volume even when inflow, or has a small volume change and a volume that is substantially unchanged. With this configuration, SO_XIt is possible to more reliably desorb the catalyst carrier holding the.
As a material whose volume changes, a material having strong basicity can be exemplified. Material with strong basicity is SO_XIt is easily modified into a sulfate by contacting with and changes its volume. Examples of such substances that can be easily modified to sulfate include magnesium oxide MgO and lanthanum oxide La.₂O₃Or Cerium dioxide CeO₂Can be illustrated. Aluminum oxide Al₂O₃Is relatively easily modified to sulfate and changes in volume.
As a material having a small volume change, a material close to neutrality can be exemplified. A material close to neutrality is not easily modified to sulfate. Zirconium dioxide ZrO is a material that is difficult to be modified to sulfate.₂Or titanium dioxide TiO₂Can be illustrated. Titanium dioxide TiO₂Is sulfided to titanium sulfate Ti (SO₄)₂However, since it easily returns to an oxide, it is substantially difficult to be modified into a sulfate. In addition, as a material having no volume change, silicon dioxide SiO₂Can be illustrated.
By the way, the volume of the catalyst carrier is larger than the volume of the binder. By forming the catalyst support from a material that is easily modified to sulfate and forming the binder from a material that is difficult to be modified to sulfate or an invariable material, a large amount of SO_XCan be held. As a result, SO_XSaturated SO of trap catalyst_XThe holding amount can be increased.
When the catalyst carrier is formed from a material that is not easily modified to sulfate and the binder is formed from a material that is easily modified to sulfate, SO_XMay enter through the gap between the catalyst carriers and be preferentially occluded by the binder inside the coat layer. Since the volume of the binder is small, a small amount of SO is required compared to the catalyst support._XThe volume expands. For this reason, the catalyst carrier may be detached from the inside of the coat layer. Catalyst carrier and SO_XSO as absorbent_XThe catalyst carrier may be desorbed in a state where the catalyst is not sufficiently occluded.
On the other hand, the catalyst carrier is formed from a material that is easily modified into a sulfate, and the binder is formed from a material that is difficult to be modified into a sulfate or an invariable material, thereby desorbing the catalyst carrier in order from the surface be able to. In addition, when the catalyst support is sulfate, the SO supported on the catalyst support_XSO for absorbent_XIs occluded. For this purpose, SO_XSO as absorbent_XCan be desorbed in order from the catalyst carrier on which is retained.
The material used for the catalyst carrier and the binder is not limited to an oxide containing a single component, and may be a complex oxide (an oxide containing two or more kinds of metal elements). Furthermore, as a material used for the catalyst carrier and the binder, a plurality of oxides may be mixed and used.
By the way, SO in this embodiment_XThe trap catalyst preferably has a smaller particle size of the catalyst carrier 48. For example, the average particle size of the catalyst support is preferably less than 5 μm.
FIG. 10 shows the SO of the second comparative example in this embodiment._XThe enlarged schematic sectional drawing of a trap catalyst is shown. In the second comparative example, a catalyst carrier 48 having a large average particle diameter is employed. The average particle diameter of the catalyst carrier 48 is larger than 5 μm, for example. When the particle size of the catalyst carrier 48 increases, the SO_XBecomes easy to invade. For this reason, the catalyst carrier 48 or the binding material 51 disposed in the coat layer 53 has no SO._XIs retained. In the coat layer 53, the bond between the catalyst carrier 48 and the binder 51 is easily released. As a result, as shown by the arrow 203, the catalyst carrier 48 becomes a lump and is detached. At this time, SO_XThe catalyst carrier 48 that is not sufficiently occluded is detached at the same time. Or SO_XSO enough for absorbent_XThe catalyst carrier 48 that is not occluded is desorbed. As a result, SO_XSO of trap catalyst_XThe amount that can be held decreases.
Referring to FIGS. 6 and 7, on the other hand, by reducing the particle size of the catalyst carrier 48, the interval between the catalyst carriers 48 is reduced. Exhaust gas is prevented from entering through the gap between the catalyst carriers 48 and diffusing inside the coat layer 53. As a result, SO_XIs preferentially held on the catalyst carrier 48 disposed on the surface of the coat layer 53. From the surface of the coat layer 53, the catalyst carrier 48a that has become sulfate in order can be detached. Also, SO_XIt is possible to preferentially desorb the catalyst carrier 48a having sufficiently occluded.
Next, the SO in this embodiment_XA method for producing the trap catalyst will be described. In particular, catalytic metal and SO_XA method for supporting the catalyst carrier holding the absorbent will be described.
Fig. 11 shows the SO in this embodiment._XIt is explanatory drawing of the 1st process of the manufacturing method of a trap catalyst. First, the particulate catalyst carrier 48 constituting the coat layer is prepared. In the present embodiment, a catalyst carrier 48 having an average particle size of less than 5 μm is prepared. A catalyst metal is supported on the catalyst carrier 48 in advance. In the present embodiment, platinum Pt is supported. For example, platinum can be supported on the surface of the catalyst carrier 48 by immersing the catalyst carrier 48 in a platinum solution.
Catalyst support 48 supporting platinum and aluminum nitrate Al (NO₃)₃The solution 70 is put into the solvent 71. As the solvent 71, for example, water can be used. By stirring the solvent 71, a slurry in which the catalyst carrier 48 is uniformly dispersed in the solvent 71 can be formed.
Fig. 12 shows the SO in this embodiment._XExplanatory drawing of the 2nd process of the manufacturing method of a trap catalyst is shown. A slurry 71 a including the catalyst carrier 48 flows into the base 52. The slurry 71 a is disposed on the surface of the base 52. In the present embodiment, the base 52 is cordierite (2MgO · 2Al₂O₃・ 5SiO₂). The substrate 52 in the present embodiment is formed in a honeycomb shape.
Next, the substrate 52 on which the slurry 71a is arranged on the surface of each cell is sintered. The aluminum nitrate aqueous solution 70 changes to the binder 51. The catalyst carriers 48 can be fixed to each other by the binder 51. Further, the catalyst carrier 48 can be fixed to the base 52.
Next, SO is applied to the catalyst carrier 48._XThe absorbent 50 is supported. In the present embodiment, SO_XBarium is used as a component constituting the absorbent. The substrate 52 is immersed in an aqueous solution containing barium. The aqueous solution enters between the catalyst carriers 48 due to a capillary phenomenon or the like. Thereafter, SO is contained in the surface of the catalyst carrier 48 by evaporating water._XAn absorbent 50 can be formed. Thus, the coat layer 53 can be formed on the surface of the substrate.
SO in this embodiment_XIn the method for producing a trap catalyst, a catalyst metal is supported on the catalyst carrier before the catalyst carrier is fixed to the substrate. As a method for supporting the catalyst metal, the catalyst metal can be supported on the surface of the catalyst carrier after the catalyst carrier is fixed to the substrate. For example, after disposing the catalyst carrier on the surface of the substrate, the catalyst metal can be supported on the surface of the catalyst carrier by immersing the substrate in a platinum solution.
[SO of this embodiment]_XIn the trap catalyst, since the catalyst carrier is detached during the operation period, it is preferable that the catalyst metal is uniformly supported on the surface of the catalyst carrier even inside the coat layer. In particular, when the particle size of the catalyst carrier is reduced, the gap between the catalyst carriers is reduced. In the production method in which the catalyst metal is supported after the catalyst carrier is fixed to the substrate, the catalyst metal may not be sufficiently supported on the catalyst carrier disposed inside the coat layer. However, after the catalyst metal is supported on the catalyst support, the catalyst support is fixed to the substrate, so that the catalyst metal is sufficiently disposed even inside the coat layer. As a result, SO_XSuitable SO from the start of use of the trap catalyst until all catalyst carriers are desorbed_XCan be maintained.
SO in this embodiment_XIn the trap catalyst, the SO_XAlthough the absorbent is disposed, the present invention is not limited to this form, and the saturated SO of at least one of the catalyst support and the binder is used._XIf the holding amount is sufficient, SO_XThe absorbent may not be arranged.
Next, SO_XSO of trap catalyst_XThe estimation of the holdable amount will be described. In the present embodiment, SO thickness is estimated by estimating the thickness of the coat layer 53._XCalculate the holdable amount. The exhaust gas purification apparatus for an internal combustion engine in the present embodiment is an SO_XA detection device for detecting the thickness of the coating layer of the trap catalyst is provided. Using the thickness of the coat layer, SO_XSO of trap catalyst_XEstimate the amount that can be held. SO_XThe amount that can be held is the SO at an arbitrary time._XIs equivalent to the total amount that can be held. SO_XIntegrated SO of trap catalyst_XWhen the retention amount reaches the saturation amount, SO_XThe holdable amount becomes zero.
