JP2012013059A - Exhaust gas cleaning device - Google Patents

Abstract

The present invention relates to an exhaust gas purifying apparatus, which makes the distribution of collected particulate matter uniform and improves the regeneration efficiency of the filter.
A first filter for collecting particulate matter contained in exhaust gas is provided in an exhaust passage of an engine, and a second filter is provided downstream thereof. The porosity of the carrier of the first filter 1 is set to be higher than the porosity of the carrier of the second filter 2.
[Selection] Figure 2

Description

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

  Conventionally, as a purification device for removing particulate matter (Particulate Matter; hereinafter abbreviated as PM) contained in exhaust gas of an internal combustion engine, particularly a diesel engine, a diesel particulate filter (DPF, Diesel Particulate Filter; hereinafter) (Abbreviated as “filter”). PM is a particulate substance with fuel, lubricant components, sulfur compounds, etc. attached to the surroundings of black smoke (soot) made of carbon. A large number of pores are formed.

  PM in the exhaust gas is collected by the filter, but if PM continues to be collected, the filter will be clogged and eventually the exhaust gas will not flow. For this reason, the collected PM needs to be removed by burning (incineration). As a method for removing PM, a method of forcibly burning and removing PM collected on the filter by intentionally raising and maintaining the temperature of the filter to the temperature required for PM combustion (forced regeneration type) In addition, there is a method of burning and removing during normal operation (continuous regeneration type, natural regeneration type) without intentionally increasing the temperature of the filter.

As a continuous regeneration type exhaust purification device, for example, an oxidation catalyst disposed upstream of a filter generates nitrogen dioxide (NO ₂ ) from nitrogen monoxide (NO) in exhaust gas, and is collected on the filter. There is a technique in which PM is continuously burned and removed by reacting with nitrogen dioxide produced by the above method. Further, a catalyst may be supported on the surface of the filter. In this case, the reaction between nitrogen dioxide in the exhaust gas and PM collected on the filter can be promoted.

  On the other hand, as a forced regeneration type exhaust purification device, for example, reaction heat generated when unburned fuel (HC) is supplied to an oxidation catalyst disposed upstream of a filter and the unburned fuel is oxidized by the oxidation catalyst. There is a method of raising the temperature of the filter by using. By such a method, PM collected by the filter is removed, and the filter is regenerated and purified.

The regeneration efficiency of such a filter is improved by collecting PM uniformly throughout the filter and promoting the oxidation reaction of PM at a uniform temperature. Therefore, a filter structure for making the PM distribution in the exhaust gas distribution direction uniform has been proposed.
For example, Patent Document 1 discloses an exhaust gas purifying apparatus using a plurality of filters with a catalyst having different pore diameters of cell partition walls. In this technique, a plurality of filters are arranged in series in order from the largest to the smallest average pore diameter from the upstream side to the downstream side of the exhaust gas. With such a configuration, the particle size of PM collected by each filter is made different, and the collected amount of PM is dispersed in the flow direction of the exhaust gas.

JP 2003-225540 A

  However, the particle size distribution of PM contained in the exhaust gas introduced into the filter is not necessarily uniform. For this reason, the distribution of the collected amount of PM is biased, and good regeneration efficiency may not be obtained. Since the inflow PM is collected in order from the upstream part of the filter, the downstream part of the filter functions sufficiently, especially when a large amount of PM with a large particle size is contained in the exhaust gas. As a result, the reproduction efficiency is greatly reduced. Furthermore, since a large amount of PM is collected in the upstream portion of the filter and the pressure loss in the exhaust passage increases remarkably, there is a concern that the output of the engine and the fuel consumption may be reduced.

Further, with the technique such as Patent Document 1, it is not possible to disperse the collected amount of PM in the direction perpendicular to the flow direction of the exhaust gas.
For example, in an exhaust gas purification apparatus having a straight type casing into which exhaust gas is introduced into the center of the filter, the amount of collection at the center of the filter is more likely to increase than the outer periphery of the filter, but the exhaust gas flow is in the center. Since it is introduced and the reaction heat generated when PM burns increases, the temperature at the center of the filter is relatively likely to rise. Therefore, PM collected in the filter center is preferentially removed, and due to pressure loss, newly entering exhaust gas is biased toward the filter center where the collected PM is removed. As a result, PM remains unburned easily on the outer periphery of the filter, making it difficult to improve the regeneration efficiency.

