JP2010223076A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of simultaneously efficiently performing sulfur removal of an NOx removing catalyst and burning-removal of PM (Particulate Matter) of a DPF (Diesel Particulate Filter). <P>SOLUTION: This exhaust emission control device includes the NOx removing catalyst 2 having an oxygen storage-releasing material for storing oxygen on the lean side and releasing the stored oxygen on the rich side, and includes a regeneration performing part 51 for repeatedly performing control for performing enriching control for setting the exhaust air-fuel ratio again to the rich side, after performing lean forming control for a predetermined time for returning the exhaust air-fuel ratio once to the lean side, after performing the enriching control for setting the exhaust air-fuel ratio of exhaust gas flowing in the NOx removing catalyst 2 to the rich side from the lean side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine (hereinafter referred to as an engine). In particular, the present invention relates to an exhaust purification device including a NOx purification catalyst and a particulate filter.

  In the present invention, the term “rich” means that the air / fuel ratio (hereinafter referred to as air-fuel ratio) is smaller than the stoichiometric air-fuel ratio, and the term “lean” means that the air-fuel ratio is Means greater than the stoichiometric air-fuel ratio described above.

  Conventionally, in a lean combustion engine, purification of NOx and particulate matter (hereinafter referred to as PM) contained in exhaust gas has been a problem. For example, for the purpose of purifying NOx and PM, a NOx purifying catalyst that stores NOx on the lean side, purifies the stored NOx on the rich side, and a diesel particulate filter (hereinafter referred to as DPF) that collects PM. An exhaust purification device that is sequentially disposed in an exhaust passage is disclosed (for example, see Patent Document 1).

According to Patent Document 1, occludes the NOx purifying catalyst at a low temperature, by releasing the NO ₂ and stored NOx in high temperature, results capable of supplying NO ₂ on the downstream side DPF, the PM deposited in the DPF It is said that it can be burned at a low temperature.
However, when NOx is not occluded at low temperatures, NO ₂ cannot be supplied to the downstream DPF, and therefore PM cannot be combusted at low temperatures. In addition, it is indispensable to remove sulfur for the NOx purification catalyst and combustion removal of PM for the DPF, and it is desirable to perform these regeneration processes as efficiently as possible.

  In view of this, a technology has been disclosed in which the regeneration of the NOx purification catalyst and the DPF can be performed simultaneously to shorten the total regeneration time and prevent the deterioration of fuel consumption (for example, see Patent Document 2).

JP 2002-276337 A Japanese Patent Laid-Open No. 2003-201828

However, in the exhaust purification device of Patent Document 2, it is necessary to provide an air introduction port before the DPF, and a control mechanism for the air introduction timing is required, so that the system does not have the expected effects due to complexity. .
Therefore, there is a need for an exhaust purification device that can efficiently and efficiently simultaneously remove sulfur from the NOx purification catalyst and PM combustion removal from the DPF.

  The present invention has been made in view of the above-described problems, and an object of the present invention is an exhaust purification device including a NOx purification catalyst and a particulate filter, which removes sulfur from the NOx purification catalyst and PM combustion removal from the DPF. Another object of the present invention is to provide an exhaust emission control device that can be efficiently executed at the same time.

  In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage (4) of an internal combustion engine (1) and purifies NOx by repeating lean and rich, and the exhaust gas. An exhaust gas purification apparatus for an internal combustion engine provided with a particulate filter (3) provided downstream of the NOx purification catalyst in the passage and collecting particulates in the exhaust gas, wherein the NOx purification catalyst is on the lean side And the oxygen storage / release material that releases the stored oxygen on the rich side, and the exhaust purification device changes the exhaust air-fuel ratio of the exhaust flowing into the NOx purification catalyst from the lean side to the rich side. After performing the enrichment control, a lean control for returning to the lean side is performed for a predetermined time, and then a series of controls for performing the enrichment control to the rich side again is executed at least once. Result, the purifying sulfur trapped in the NOx purifying catalyst, characterized in that it comprises a and a reproducing means (51) for purifying the particulates captured on the particulate filter.

  According to a second aspect of the present invention, the rich first target air-fuel ratio is set as the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst at the time of the enrichment control. First target air-fuel ratio setting means (52) and second target air-fuel ratio setting means for setting a lean-side second target air-fuel ratio as the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst during the leaning control (53) and when the exhaust air-fuel ratio of the exhaust gas flowing into the particulate filter falls below a predetermined threshold, the target air-fuel ratio is temporarily switched from the first target air-fuel ratio to the second target air-fuel ratio. And a switching means (55) for switching to the first target air-fuel ratio again after the lapse of the predetermined time, wherein the regeneration means exhausts the exhaust air fuel flowing into the NOx purification catalyst. Is controlled so as to coincide with the first target air-fuel ratio or the second target air-fuel ratio in accordance with the switching of the target air-fuel ratio by the switching means, thereby purifying the sulfur content captured by the NOx purification catalyst. In addition, the particulate matter collected by the particulate filter is purified.

  According to a third aspect of the present invention, in the exhaust purification device according to the second aspect, the first target air-fuel ratio setting means includes a temperature of the NOx purification catalyst, a temperature of exhaust flowing into the NOx purification catalyst, and the NOx purification. The first target air-fuel ratio is set based on at least one of a flow rate of exhaust gas flowing into the catalyst and a degree of deterioration of the NOx purification catalyst.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus according to the third aspect, a catalyst deterioration degree estimating means (54) for estimating the deterioration degree of the NOx purification catalyst based on an integrated value of the fuel injection amount of the internal combustion engine. ), And the first target air-fuel ratio setting means sets the first target air-fuel ratio higher as the deterioration degree of the NOx purification catalyst estimated by the catalyst deterioration degree estimation means is larger. To do.

  According to a fifth aspect of the present invention, in the exhaust purification apparatus according to any one of the second to fourth aspects, the second target air-fuel ratio setting means includes a temperature of the NOx purification catalyst and a temperature of the exhaust gas flowing into the NOx purification catalyst. The second target air-fuel ratio is set based on at least one of a flow rate of exhaust gas flowing into the NOx purification catalyst and a deterioration degree of the NOx purification catalyst.

  According to a sixth aspect of the present invention, the exhaust gas purification apparatus according to the fifth aspect further comprises a catalyst deterioration degree estimating means for estimating a deterioration degree of the NOx purification catalyst based on an integrated value of the fuel injection amount of the internal combustion engine. And the second target air-fuel ratio setting means sets the second target air-fuel ratio higher as the deterioration degree of the NOx purification catalyst estimated by the catalyst deterioration degree estimating means is larger.

  According to a seventh aspect of the present invention, in the exhaust purification device according to any one of the first to sixth aspects, the second target air-fuel ratio setting means sets the second target air-fuel ratio as the temperature of the NOx purification catalyst is higher. It is characterized by being set low.

  The invention according to claim 8 is the exhaust purification apparatus according to any one of claims 1 to 7, further comprising time setting means (57) for setting the predetermined time shorter as the temperature of the NOx purification catalyst is higher. It is characterized by.

  The invention according to claim 9 is the exhaust purification apparatus according to any one of claims 1 to 8, wherein the NOx purification catalyst includes a first catalyst layer containing a noble metal and a cerium oxide-based material.

According to a tenth aspect of the present invention, in the exhaust gas purification apparatus according to the ninth aspect, the NOx purification catalyst further includes a second catalyst layer containing zeolite as an NH ₃ adsorbent.

  The invention according to claim 11 is the exhaust purification apparatus according to claim 10, wherein the second catalyst layer is provided on the first catalyst layer in the NOx purification catalyst.

  A twelfth aspect of the present invention is the exhaust gas purification apparatus according to any one of the first to eleventh aspects, wherein the particulate filter carries a combustion catalyst for burning the collected particulates. And

  According to a thirteenth aspect of the present invention, in the exhaust emission control device according to the twelfth aspect, the combustion catalyst is formed by supporting Ag on a complex oxide having an oxygen storage / release capability.

The invention of claim 14, wherein, in the exhaust gas purification device according to any of claims 1 13, wherein the particulate filter, is NO ₂ generating catalyst is supported to convert the NO to NO ₂ in the exhaust It is characterized by being.