Fig. 13 shows the SO in this embodiment._XThe schematic of the detection apparatus of the thickness of the coating layer of a trap catalyst is shown. The coat layer thickness detection device includes an electrode 61 arranged on the coat layer 53. The electrode 61 is formed in a plate shape. The electrode 61 is erected on the surface of the base 52 and penetrates the coat layer 53. In the example shown in FIG. 13, two electrodes 61 are arranged apart from each other. The two electrodes 61 are arranged such that the maximum area surfaces with the maximum area are parallel to each other. Each electrode 61 is connected to each other via an ammeter 64, a resistor 63, and an AC power supply 62.
The two plate-like electrodes 61 function as a capacitor. The capacitance C of the capacitor can be expressed by the following formula.
C = ε · S / d (1)
Here, the constant ε is a dielectric constant depending on the substance between the electrodes, the variable S is the area of the maximum area of the electrode 61, and the variable d is the distance between the electrodes 61. For example, aluminum oxide Al₂O₃The dielectric constant when the catalyst carrier 48 is filled between the electrodes 61 is larger than the dielectric constant when air is present between the electrodes 61.
When an AC voltage having a predetermined frequency is applied from the AC power supply 62, a current flows according to the capacitance C of the capacitor. By detecting the current flowing through the circuit by the ammeter 64, the reactance of the capacitor can be calculated, and further, the capacitance C of the capacitor can be calculated.
SO_XBy continuing to use the trap catalyst, the thickness of the coat layer 53 gradually decreases. The dielectric constant ε of the capacitor gradually decreases. For this reason, the capacitance C of the capacitor gradually decreases. In the present embodiment, the thickness tc of the coat layer is estimated from the calculated capacitance C. The thickness tc of the coat layer with respect to the capacitance C of the capacitor is stored in the ROM 32 of the electronic control unit 30, for example. By calculating the capacitance C, the thickness tc of the coat layer can be estimated.
In addition, the detection method of an electrostatic capacitance is not restricted to said form, It can detect with arbitrary methods and arbitrary electric circuits. For example, the capacitance may be calculated by connecting a DC power source to a capacitor and measuring the charging time of the capacitor.
Figure 14 shows total SO_XThe graph explaining the relationship between a holding amount and the thickness of a coat layer is shown. Integration SO_XThe amount retained is the SO contained in the exhaust gas from the start of use to an arbitrary time._XSO with_XIt is the total amount. SO_XThe trap catalyst is integrated SO_XRetention amount is saturated SO_XSO until the holding amount is reached_XCan be maintained. Saturated SO_XAccumulated SO at an arbitrary time from the holding amount_XBy subtracting the holding amount, SO_XThe holdable amount can be calculated.
Accumulated SO for coat layer thickness shown in FIG._XThe relationship of the holding amount is stored in the ROM 32 of the electronic control unit 30, for example. Using the estimated coat layer thickness,_XThe holding amount can be estimated. In addition, SO_XThe holdable amount can be calculated. Thus, SO_XIntegrated SO of trap catalyst_XBy estimating the holding amount, SO_XThe trap catalyst can be managed. For example, total SO_XRetention amount is saturated SO_XSO when the holding amount is reached_XWhen replacing the trap catalyst, SO_XThe replacement time of the trap catalyst can be estimated. Or integrated SO_XRetention amount is saturated SO_XWhen the holding amount is reached, NO arranged downstream_XA sulfur poisoning recovery process for the storage reduction catalyst is required. Even in this case, the start time of the sulfur poisoning recovery process can be determined.
Fig. 15 shows the accumulated fuel consumption and accumulated SO_XThe graph explaining the relationship with the holding | maintenance amount is shown. SO_XIntegrated SO of trap catalyst_XBy estimating the retention amount, the content of the sulfur component contained in the fuel can be estimated. The accumulated fuel consumption is an accumulation of the amount of fuel used up to an arbitrary time. The accumulated fuel usage can be calculated, for example, by integrating the amount of fuel injected from the fuel injection valve. As the accumulated fuel consumption increases, the accumulated SO_XIncreased retention. The content of the sulfur component contained in the fuel can be calculated from the slope of this graph.
By calculating the content of the sulfur component contained in the fuel, for example, the properties of the fuel, the type of fuel, and the like can be determined. The combustion pattern in the combustion chamber can be optimized according to the determined fuel properties and fuel type. Moreover, when the content rate of the sulfur component of the fuel is stored in advance in the electronic control unit 30 or the like, the content rate of the already stored sulfur component can be corrected.
In the example shown in FIG. 13, two electrodes serving as capacitors are arranged at one place on the substrate. However, the present invention is not limited to this configuration, and even if a coating layer thickness detecting device is arranged at a plurality of places. I do not care. For example, SO_XIn the flow direction of the exhaust gas of the trap catalyst, a coating layer thickness detection device may be arranged at the upstream end and the downstream end. Exhaust gas is SO_XSince the gas flows from the upstream end of the trap catalyst, the catalyst carrier is preferentially detached from the upstream end rather than the downstream end. That is, when the catalyst carrier is desorbed, a gradient is formed in which the thickness of the coat layer gradually increases toward the downstream side in the exhaust gas flow direction. Even in the case where such a gradient is formed, the gradient can be estimated by measuring the thicknesses of a plurality of coat layers in the flow direction of the exhaust gas. Accumulated SO more accurately_XA holding amount or the like can be estimated.
The coating layer thickness detection device is not limited to the above-described form, and the coating layer thickness can be detected by an arbitrary device. For example, SO_XA differential pressure sensor for detecting the differential pressure between the inlet and outlet of the trap catalyst is disposed. As the coat layer becomes thinner, SO_XThe opening ratio of the trap catalyst increases and SO_XThe pressure loss in the trap catalyst is reduced. When exhaust gas flow rate is high, SO_XBy measuring the differential pressure between the upstream side and the downstream side of the trap catalyst, the thickness of the coat layer can be estimated. Or SO_XThe thickness of the coat layer may be estimated by disposing a distance sensor or the like inside the trap catalyst cell and detecting the distance between the surfaces of the facing coat layers.
The thickness of the coat layer can be estimated at any time. For example, the thickness of the coat layer can be estimated for each predetermined travel distance. Alternatively, the thickness of the coat layer may be estimated continuously.
Embodiment 2
With reference to FIGS. 16 to 22, an exhaust gas purification apparatus for an internal combustion engine according to Embodiment 2 will be described.
Fig. 16 shows the SO in this embodiment._XThe enlarged schematic sectional drawing of a trap catalyst is shown. SO_XSO as holding material_XSO containing trap catalyst in exhaust gas_XAnd the catalyst carrier is detached from the coating layer in the same manner as in the first embodiment.
On the surface of the catalyst carrier 48, catalyst metal 49 and SO_XAn absorbent 50 is supported. The catalyst carrier 48 is SO_XIt is made of a material that expands when it is held. The catalyst carrier 48 in the present embodiment is made of MgO.
SO in this embodiment_XThe trap catalyst includes auxiliary particles 55 interposed between the catalyst carriers 48. The auxiliary particles 55 are formed so that the average particle size is smaller than the average particle size of the catalyst carrier 48. In the present embodiment, catalyst metal 49 and SO are provided on the surfaces of the auxiliary particles 55._XAn absorbent 50 is supported. The binding material 51 binds the auxiliary particles 55 to each other. The binding material 51 binds the auxiliary particles 55 to the base body 52.
The auxiliary particles 55 and the binding material 51 in the present embodiment are formed of a material different from that of the catalyst carrier 48. The auxiliary particles 55 in the present embodiment are made of aluminum oxide Al₂O₃It is formed by. The binding material 51 in the present embodiment is formed of the same material as the auxiliary particles 55. That is, the binder 51 is made of aluminum oxide Al.₂O₃It is formed by.
SO in this embodiment_XThe trap catalyst is the SO described in the first embodiment._XIn the trap catalyst manufacturing method, auxiliary particles 55 supporting catalyst metal are prepared in addition to the catalyst carrier 48 previously supporting the catalyst metal. The catalyst carrier 48 and the auxiliary particles 55 are combined with aluminum nitrate Al (NO₃)₃Mix with solution 70. It can manufacture by arrange | positioning the produced | generated slurry on the surface of a base | substrate, and then sintering (refer FIG. 11).