Alternatively, even in a bent type casing in which the flow direction of the exhaust gas changes near the inlet of the filter, the exhaust gas easily flows to the outside rather than the inside of the bent exhaust passage, and good regeneration efficiency is obtained at a position closer to the inside of the filter. It is difficult to obtain.
These phenomena occur similarly in the continuous regeneration type and the forced regeneration type. In the case of the continuous regeneration type, not only the temperature but also nitrogen dioxide generated by the oxidation catalyst upstream of the filter is necessary as an element necessary for PM combustion, so the influence of the gas flow is the same level as the forced regeneration type. .

One of the purposes of this case was created in view of the above-described problems. The PM collection amount distribution in the exhaust gas purification device is made uniform, and the filter is arranged in each of the exhaust gas distribution direction and the direction perpendicular thereto. It is to improve the reproduction efficiency.
The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) An exhaust gas purifying device disclosed herein is provided in an exhaust passage of an internal combustion engine, a first porous body that collects particulate matter contained in exhaust gas, and the first porous body of the exhaust passage And a second porous body that collects particulate matter contained in the exhaust gas, and the first porous body has a higher porosity than the second porous body. It is what you have.
(2) In addition, the first porous body is provided as an open flow type carrier that forms a channel in which both the upstream end and the downstream end are open.

(3) Further, the second porous body is provided as a closed flow type carrier that forms a channel in which at least one of the upstream end and the downstream end is closed.
(4) Moreover, in the cross section perpendicular to the flow direction of the exhaust gas, the cross-sectional area of the first porous body is larger than the cross-sectional area of the second porous body.

(5) Moreover, said 1st porous body has a larger pore diameter than said 2nd porous body.
(6) Further, the first porous body and the second porous body are a carrier having a honeycomb structure partitioned by a plurality of cell walls, and the cell wall thickness of the first porous body is the first porous body. It is smaller than the cell wall thickness of the biporous body.

(7) Moreover, said 1st porous body and said 2nd porous body are arrange | positioned in a single casing.
(8) Moreover, the first porous body has a porosity of 70% or more.
(9) Further, the second porous body has a porosity of 55% or less.

  According to the disclosed exhaust gas purifying apparatus, by making the porosity of the first porous body higher than the porosity of the second porous body, the pressure loss on the upstream side of the exhaust is more than the pressure loss on the downstream side. Therefore, the particulate matter (PM) collection rate on the downstream side can be relatively improved. Thereby, the collection amount of the particulate matter in the flow direction of the exhaust gas can be made uniform, and the collection efficiency of the particulate matter in the entire apparatus can be improved.

It is a figure which shows typically the structure of the exhaust gas purification apparatus which concerns on one Embodiment. FIG. 2 illustrates an internal configuration of a filter of the exhaust gas purifying apparatus of FIG. 1, (a) is a perspective view showing the carrier through, (b) is an end surface of the carrier on the upstream side [Part A of FIG. ] Is an enlarged perspective view, (c) is an enlarged perspective view of the end face of the carrier on the downstream side (B portion in FIG. 2 (a)), and (d) is a sectional view of the main part thereof. FIG. 3 is a view showing a flow velocity distribution of exhaust gas inside the filter of FIG. 2, (a) is a flow velocity distribution in the vicinity of the inlet side end surface of the upstream carrier (cross section CC in FIG. 2 (a)); Is a flow velocity distribution in the vicinity of the inlet side end face of the downstream carrier (cross section DD in FIG. 2A). FIG. 3 is a diagram showing a temperature distribution inside the filter of FIG. 2, (a) is a temperature distribution on the inlet side of the upstream carrier, and (b) is a temperature distribution on the outlet side of the downstream carrier. It is a perspective view which shows the structure of the exhaust gas purification apparatus as a modification.

  The exhaust gas purification apparatus will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. overall structure]
The exhaust gas purifying apparatus is applied to an exhaust passage of an internal combustion engine (engine) as shown in FIG.
An engine 8 shown in FIG. 1 is a diesel engine using light oil as a fuel, and an exhaust passage 5 and an intake passage 6 are connected to the engine 8. Intake air is introduced into the combustion chamber of each cylinder of the engine 8 through the intake passage 6, and the exhaust gas after combustion is discharged to the outside through the exhaust passage 5.