According to a fifteenth aspect of the present invention, in the exhaust gas purification apparatus according to the fourteenth aspect, the NO ₂ generation catalyst is such that at least one element of Pt, Pd, and Rh is alumina, silica, silica alumina, zirconia. , And ceria, and is supported on at least one carrier.

The exhaust emission control device according to claim 1 includes an NOx purification catalyst having an oxygen storage / release material. Further, after performing enrichment control for changing the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst from the lean side to the rich side, after performing the leaning control for returning to the lean side for a predetermined time, the exhaust air / fuel ratio is again made rich. The reproduction means for executing the series of control for performing the enrichment control at least once is configured.
Accordingly, the air-fuel ratio of the exhaust gas flowing into the particulate filter can be kept lean by the oxygen storage capacity (OSC) of the NOx purification catalyst while enriching the exhaust air-fuel ratio flowing into the NOx purification catalyst. In addition, after the enrichment control is performed, the lean storage control that is once returned to the lean side is performed, so that the oxygen storage capacity (OSC) of the NOx purification catalyst can be maintained for a long time. As a result, the air-fuel ratio of the exhaust gas flowing into the particulate filter Can be kept lean for a long time.
For this reason, sulfur removal of the NOx purification catalyst and combustion removal of PM collected by the particulate filter can be performed simultaneously. Therefore, energy required for sulfur removal and PM combustion removal can be reduced, and deterioration of fuel consumption can be reduced.

The exhaust emission control device according to claim 2 is configured so that the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst coincides with the first target air-fuel ratio or the second target air-fuel ratio in accordance with switching of the target air-fuel ratio by the switching means. And a reproducing means for controlling.
As a result, the exhaust air-fuel ratio can be controlled as desired, and the air-fuel ratio of the exhaust flowing into the particulate filter can always be kept lean, so that the effect of claim 1 can be achieved more remarkably.

According to a third aspect of the present invention, at least one of the temperature of the NOx purification catalyst, the temperature of the exhaust gas flowing into the NOx purification catalyst, the flow rate of the exhaust gas flowing into the NOx purification catalyst, and the degree of deterioration of the NOx purification catalyst. And a first target air-fuel ratio setting means for setting the first target air-fuel ratio based on the above.
As a result, the exhaust air-fuel ratio flowing into the NOx purification catalyst can be controlled in accordance with the oxygen storage capacity (OSC) of the NOx purification catalyst, so that sulfur removal and PM combustion removal can be executed more efficiently, and fuel consumption deteriorates. It can be reduced more.

The exhaust emission control device according to claim 4 includes a catalyst deterioration degree estimating means, and the first target air-fuel ratio is set higher as the deterioration degree of the NOx purification catalyst estimated by the catalyst deterioration degree estimating means is larger. An air-fuel ratio setting means is included.
Thereby, oxygen can be supplied without excess and deficiency during sulfur removal and PM combustion removal. For this reason, it is possible to avoid a decrease in PM combustion efficiency due to oxygen shortage and a decrease in sulfur removal efficiency due to excessive oxygen. In addition, when the deterioration of the NOx purification catalyst progresses and the OSC decreases, the first target air-fuel ratio that is the target air-fuel ratio at the time of enrichment control is set high so that the exhaust air flowing into the particulate filter is exhausted. It is possible to avoid the problem that the PM combustion efficiency is lowered because the fuel ratio is lower than the stoichiometric ratio.

The exhaust purification device according to claim 5 is at least one of the temperature of the NOx purification catalyst, the temperature of the exhaust gas flowing into the NOx purification catalyst, the flow rate of the exhaust gas flowing into the NOx purification catalyst, and the degree of deterioration of the NOx purification catalyst. And a second target air-fuel ratio setting means for setting a second target air-fuel ratio based on the above.
Thereby, the oxygen concentration flowing into the NOx purification catalyst can be adjusted when the target air-fuel ratio is switched during sulfur removal and PM combustion removal in accordance with the oxygen storage capacity (OSC) of the NOx purification catalyst. For this reason, it is possible to always avoid a decrease in PM combustion efficiency due to lack of oxygen and a decrease in sulfur removal efficiency due to excessive oxygen.

The exhaust purification device according to claim 6 includes a catalyst deterioration degree estimating means, and a second target air-fuel ratio that is set higher as the NOx purification catalyst deterioration degree estimated by the catalyst deterioration degree estimating means is larger. An air-fuel ratio setting means is included.
Thereby, similarly to the invention described in claim 4, it is possible to avoid a decrease in PM combustion efficiency due to insufficient oxygen and a decrease in sulfur removal efficiency due to excessive oxygen. In addition, it is possible to avoid the problem that the PM combustion efficiency is lowered because the air-fuel ratio of the exhaust gas flowing into the particulate filter becomes less than stoichiometric.

The exhaust emission control device according to claim 7 includes second target air-fuel ratio setting means for setting the second target air-fuel ratio to be lower as the temperature of the NOx purification catalyst is higher.
The OSC function of the NOx purification catalyst increases as the temperature of the NOx purification catalyst decreases. In this regard, according to the present invention, the higher the temperature of the NOx purification catalyst, the lower the second target air-fuel ratio is set. Therefore, the NOx purification catalyst can be prevented from increasing in temperature, and more oxygen can be stored in the NOx purification catalyst. Can do. Therefore, sulfur removal and PM combustion removal can be executed more efficiently, and deterioration of fuel consumption can be further reduced.

The exhaust purification device according to claim 8 includes a time setting means for setting the lean control time in the regeneration means to be shorter as the temperature of the NOx purification catalyst is higher.
As a result, the higher the temperature of the NOx purification catalyst, the shorter the lean control time in the regenerating means, so that the temperature of the NOx purification catalyst can be suppressed and more oxygen can be stored in the NOx purification catalyst. . Therefore, sulfur removal and PM combustion removal can be executed more efficiently, and deterioration of fuel consumption can be further reduced.

  The exhaust emission control device according to claim 9 includes an NOx purification catalyst including a first catalyst layer containing a noble metal and a cerium oxide-based material. Thereby, high NOx purification performance is exhibited even in a low temperature state such as immediately after start-up or during idling due to the low-temperature NOx adsorption ability of the cerium oxide-based material. In addition, since the OSC of the NOx purification catalyst is dramatically increased, the time during which the sulfur removal and the PM combustion removal can be performed at the same time is lengthened. As a result, the total time required for the regeneration process can be shortened.

The exhaust emission control device according to claim 10 includes an NOx purification catalyst further including a second catalyst layer containing zeolite as an NH ₃ adsorbent. Thereby, the amount of NH ₃ adsorption can be increased, and the reactivity with NOx at the time of lean can be improved.

The exhaust emission control device according to claim 11 includes the NOx purification catalyst in which the second catalyst layer is provided on the first catalyst layer. Accordingly, the NH ₃ generated during enrichment control efficiently captured, it is possible to use efficiently the NOx purification in the next lean, NOx purification performance is further improved.

  The exhaust emission control device according to claim 12 includes a particulate filter carrying a combustion catalyst for burning the collected particulates. Thereby, even if the temperature of a particulate filter is 600 degrees C or less, PM removal of combustion is possible. For this reason, the particulate filter can be efficiently regenerated at a low temperature, and the deterioration of fuel consumption can be further reduced.