SO in this embodiment_XIn the trap catalyst, the binding material 51 is preferentially bound to the auxiliary particles 55 over the catalyst carrier 48. The catalyst carrier 48 is supported by contacting the auxiliary particles 55. The catalyst carrier 48 is mechanically supported on the auxiliary particles 55.
FIG. 17 shows the SO in this embodiment._XTrap catalyst is SO_XThe expanded schematic sectional view when holding is shown. SO in this embodiment_XThe trap catalyst has a SO_XAbsorbent 50 with SO_XIs occluded. Further, the catalyst carrier 48 itself has SO._XIs occluded. The oxide catalyst carrier 48 is SO_XIs occluded to the sulfate catalyst carrier 48a. The volume of the oxide catalyst carrier 48 expands when it becomes the sulfate catalyst carrier 48a. The auxiliary particles 55 are pressed against the catalyst carrier 48. The position of the auxiliary particle 55 moves. At this time, distortion occurs between the auxiliary particles 55 and the binder 51. As a result, the binding between the auxiliary particles 55 and the binding material 51 is released. The restriction of the catalyst carrier 48 a that has become sulfate is released, and the catalyst carrier 48 a is detached from the coat layer 53.
SO in this embodiment_XIn the trap catalyst, auxiliary particles 55 smaller than the catalyst carrier 48 are interposed between the catalyst carriers 48. For this reason, SO contained in the exhaust gas_XCan be prevented from entering the coat layer 53 through the gap between the catalyst carriers 48. SO_XThe catalyst carrier 48 disposed on the surface of the coat layer 53 and the SO supported on the catalyst carrier 48_XThe absorbent 50 is preferentially occluded. For this reason, the catalyst carrier 48 arranged on the surface of the coat layer 53 can be desorbed preferentially. It is placed inside the coat layer 53 and fully SO._XIt is possible to prevent the catalyst carrier 48 that does not hold the catalyst from being detached. Alternatively, it is possible to suppress the plurality of catalyst carriers 48 from being separated in a lump.
Since the auxiliary particles 55 and the binder 51 are formed of substantially the same material, the binder 51 can be preferentially bound to the auxiliary particles 55 over the catalyst carrier 48. Further, in the present embodiment, the binding material 51 is bound to the auxiliary particles 55, but the present invention is not limited to this configuration, and the binding material 51 may be bound to the catalyst carrier 48 together with the auxiliary particles 55.
The auxiliary particles 55 in the present embodiment have catalytic metal 49 and SO on the surface._XAlthough the absorbent 50 is supported, the present invention is not limited to this form._XThe absorbent may not be arranged. Or catalytic metal 49 and SO_XOne of the absorbents 50 may be carried.
In this embodiment, the catalyst carrier, auxiliary particles, and binder are SO_XHowever, the present invention is not limited to this configuration, and at least one member of the catalyst carrier, auxiliary particles, and binder is formed of a material that expands, and the other members are SO._XIt may be formed of an invariable material even if it is in contact with.
In this embodiment, when exhaust gas is being purified, SO_XDesorption promotion control is performed to increase the temperature of the trap catalyst. By increasing the temperature, desorption of the catalyst support is promoted. The binder and auxiliary particles in the present embodiment are SO_XIt has a decomposition temperature at which the sulfate produced by occlusion of is decomposed. Table 2 shows decomposition temperatures of substances used for the catalyst carrier, auxiliary particles, and binder in the present embodiment. Table 2 shows the decomposition temperatures of oxides and sulfates.

From Table 2, aluminum oxide Al, which is the material of the binder and auxiliary particles₂O₃Sulfate Al produced from₂(SO₄)₃The decomposition temperature of is approximately 770 ° C. In contrast, sulfate MgSO produced from MgO which is the material of the catalyst support₄The decomposition temperature of is approximately 1100 ° C. In desorption promotion control, SO_XControl is performed so that the temperature of the trap catalyst becomes equal to or higher than the decomposition temperature of the sulfate of the material of the binder and auxiliary particles. At this time, SO_XIt is preferable to control so that the temperature of the trap catalyst is lower than the decomposition temperature of the sulfate of the catalyst carrier material. In the present embodiment, SO_XThe temperature of the trap catalyst is about 770 ° C. or higher and lower than about 1100 ° C._XThe temperature of the exhaust gas flowing into the trap catalyst is raised.
By performing desorption promotion control, the catalyst carrier is not decomposed and the sulfate form is maintained. On the other hand, the binder and the sulfate of the auxiliary particles are decomposed into oxides. The binder and auxiliary particles shrink. That is, while the volume of the catalyst support is unchanged, the volume of the binder and auxiliary particles is reduced. At this time, stress acts on the auxiliary particles, and the strain between the auxiliary particles and the binder increases. As a result, it is possible to promote the release of the bond between the auxiliary particles and the binder, and to promote the desorption of the catalyst carrier.
FIG. 18 shows a flowchart of operation control in the present embodiment. The operation control shown in FIG. 18 can be repeatedly performed at predetermined time intervals.
In step 101, SO_XSO in trap catalyst_XEstimate the amount retained. The exhaust purification apparatus in the present embodiment is configured to perform SO at an arbitrary time._XSO of trap catalyst_XA detection device capable of estimating the holding amount is provided. In this embodiment, SO_XThe calculation of the holding amount is continuously performed during the operation of the internal combustion engine. In this embodiment, every time desorption promotion control is performed, SO_XSO of trap catalyst_XThe holding amount is made zero.
Fig. 19 shows SO with engine speed and required torque as functions._XSO retained in the trap catalyst per unit time_XShows a map of quantities. By detecting the engine speed N and the required torque TQ, SO_XSO retained in the trap catalyst_XThe quantity SOXZ can be determined. This map is stored in the ROM 32 of the electronic control unit 30, for example. The SO is maintained per unit time from this map at predetermined time intervals while continuing operation._XFind the amount. SO held per unit time_XBy multiplying the amount by a predetermined time, SO_XThe holding amount can be calculated. Calculated SO_XBy integrating the holding amount, SO at any time_XThe holding amount can be detected. SO_XThe holding amount is stored in the RAM 33, for example. SO_XSO stored in the trap catalyst_XThe holding amount detection device is not limited to this form, and the SO_XAny device that can detect the holding amount can be employed.
Referring to FIG. 18, in step 102, the calculated SO_XSO in trap catalyst_XIt is determined whether or not the holding amount is larger than a determination value for performing desorption promotion control. This determination value is predetermined. In the present embodiment, SO_XSO retained in the trap catalyst_XDesorption promotion control is performed when the holding amount exceeds a predetermined determination value. The determination value includes a catalyst carrier disposed on the surface of the coat layer and an SO supported on the catalyst carrier disposed on the surface of the coat layer._XAlmost all of the absorbent is SO_XSO when the state is maintained_XIt is preferable to employ a holding amount. SO_XWhen the holding amount is equal to or smaller than the determination value, this control is terminated. SO_XWhen the holding amount is larger than the determination value, the process proceeds to step 103.
Next, it is determined whether or not the amount of desorbed particles collected by the particulate filter 16 is larger than the determination value. SO_XThe desorbed particles including the catalyst carrier desorbed from the trap catalyst 14 are collected by the particulate filter 16. When the amount of desorbed particles deposited on the particulate filter 16 increases, the differential pressure across the particulate filter 16 increases, and the performance may be significantly degraded or operation may become impossible. In the present embodiment, control for prohibiting desorption promotion control is performed when the amount of desorbed particles collected by the particulate filter becomes larger than a predetermined allowable value.
In step 103, the differential pressure across the particulate filter 16 is read. In the present embodiment, regeneration control for increasing the temperature of the particulate filter 16 and burning the particulate matter is performed. The differential pressure before and after the end of the regeneration control of the particulate filter 16 is stored in the electronic control unit 30. Referring to FIG. 1, the differential pressure sensor 28 can detect the differential pressure across the particulate filter 16.
In the present embodiment, the deposition amount of the desorbed particles is estimated based on the differential pressure across the particulate filter 16. However, the differential pressure across the particulate filter 16 also depends on the amount of particulate matter other than the desorbed particles collected by the particulate filter 16. For this reason, in the present embodiment, the front-rear differential pressure is detected immediately after the regeneration control is performed. In step 103, the differential pressure before and after the end of the nearest regeneration control is read.