  On the exhaust passage 5, a turbocharger 7, an oxidation catalyst 3, and a filter 4 are interposed in order from the upstream side of the exhaust gas flow. The turbocharger 7 is a supercharger interposed so as to straddle the exhaust passage 5 and the intake passage 6. The turbocharger 7 rotates the turbine with the exhaust pressure of the exhaust gas flowing through the exhaust passage 5 and uses the rotational force. By driving the compressor, the intake air from the intake passage 6 is compressed and the engine 8 is supercharged.

  The oxidation catalyst 3 is, for example, a three-way catalyst, which oxidizes nitrogen monoxide contained in the exhaust gas to generate nitrogen dioxide, and supplies this to the downstream filter 4. The oxidation catalyst 3 has a function of oxidizing and purifying harmful components such as unburned fuel (HC) and carbon monoxide (CO) in the exhaust gas flowing in, and a function of increasing the temperature of the exhaust gas by the reaction heat. Also have.

  The filter 4 is a forced regeneration filter that collects PM contained in the exhaust gas and burns and removes it. A catalyst is supported on the surface of the filter 4. The reaction heat generated by oxidizing the unburned fuel with the oxidation catalyst 3 is used to raise and maintain the filter 4 to a predetermined temperature, and the PM collected on the filter 4 is subjected to a predetermined temperature condition. Burn with.

[2. Filter details]
As shown in FIG. 2A, the filter 4 includes a casing 9 and a first filter 1 and a second filter 2 arranged in series in the casing 9. The first filter 1 and the second filter 2 have a cylindrical shape with the same diameter, are arranged so that their circular end faces face each other in parallel, and are fixed in the casing 9. A predetermined gap 11 is provided between the first filter 1 and the second filter 2 so that the filters are not physically in contact with each other. In the gap 11, the flow of the exhaust gas is allowed and the mixing of the exhaust gas is promoted.

  The casing 9 is a metal container, and includes a main body portion 9 a formed in a cylindrical shape, and a truncated cone-shaped inlet portion 9 b and an outlet portion 9 c that are connected to the exhaust passage 5 by reducing the diameter of the upper and lower ends. The casing 9 is a bent type, and the flow path center axis at the portion where the exhaust passage 5 is connected to the inlet portion 9b is slightly inclined with respect to the cylinder axis of the main body portion 9a. Similarly, the flow path center of the exhaust passage 5 connected to the outlet portion 9c is also inclined with respect to the cylinder axis of the main body portion 9a.

  The first filter 1 is an upstream filter. Inside the first filter 1, a plurality of honeycomb structures divided into a plurality of passages along the flow direction of the exhaust gas by the cell walls 1a (first porous body). Cell 1b is formed. These cells 1b are of an open flow type as shown in FIG. 2 (b), and the upstream and downstream ends are opened. As a result, the exhaust gas flows from the upstream side to the downstream side of the cell 1b of the first filter 1, or moves through the void inside the cell wall 1a to the adjacent cell 1b.

  On the other hand, the second filter 2 is a filter disposed on the downstream side of the first filter 1. Also in the second filter 2, a plurality of cells 2b having a honeycomb structure divided into a plurality of passages along the flow direction of the exhaust gas are formed by the cell walls 2a (second porous body). These cells 2b are of a closed flow type as shown in FIG. 2 (c), and one of the upstream and downstream ends is closed with a seal 2c made of the same material as the cell wall 2a. Thereby, all the exhaust gas flows through the cell 2b of the second filter 2 and flows downstream.

  The cell wall 1a of the first filter 1 and the cell wall 2a of the second filter 2 are porous bodies that collect PM on the surface or inside thereof. A catalyst layer for oxidizing the collected PM is provided on the surfaces of these cell walls 1a and 2a. The chemical structure of the catalyst layer is arbitrary. The material of the cell walls 1a, 2a may be, for example, a metal, a porous metal (metal support), or a ceramic (ceramic support) such as cordierite, silicon carbide, or silicon nitride.

