JP2016148285A - Particulate filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of increasing a temperature of an entire particulate filter uniformly during execution of filter regeneration processing in the wall flow type particulate filter in which an oxidation catalyst is supported.SOLUTION: A wall flow type particulate filter includes: a plurality of first passages each having a closed end on the upstream side in an exhaust gas flowing direction; a plurality of second passages each having a closed end on the downstream side in the exhaust gas flowing direction; partition walls each of which is a porous member for partitioning the first passage and the second passage and is formed so that the thickness and an exhaust gas permeability coefficient are uniform between a portion on the upstream side and a portion on the downstream side of the member; and an oxidation catalyst supported by the partition walls and having capacity for oxidizing PMs. Since the amount of the oxidation catalyst supported by the portion on the upstream side of the partition wall is made larger than that supported by the portion on the downstream side, the PM oxidation capacity of the portion on the upstream side of the partition wall is enhanced compared to that of the portion on the downstream side.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a particulate filter disposed in an exhaust passage of an internal combustion engine.

  As a particulate filter for collecting particulate matter (PM) contained in exhaust gas from an internal combustion engine, the first passage whose upstream end is closed by a plug and the downstream end are closed by a plug A wall flow type particulate filter is known in which the second passages are alternately arranged and a porous partition wall is disposed between the first passage and the second passage.

  Moreover, as a wall flow type particulate filter, a catalyst containing platinum (Pt) and oxidizing hydrocarbon (HC) and carbon monoxide (CO) is supported on the upstream side of the particulate filter, There is also known one in which silver (Ag) is contained at a site and a catalyst that oxidizes PM is supported (for example, see Patent Document 1).

JP 2012-172597 A

  If the amount of PM trapped in the particulate filter (PM trapping amount) becomes excessively large, problems such as an increase in back pressure acting on the internal combustion engine occur, so the PM trapped in the particulate filter is removed. Therefore, it is necessary to appropriately execute the filter regeneration process. In the filter regeneration process, for example, an unburned fuel component such as hydrocarbon (HC) or carbon monoxide (CO) is supplied to the particulate filter, and the unburned fuel component is supported on the particulate filter. In this process, the temperature of the particulate filter is raised to the temperature range where PM can be oxidized by the reaction heat generated at that time.

  By the way, when the oxidation catalyst is supported on the particulate filter, if the supported amount is made uniform over the entire area of the particulate filter, the upstream side of the particulate filter when the filter regeneration process as described above is performed. There is a possibility that a temperature difference occurs between this part and the downstream part, and the upstream part does not rise to a temperature range where PM can be oxidized. As a result, there is a possibility that PM collected in the upstream portion of the particulate filter is not sufficiently removed.

  The present invention has been made in view of the above-described various circumstances, and an object of the present invention is to provide a wall flow type particulate filter carrying an oxidation catalyst, in which the entire particulate filter is subjected to filter regeneration processing. It is to provide a technique capable of raising the temperature uniformly.

The present invention employs the following means in order to solve the above-described problems. That is, the particulate filter of the present invention includes a plurality of first passages whose upstream ends are closed in the exhaust flow direction and a plurality of second passages whose downstream ends are closed in the exhaust flow direction. And a porous member that separates the first passage and the second passage, and is formed so that the thickness and the exhaust permeation coefficient of the upstream portion and the downstream portion of the member are uniform. A partition,
A particulate filter having an oxidation catalyst supported on the partition wall, wherein the oxidation catalyst is supported on the partition wall so that an oxidation ability in an upstream portion is higher than that on a downstream portion of the partition wall. It is characterized by being.

  As a method for increasing the oxidation capacity in the upstream portion as compared with the downstream portion of the partition wall, the amount of the oxidation catalyst supported in the upstream portion is increased as compared with the downstream portion of the partition wall. A method or a method of changing the type of the oxidation catalyst supported on the upstream portion of the partition and the type of the oxidation catalyst supported on the downstream portion can be used.

  According to the present invention, in a wall flow type particulate filter carrying an oxidation catalyst, the temperature of the entire particulate filter can be raised uniformly during the execution of the filter regeneration process.

It is a longitudinal cross-sectional view which shows schematic structure of the particulate filter to which this invention is applied. It is a cross-sectional view showing a schematic configuration of a particulate filter to which the present invention is applied. It is a figure which shows the temperature distribution of the partition at the time of filter regeneration process execution, when it is comprised so that PM oxidation capability of an oxidation catalyst may become uniform in the whole region from the upstream edge part of a partition to a downstream edge part. It is a figure which shows the example of formation of a catalyst coat layer in a present Example.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a longitudinal sectional view of a particulate filter to which the present invention is applied, and FIG. 2 is a transverse sectional view of a particulate filter to which the present invention is applied. The particulate filter 1 shown in FIGS. 1 and 2 is disposed in the exhaust passage of the internal combustion engine and collects PM contained in the exhaust of the internal combustion engine. The particulate filter 1 includes a cylindrical base 3 in a cylindrical case 2.