Next, in step 104, it is determined whether or not the differential pressure across the particulate filter 16 is greater than a predetermined determination value. When the differential pressure across the particulate filter 16 is greater than the determination value, it can be determined that the amount of desorbed particles collected by the particulate filter is greater than the allowable value. If the differential pressure across the particulate filter 16 is greater than the determination value, this control is terminated. That is, desorption promotion control is prohibited. By performing this control, it is possible to prevent the purification performance of the particulate filter from significantly decreasing. Alternatively, it can be avoided that the differential pressure across the particulate filter exceeds the operable range and the internal combustion engine cannot be used.
The estimation of the amount of desorbed particles collected by the particulate filter is not limited to this form, and the amount of desorbed particles collected by the particulate filter can be estimated by any method. For example, as the amount of desorbed particles collected by the particulate filter, SO_XAccumulate the amount of desorbed particles desorbed from the trap catalyst._XIt can be estimated from the holding amount.
In step 104, if the differential pressure across the particulate filter 16 is less than or equal to the determination value, the process proceeds to step 105. In step 105, desorption promotion control is performed.
FIG. 20 shows a time chart of the desorption promotion control in the present embodiment. Time t₁Until then, normal operation is performed. Time t₁To time t₂Up to this point, desorption promotion control is performed. Time t₂Thereafter, normal operation is performed. In the desorption promotion control, SO_XThe temperature of the trap catalyst is raised. In the present embodiment, the SO pattern is changed by changing the injection pattern in the combustion chamber._XThe temperature of the exhaust gas flowing into the trap catalyst is raised. Here, an injection pattern for increasing the temperature of the exhaust gas discharged from the engine body will be described.
FIG. 21 shows a fuel injection pattern during normal operation of the internal combustion engine in the present embodiment. The injection pattern A is a fuel injection pattern during normal operation. During normal operation, the main injection FM is performed at a compression top dead center TDC. Main injection FM is performed at a crank angle of approximately 0 °. Further, in order to stabilize the combustion of the main injection FM, the pilot injection FP is performed before the main injection FM. The pilot injection FP is performed, for example, in a range where the crank angle is approximately 10 ° to approximately 40 ° before the compression top dead center TDC.
During normal operation, as shown in the injection pattern B, the pilot injection FP may not be performed and only the main injection FM may be performed. In this embodiment, an injection pattern in which pilot injection FP is performed will be described as an example. When operating with the injection pattern A or the injection pattern B in normal operation, the air-fuel ratio of the exhaust gas discharged from the engine body is lean.
FIG. 22 shows an injection pattern when the temperature of the exhaust gas discharged from the engine body is increased. In the injection pattern C, after the main injection FM, after injection FA as auxiliary injection is performed. The after injection FA is performed at a combustible time after the main injection. The after injection FA is performed, for example, in a range where the crank angle after compression top dead center is approximately 40 °. By performing after-injection FA, the afterburning period becomes longer, so the temperature of the exhaust gas discharged from the engine body can be raised.
Furthermore, in the injection pattern C, the injection timing of the main injection FM is delayed from the compression top dead center TDC. That is, the injection timing of the main injection FM is retarded. As the injection timing of the main injection FM is retarded, the injection timing of the pilot injection FP is also retarded. By delaying the injection timing of the main injection FM, the temperature of the exhaust gas can be raised. By increasing the temperature of the exhaust gas, the SO disposed in the engine exhaust passage_XThe temperature of the trap catalyst can also be increased.
Referring to FIG. 20, time t₁By raising the temperature of the exhaust gas from_XIncrease trap catalyst bed temperature. SO_XThe SO is set so that the maximum temperature of the trap catalyst bed temperature is not less than the lower limit temperature and less than the upper limit temperature._XIncrease the temperature of the trap catalyst. As described above, in the present embodiment, SO_XThe temperature is raised so that the maximum bed temperature of the trap catalyst is 770 ° C. or higher and lower than 1100 ° C.
In the present embodiment, when the desorption promotion control is performed, the catalyst carrier 48a is not decomposed but MgSO₄The sulfate form of is maintained. On the other hand, the auxiliary particles 55 and the binder 51 are made of sulfate Al.₂(SO₄)₃Decomposes into oxide Al₂O₃Return to. At this time, the auxiliary particles 55 and the binding material 51 contract, and the detachment of the catalyst carrier 48a is promoted. As the catalyst carrier 48a is detached, the SO_XThe amount of catalyst support in the trap catalyst is reduced. SO_XSO of trap catalyst_XThe holding amount decreases.
SO in this embodiment_XIn the trap catalyst, the catalyst carrier, the auxiliary particles, and the binder are produced in the form of an oxide. The catalyst support, auxiliary particles and binder are SO_XOccludes and becomes sulfate and expands. By performing the desorption promotion control and the auxiliary particles and the binder return to the original oxide form, the form is substantially the same as the form in which only the catalyst support is sulfated and expanded from the initial state. As a result, the auxiliary particles are pressed by the catalyst carrier, and the distortion increases between the auxiliary particles and the binder. The bond between the auxiliary particles and the binding material is released, and the detachment of the catalyst support can be promoted.
The desorption promotion control in this embodiment increases the temperature of the exhaust gas by increasing the amount of fuel combusted in the combustion chamber. By performing this control, the temperature of the exhaust gas can be rapidly increased, and desorption promotion control can be performed in a short time. The desorption promotion control is not limited to this form, but SO_XAny device that raises the temperature of the trap catalyst can be employed.
Also, in the desorption promotion control, SO_XYou may raise the temperature of a trap catalyst. For example, SO_XWhen an oxidation catalyst is disposed upstream of the trap catalyst, when unburned fuel is supplied to the oxidation catalyst, reaction heat is generated during the oxidation reaction of the unburned fuel. This reaction heat can raise the temperature of the exhaust gas. SO by increasing the temperature of exhaust gas_XThe temperature of the trap catalyst can be raised.
In this embodiment, MgO catalyst carrier and Al₂O₃Auxiliary particles and binders are selected. The material of the catalyst carrier, auxiliary particles, and binder when performing desorption promotion control is not limited to this form._XWhen the temperature of the trap catalyst rises, it is possible to select a material in which the temperature range in which the sulfate of the auxiliary carrier and the binder is decomposed without the decomposition of the sulfate of the catalyst carrier is determined.
For example, titanium dioxide TiO as a material for auxiliary particles and binder₂Can be selected. Titanium sulfate Ti (SO₄)₂Is decomposed at about 600 ° C., the desorption of the catalyst carrier can be promoted by setting the temperature of the desorbed particles to 600 ° C. or higher in the desorption promotion control.
In addition, the decomposition temperature of sulfate depends on the air-fuel ratio of the exhaust gas. For example, in a reducing atmosphere, the decomposition temperature of sulfate decreases. Therefore, the decomposition temperature of sulfate is estimated according to the state of the exhaust gas, and SO is calculated based on this decomposition temperature._XIt is preferable to define the temperature range of the maximum temperature reached by the trap catalyst.
The desorption promotion control in this embodiment is performed by SO_XSO retained in the trap catalyst_XThis is done each time the amount reaches the judgment value. The desorption promotion control is not limited to this mode. For example, the desorption promotion control may be performed for each predetermined travel distance or for each predetermined fuel injection amount.
Other configurations, operations, and effects are the same as those in the exhaust gas purification apparatus for an internal combustion engine in the first embodiment, and thus description thereof will not be repeated here.
Embodiment 3
With reference to FIGS. 23 to 29, an exhaust gas purification apparatus for an internal combustion engine according to Embodiment 3 will be described.
FIG. 23 is a schematic view of the internal combustion engine in the present embodiment. In the engine exhaust passage, SO_XSO as holding material_XTrap catalyst 14 and NO_XThe storage reduction catalyst 17 is arranged in this order. NO_XA particulate filter 16 and an oxidation catalyst 13 are disposed in the engine exhaust passage downstream of the storage reduction catalyst 17. SO in this embodiment_XThe trap catalyst consists of catalytic metal and SO_XIt includes a catalyst carrier on which an absorbent is supported. SO in this embodiment_XThe catalyst metal of the trap catalyst includes a noble metal. The catalyst metal in the present embodiment contains platinum Pt.