  The cell wall 1 a of the first filter 1 has a higher porosity than the cell wall 2 a of the second filter 2. For example, the porosity of the cell wall 1a is set to 70 [%] or more, and the porosity of the cell wall 2a is set to 55 [%] or less. That is, the PM collection efficiency of the first filter 1 is set lower than the collection efficiency of the second filter 2. The distribution of the pores in the cell walls 1a and 2a may be uniform, or the number of pores is more biased on the surface side than the inside of the cell walls 1a and 2a (on the surface of the cell walls 1a and 2a). It is good also as a thing with many exposed pores.

  The porosity here means the apparent volume of only the cell walls 1a, 2a excluding the spaces of the cells 1b, 2b (the volume defined by the outer shape of the cell walls 1a, 2a, which is included in the cell walls 1a, 2a). The ratio of the volume of the pores to the volume including the pores to be produced). Therefore, the porosity is determined only by the cell walls 1a and 2a and does not depend on the size of the cells 1b and 2b.

  The average pore diameter of the cell wall 1 a of the first filter 1 is larger than the average pore diameter of the cell wall 2 a of the second filter 2. For example, the average pore diameter of the cell wall 1a is set to 50 [μm] or more, and the average pore diameter of the cell wall 2a is set to 25 [μm] or less. Furthermore, the thickness (cell wall thickness) of the cell wall 1 a of the first filter 1 is made smaller than the thickness of the cell wall 2 a of the second filter 2. Thus, a porous body that is less likely to collect PM than the second filter 2 and has many voids is used as the carrier for the first filter 1.

[3. Action, effect]
[3-1. Rectification]
The cell wall 1a has a high porosity, and there are many pores 1c to be included. Therefore, a large number of openings are exposed on the surface of the cell wall 1a, and the movement direction of the exhaust gas in the vicinity of the surface is likely to be disturbed. For example, as shown in FIG. 2 (d), when the flow direction of the exhaust gas is from the top to the bottom of the page, a part of the exhaust gas flows along the inner surface of the pore 1c exposed on the surface of the cell wall 1a. An attempt is made to move toward the inside of the wall 1a, and another part of the exhaust gas tends to move from the pore 1c toward the cell 1b (outside). Thereby, the diffusion and mixing of the exhaust gas are promoted toward the downstream side.

  Moreover, since the cell wall 1a has a high porosity of 70% or more, it can be said that the exhaust gas easily moves from one cell 1b to another adjacent cell 1b. That is, coupled with the diffusion action of the exhaust gas in the left-right direction, the exhaust gas moves in the first filter 1 in a direction perpendicular to the flow direction. Thereby, diffusion and mixing of exhaust gas are promoted. Furthermore, since the cell 1b of the first filter 1 is an open flow type, the exhaust gas flowing from the downstream end of the cell 1b diffuses in the left-right direction in the gap 11 immediately after that.

  On the other hand, the cell wall 2a of the second filter 2 has a porosity set to be as low as 55 [%] or less, and has a structure in which the exhaust gas hardly moves from one cell 2b to another adjacent cell 2b. Moreover, since the cell 2b of the second filter 2 is a closed flow type, the exhaust gas flows out from the downstream end after passing through the cell wall 2a, and the flow path resistance increases. Thereby, a part of the exhaust gas diffuses while staying in the gap 11 between the first filter 1 and the second filter 2. Such a tendency is further promoted by the small average pore diameter of the cell wall 2a (25 [μm] or less).

Accordingly, it is possible to equalize the distribution direction of the exhaust gas that has passed through the first filter 1, and to rectify the exhaust gas downstream of the first filter 1.
Further, since the cell wall 1a has not only a porosity but also a pore diameter larger than that of the cell wall 2a (average pore diameter is 50 [μm] or more), the cell wall 1a has a characteristic that it is easy to equalize the distribution direction of the exhaust gas. Thereby, the rectification effect of the exhaust gas downstream of the first filter 1 can be further improved.

[3-2. Improved flow velocity distribution]
Not only the flow direction of the exhaust gas but also the flow velocity is made uniform. The flow velocity distribution diagrams of the exhaust gas are shown in FIGS. Since the casing 9 of the filter 4 is a bent type, the flow rate of the exhaust gas at the inlet end surface of the first filter 1 increases toward the outside of the bent exhaust passage 5.