  The exhaust emission control device according to claim 13 includes a combustion catalyst in which Ag is supported on a composite oxide having oxygen storage / release capability. As a result, PM can be removed by combustion even at about 500 ° C. Therefore, even when the temperature of the particulate filter is reduced to about 500 ° C. during vehicle travel, PM can be removed by combustion. The regeneration speed of the particulate filter can be greatly improved. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

Exhaust purification device according to claim 14 is, NO ₂ generating catalyst to convert the NO in the exhaust to NO ₂ is configured to include a particulate filter that is supported. Thereby, the combustion of PM can be further promoted, and the regeneration speed of the particulate filter can be improved. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

The exhaust emission control device according to claim 15, wherein at least any one element of Pt, Pd, and Rh is supported on at least one of alumina, silica, silica alumina, zirconia, and ceria. A NO ₂ production catalyst was included. As a result, the ability to generate NO ₂ can be increased by the action of the noble metal supported on the high specific surface area carrier, and NO ₂ can be used more efficiently for PM combustion. As a result, the regeneration speed of the particulate filter can be reduced. It can be improved further. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

It is a figure showing composition of an exhaust-air-purification device of an internal-combustion engine concerning one embodiment of the present invention. It is a schematic diagram of DPF3 when it sees from the flow direction of exhaust gas. It is a schematic diagram of DPF3 when it sees from the direction orthogonal to the flow direction of exhaust_gas | exhaustion. It is the elements on larger scale of DPF3. It is a figure which shows the relationship between a target air fuel ratio and ( _{SIGMA) Q fuel_total} . It is a figure which shows the relationship between the correction coefficient Ktemp and NOx purification catalyst temperature. It is a figure for demonstrating the change of the target air fuel ratio in one Embodiment of this invention, and the setting of regeneration process time. It is a figure which shows the relationship between a counter subtraction value and Rear_A / F. It is a figure for demonstrating determination of the reproduction time in one Embodiment of this invention. It is a flowchart of the reproduction | regeneration processing procedure in one Embodiment of this invention. It is a figure for demonstrating the reproduction | regeneration processing in one Embodiment of this invention. It is a figure which shows the structure of the exhaust gas purification apparatus of a present Example. It is a figure which shows the amount of S desorption of a present Example and a comparative example. It is a figure which shows the emitted-heat amount accompanying PM combustion of a present Example and a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an engine 1 and an exhaust purification device thereof according to an embodiment of the present invention. The engine 1 is a diesel engine that directly injects fuel into a combustion chamber of each cylinder (not shown), and each cylinder is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as ECU) 5, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 5.

The engine 1 is provided with an intake pipe (not shown) through which intake air flows and an exhaust pipe 4 through which exhaust flows.
In the exhaust pipe 4 through which the exhaust discharged from the engine 1 flows, a NOx purification catalyst 2 and a diesel particulate filter 3 (hereinafter referred to as DPF) are provided in order from the upstream side.

The configuration of the NOx purification catalyst 2 will be described.
The NOx purification catalyst 2 has a two-layer structure in which a first catalyst layer and a second catalyst layer are laminated in this order on a carrier. The first catalyst layer includes a noble metal and a cerium oxide-based material that is a NOx adsorbent. The second catalyst layer includes an NH ₃ adsorbent such as zeolite and at least one of Fe and Cu.
As the carrier, a honeycomb structure such as cordierite, alumina, aluminum titanate, stainless steel or SiC is used.
As the noble metal, any one of Pt, Pd, and Rh is used alone or in combination of two or more. Pt and Pd mainly play a role of oxidizing NO to NO ₂ when lean, and a role of generating NH ₃ from H ₂ and HC in the exhaust and adsorbed NOx when rich. Rh plays a role of reducing adsorbed NOx to N ₂ by a reducing agent when rich.
The coating amount of Pt is preferably 1.0 to 10 g / L per liter of carrier, the coating amount of Pd is preferably 0.1 to 10 g / L per liter of carrier, and the coating amount of Rh is 0.1 to 4. 0 g / L is preferred.
The cerium oxide-based material as the NOx adsorbent does not “occlude” NOx into the inside like an alkaline earth metal, but “adsorbs” NOx. For this reason, noble metal catalytic activity does not decrease even at low temperatures.
As the cerium oxide-based material, ceria, ceria zirconia composite oxide, or a material containing at least one rare earth element is used. Examples of rare earth elements include La, Nd, Pr, and Sm. By including Zr, the structural stability is improved and the heat resistance is improved. In addition, rare earth elements have the effect of changing the chemical state of the adsorption point and extending the NOx adsorption temperature range.
The NH ₃ adsorbent is not particularly limited as long as it is a solid material having an acid point. Particularly effective ones include zeolite, ferrierite, and silica alumina. Among zeolites, β type, MFI type, Y type, and mordenite type are preferable. Further, from the viewpoint of improving NOx reduction performance, it is preferable to simultaneously contain Fe and Cu in these solid materials. In this case, Fe and Cu are effective in any state of mixing, supporting, and ion exchange.

The reaction mechanism of the NOx purification catalyst 2 will be described.
When the exhaust air-fuel ratio is lean, NO in the exhaust is oxidized to NO ₂ by a noble metal such as platinum in the first catalyst layer and is adsorbed by the cerium oxide-based material. Next, when the exhaust air-fuel ratio is made rich, NOx adsorbed on the first catalyst layer at the time of lean is converted into NH ₃ or N ₂ by CO, HC, or H ₂ generated by the water gas shift reaction. The produced NH ₃ moves to the second catalyst layer and is adsorbed by the NH ₃ adsorbent. This adsorption is easily performed because the first catalyst layer and the second catalyst layer are laminated adjacent to each other. Then, when returning the exhaust air-fuel ratio to lean, the NOx contained in the exhaust and NH _3, which is again stored in the second catalyst layer, NH ₃ selective catalytic reduction reaction is converted into N ₂ and H _{2 O} by the release Is done. At this time, since the second catalyst layer is the uppermost layer, the produced N ₂ is efficiently released.
In this way, NOx in the exhaust gas is purified by the NOx purification catalyst 2.

The NOx purification catalyst 2 having the above configuration has the following characteristics.
The NOx purification catalyst 2 of the present embodiment has high NOx purification performance at 150 to 400 ° C. due to the reaction mechanism as described above. In addition, when rich, NOx adsorbed during lean progresses simultaneously with a reducing agent such as CO, HC, H _{2 and the} like, and the reaction proceeds directly to N _2. Depending on the conditions, this reaction selectively proceeds to cause NOx. Purification efficiency increases dramatically.
In addition, when the sulfur content such as SOx is captured and accumulated in the NOx purification catalyst, the NOx adsorption performance deteriorates. Therefore, it is necessary to periodically raise the temperature above the temperature at which the sulfur content is desorbed to remove the sulfur content. is there. In the conventional alkali and alkaline earth NOx absorbents, about 700 ° C. is necessary for the removal of the sulfur content. In the NOx purification catalyst 2 of the present embodiment, the sulfur content can be removed at about 600 ° C. For this reason, according to the NOx purification catalyst 2 of the present embodiment, it is possible to suppress the temperature rising energy necessary for the removal of the sulfur content and to suppress the deterioration of the fuel consumption.

Next, the DPF 3 of this embodiment will be described.
The DPF 3 of this embodiment is a three-dimensional structure made of porous ceramics. The material is a porous material such as cordierite, SiC, alumina, titania, and a structure such as a wall flow type or a foam type is preferably employed. The center pore diameter is preferably 10 to 30 μm, and the porosity is preferably 40 to 60%.
Further, the DPF 3 of the present embodiment includes a PM combustion catalyst and a NO ₂ generation catalyst described later.

FIG. 2 shows a schematic diagram of the DPF 3 viewed from the exhaust flow direction, and FIG. 3 shows a schematic diagram of the DPF 3 viewed from a direction orthogonal to the exhaust flow direction. As shown in FIGS. 2 and 3, the DPF 3 has a honeycomb structure and includes a number of exhaust passages extending in parallel with each other. More specifically, an exhaust inflow passage 32 in which the downstream end of the DPF 3 is closed by a plug 34 and an exhaust outflow passage 33 in which an upstream end is closed by the plug 34 are alternately provided in the front, rear, left, and right. The path 33 is separated by a thin partition wall 35.
Since the filter body of the DPF 3 is formed of the above porous material, the exhaust gas flowing into the exhaust inflow passage 32 passes through the surrounding partition wall 35 as shown by the arrow in FIG. It flows into the outflow passage 33. That is, as shown in FIG. 4, the partition wall 35 has fine pores 36 communicating with the exhaust inflow passage 32 and the exhaust outflow passage 33. Pass through 36.

Further, a catalyst coat layer 37 is formed on the exhaust passage of the filter body of the DPF 3, that is, the wall surfaces of the exhaust inflow passage 32, the exhaust outflow passage 33, and the pores 36. The catalyst coat layer 37 is formed by uniformly coating the surface of each exhaust passage. Although the PM combustion catalyst and the NO ₂ production catalyst may be mixed in the coat layer, it is preferable that these are separated into two layers. Specifically, it is preferable to form the PM combustion catalyst layer as the first layer (lower layer) on the surface side of the exhaust flow path and form the NO ₂ generation catalyst layer as the second layer (upper layer). Most NOx in the exhaust gas to be discharged in the state NO, the is because it is possible to supply the NO ₂ to NO ₂ generated by the upper layer of the NO ₂ generation catalysts under the PM combustion catalyst. Further, at a high temperature of around 600 ° C., when the NO ₂ production catalyst is used as in the prior art, the NO ₂ concentration becomes extremely low due to the equilibrium, so that the reaction between NO ₂ and PM is difficult to proceed. . On the other hand, when the two-layer structure of the NO ₂ production catalyst and the PM combustion catalyst is adopted, the produced NO ₂ is adsorbed on the complex oxide having the oxygen releasing ability of the PM combustion catalyst before returning to NO. As a result, a state in which there is a large amount of NO ₂ can be formed in the vicinity of the catalyst, so that PM combustion easily proceeds.