The exhaust gas purification apparatus for an internal combustion engine in the present embodiment includes a fuel addition valve 60 serving as a reducing agent supply device disposed on the upstream side of the particulate filter 16. The fuel addition valve 60 is formed so as to supply fuel as a reducing agent into the engine exhaust passage. The fuel addition valve 60 in the present embodiment is formed so as to inject the same fuel as that of the engine body 1. The fuel addition valve 60 is NO_XA fuel is injected between the storage reduction catalyst 17 and the particulate filter 16.
SO in this embodiment_XAs in the first or second embodiment, the trap catalyst 14 is made of SO._XBy storing the catalyst, the catalyst carrier is formed to be detached. SO_XThe desorbed particles desorbed from the trap catalyst 14 are collected by the particulate filter 16. At this time, the catalyst carrier and the like contained in the desorbed particles are SO_XHolding.
The exhaust gas purification apparatus for an internal combustion engine in the present embodiment is an SO that the desorbed particles collected by the particulate filter 16 hold._XSO to release_XRelease control is performed. The desorbed particles collected by the particulate filter 16 become SO_XNO by releasing_XCan be retained. Thus, in the present embodiment, the desorbed particles collected by the particulate filter 16 are NO._XUsed for holding.
FIG. 24 shows a time chart of the first operation control in the present embodiment. The first operation control is to perform SO on the desorbed particles collected by the particulate filter._XRelease control is performed. SO retained by desorbed particles_XSO to release_XWhen performing release control, the temperature of the desorbed particles is previously set to SO._XThe temperature is raised until the temperature is higher than the temperature at which the release of oxygen is possible. Set the temperature of the desorbed particles to SO_XThe air-fuel ratio of the exhaust gas flowing into the particulate filter is made the stoichiometric air-fuel ratio or rich while maintaining the temperature above the temperature at which discharge is possible. By this control, SO_XCan be released.
In the first operation control of the present embodiment, the SO_XAfter all of the catalyst carrier contained in the trap catalyst has been desorbed, the SO is removed from the desorbed particles collected in the particulate filter._XControlled release. Time t₀In SO_XAll the catalyst carriers contained in the trap catalyst are desorbed and collected by the particulate filter. Time t₀To time t₁Up to this point, the temperature rise control for increasing the temperature of the desorbed particles is performed.
In the temperature increase control of the present embodiment, the temperature of the exhaust gas is raised by performing after injection as auxiliary injection in the combustion chamber. Further, the temperature of the exhaust gas is raised by retarding the main injection (see FIG. 22). Time t₁The temperature of the particulate filter is SO_XThe target temperature has been reached for release. SO_XThe target temperature for releasing_XThe temperature is set to be higher than the temperature at which it can be released.
Time t₁To time t₂Up to this point, SO is removed from the desorbed particles collected in the particulate filter._XRelease control is performed. Time t₁To time t₂Even during the period up to, the bed temperature of the particulate filter is maintained above the target temperature by maintaining the exhaust gas in a heated state. The temperature of the desorbed particles collected in the particulate filter is set to SO._XIt can be maintained above the releasable temperature.
SO_XIn the discharge control, the air-fuel ratio of the exhaust gas flowing into the particulate filter is made the stoichiometric air-fuel ratio or rich. In the present embodiment, by supplying fuel from the fuel addition valve 60, the air-fuel ratio of the exhaust gas flowing into the particulate filter is made rich. SO_XFor the release control, it is preferable to select an operation condition in accordance with the amount of desorbed particles collected in the particulate filter.
In the first operation control of the present embodiment, the SO_XFor all desorbed particles contained in the trap catalyst, SO_XControlled release. SO_XThe amount of all desorbed particles contained in the trap catalyst is known. For this reason, under predetermined operating conditions, SO_XControlled release. That is, SO is determined under conditions such as a predetermined air-fuel ratio, time and temperature._XControlled release.
SO for desorbed particles_XBy performing release control, SO particles are removed from the desorbed particles collected in the particulate filter._XCan be released. That is, the SO retained on the catalyst carrier contained in the desorbed particles._XCan be released. SO of the desorbed particles_XRetention amount decreases. In the present embodiment, the SO of the desorbed particles_XUntil the holding amount becomes almost zero, SO_XControlled release.
SO from desorbed particles_XIs released, so that the desorbed particles are NO._XCan be retained. NO_XIt can be used as an occlusion reduction catalyst. That is, the desorbed particles are NO when the air-fuel ratio of the exhaust gas is lean._XAnd the retained NO when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio or rich_XAnd N₂Can be reduced.
By the way, SO in this embodiment_XSO of trap catalyst_XThe absorbent contains potassium K. Also, SO_XIn addition to potassium K, the absorbent contains lithium Li and magnesium Mg. Potassium is SO_XSO_XIt is suitable for occlusion in the absorbent. However, potassium has a strong basicity and cancels the oxidizing action of platinum. For this reason, NO_XNO that needs to be oxidized_XIn the storage reduction catalyst, NO_XIn some cases, the oxidation ability of the is insufficient.
In the present embodiment, the SO of the desorbed particles_XPerform potassium release control to release potassium from the absorbent. In potassium release control, the temperature of the particulate filter in which the desorbed particles are collected is raised to a temperature higher than the temperature at which potassium is scattered. Potassium can be scattered by raising the temperature of the desorbed particles above the boiling point of potassium. The target temperature for releasing potassium can be set higher than the temperature at which potassium can be released. Here, since the boiling point of potassium is 774 ° C., for example, the target temperature for releasing potassium can be set to about 800 ° C.
Note that potassium may be included in the form of nitrate (potassium nitrate). Since the boiling point of potassium nitrate is about 400 ° C., it is possible to release potassium nitrate at the same time by raising the temperature above the temperature at which potassium is released.
Referring to FIG. 24, in the present embodiment, SO_XFollowing release control, potassium release control is performed. Time t₂To time t₃Until then, temperature rise control is performed. In the present embodiment, the amount of fuel burned in the combustion chamber is increased. The amount of after-injection is increased. Time t₃, The bed temperature of the particulate filter has reached the target temperature for releasing potassium. The temperature of the desorbed particles has reached a temperature at which potassium can be released.
Time t₃To time t₄By maintaining the temperature of the particulate filter above the temperature at which potassium is released, SO_XPotassium contained in the absorbent can be scattered. SO_XThe potassium content of the absorbent decreases. When performing potassium release control, it is preferable to select operating conditions based on the amount of desorbed particles. For example, it is preferable to determine the time for controlling potassium release based on the amount of desorbed particles. The potassium release control in the present embodiment is performed at a predetermined time. In the present embodiment, the potassium release control is performed until the potassium content becomes substantially zero.
Here, the SO in this embodiment_XSO of trap catalyst_XThe absorbent contains barium, lithium and magnesium in addition to potassium. These components other than potassium are SO._XHigh NO when removing potassium from absorbent_XA composition that can exhibit purification performance is preferred. For example, SO_XEach component in the absorbent preferably has a barium content higher than the lithium content and a barium content higher than the magnesium content. That is, SO_XSO in trap catalyst_XThe components contained in the absorbent preferably have the relationship of the following formula.
K> Ba> Li, Mg (2)
SO having the composition of the above formula (2)_XBy adopting the absorbent, after removing potassium, the desorbed particles collected in the particulate filter are changed to NO._XHigh NO when used as a storage reduction catalyst_XA purification rate can be exhibited. Furthermore, the composition of barium, lithium and magnesium is high NO._XIt is preferable to adjust so that a purification rate may be exhibited.
In controlling the release of potassium, it is preferable to keep the temperature of the particulate matter below the boiling point of components other than potassium so that components other than potassium such as barium, lithium and magnesium do not scatter. Here, the boiling point of barium is 1870 ° C., the boiling point of lithium is 1340 ° C., and the boiling point of magnesium is 1090 ° C. Since the boiling point of these bariums and the like is higher than the maximum temperature at which a normal internal combustion engine can be operated, only potassium can be released in the potassium release control.
In this embodiment, SO_XAlthough all potassium contained in the absorbent is removed, the present invention is not limited to this form, and control for removing part of potassium may be performed. Or, even if potassium release control is not performed, the desorbed particles collected in the particulate filter are changed to NO._XIt can be used as an occlusion reduction catalyst. Time t₄At the time t₄Thereafter, normal operation is performed.