  In the example shown in FIG. 3A, it can be read that the region where the exhaust gas flows at high speed and the region where the exhaust gas flows slowly are separated from the substantially center of the first filter 1 in the left-right direction on the paper surface. On the other hand, the flow velocity distribution of the exhaust gas at the inlet end face of the second filter 2 is uniform as shown in FIG.

In this way, by applying the cell wall 1a having a large void ratio to the first filter 1, it is possible to equalize the deviation of the flow velocity of the exhaust gas passing through the inside, and to the entire surface of the inlet end face of the second filter 2. On the other hand, exhaust gas can be introduced at substantially the same speed. In particular, since the porosity of the cell wall 1a is set to 70 [%] or more, the action of equalizing the flow rate of the exhaust gas can be improved.
Furthermore, since the cell wall 1a has not only a porosity but also a larger pore diameter than the cell wall 2a, the cell wall 1a has a characteristic that is easy to level with respect to the deviation of the flow velocity of the exhaust gas. In particular, since the average pore diameter is 50 [μm] or more, the action of equalizing the flow rate of exhaust gas is improved. Therefore, the deviation of the flow rate of the exhaust gas can be more effectively leveled, and the flow rate distribution in the plane perpendicular to the flow direction of the exhaust gas can be easily made uniform.

[3-3. Improved temperature distribution]
Further, the temperature distribution of the exhaust gas is also equalized. FIGS. 4A and 4B show temperature distribution diagrams of exhaust gas in the vicinity of the inlet of the first filter 1 and in the vicinity of the outlet of the second filter 2. As described above, since the flow velocity distribution of the exhaust gas is uneven near the inlet of the first filter 1, as shown in FIG. 4 (a), the temperature distribution also becomes higher at the outer side of the bent exhaust passage 5, and at the inner side. It becomes low temperature.

  On the other hand, since the cell wall 1a of the first filter 1 has a high porosity, heat easily moves from one cell 1b to another adjacent cell 1b. In particular, since the porosity of the cell wall 1a is 70 [%] or more, the movement of heat is promoted. Therefore, the heat of the exhaust gas moves in the first filter 1 in a direction perpendicular to the flow direction. Thereby, the heat of the exhaust gas diffuses in the first filter 1.

Further, since the gap 11 is provided between the first filter 1 and the second filter 2, the exhaust gas further flows and mixes in the gap 11. Furthermore, since the flow rate of the exhaust gas decreases in the second filter 2 having a low porosity, the exhaust gas temporarily stops in the gap 11 and then flows into the second filter 2. In particular, since the porosity of the cell wall 2a is 55 [%] or less, the amount of decrease in the flow rate of the exhaust gas is appropriate. In these processes, the heat of the exhaust gas diffuses in the gap 11.
Therefore, as shown in FIG. 4B, the thermal deviation of the exhaust gas that has passed through the first filter 1 can be leveled, and the distribution of the exhaust gas temperature and the catalyst temperature in the second filter 2 can be made uniform. it can.

  Furthermore, since the cell wall 1a has not only the porosity but also a larger pore diameter than the cell wall 2a, it has a characteristic that it is easy to equalize the heat deviation of the exhaust gas. Such characteristics are further promoted by setting the average pore diameter to 50 [μm] or more. Thereby, the temperature distribution on the downstream side of the first filter 1 can be further improved. In addition, since the cell wall 1a has a cell wall thickness thinner than that of the cell wall 2a of the second filter 2, the cell wall 1a has a characteristic of easily transferring heat. This is also advantageous for homogenizing the temperature distribution.

[3-4. Pressure loss reduction]
Since the porosity of the cell wall 1a of the first filter 1 is higher than the porosity of the cell wall 2a of the second filter 2, the pressure loss in the exhaust passage 5 can be reduced. In particular, since the cell wall 1a has a high porosity of 70% or more, the effect of reducing pressure loss is high. In addition, since the average pore diameter of the cell wall 1a is 50 [μm] or more, the pressure loss is further reduced.
Further, since the cell 1b of the first filter 1 is an open flow type, the pressure loss is small and there is no possibility of increasing the load of the engine 8. Furthermore, since the upstream cell wall 1a has a thinner cell wall thickness than the downstream cell wall 2a, the pressure loss can be further reduced.