In the case of a two-layer structure, the coating amount of the lower layer PM combustion catalyst is preferably 20 to 60 g per 1 L of the filter body. If it is less than 20 g, the surface in the pores 36 cannot be sufficiently covered, and the contact property with the PM becomes worse. If it exceeds 60 g, the pressure loss increases due to clogging of the pores 36.
Further, the coating amount of the upper NO ₂ production catalyst is preferably 10 to 30 g per 1 L of the filter body. If it is less than 10 g, the NO ₂ generation capacity is insufficient. When it exceeds 30 g, the thickness of the layer increases and the contact property between the PM combustion catalyst and PM decreases.

As said PM combustion catalyst, what carried Ag on the complex oxide which has oxygen storage-release capability is used. Specifically, it is preferable to use a catalyst in which Ag is supported on CeO ₂ —ZrO ₂ .
As the composite oxide, one or two selected from the group consisting of perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type can be used. Among these, the perovskite type and the fluorite type are preferable from the viewpoint of heat resistance.
The composite oxide is composed of one or a combination of two or more elements selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, transition metals, and noble metals. From the viewpoint of oxygen releasing ability, the composite oxide preferably contains at least one kind of element having polyvalence. This is because oxygen release is a phenomenon in which oxygen in the lattice of the composite oxide is desorbed in order to maintain a charge balance according to changes in the valence of the constituent atoms.
Examples of transition metals include V, Cr, Mn, Fe, Co, Cu, Nb, Ta, Mo, and W. Examples of rare earths include Ce, Pr, Sm, Eu, Tb, and Yb. Is exemplified by Na, K, and Cs. Further, as noble metals, Pt, Pd, Rh, Ir, and Ru are preferably exemplified because they are unstable as oxides and exhibit characteristics of releasing oxygen when metallized. Further, from the viewpoint of structural stability, La, Nd, Y, Sc, Hf, Ca, Sr, and Ba having a relatively large ionic radius with no valence change are preferably included.
The method for preparing the composite oxide is not particularly limited, but a nitrate decomposition method, an organic acid complex polymerization method, or the like can be preferably used. The method for supporting Ag on the composite oxide is not particularly limited, but an impregnation method, a precipitation method, or the like can be suitably used.

On the other hand, as the NO ₂ production catalyst, a catalyst in which a noble metal (Pt, Pd, Rh, etc.) is supported on at least one of alumina, silica, zirconia, magnesia, and titania having a high specific surface area is preferably used. It is done.
The method for supporting the noble metal on these high specific surface area carriers is not particularly limited, and an impregnation method, a precipitation method, or the like can be suitably used.

The DPF 3 having the above configuration has the following characteristics.
Normally, when PM accumulates over a certain amount in the DPF, pressure loss increases due to clogging, and fuel consumption deteriorates. Therefore, it is necessary to raise the exhaust temperature regularly above the temperature at which PM burns. . In this respect, since the DPF 3 of the present embodiment carries the catalyst having the high low temperature combustion activity as described above, the regeneration can be performed by burning and removing PM at 500 ° C. or less. For this reason, the temperature rising energy required for removal of PM can be suppressed, and deterioration of fuel consumption can be suppressed.

Returning to FIG. 1, the ECU 5 includes an accelerator sensor 11 that detects the amount of depression of the accelerator pedal of the vehicle driven by the engine 1, and a first air-fuel ratio sensor 12 that detects the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2. The second air-fuel ratio sensor 13 for detecting the air-fuel ratio of the exhaust gas flowing into the DPF 3 and the catalyst temperature sensor 14 for detecting the temperature of the NOx purification catalyst 2 are connected. The detection signals of these sensors are supplied to the ECU 5. The
Here, the degree of deterioration of the NOx purification catalyst 2 is estimated based on the integrated value of the fuel injection amount of the engine 1, and the fuel injection amount of the engine 1 is calculated by the ECU 5 based on the output of the accelerator sensor 11.

  The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, and converts an analog signal value into a digital signal value, and a central processing unit (hereinafter referred to as a central processing unit). CPU). In addition, the ECU 5 includes a storage circuit that stores various calculation programs and calculation results executed by the CPU, and an output circuit that outputs a control signal to the fuel injection valve of the engine 1.

  With the hardware configuration as described above, the ECU 5 includes the regeneration execution unit 51, the first target air-fuel ratio setting unit 52, the second target air-fuel ratio setting unit 53, the catalyst deterioration degree estimation unit 54, the switching unit 55, the regeneration processing time. Each module of the setting unit 56 and the enrichment control interruption time setting unit 57 is configured. Hereinafter, the function of each module will be described.

The regeneration executing unit 51 purifies sulfur content such as SOx trapped by the NOx purification catalyst 2 and executes a regeneration process for purifying PM trapped in the DPF 3. Specifically, after performing the enrichment control to change the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 from the lean side to the rich side, and once performing the leaning control to return to the lean side for a predetermined time, again By performing enrichment control on the rich side, the regeneration process of the NOx purification catalyst 2 and the DPF 3 is executed.
In the present embodiment, the enrichment control is executed by post-rich. Here, post-rich means that unburned fuel is produced by post-injecting additional fuel that does not contribute to torque from the fuel injection valve into the cylinder in the vicinity of each cylinder of the engine 1 from the explosion process to the exhaust process. Is circulated in the exhaust passage to make the exhaust air-fuel ratio rich.
Further, in the enrichment control, the fuel injection valve opening time is set so that the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 detected by the first air-fuel ratio sensor 12 matches a first target air-fuel ratio described later. The fuel injection amount is adjusted by adjusting the valve closing time.
In addition, since the engine 1 of the present embodiment is a diesel engine, the lean control is executed by interrupting the rich control. In the lean control, the fuel injection valve opening time and closing time are set so that the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 detected by the first air-fuel ratio sensor 12 matches the second target air-fuel ratio described later. Adjust the valve time to adjust the fuel injection amount.

The first target air-fuel ratio setting unit 52 sets the first target air-fuel ratio richer than stoichiometric as the target air-fuel ratio of the exhaust flowing into the NOx purification catalyst 2 during the enrichment control. In the present embodiment, the integrated value of the fuel injection amount of the engine 1 is used as the deterioration degree of the NOx purification catalyst 2 estimated by the catalyst deterioration degree estimating unit 54 described later, and the first value is based on the integrated value of the fuel injection amount. Set the target air-fuel ratio.
Specifically, the relationship between the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1 which is set based on a predetermined experiment and stored in the ECU 5 in advance and the first target air-fuel ratio (target A / F1) is shown. Search the map (see FIG. 5). Thus, the first target air-fuel ratio (target A / F1) corresponding to the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount calculated by the ECU 5 based on the output of the accelerator sensor 11 is calculated.
As shown in FIG. 5, the first target air-fuel ratio (target A / F1) is set higher as the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount increases.