In the first operation control of the present embodiment, the SO_XAfter all of the catalyst carrier contained in the trap catalyst is desorbed, the SO particles are removed from the desorbed particles collected in the particulate filter._XAlthough release control is performed, the present invention is not limited to this form._XWhen a part of the catalyst carrier contained in the trap catalyst is desorbed, the SO is removed from the desorbed particles collected in the particulate filter._XRelease control may be performed. In this case, depending on the amount of desorbed particles collected in the particulate filter, SO_XIt is preferable to select operating conditions for the release control.
The amount of desorbed particles collected on the particulate filter is SO_XIt can be estimated from the thickness of the coat layer in the trap catalyst. Or SO_XAccumulated SO in trap catalyst_XIt can be estimated from the holding amount. For example, coat layer thickness or integrated SO_XThe amount of desorbed particles as a function of the amount retained can be stored in the electronic control unit. Estimated coat layer thickness or total SO_XBased on the amount retained, the amount of desorbed particles can be estimated. Based on the estimated amount of desorbed particles, SO_XRelease control operating conditions can be selected. For example, as the amount of desorbed particles increases, SO_XIt is possible to perform control to increase the time for performing the release control. By this control, SO_XThe amount of fuel consumed in the emission control can be optimized. For example, excessive fuel consumption can be suppressed.
Also, SO of desorbed particles_XRelease control and potassium release control can be performed continuously with regeneration control of the particulate filter. In the regeneration control of the particulate filter, the bed temperature of the particulate filter is raised to, for example, 600 ° C. or higher in order to burn particulate matter. The particulate matter can be burned by maintaining the air-fuel ratio of the exhaust gas lean. Following the regeneration control of this particulate filter, SO_XRelease control can be performed. For example, the temperature of the particulate filter is maintained at 600 ° C. or higher. In this state, by making the air-fuel ratio of the exhaust gas flowing into the particulate filter rich, the SO_XCan be released. Furthermore, potassium release control can be performed by raising the temperature of the particulate filter.
In this embodiment, SO_XAlthough the release control and the potassium release control are performed separately, the present invention is not limited to this form._XRelease control and potassium release control may be performed simultaneously. For example, the temperature of the particulate filter is raised to a temperature higher than the temperature at which potassium can be released. In this state, by making the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich, potassium is removed and SO_XCan be released.
Next, for the desorbed particles collected by the particulate filter, SO_XOperation control after performing release control will be described. The desorbed particles collected by the particulate filter are NO_XSince it has a function of an occlusion reduction catalyst, the exhaust purification device in the present embodiment is NO_XThis is equivalent to an exhaust purification device in which two storage reduction catalysts are connected in series.
FIG. 25 is a time chart of the second operation control in the present embodiment. The second operation control is to perform SO on the desorbed particles collected by the particulate filter._XThis is the operation control after performing the release control. When the engine body is driven, NO from the combustion chamber_XIs released and the upstream NO_XNO is absorbed into the occlusion reduction catalyst 17 and the desorbed particles collected in the particulate filter 16._XIs retained. For this reason, NO_XControl the release.
In this embodiment, time t₁Until upstream NO_XNO in the occlusion reduction catalyst 17_XIs retained. Time t₁NO_XThe occlusion reduction catalyst 17 is saturated. Ie NO_XNO of storage reduction catalyst 17_XThe holdable amount is almost zero. Time t₁Thereafter, NO discharged from the engine body 1_XIs NO_XIt passes through the storage reduction catalyst 17 and flows into the particulate filter 16. NO contained in exhaust gas_XIs held by the desorbed particles collected by the particulate filter 16. Thus, time t₁To time t₂Up to this point, NO is released by the desorbed particles collected in the particulate filter 16._XIs being removed. Time t₂NO of the desorbed particles_XThe holding amount has reached the allowable value.
NO of the desorbed particles collected in the particulate filter 16_XThe allowable value of the retention amount is preferably determined based on the amount of desorbed particles. The more desorbed particles, the more NO_XThe allowable value of the holding amount can be increased. For example, NO as a function of the amount of desorbed particles_XThe allowable value of the holding amount is stored in the electronic control unit. Estimated SO_XIntegrated SO of trap catalyst_XThe amount of desorbed particles is estimated from the retained amount. Based on the estimated amount of desorbed particles, NO_XAn allowable value of the holding amount can be determined. The NO of the desorbed particles_XThe allowable amount of retention is the saturation NO of desorbed particles_XIt is preferable to set it smaller than the holding amount.
Here, NO_XOcclusion reduction catalyst and NO of desorbed particles_XAn example of a method for calculating the holding amount will be described.
Fig. 26 shows the NO discharged from the engine body per unit time in the present embodiment._XShows a map of quantities. NO per unit time as a function of the engine speed N and the injection amount TAQ of the fuel injected into the combustion chamber 2_XA map of NOxA emissions is prepared in advance. This map is stored in the ROM 32 of the electronic control unit 30, for example.
¡NO emitted from the engine body per unit time according to the map shown in Fig. 26_XQuantity, ie NO_XNO flowing into the storage reduction catalyst 17_XThe amount can be calculated. Inflowing NO per unit time_XBy integrating the amount, NO at any time_XNO flowing into the storage reduction catalyst 17_XThe amount can be calculated.
Referring to FIG. 25, in this embodiment, NO_XThe occlusion reduction catalyst 17 is saturated, and NO of the desorbed particles collected in the particulate filter._XUntil the holding amount reaches the allowable value, NO_XContinue holding. NO_XNO flowing into the storage reduction catalyst 17_XThe accumulated amount is NO_XUntil reaching the sum of the saturation amount of the storage reduction catalyst 17 and the allowable value of the desorbed particles, NO is reached._XContinue holding. NO of desorbed particles collected in the particulate filter_XTime t when the holding amount reaches the allowable value₂Can be detected.
Next, time t₂To time t₃In the period up to_XNO with respect to the desorbed particles collected in the storage reduction catalyst 17 and the particulate filter._XRelease control is performed. In this embodiment, NO_XNO for the storage reduction catalyst 17 and the desorbed particles simultaneously_XRelease control is performed.
NO in this embodiment_XNO for the storage reduction catalyst 17_XIn the release control, post-injection as auxiliary injection is performed in the combustion chamber 2 to enrich the air-fuel ratio of the exhaust gas discharged from the engine body. NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst 17 is made rich.
FIG. 27 shows an injection pattern when the air-fuel ratio of the exhaust gas discharged from the engine body is made the stoichiometric air-fuel ratio or rich. In the injection pattern D, post injection FPO is performed after the main injection FM. The post-injection FPO is performed after the fuel is burned in the combustion chamber 2. The post injection FPO is an injection in which fuel does not burn in the combustion chamber. The post injection FPO is an auxiliary injection as with the after injection. The post injection FPO is performed, for example, when the crank angle after compression top dead center is in the range of approximately 90 ° to approximately 120 °. By performing post injection FPO in the combustion chamber, NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst can be made the stoichiometric air-fuel ratio or rich.
Referring to FIG. 23, NO for desorbed particles_XIn the discharge control, by supplying fuel from the fuel addition valve 60, the air-fuel ratio of the exhaust gas flowing into the particulate filter 16 is made the stoichiometric air-fuel ratio or rich. In the example shown in FIG. 25, the air-fuel ratio of the exhaust gas flowing into the particulate filter is made rich. NO against desorbed particles_XIn controlled release, the amount of desorbed particles or NO of desorbed particles_XDepending on the allowable value of the holding amount, NO_XIt is preferable to select operating conditions for the release control. By this control, NO_XThe fuel consumption in the emission control can be optimized. For example, the greater the amount of desorbed particles, the greater the total amount of fuel supplied from the fuel addition valve.
NO_XNO with respect to the storage reduction catalyst 17_XBy controlling the release, NO_XNO retained in the storage reduction catalyst_XCan be released. NO for the desorbed particles collected in the particulate filter_XBy controlling the release, NO retained in the desorbed particles_XCan be released. NO released_XN₂Can be reduced.
Referring to FIG. 25, time t₃Thereafter, the same operation is repeated. Time t₃To time t₄Until NO_XNO with occlusion reduction catalyst_XHolding. Time t₄To time t₅Up to NO by the desorbed particles collected in the particulate filter._XHolding. Time t₅To time t₆Until NO_XRelease control is performed. Time t₆Thereafter, the same operation control is repeated.
In this embodiment, the upstream NO_XNO for the storage reduction catalyst 17_XRelease control and NO for desorbed particles collected in downstream particulate filter_XRelease control is performed simultaneously. By performing this control, NO_XUsing a reducing agent such as unburned fuel or carbon monoxide contained in the exhaust gas flowing out from the storage reduction catalyst, NO_XCan be released. As a result, NO_XThe amount of fuel consumed for emission control can be reduced.