  A plurality of passages 4 and 5 extending in the axial direction (exhaust flow direction) are formed in the base material 3, and the plurality of passages 4 and 5 are arranged in a honeycomb shape. In other words, the base material 3 is formed so as to define a plurality of passages 4 and 5 arranged in a honeycomb shape. The number of the passages 4 and 5 shown in FIGS. 1 and 2 is merely an example, and the number of the passages 4 and 5 may be appropriately determined according to the specifications of the vehicle and the internal combustion engine.

  Among the plurality of passages 4 and 5, a part of the passages 4 is closed at the upstream end in the exhaust flow direction by a plug 40. Of the plurality of passages 4, 5, the remaining passage 5 is closed at the downstream end in the exhaust flow direction by a plug 50. The passages 4 and the passages 5 are alternately arranged. Hereinafter, the passage 4 is referred to as a first passage 4 and the passage 5 is referred to as a second passage 5.

In the base material 3, the member (partition wall) 30 that separates the first passage 4 and the second passage 5 is formed of a porous body. In addition, only the partition 30 of the said base material 3 may be formed with the porous body, and the whole said base material 3 may be formed with the porous body. As the material for the porous body here, a known material suitable for collecting PM in the exhaust gas can be employed. However, from the viewpoint of strength and heat resistance, ceramics such as silicon carbide, silicon nitride, cordierite, zirconia, titania, alumina, silica, mullite, lithium aluminum silicate, or zirconium phosphate can be preferably used.

  The partition wall 30 is formed to have a uniform thickness from the upstream end to the downstream end. The partition wall 30 is formed such that the permeability (gas permeability coefficient) when exhaust passes through the pores is uniform from the upstream end to the downstream end. Here, the transmittance is a transmittance when the particulate filter 1 is in a new state where PM is not collected. When the partition wall 30 is configured in this way, when exhaust gas flows into the case 2, PM in the exhaust gas is collected substantially uniformly over the entire region from the upstream end portion to the downstream end portion of the partition wall 30. As a result, PM in the exhaust can be efficiently collected.

  In the particulate filter 1 configured in this way, when the amount of PM trapped by the particulate filter 1 increases excessively, the back pressure acting on the internal combustion engine increases as the pressure loss of the particulate filter 1 increases. Therefore, problems such as a decrease in the fuel consumption rate of the internal combustion engine occur. Therefore, it is necessary to remove PM collected in the particulate filter 1 before the pressure loss of the particulate filter 1 becomes excessively large.

  Since PM is oxidized when it is in a high-temperature and oxygen-excess atmosphere, when removing PM trapped in the particulate filter 1, the air-fuel ratio of the exhaust discharged from the internal combustion engine is leaner than the stoichiometric air-fuel ratio. What is necessary is just to raise the temperature of the particulate filter 1 to the temperature range which can oxidize PM under the condition which becomes an air fuel ratio. Therefore, an oxidation catalyst is disposed in the exhaust passage upstream of the particulate filter 1 and an unburned fuel component (HC or CO) is supplied to the oxidation catalyst, so that the particulate filter 1 is generated by the oxidation reaction heat of the unburned fuel component. It is conceivable to raise the temperature of the exhaust gas flowing into the exhaust gas to a temperature range where PM can be oxidized. By the way, if an oxidation catalyst that is separate from the particulate filter 1 is disposed in the exhaust passage, vehicle mountability may be reduced. In view of such circumstances, it is desirable to support the oxidation catalyst having PM oxidation ability and the oxidation catalyst having oxidation ability of unburned fuel components on the base material 3 of the particulate filter 1. Specifically, an oxidation catalyst may be supported on the surface of the partition wall 30 or in the pores. When removing PM collected by the particulate filter 1, unburned fuel is contained in the exhaust gas flowing into the particulate filter 1 when the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is a lean air-fuel ratio. What is necessary is just to perform the process which supplies a component (filter reproduction | regeneration process).

  In the configuration in which the oxidation catalyst is supported on the surface of the partition wall 30 or in the pores, when the PM oxidation ability of the oxidation catalyst is made uniform from the upstream end portion to the downstream end portion of the partition wall 30, the filter regeneration process is performed. There is a possibility that the temperature of the upstream portion of the partition wall 30 is not increased to the temperature range where PM can be oxidized. Here, in the case where the PM oxidation ability of the oxidation catalyst is made uniform in the entire region from the upstream end portion to the downstream end portion of the partition wall 30, the temperature distribution of the partition wall 30 at the time of executing the filter regeneration process is illustrated. 3 shows. The horizontal axis in FIG. 3 indicates the position of the partition wall 30 in the exhaust flow direction, and the vertical axis in FIG. 3 indicates the temperature of each part of the partition wall 30. As shown in FIG. 3, a portion (in FIG. 3) downstream from a predetermined position P0 between the upstream end (Pu in FIG. 3) and the downstream end (Pd in FIG. 3) of the partition wall 30. B) rises above the target temperature suitable for oxidation of PM, but the part upstream of the predetermined position P0 (A in FIG. 3) does not rise to the target temperature. Therefore, there is a possibility that PM collected in the portion A upstream from the predetermined position P0 is not sufficiently oxidized and removed.