The second target air-fuel ratio setting unit 53 sets the second target air-fuel ratio leaner than the stoichiometry as the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 during the leaning control. In the present embodiment, the integrated value of the fuel injection amount of the engine 1 is used as the deterioration degree of the NOx purification catalyst 2 estimated by the catalyst deterioration degree estimating unit 54 described later, and the second value based on the integrated value of the fuel injection amount is used. Set the target air-fuel ratio.
Further, the second target air-fuel ratio setting unit 53 of the present embodiment sets the second target air-fuel ratio lower as the temperature of the NOx purification catalyst 2 is higher.
Specifically, first, an integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1 and a reference value of the second target air-fuel ratio (target A / F2) that are set based on a predetermined experiment and stored in the ECU 5 in advance. The map (refer FIG. 5) which shows the relationship with is searched. As a result, a reference value of the second target air-fuel ratio (target A / F2) corresponding to the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount calculated by the ECU 5 based on the output of the accelerator sensor 11 is calculated.
As shown in FIG. 5, the reference value of the second target air-fuel ratio (target A / F2) is set higher as the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount increases.
Next, a map (see FIG. 6) showing the relationship between the temperature of the NOx purification catalyst 2 and the correction coefficient Ktemp that is set based on a predetermined experiment and stored in the ECU 5 in advance is searched. As shown in FIG. 6, the correction coefficient Ktemp is set to a smaller value as the temperature of the NOx purification catalyst 2 is higher. Thereby, the correction coefficient Ktemp corresponding to the temperature of the NOx purification catalyst 2 detected by the catalyst temperature sensor 14 is calculated.
Finally, the second target air-fuel ratio is calculated by correcting the calculated correction coefficient Ktemp by multiplying the reference value of the second target air-fuel ratio (target A / F2).

The catalyst deterioration degree estimation unit 54 estimates the deterioration degree of the NOx purification catalyst 2 based on the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1. In this embodiment, the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1 is used as the degree of deterioration of the NOx purification catalyst 2. That is, as described above, the first target air-fuel ratio (target A / F1) and the second target air-fuel ratio (target A / F2) are calculated according to the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount.
Note that the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1 is not reset even when the regeneration process ends, unlike a fuel injection amount (ΣQ _fuel ) described later.

When the exhaust air / fuel ratio of the exhaust gas flowing into the DPF 3 falls below a predetermined threshold, the switching unit 55 sets the target air / fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 to the first target air / fuel ratio (target A / F1). Is temporarily switched to the second target air-fuel ratio (target A / F2). Next, processing for switching to the first target air-fuel ratio is executed again after a predetermined time has elapsed.
A value detected by the second air-fuel ratio sensor 13 is used as the exhaust air-fuel ratio of the exhaust gas flowing into the DPF 3. The predetermined threshold is set based on a predetermined experiment and is stored in the ECU 5 in advance.

Here, the switching of the target air-fuel ratio by the switching unit 55 will be described in detail with reference to FIG. In the following description, the exhaust air / fuel ratio of the exhaust flowing into the NOx purification catalyst 2 is defined as Front_A / F, and the exhaust air / fuel ratio of the exhaust flowing into the DPF 3 is defined as Rear_A / F.
First, when executing the enrichment control from the lean side to the rich side, if the target air-fuel ratio of the exhaust flowing into the NOx purification catalyst 2 is set to the first target air-fuel ratio (target A / F1), Front_A / F Is an air-fuel ratio that matches the first target air-fuel ratio (target A / F1) with good responsiveness. At this time, the Rear_A / F gradually shifts to the rich side while maintaining the lean state for a certain time due to the oxygen storage / release ability of the NOx purification catalyst 2. That is, a state is formed in which Front_A / F is on the rich side and Rear_A / F is on the lean side.
Then, when the Rear_A / F falls below a predetermined threshold value (Thresh_A / F) set in advance, the second target air-fuel ratio (target) that is leaner than the stoichiometric value from the first target air-fuel ratio (target A / F1). Switching to A / F2) is performed, the enrichment control is interrupted, and the leaning control is executed. At this time, Front_A / F has an air-fuel ratio that matches the second target air-fuel ratio (target A / F2) with good responsiveness, while Rear_A / F gradually shifts to the lean side.
The enrichment control is interrupted, that is, after the leaning control is executed and a predetermined time has elapsed, the enrichment control is executed again by switching to the first target air-fuel ratio (target A / F1) on the richer side than the stoichiometry. Is done. At this time, as in the first enrichment control, Front_A / F has an air-fuel ratio that matches the first target air-fuel ratio (target A / F1) with good responsiveness, while Rear_A / F is NOx Due to the oxygen storage / release capability of the purifying catalyst 2, it gradually shifts to the rich side while maintaining the lean state for a certain period of time. That is, a state is formed in which Front_A / F is on the rich side and Rear_A / F is on the lean side.
As described above, by switching the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2, the target air-fuel ratio of the exhaust gas flowing into the DPF 3 can always be kept lean. As a result, in the NOx purification catalyst 2 While removing sulfur, PM can be removed by combustion in the DPF 3. This will be described in detail later.
When the enrichment control is finished and the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 is lean-controlled from the rich side to the lean side, the Front_A / F shifts to the lean side with good responsiveness, and the Rear_A / F moves to the lean side with a delay.

  The regeneration processing time setting unit 56 sets the regeneration processing time to be shorter as the exhaust air-fuel ratio of the exhaust gas flowing into the DPF 3, that is, the Rear_A / F is lower. Specifically, a map (see FIG. 8) that shows the relationship between the Rear_A / F that is set based on a predetermined experiment and is stored in advance in the ECU 5 and the counter subtraction value of the reproduction processing time is searched. Thereby, the counter subtraction value corresponding to the Rear_A / F detected by the second air-fuel ratio sensor 13 is calculated. Next, the reproduction processing time is calculated by subtracting the calculated counter subtraction value from a predetermined reproduction processing time set in advance.

The enrichment control interruption time setting unit 57 sets the time during which the enrichment control is interrupted, that is, the execution time of the leaning control. The higher the temperature of the NOx purification catalyst, the shorter the enrichment control interruption time (lean control execution time).
Specifically, when setting the interruption time, a map (FIG. 5) showing the relationship between the temperature of the NOx purification catalyst that is set based on a predetermined experiment and stored in advance in the ECU 5 and the counter subtraction value of the enrichment control interruption time. (Not shown). Thereby, the counter subtraction value corresponding to the temperature of the NOx purification catalyst 2 detected by the catalyst temperature sensor 14 is calculated. Next, the enrichment control interruption time is calculated by subtracting the calculated counter subtraction value from a predetermined enrichment control interruption time set in advance.

Further, the ECU 5 has a regeneration time determination unit (not shown). The regeneration time determination unit executes the regeneration process by the regeneration execution unit 51 when the fuel injection amount (ΣQ _fuel ) of the engine 1 reaches a predetermined determination value.
Here, the determination of the reproduction time by the reproduction time determination unit will be described with reference to FIG. As shown in FIG. 9, the fuel injection amount (ΣQ _fuel ) calculated by the ECU 5 based on the output of the accelerator sensor 11 is set based on a predetermined experiment, and the judgment value (in FIG. 9) stored in the ECU 5 in advance. When the determination line is reached, the reproduction process by the reproduction execution unit 51 is executed. As described above, the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount does not reset and increases with time, whereas the fuel injection amount (ΣQ _fuel ) increases with the start of the regeneration process. At the same time, it is reset and newly counted. As a result, the reproduction process can be repeatedly executed at an appropriate time.

Next, the procedure of the reproduction process of this embodiment will be described.
FIG. 10 is a flowchart showing the procedure of the regeneration process performed by the ECU 5 of the present embodiment. This flowchart is repeatedly executed by the ECU 5 after the engine 1 is started.

  As shown in FIG. 10, in the regeneration process of the present embodiment, the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 is set to a rich-side first target air-fuel ratio (target A / F1) and a lean-side second target. The air-fuel ratio (target A / F2) can be switched and executed according to a predetermined condition.

In step S11, it is determined whether or not the reproduction request flag FRR is “1”. If this determination is YES, a reproduction process is executed, and the process proceeds to step S12. If NO, the process proceeds to step S27.
The regeneration request flag FRR is set to “1” when the fuel injection amount (ΣQ _fuel ) of the engine 1 exceeds a predetermined determination value (Thresh_fuel). When the reproduction request flag FRR is “1”, reproduction processing, specifically, enrichment control by post-rich is executed.

  In step S12, a preset reproduction timer is started, and the process proceeds to step S13.

In step S13, it is determined whether or not the enrichment control interruption request flag FRIR is “1”. If this determination is YES, the process proceeds to step S16, and if NO, the process proceeds to step S14.
The enrichment control interruption request flag FRIR is set to “1” when the Rear_AF that is the exhaust air / fuel ratio of the exhaust gas flowing into the DPF 3 is lower than a predetermined threshold value (Thresh_AF) stored in the ECU 5 in advance. . When the enrichment control interruption request flag FRIR is “1”, the enrichment control is interrupted for a predetermined time.