NO_XIn the release control, the upstream NO_XNO for the storage reduction catalyst 17_XRelease control and NO for desorbed particles collected in the downstream particulate filter_XYou may perform discharge | release control separately.
In this embodiment, the air-fuel ratio of the exhaust gas flowing into the particulate filter is made the stoichiometric air-fuel ratio or rich by supplying the fuel from the fuel addition valve. The air-fuel ratio of the exhaust gas flowing into the particulate filter can be made the stoichiometric air-fuel ratio or rich. For example, without using the fuel addition valve, by changing the combustion injection pattern in the combustion chamber, the air-fuel ratio of the exhaust gas flowing out from the engine body is kept in the stoichiometric or rich state. Upstream NO_XNO of storage reduction catalyst_XAfter release control, NO of the desorbed particles collected in the particulate filter_XRelease control can be performed.
In this embodiment, desorbed particles are NO_XUsed as an occlusion reduction catalyst. For this reason, SO_XAs the catalyst metal supported on the catalyst carrier of the trap catalyst, a metal having a strong oxidizing power is preferably disposed. For example, SO_XAs the catalyst metal of the trap catalyst, a noble metal is preferably supported. With this configuration, the desorbed particles collected by the particulate filter are reduced to NO._XCan be more reliably oxidized. NO with high desorbed particles collected by the particulate filter_XA purification rate can be achieved.
Also, the second operation control is SO_XIn addition to when all of the catalyst support contained in the trap catalyst is desorbed, SO_XThis can be performed when a part of the catalyst carrier contained in the trap catalyst is detached.
FIG. 28 shows a time chart of the third operation control in the present embodiment. In the third operation control, time t_XIn SO_XAll the catalyst carriers of the trap catalyst are detached. Time t₁, Time t₂, Time t₃And time t₄, The particulate matter accumulation amount in the particulate filter reaches an allowable value, and the particulate filter is regenerated. The regeneration time of the particulate filter can be determined by the differential pressure across the front and back. Following the regeneration control of the particulate filter, the air-fuel ratio of the exhaust gas flowing into the particulate filter is further made the stoichiometric air-fuel ratio or rich so that the desorbed particles collected in the particulate filter are SO._XRelease control is performed.
Time t₁Until, the SO of the desorbed particles collected in the particulate filter_XIncreased retention. Time t₁SO_XBy controlling the release, SO_XThe holding amount becomes almost zero. As described above, in this embodiment, every time the particulate filter regeneration control is performed, the SO with respect to the desorbed particles is controlled._XRelease control is performed. Time t₂, Time t₃And time t₄The same control is performed in FIG.
Particulate filter regeneration control and desorbed particle SO_XBy continuously performing the release control, it is possible to suppress the amount of fuel consumed for raising the temperature of the particulate filter. Also, SO in the atmosphere_XIn the case of release of SO._XIs preferably discharged at a low concentration. In this embodiment, when regeneration control of the particulate filter is performed, the SO retained on the desorbed particles is controlled._XThe amount is small. For this reason, SO at a low concentration_XCan be released into the atmosphere.
Time t_XIn SO_XAlmost all of the catalyst support of the trap catalyst is detached. Time t_XIn SO_XSO of trap catalyst_XThe holdable amount is almost zero. That is, SO_XIntegrated SO of trap catalyst_XRetention amount is saturated SO_XRetention amount has been reached.
In this embodiment, SO_XTime t after the trap catalyst is saturated₅In addition, the regeneration control of the particulate filter and the SO of the desorbed particles_XRelease control is performed. Time t₅SO_XBy performing release control, the SO of the desorbed particles collected by the particulate filter_XThe holding amount is almost zero. SO of desorbed particles collected by the particulate filter_XThe holdable amount is the time t₅Increase to.
By the way, time t_XIn the following, SO contained in the exhaust gas_XThat is, SO₂Is NO_XIt flows into the storage reduction catalyst 17. NO_XSulfur poisoning appears in the occlusion reduction catalyst 17. To recover from sulfur poisoning, the same SO_XRelease control is performed. SO_XIn release control, NO_XSet the temperature of the storage reduction catalyst to SO_XRaise to a temperature where release is possible. NO in this state_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is made rich or stoichiometric. SO_XBy controlling the release, NO_XFrom storage reduction catalyst to SO_XCan be released.
Time t_XIn the following, NO_XThe storage reduction catalyst 17 has SO_XIs retained, so NO_XSO of storage reduction catalyst_XIncreased retention. Time t₆NO_XSO of storage reduction catalyst 17_XThe holding amount has reached a predetermined allowable value. Time t₆NO_XSO for storage reduction catalyst 17_XControlled release. NO_XFrom storage reduction catalyst 17 to SO_XIs released. SO released_XIs NO_XIt is held by the desorbed particles collected by the particulate filter 16 disposed downstream of the storage reduction catalyst 17. The desorbed particles are SO_XThe holding amount increases and SO_XThe amount that can be held decreases.
Figure 29, NO_XThe graph explaining the operation area | region of a storage reduction catalyst is shown. The horizontal axis is NO_XIt is the bed temperature of the storage reduction catalyst, the vertical axis is NO_XThis is the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst. SO in the operable range_XAn emission area is defined. As indicated by an arrow 205, the smaller the air-fuel ratio of the exhaust gas, that is, the deeper the rich, the more SO_XAre released at high concentrations. NO_XThe higher the bed temperature of the storage reduction catalyst, the higher the concentration of SO_XIs released.
By the way, SO_XWhen is released into the atmosphere, it is preferably released at a low concentration. NO in conventional technology_XSO of storage reduction catalyst_XIn controlled release, SO at low concentrations_XSO to release_XWas kept released gradually. For example, the air-fuel ratio of the exhaust gas is controlled so as not to become too low. NO_XThe bed temperature of the storage reduction catalyst was controlled so as not to become too high. On the other hand, in this embodiment, NO_XSO released from the storage reduction catalyst_XCan be held by the desorbed particles collected by the particulate filter. For this reason, NO_XHigh concentration of SO from the storage reduction catalyst_XCan be released.
Conventional SO_XIn release control, NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is, for example, in the range of 14 to 14.5. On the other hand, in the present embodiment, the air-fuel ratio of the exhaust gas can be made less than 14. Furthermore, in this embodiment, NO_XThe temperature of the exhaust gas flowing into the storage reduction catalyst can be increased within a range in which the components of the exhaust purification device are not damaged.
This way, NO_XSO of storage reduction catalyst_XIn controlled release, high concentration of SO_XBy efficiently releasing SO_XCan be released. SO_XRelease control can be performed in a short time. Or many SO_XCan be released. As a result, SO_XThe amount of fuel consumed to perform release control can be reduced.
NO_XSO for storage reduction catalyst_XExhaust gas air-fuel ratio and NO when performing emission control_XThe temperature of the storage reduction catalyst is preferably determined based on the amount of desorbed particles collected in the particulate filter. The greater the amount of desorbed particles, the higher the concentration of SO_XNO_XIt can be discharged from the storage reduction catalyst. By this control, SO_XCan be released. For example, the greater the amount of desorbed particles collected in the particulate filter, the more NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst can be reduced. Further, as the amount of desorbed particles collected in the particulate filter increases, the NO._XThe temperature of the storage reduction catalyst can be increased.
In the third operation control in this embodiment, NO_XSO of storage reduction catalyst 17_XAt the time of release control, the desorbed particles collected in the particulate filter_XIs preferably captured. That is, SO_XIt is preferable that no is released. For this reason, SO_XNO to release_XWhen the temperature of the storage reduction catalyst 17 is raised, the temperature of the desorbed particles is SO._XIt is preferred to maintain below the temperature at which release is possible. For example, the particulate filter is NO_XIt is preferable to arrange it sufficiently away from the storage reduction catalyst.
Or NO_XWhen the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is the stoichiometric air-fuel ratio or rich, it is preferable that the air-fuel ratio of the exhaust gas flowing into the particulate is lean. For example, NO_XIt is preferable that an air-fuel ratio adjustment valve for introducing air is disposed between the storage reduction catalyst and the particulate filter. NO_XSO of storage reduction catalyst_XAt the time of release control, the air-fuel ratio of the exhaust gas flowing into the particulate filter can be made lean by introducing air into the engine exhaust passage upstream of the particulate filter.