Therefore, in the particulate filter 1 of the present embodiment, the oxidation catalyst is supported so that the PM oxidation capability in the site A upstream from the predetermined position P0 is higher than the PM oxidation capability in the site B downstream. I made it. Specifically, the catalyst coat layer 310 is formed on the surface of the partition wall 30 and in the pores 300 at the site A upstream from the predetermined position P0, as shown in FIG. Here, the catalyst coat layer 310 includes an oxidation catalyst (for example, Pt or Pd) having an oxidation ability of an unburned fuel component and an oxidation catalyst having a PM oxidation ability (for example, Pt, Pd, NdCeZr-based powder, CeAg, or A coating layer containing Ag ₂ SO ₄ or the like), which is formed by applying a slurry containing the above-described oxidation catalyst to the surface or pores of the partition walls 30 and then drying and firing. On the other hand, in the portion B downstream of the predetermined position P0, as shown in FIG. 4B, no catalyst coat layer is formed on the surface of the partition wall 30 or in the pores 300. When the partition wall 30 is formed in this way, the PM oxidation ability at the site A upstream of the partition wall 30 becomes higher than the oxidation ability of the site B downstream.

  As shown in FIG. 4, when the PM oxidation capacity in the upstream part A of the partition wall 30 becomes higher than the oxidation capacity of the downstream part B, when the filter regeneration process is executed, The collected PM is oxidized in preference to the PM collected in the downstream portion B. Therefore, the exhaust permeability in the upstream part A is higher than the exhaust permeability in the downstream part B, and accordingly, the permeation into the pores 300 in the upstream part A per unit time. The amount of exhaust gas flowing into the exhaust gas becomes larger than the amount of exhaust gas flowing into the pores 300 of the downstream portion B per unit time. As a result, when the filter regeneration process is executed, the amount of unburned fuel component flowing into the pores 300 of the upstream portion A increases, so that the unburned fuel component oxidized in the upstream portion A is reduced. The amount increases. As the amount of unburned fuel component oxidized in the upstream portion A increases, the amount of heat of oxidation reaction generated in the upstream portion A increases, so that the upstream portion A can oxidize PM. It becomes easy to raise the temperature above a suitable target temperature. Therefore, according to the particulate filter 1 of the present embodiment, the temperature of the entire area of the particulate filter 1 can be raised to the target temperature or higher when the filter regeneration process is executed, so that PM is oxidized in the entire area of the particulate filter 1. And can be removed.

  In the present embodiment, an example in which neither the catalyst having the ability to oxidize the unburned fuel component nor the catalyst having the PM oxidation ability is carried in the portion B on the downstream side of the partition wall 30 has been described. You may make it carry | support only the catalyst which has this. However, the loading amount at that time is smaller than that of the upstream portion A (for example, an oxidation catalyst having PM oxidation ability is supported only on the surface of the partition wall 30), or the oxidation catalyst supported on the upstream portion A. An oxidation catalyst having a weaker PM oxidation capability may be supported.

  In addition, if the temperature of the partition wall 30 is rapidly increased during the filter regeneration process, cracks or the like may occur in the base material 3 constituting the partition wall 30, and therefore a part of the upstream portion A (for example, In the range from the upstream end portion to the downstream side to the predetermined distance), the catalyst coat layer may not be formed, or the amount of the oxidation catalyst contained in the catalyst coat layer may be reduced.

DESCRIPTION OF SYMBOLS 1 Particulate filter 2 Case 3 Base material 4 1st channel | path 5 2nd channel | path 30 Partition 40 Plug body 50 Plug body 300 Pore 310 Catalyst coating layer

Claims (1)

A plurality of first passages whose upstream ends are closed in the exhaust flow direction;
A plurality of second passages whose downstream ends are closed in the exhaust flow direction;
A porous member that separates the first passage and the second passage, and is formed so that the thickness and exhaust permeability at the upstream portion and the downstream portion of the member are uniform. ,
In a particulate filter comprising a catalyst supported on the partition wall and an oxidation catalyst having an ability to oxidize particulate matter,
The particulate filter is characterized in that the oxidation catalyst is supported on the partition wall so that the oxidation ability in the upstream part is higher than the downstream part of the partition wall.

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