In step S14, as the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2, a first target air-fuel ratio (target A / F1) that is richer than stoichiometric is set, and the target air-fuel ratio is set to the target A / F1 rich. Control is executed, and the routine goes to Step S15.
Here, the target A / F1 is set based on the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount of the engine 1. Specifically, the map shown in FIG. 5 is searched, and the target A / F1 is calculated and set according to the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount calculated by the ECU 5 based on the output of the accelerator sensor 11. To do.

In step S15, it is determined whether or not Rear_AF, which is the exhaust air-fuel ratio of the exhaust gas flowing into the DPF 3, is below a predetermined threshold value (Thresh_AF). If this determination is YES, the process proceeds to step S16, and if NO, the process proceeds to step S23.
Here, the value detected by the second air-fuel ratio sensor 13 is used as the Rear_AF, and the value stored in the ECU 5 in advance is used as the predetermined threshold (Thresh_AF).

In step S16, the second target air-fuel ratio (target A / F2) leaner than the stoichiometric value is set as the target air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2, and the target air-fuel ratio is set to the target A / F2. Control is executed (ie, enrichment control is interrupted), and the process proceeds to step S17.
Here, the target A / F2 is first searched for the map shown in FIG. 5, and the target A / F2 corresponding to the integrated value (ΣQ _{fuel_total} ) of the fuel injection amount calculated by the ECU 5 based on the output of the accelerator sensor 11 is searched. A reference value of F2 is calculated. Next, the map shown in FIG. 6 is searched, and a correction coefficient Ktemp corresponding to the temperature of the NOx purification catalyst 2 detected by the catalyst temperature sensor 14 is calculated. Finally, the calculated correction coefficient Ktemp is corrected by multiplying the reference value of the target A / F2, and the target A / F2 is calculated and set.

In step S17, the enrichment control interruption request flag FRIR is set to “1”, and the process proceeds to step S18.
In step S18, a preset interruption timer is started, and the process proceeds to step S19.

In step S19, an interruption timer is subtracted based on the temperature of the NOx purification catalyst 2, and the process proceeds to step S20.
Specifically, a catalyst temperature sensor 14 is searched by searching a map (not shown) showing the relationship between the temperature of the NOx purification catalyst and the enrichment control interruption time that is set based on a predetermined experiment and stored in advance in the ECU 5. The counter subtraction value corresponding to the temperature of the NOx purification catalyst 2 detected by the above is calculated. Next, the enrichment control interruption time is calculated by subtracting the calculated counter subtraction value from a predetermined interruption timer set in advance.

  In step S20, it is determined whether or not the interruption timer is zero. If this determination is YES, the process proceeds to step S21, and if this determination is NO, the process proceeds to step S24.

In step S21, the enrichment control interruption request flag FRIR is set to “0”, and the process proceeds to step S22.
In step S22, the interruption timer is reset and the process proceeds to step S24.

In step S23, the reproduction timer is subtracted based on Rear_A / F, and the process proceeds to step S24.
Specifically, the map shown in FIG. 8 is searched, and the counter subtraction value corresponding to the Rear_A / F detected by the second air-fuel ratio sensor 13 is calculated. Next, the reproduction processing time is calculated by subtracting the calculated counter subtraction value from a predetermined reproduction timer set in advance.

  In step S24, it is determined whether or not the playback timer is zero. If this determination is NO, the playback process ends, and if YES, the process proceeds to step S25, the playback request flag FRR is set to “0”, and the process proceeds to step S26 to reset the playback timer and perform the playback process. finish.

In step S27, the fuel injection amount (ΣQ _fuel ) of the engine 1 is integrated and the process proceeds to step S28. Specifically, the ECU 5 calculates the _fuel injection amount (ΣQ _fuel ) based on the output of the accelerator sensor 11.

In step S28, it is determined whether or not the fuel injection amount (ΣQ _fuel ) of the engine 1 exceeds a predetermined determination value (Thresh_fuel). If this determination is NO, the reproduction process is terminated, and if YES, the process proceeds to step S29.

In step S29, the regeneration request flag FRR is set to “1”, the process proceeds to step S30, the fuel injection amount (ΣQ _fuel ) of the engine 1 is set to “0”, and the regeneration process ends.

As described above, the following effects can be obtained by using the NOx purification catalyst 2 using the cerium oxide-based adsorbent and the DPF 3 including the PM combustion catalyst in which Ag is supported on the composite oxide having oxygen releasing ability. Is played.
The temperature required for sulfur removal of the NOx purification catalyst 2 using the cerium oxide-based adsorbent is about 600 ° C., and sulfur can be removed at a lower temperature than the 700 ° C. of alkali metals and alkaline earth metals. it can. In the exhaust system layout of the present embodiment, the regeneration process of the DPF 3 is also performed simultaneously with the regeneration of the NOx purification catalyst 2, so that the DPF 3 disposed on the downstream side of the NOx purification catalyst 2 is 600 ° C. or 600 ° C. or less. It will be exposed to the temperature of.
By the way, it is known that the temperature required for PM combustion in gas-phase oxygen without using a catalyst is 600 ° C. or higher. Therefore, in order to efficiently remove sulfur from the NOx purification catalyst 2 and remove PM from the DPF 3 at the same time, it can be said that it is desirable to support the catalyst for burning the PM at a low temperature on the DPF 3.
Therefore, in the present embodiment, a PM combustion catalyst in which Ag is supported on a complex oxide having an oxygen releasing ability capable of burning PM at about 350 to 500 ° C. is supported on the DPF 3. Thereby, in this embodiment, even when DPF 3 is exposed to a temperature of 600 ° C. or lower, PM can be burned and removed, and DPF regeneration can proceed continuously.
Further, the lean time can be secured longer toward the downstream side in the DPF 3 by the oxygen released from the complex oxide. As a result, the PM combustion removal efficiency (DPF regeneration efficiency) is improved, and the total processing time required for regeneration by removing sulfur from the NOx purification catalyst 2 and regeneration by removing PM combustion from the DPF 3 can be shortened.

By the way, by repeating lean and rich, the advantage of simultaneously performing sulfur removal of the NOx purification catalyst 2 and PM combustion removal of the DPF 3 is that a high temperature of 600 ° C. or more is required, so that deterioration of fuel consumption due to temperature rise is caused. In order to suppress, it is preferable to carry out simultaneously. Further, since the exhaust gas temperature decreases when the enrichment control is continued, the exhaust gas temperature can be kept high by repeating lean and rich.
However, conventionally, only the sulfur removal of the NOx purification catalyst 2 proceeds on the rich side, and only the PM combustion removal of the DPF 3 proceeds on the lean side.
Therefore, in the present embodiment, by using a cerium oxide-based adsorbent for the NOx purification catalyst 2, the oxygen storage of cerium oxide is performed even when the exhaust air removal is progressing on the rich side of the exhaust air-fuel ratio. As a result of the ability (OSC) to keep the exhaust air-fuel ratio downstream of the NOx purification catalyst 2 lean, PM combustion removal of the downstream DPF 3 can also proceed simultaneously (see FIG. 11). In addition, when the enrichment control is continued for a long time, this effect is gradually reduced as the OSC is consumed. In this embodiment, the Front_A / F is enriched as shown in FIG. After that, it is possible to always keep the Rear_A / F lean by returning it to lean and enriching it again. For this reason, sulfur removal and DPF regeneration can proceed simultaneously, and the total regeneration time can be greatly reduced.

Next, the effects of the present embodiment involving the reproduction process are summarized as follows.
The exhaust purification apparatus of this embodiment is configured to include the NOx purification catalyst 2 having an oxygen storage / release material. In addition, after performing the enrichment control for changing the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2 from the lean side to the rich side, the leaning control for once returning to the lean side is performed for a predetermined time, and then again the rich side The reproduction execution unit 51 is configured to execute a series of control for performing the enrichment control to be performed at least once.
Thereby, the air-fuel ratio of the exhaust gas flowing into the DPF 3 can be kept lean by the oxygen storage capacity (OSC) of the NOx purification catalyst 2 while enriching the exhaust air-fuel ratio flowing into the NOx purification catalyst 2. In addition, after performing the enrichment control, the lean storage control that once returns to the lean side can be performed to maintain the oxygen storage capacity (OSC) of the NOx purification catalyst 2 for a long time. Can be kept lean for a long time.
For this reason, sulfur removal of the NOx purification catalyst 2 and combustion removal of PM collected in the DPF 3 can be performed simultaneously. Therefore, energy required for sulfur removal and PM combustion removal can be reduced, and deterioration of fuel consumption can be reduced.