Referring to FIG. 28, time t₆After that, NO_XSO of storage reduction catalyst_XEach time the holding amount reaches a predetermined tolerance, a similar SO_XRelease control can be performed. In the example shown in FIG. 28, time t₇In SO_XControlled release. SO released_XIs held by the desorbed particles collected by the particulate filter. SO of the desorbed particles_XThis control is continued until the holding amount reaches a predetermined allowable value. SO of the desorbed particles_XWhen the holding amount reaches a predetermined allowable value, the particulate filter is replaced.
Time t₅Thereafter, regeneration control for burning the particulate matter collected by the particulate filter continues. Meanwhile, time t₅Thereafter, SO for the desorbed particles collected by the particulate filter is used._XRelease control is not performed. However, time t₆Thereafter, SO with respect to the desorbed particles collected in the particulate filter will be described._XRelease control may be performed. In this case, SO released from the desorbed particles_XIt is preferable to adjust the air-fuel ratio of the exhaust gas flowing into the particulate filter and the temperature of the particulate filter so as to reduce the concentration.
Other configurations, operations, and effects are the same as those of the exhaust gas purification apparatus for an internal combustion engine described in the first or second embodiment, and thus description thereof will not be repeated here.
The above embodiments can be combined as appropriate. In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes included in the scope of claims are intended.

DESCRIPTION OF SYMBOLS 1 ... Engine main body 14 ... SO _X trap catalyst 16 ... Particulate filter 17 ... NO _X storage reduction catalyst 30 ... Electronic control unit 48 ... Catalyst support 48a ... Catalyst support (sulfate)
49 ... Catalyst metal 50 ... SO _X absorbent 51 ... Binder 52 ... Base 53 ... Coat layer 54 ... Auxiliary particles 60 ... Fuel addition valve

Claims

Disposed engine exhaust passage, when the air-fuel ratio of the inflowing exhaust gas is lean holds the NO X contained in the exhaust gas, the air-fuel ratio of the inflowing exhaust gas was maintained to be the stoichiometric air-fuel ratio or rich NO X and the NO X storage reduction catalyst which releases, is disposed upstream of the engine exhaust passage of the NO X occluding and reducing catalyst, and a stored SO X material for holding the SO X,
The SO X holding material includes a particulate catalyst carrier that supports the catalyst metal, and a binder that is formed of a material different from that of the catalyst carrier and bonds the catalyst carriers to each other.
At least one of the catalyst carrier and the binding material absorbs SO X contained in the exhaust gas and is reformed to sulfate, whereby the volume expands and the bond between the catalyst carrier and the binding material is released. An exhaust gas purification apparatus for an internal combustion engine, wherein the catalyst carrier is desorbed in the form of particles.
The catalyst carrier is formed of a material that expands in volume when SO X is occluded and reformed to sulfate, and the binding material occludes an invariable material or SO X when SO X flows in. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is formed of a material whose volume is substantially unchanged when it is reformed into sulfate.
In the SO X holding material, the catalyst carrier is arranged in layers on the surface of the substrate,
2. The exhaust gas of an internal combustion engine according to claim 1, wherein the thickness of the catalyst carrier layer is estimated, and the integrated SO X retention amount of the SO X retention material is calculated using the layer thickness of the catalyst carrier. Purification equipment.
A collection filter that is disposed in the engine exhaust passage downstream of the NO X storage reduction catalyst and collects desorbed particles including the catalyst carrier desorbed from the SO X holding material;
2. The internal combustion engine according to claim 1, wherein the NO X contained in the exhaust gas is held by the desorbed particles after the SO X is released from the desorbed particles collected by the collection filter. Exhaust purification device.
Based on the amount of desorbed particles collected by the collection filter, estimate the allowable value that the desorbed particles can hold NO X ,
When the NO X holding amount of desorbed particles exceeds an allowable value, the air-fuel ratio of the exhaust gas flowing into the collection filter to the stoichiometric air-fuel ratio or rich, NO X to release the NO X held in the desorption particles 5. The exhaust emission control device for an internal combustion engine according to claim 4, wherein release control is performed.
When almost all of the particulate catalyst carrier contained in the SO X holding material is desorbed, SO X contained in the exhaust gas is held in the NO X storage reduction catalyst,
When the temperature of the NO X storage reduction catalyst is raised to a temperature at which SO X can be released and SO X release control is performed to make the air-fuel ratio of the exhaust gas flowing into the NO X storage reduction catalyst the stoichiometric air-fuel ratio or rich , based on the amount of desorbed particles trapped in the collection filter, and characterized by determining at least one of the air-fuel ratio of the exhaust gas flowing into the temperature and the NO X storage reduction catalyst of the NO X occluding and reducing catalyst The exhaust emission control device for an internal combustion engine according to claim 4.
Disposed engine exhaust passage, when the air-fuel ratio of the inflowing exhaust gas is lean holds the NO X contained in the exhaust gas, the air-fuel ratio of the inflowing exhaust gas was maintained to be the stoichiometric air-fuel ratio or rich NO X and the NO X storage reduction catalyst which releases, is disposed upstream of the engine exhaust passage of the NO X occluding and reducing catalyst, and a stored SO X material for holding the SO X,
The SO X holding material is formed of a particulate catalyst carrier supporting a catalyst metal, a material different from the catalyst carrier, an auxiliary particle having an average particle size smaller than that of the catalyst carrier, and a material substantially the same as the auxiliary particle, And a support for binding the auxiliary particles to each other, the catalyst carrier is supported by the auxiliary particles,
The catalyst carrier absorbs SO X contained in the exhaust gas and is reformed into sulfate, so that the volume expands, the support of the catalyst carrier by the auxiliary particles is released, and the catalyst carrier is detached in the form of particles. An exhaust gas purifying device for an internal combustion engine, characterized by the above.
The binder and the auxiliary particles have a decomposition temperature at which the sulfate decomposes when SO X is occluded to become sulfate.
By performing desorption promotion control that raises the temperature of the SO X holding material above the decomposition temperature, the sulfate is decomposed to reduce the volume of the binder and auxiliary particles, and the support of the catalyst carrier by the auxiliary particles is released. The exhaust emission control device for an internal combustion engine according to claim 7, wherein:
A collection filter that is disposed in the engine exhaust passage downstream of the NO X storage reduction catalyst and collects desorbed particles including the catalyst carrier desorbed from the SO X holding material;
9. The internal combustion engine according to claim 8, wherein when the amount of desorbed particles collected by the collection filter exceeds a predetermined allowable value, desorption promotion control is prohibited. Exhaust purification equipment.
In the SO X holding material, the catalyst carrier is arranged in layers on the surface of the substrate,
The exhaust gas of an internal combustion engine according to claim 7, wherein the thickness of the catalyst carrier layer is estimated, and the integrated SO X retention amount of the SO X retention material is calculated using the layer thickness of the catalyst carrier. Purification equipment.
A collection filter that is disposed in the engine exhaust passage downstream of the NO X storage reduction catalyst and collects desorbed particles including the catalyst carrier desorbed from the SO X holding material;
8. The internal combustion engine according to claim 7, wherein the NO X contained in the exhaust gas is retained by the desorbed particles after the SO X is released from the desorbed particles collected by the collection filter. Exhaust purification device.
Based on the amount of desorbed particles collected by the collection filter, an allowable value capable of holding NO X of desorbed particles is estimated,
When the NO X holding amount of desorbed particles exceeds an allowable value, the air-fuel ratio of the exhaust gas flowing into the collection filter to the stoichiometric air-fuel ratio or rich, NO X to release the NO X held in the desorption particles The exhaust emission control device for an internal combustion engine according to claim 11, wherein the emission control is performed.
When almost all of the particulate catalyst carrier contained in the SO X holding material is desorbed, SO X contained in the exhaust gas is held in the NO X storage reduction catalyst,
When the temperature of the NO X storage reduction catalyst is raised to a temperature at which SO X can be released, and SO X release control is performed to make the air-fuel ratio of the exhaust gas flowing into the NO X storage reduction catalyst the stoichiometric air-fuel ratio or rich , based on the amount of desorbed particles trapped in the collection filter, and characterized by determining at least one of the air-fuel ratio of the exhaust gas flowing into the temperature and the NO X storage reduction catalyst of the NO X occluding and reducing catalyst The exhaust emission control device for an internal combustion engine according to claim 11.