[3-5. Improving the distribution of deposition in the filter cross-section direction]
Regarding the PM accumulation amount distribution in a plane perpendicular to the flow direction of the exhaust gas, as described above, the deviation in the flow direction of the exhaust gas is eliminated in the vicinity of the inlet of the second filter 2, and the flow velocity becomes uniform. Thereby, distribution of PM collected by the 2nd filter 2 can be made uniform. Further, since the cell wall 2 a of the second filter 2 has a lower porosity than the cell wall 1 a of the first filter 1, more PM can be recovered than the first filter 1.

  Although the PM accumulation amount distribution collected in the first filter 1 may be biased to the outside of the bend, since the cell wall 1a of the first filter 1 has a high porosity, the PM accumulation amount is the first. There are merits that it is less than the two filters 2 and the risk of over-deposition and excessive temperature rise is small.

[3-6. Improving sediment distribution in the exhaust gas distribution direction]
Regarding the PM accumulation amount distribution in the exhaust gas flow direction, for example, when filters having the same collection efficiency are arranged in tandem in the exhaust passage 5, the accumulation amount increases toward the upstream side, and the accumulation amount on the downstream side increases. It can be considered that the distribution becomes less uneven.
On the other hand, in the present exhaust gas purification apparatus, the first filter 1 arranged on the upstream side has a structure with lower collection efficiency than the second filter 2, so that the PM is easily deposited and the first filter is arranged. The difficulty in depositing PM derived from the structure of 1 is offset and the amount of deposition is optimized.

On the other hand, since the second filter 2 has a closed flow type cell 2b and has a high collection efficiency, it is difficult to deposit PM derived from the arrangement, and PM derived from the structure of the second filter 2 is easily deposited. And the amount of deposition is optimized. Thereby, PM collection efficiency can be improved over the entire end face on the upstream side of the second filter 2 into which the rectified exhaust gas is introduced.
Further, as described above, in this exhaust gas purification apparatus, the pressure loss in the upstream first filter 1 is smaller than the pressure loss in the downstream second filter 2, so that the PM collection rate on the downstream side is low. Relatively improved. Therefore, the PM accumulation amount distribution in the entire filter 4 can be made uniform in the exhaust flow direction.

  In particular, in the above-mentioned embodiment, the porosity of the cell wall 1a of the first filter 1 is 70 [%] or more, whereas the porosity of the cell wall 2a of the second filter 2 is 55 [%] or less. Therefore, the effect of uniformizing the PM deposition amount distribution is enhanced. In addition, since the average pore diameter of the cell wall 1a of the first filter 1 is 50 [μm] or more, the average pore diameter of the cell wall 2a of the second filter 2 is 25 [μm] or less. The effect of uniforming the deposit amount distribution is further enhanced.

  Further, since the cell wall 1 a of the first filter 1 has a larger average pore diameter than the cell wall 2 a of the second filter 2, PM having a larger particle diameter than that of the second filter 2 is collected. On the other hand, since the cell wall 1a has a high porosity and a large amount of voids, even if PM having a large particle diameter is collected, the voids are not completely blocked. Therefore, even if the particle size distribution of PM contained in the exhaust gas introduced into the filter 4 is not uniform, this can be dealt with. For example, even when a large amount of PM having a large particle size is contained in the exhaust gas, the large amount of PM having a large diameter can be collected by the first filter 1.

[3-7. Other effects]
In addition to the above-described effects, the exhaust gas purification apparatus makes the PM accumulation distribution and temperature distribution uniform, thereby improving the regeneration efficiency and enabling control close to the control logic assumed in advance. . Moreover, it becomes easy to assume the collection state of PM on the 2nd filter 2, and the stability and accuracy of regeneration control can be improved.

  In addition, if the regeneration control is accurate, the amount of PM remaining on the filter 4 after the control is reduced, so that an unexpected excessive temperature rise can be prevented. Furthermore, since the regeneration efficiency is increased and the margin for excessive temperature rise is increased, the regeneration time can be shortened and the regeneration control interval can be extended. As a result, the fuel consumption can be improved and the oil dilution can be reduced. Further, the exhaust gas performance can be improved by reducing the fuel post-injection amount.

  In the exhaust gas purifying apparatus, the first filter 1 and the second filter 2 are disposed in the single casing 9, so that the dimension of the gap 11 can be set accurately. This makes it easier to predict and understand the flow and mixing conditions of exhaust gas. Therefore, it is possible to make the deviation in the distribution direction of the exhaust gas, the temperature distribution, and the flow velocity distribution more uniform.