In the exhaust purification device of the present embodiment, the exhaust air / fuel ratio of the exhaust flowing into the NOx purification catalyst 2 matches the first target air / fuel ratio or the second target air / fuel ratio in accordance with the switching of the target air / fuel ratio by the switching unit 55. The reproduction execution unit 51 is controlled to be configured as described above.
As a result, the exhaust air-fuel ratio can be controlled as desired, and the air-fuel ratio of the exhaust gas flowing into the DPF 3 can always be kept lean, so the above-described effect is more remarkable.

The exhaust purification apparatus of the present embodiment is configured to include a first target air-fuel ratio setting unit 52 that sets the first target air-fuel ratio based on the degree of deterioration of the NOx purification catalyst 2.
As a result, the exhaust air / fuel ratio flowing into the NOx purification catalyst 2 can be controlled in accordance with the oxygen storage capacity (OSC) of the NOx purification catalyst 2, so that sulfur removal and PM combustion removal can be executed more efficiently, and fuel efficiency can be improved. Deterioration can be further reduced.

The exhaust purification apparatus of the present embodiment includes a catalyst deterioration degree estimation unit 54 and sets the first target air-fuel ratio higher as the deterioration degree of the NOx purification catalyst 2 estimated by the catalyst deterioration degree estimation unit 54 is larger. One target air-fuel ratio setting unit 52 is included.
Thereby, the degree of deterioration of the NOx purification catalyst 2 can be accurately estimated, and oxygen can be supplied without excess or deficiency during sulfur removal and PM combustion removal. For this reason, it is possible to avoid a decrease in PM combustion efficiency due to oxygen shortage and a decrease in sulfur removal efficiency due to excessive oxygen. Further, when the deterioration of the NOx purification catalyst 2 progresses and the OSC decreases, the air-fuel ratio of the exhaust gas flowing into the DPF 3 is set by setting the first target air-fuel ratio that is the target air-fuel ratio at the time of the enrichment control high. Therefore, it is possible to avoid the problem that the PM combustion efficiency is lowered due to the stoichiometric or less.

The exhaust purification apparatus of the present embodiment is configured to include a second target air-fuel ratio setting unit 53 that sets the second target air-fuel ratio based on the degree of deterioration of the NOx purification catalyst 2.
Thus, the oxygen concentration flowing into the NOx purification catalyst 2 can be adjusted when the target air-fuel ratio is switched during sulfur removal and PM combustion removal according to the oxygen storage capacity (OSC) of the NOx purification catalyst 2. For this reason, it is possible to always avoid a decrease in PM combustion efficiency due to lack of oxygen and a decrease in sulfur removal efficiency due to excessive oxygen.

The exhaust purification apparatus of this embodiment includes a catalyst deterioration degree estimation unit 54, and sets the second target air-fuel ratio higher as the deterioration degree of the NOx purification catalyst 2 estimated by the catalyst deterioration degree estimation unit 54 is larger. A two-target air-fuel ratio setting unit 53 is included.
Thereby, the fall of PM combustion efficiency by oxygen shortage and the fall of the sulfur removal efficiency by excessive oxygen can be avoided. Further, it is possible to avoid the problem that the PM combustion efficiency is lowered due to the air-fuel ratio of the exhaust gas flowing into the DPF 3 being less than stoichiometric.

The exhaust purification device of the present embodiment is configured to include a second target air-fuel ratio setting unit 53 that sets the second target air-fuel ratio lower as the temperature of the NOx purification catalyst 2 is higher.
The OSC function of the NOx purification catalyst 2 increases as the temperature of the NOx purification catalyst 2 decreases. In this regard, according to the present embodiment, the higher the temperature of the NOx purification catalyst 2, the lower the second target air-fuel ratio is set. Can be occluded. Therefore, sulfur removal and PM combustion removal can be executed more efficiently, and deterioration of fuel consumption can be further reduced.

  The exhaust purification device of the present embodiment is configured to include the enrichment control time setting unit 57 that sets the lean control time in the regeneration execution unit 51 to be shorter as the temperature of the NOx purification catalyst 2 is higher. Thus, as the temperature of the NOx purification catalyst 2 is higher, the lean control time in the regeneration execution unit 51 is set shorter, so that the temperature of the NOx purification catalyst 2 is prevented from being increased and more oxygen is supplied to the NOx purification catalyst 2. Can be occluded. Therefore, sulfur removal and PM combustion removal can be executed more efficiently, and deterioration of fuel consumption can be further reduced.

  The exhaust purification device of the present embodiment is configured to include the NOx purification catalyst 2 including the first catalyst layer containing a noble metal and a cerium oxide-based material. Thereby, high NOx purification performance is exhibited even in a low temperature state such as immediately after start-up or during idling due to the low-temperature NOx adsorption ability of the cerium oxide-based material. In addition, since the OSC of the NOx purification catalyst 2 is dramatically increased, the time during which the sulfur removal and the PM combustion removal can be performed at the same time is increased. As a result, the total time required for the regeneration process can be shortened.

The exhaust purification apparatus of the present embodiment is configured to include the NOx purification catalyst 2 further including a second catalyst layer containing zeolite as an NH ₃ adsorbent. Thereby, the amount of NH ₃ adsorption can be increased, and the reactivity with NOx at the time of lean can be improved.

The exhaust purification apparatus of the present embodiment is configured to include the NOx purification catalyst 2 in which the second catalyst layer is provided on the first catalyst layer. Accordingly, the NH ₃ generated during enrichment control efficiently captured, it is possible to use efficiently the NOx purification in the next lean, NOx purification performance is further improved.

  The exhaust emission control device of the present embodiment is configured to include the DPF 3 on which a combustion catalyst for burning the collected PM is supported. Thereby, even if the temperature of DPF3 is 600 degrees C or less, combustion removal of PM is possible. For this reason, the DPF 3 can be efficiently regenerated at a low temperature, and the deterioration of fuel consumption can be further reduced.

  The exhaust purification device of this embodiment is configured to include a combustion catalyst in which Ag is supported on a composite oxide having oxygen storage / release capability. As a result, PM can be burned and removed even at about 500 ° C. Therefore, PM can be burned and removed even when the temperature of the DPF 3 is lowered to about 500 ° C. while the vehicle is running. Playback speed can be greatly improved. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

Exhaust purifying apparatus of the present embodiment, NO ₂ generating catalyst to convert the NO in the exhaust to NO ₂ is configured to include a DPF3 carried. Thereby, the combustion of PM can be further promoted, and the regeneration speed of the DPF 3 can be improved. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

In the exhaust emission control device of this embodiment, at least any one element of Pt, Pd, and Rh is supported on at least any one of alumina, silica, silica alumina, zirconia, and ceria. _It comprised ₂ production | generation catalysts. As a result, the ability of NO ₂ generation can be increased by the action of the noble metal supported on the high specific surface area support, and NO ₂ can be used more efficiently for PM combustion. As a result, the regeneration rate of DPF 3 is further improved. Can be made. Therefore, the total processing time required for sulfur removal and PM combustion removal can be shortened, and deterioration of fuel consumption can be further reduced.

  In the present embodiment, the ECU 5 constitutes a regeneration unit, a first target air-fuel ratio setting unit, a second target air-fuel ratio setting unit, a switching unit, a catalyst deterioration degree estimation unit, and a time setting unit. Specifically, the means relating to step S14 in FIG. 10 corresponds to the first target air-fuel ratio setting means, the means relating to step S15 corresponds to the switching means, and the means relating to step S16 is the second target air-fuel ratio setting means. The means according to step S19 corresponds to time setting means.

In addition, this embodiment is not limited to embodiment mentioned above, A various deformation | transformation is possible.
For example, in the present embodiment, after performing enrichment control from the lean side to the rich side with respect to the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2, the leaning control for once returning to the lean side is performed for a predetermined time. Then, a series of control for executing the rich control again to the rich side is executed only once, but this series of control may be repeatedly executed a plurality of times.
Further, the first target air-fuel ratio setting unit 52 is based on any one of the temperature of the NOx purification catalyst 2, the temperature of the exhaust gas flowing into the NOx purification catalyst 2, and the flow rate of the exhaust gas flowing into the NOx purification catalyst 2. A first target air-fuel ratio may be set. Similarly, the second target air-fuel ratio setting unit 53 is based on any one of the temperature of the NOx purification catalyst 2, the temperature of the exhaust gas flowing into the NOx purification catalyst 2, and the flow rate of the exhaust gas flowing into the NOx purification catalyst 2. Thus, the second target air-fuel ratio may be set.
At this time, the value detected by the catalyst temperature sensor 14 can be used as the temperature of the NOx purification catalyst 2. As the temperature of the exhaust gas flowing into the NOx purification catalyst 2, an exhaust temperature sensor is provided in the exhaust passage upstream of the NOx purification catalyst 2, and a value detected by this exhaust temperature sensor can be used. As the flow rate of the exhaust gas flowing into the NOx purification catalyst 2, an air flow meter is provided in the exhaust passage on the upstream side of the NOx purification catalyst 2, and a value detected by this air flow meter can be used.
Further, for example, the regeneration processing time setting unit 56 may set the regeneration processing time to be shorter as the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 2, that is, Front_A / F is lower.

[NOx purification catalyst]
An NOx purification catalyst having the composition shown in Table 1 was supported on a 400 cell / 3.5 mil cordierite honeycomb structure by an impregnation method.
Further, a comparative example in which a NOx purification catalyst having a composition of PtRh / Ba / Al ₂ O ₃ was supported on a structure similar to that of the example was used.

[DPF]
Combustion catalyst with composition shown in Table 2 (lower layer is PM combustion catalyst, upper layer is NO ₂ production catalyst) supported on DPF made of wall flow type SiC (pore diameter 23μm, porosity 52%) by impregnation method Was taken as an example.
Further, an engine 101 which will be described later is operated, and only the PM is collected in the above wall flow type SiC DPF was used as a comparative example.

[Evaluation]
Using the NOx purification catalyst and DPF subjected to the above-described treatment, an exhaust purification device having an exhaust system layout as shown in FIG. 13 was configured. As the engine 101, a 2.2L diesel engine was used, the capacity of the NOx purification catalyst was 1L, and the capacity of the DPF was 2L. The engine 101 was operated for a predetermined time under predetermined conditions, the sulfur content was captured by the NOx purification catalyst, and PM was collected by the DPF.

  Regarding the NOx purification catalyst, the relationship between the amount of S desorption and the temperature was examined by the temperature-programmed desorption method. The results are shown in FIG. As shown in FIG. 14, it was confirmed that the NOx purification catalyst of this example desorbs sulfur at a lower temperature of about 600 ° C. as compared with the comparative example.

  About DPF, the relationship between the emitted-heat amount accompanying PM combustion and temperature was investigated by TG-DTA method. The results are shown in FIG. As shown in FIG. 15, it was confirmed that the combustion catalyst supported on the DPF of this example can combust PM at a low temperature of 400 ° C.

1 engine (internal combustion engine)
2 NOx purification catalyst (NOx purification catalyst)
3 DPF (Particulate Filter)
4 Exhaust pipe (exhaust passage)
5 ECU (regeneration means, first target air-fuel ratio setting means, second target air-fuel ratio setting means, catalyst deterioration degree estimation means, switching means, time setting means)

Claims (15)

An NOx purification catalyst that is provided in the exhaust passage of the internal combustion engine and purifies NOx by repeating lean and rich, and is provided on the downstream side of the NOx purification catalyst in the exhaust passage and collects particulates in the exhaust. In an exhaust gas purification apparatus for an internal combustion engine comprising a particulate filter,
The NOx purification catalyst has an oxygen storage / release material that stores oxygen on the lean side and releases the stored oxygen on the rich side,
The exhaust purification device includes:
A rich control is performed to change the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst from the lean side to the rich side, and then the lean control to temporarily return to the lean side is performed for a predetermined time, and then the rich air level is again set to the rich side. Regenerating means for purifying the particulate matter collected by the particulate filter, while purifying the sulfur content captured by the NOx purification catalyst, by executing a series of control for performing the crystallization control at least once. An exhaust emission control device comprising: First target air-fuel ratio setting means for setting a first target air-fuel ratio on the rich side as a target air-fuel ratio of exhaust flowing into the NOx purification catalyst during the enrichment control;
Second target air-fuel ratio setting means for setting a second target air-fuel ratio on the lean side as a target air-fuel ratio of exhaust flowing into the NOx purification catalyst during the leaning control;
When the exhaust air-fuel ratio of the exhaust gas flowing into the particulate filter falls below a predetermined threshold, the target air-fuel ratio is once switched from the first target air-fuel ratio to the second target air-fuel ratio, and then the predetermined air-fuel ratio is Switching means for switching to the first target air-fuel ratio again after the elapse of time,
The regeneration means matches the exhaust air / fuel ratio of the exhaust gas flowing into the NOx purification catalyst to the first target air / fuel ratio or the second target air / fuel ratio in accordance with the switching of the target air / fuel ratio by the switching means. 2. The exhaust emission control device according to claim 1, wherein the exhaust gas purifying apparatus purifies the particulate matter trapped by the particulate filter while purifying the sulfur content captured by the NOx purification catalyst.   The first target air-fuel ratio setting means includes at least one of a temperature of the NOx purification catalyst, a temperature of exhaust flowing into the NOx purification catalyst, a flow rate of exhaust flowing into the NOx purification catalyst, and a deterioration degree of the NOx purification catalyst. The exhaust emission control device according to claim 2, wherein the first target air-fuel ratio is set based on any one of them. The exhaust purification device further includes a catalyst deterioration degree estimating means for estimating the deterioration degree of the NOx purification catalyst based on an integrated value of the fuel injection amount of the internal combustion engine,
The said 1st target air fuel ratio setting means sets the said 1st target air fuel ratio so that the deterioration degree of the said NOx purification catalyst estimated by the said catalyst deterioration degree estimation means is large. The exhaust emission control device described.   The second target air-fuel ratio setting means includes at least one of a temperature of the NOx purification catalyst, a temperature of exhaust flowing into the NOx purification catalyst, a flow rate of exhaust flowing into the NOx purification catalyst, and a deterioration degree of the NOx purification catalyst. 5. The exhaust emission control device according to claim 2, wherein the second target air-fuel ratio is set based on any one of the two. The exhaust purification device further includes a catalyst deterioration degree estimating means for estimating the deterioration degree of the NOx purification catalyst based on an integrated value of the fuel injection amount of the internal combustion engine,
The said 2nd target air fuel ratio setting means sets the said 2nd target air fuel ratio so that the deterioration degree of the said NOx purification catalyst estimated by the said catalyst deterioration degree estimation means is large. The exhaust emission control device described.   The exhaust purification apparatus according to any one of claims 2 to 6, wherein the second target air-fuel ratio setting means sets the second target air-fuel ratio to be lower as the temperature of the NOx purification catalyst is higher.   The exhaust emission control device according to any one of claims 1 to 7, further comprising time setting means for setting the predetermined time shorter as the temperature of the NOx purification catalyst is higher.   The exhaust purification apparatus according to any one of claims 1 to 8, wherein the NOx purification catalyst includes a first catalyst layer containing a noble metal and a cerium oxide-based material. The NOx purification catalyst, exhaust gas purification device according to claim 9, further comprising a second catalyst layer containing zeolite as NH ₃ adsorbent.   The exhaust purification apparatus according to claim 10, wherein the NOx purification catalyst has the second catalyst layer provided on the first catalyst layer.   The exhaust emission control device according to any one of claims 1 to 11, wherein a combustion catalyst for burning the collected particulates is supported on the particulate filter.   The exhaust purification apparatus according to claim 12, wherein the combustion catalyst is formed by supporting Ag on a composite oxide having oxygen storage / release capability. Wherein the particulate filter, exhaust gas purification device according to 13 claim 1, wherein the NO ₂ synthesizing catalyst which converts the NO contained in the exhaust gas to NO ₂ is supported. The NO ₂ production catalyst is characterized in that at least one element of Pt, Pd, and Rh is supported on at least one of alumina, silica, silica alumina, zirconia, and ceria. The exhaust emission control device according to claim 14.

Images