[4. Modifications etc.]
Regardless of the embodiment described above, various modifications can be made without departing from the spirit of the invention. Each structure of this embodiment can be selected as needed, or may be combined appropriately.

In the above-described embodiment, the first filter 1 and the second filter 2 are formed with the same diameter. However, as shown in FIG. 5, the carrier diameter D ₁ of the first filter 1 is changed to the second filter 2. The diameter may be larger than the carrier diameter D ₂ (D ₁ ≧ D ₂ ). In this case, the fluidity and mixing properties of the exhaust gas that has passed through the first filter 1 can be improved, and the deviation in the distribution direction of the exhaust gas, the temperature distribution, and the flow velocity distribution can be made uniform. Also, the more increases the carrier diameter D ₁ of the first filter 1, it is possible to further reduce the pressure loss of the exhaust passage 5.

In the above-described embodiment, an example in which an open flow type carrier is used for the first filter 1 on the upstream side and a closed flow type carrier is used for the second filter 2 on the downstream side is illustrated. Is not limited to such a combination. If a carrier having a higher porosity than the downstream side is used at least on the upstream side, the above-described effects can be obtained.
The filter 4 of the above-described embodiment is such that both the first filter 1 and the second filter 2 are fixed in a single casing 9, but two types of filters are fixed to separate casings and the exhaust passage. 5 may be arranged in series.

  In the above-described embodiment, the exhaust passage 5 is illustrated in which two filters are arranged in tandem in series. However, the number of filters is not limited to this, and three or more filters may be arranged in series. . In this case, a filter with the lowest collection efficiency (for example, a filter with a high porosity, a high pore diameter, and a small (thin) cell wall thickness) is provided on the most upstream side, and is arranged so that the collection efficiency is higher on the downstream side. To do.

  As for the number of filters, in addition to the above, a single filter whose collection efficiency is changed along the exhaust flow direction is disposed, and the collection efficiency of the filter on the upstream side is lowered, and the downstream side You may form so that collection efficiency may become high. In this case, it is conceivable that the cell walls 1a and 2a are continuously formed without providing the predetermined gap 11 at the boundary portion where the collection efficiency is different. For example, a single filter having different collection efficiencies is formed on one end side and the other end side, and the low collection efficiency side (such as the high porosity side or the large pore diameter side) is the upstream side of the exhaust. As shown in FIG.

Even with such a configuration, the pressure loss on the upstream side of the exhaust gas can be made smaller than the pressure loss on the downstream side, as in the above-described exhaust gas purification apparatus. Further, the amount of PM collected in the exhaust flow direction can be made uniform, and the PM collection efficiency of the entire apparatus can be improved.
Moreover, although what applied this invention to the exhaust system of the diesel engine illustrated in the above-mentioned embodiment, the application to the exhaust system of a gasoline engine is also possible.

1 First filter 1a Cell wall (first porous body)
1b Cell 1c Pore 2 Second filter 2a Cell wall (second porous body)
2b Cell 2c Seal 3 Oxidation catalyst 4 Filter 5 Exhaust passage 6 Intake passage 7 Turbocharger 8 Engine 9 Casing 9a Body portion 9b Inlet portion 9c Outlet portion 11 Gap

Claims (9)

A first porous body that is provided in an exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust;
Provided on the downstream side of the first porous body of the exhaust passage, and comprises a second porous body for collecting particulate matter contained in the exhaust,
The exhaust gas purification apparatus, wherein the first porous body has a higher porosity than the second porous body. 2. The exhaust gas purification according to claim 1, wherein the first porous body is provided as an open flow type carrier that forms a flow path in which both an upstream end and a downstream end are open. apparatus. The said 2nd porous body is provided as a closed flow type support | carrier which forms the flow path by which at least any one of the upstream edge part and the downstream edge part was closed. Or the exhaust gas purification apparatus of 2. The cross-sectional area of the first porous body in a cross section perpendicular to the flow direction of the exhaust gas is greater than or equal to the cross-sectional area of the second porous body. The exhaust gas purifying apparatus according to item 1. The exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the first porous body has a larger pore diameter than the second porous body. The first porous body and the second porous body are honeycomb structure carriers defined by a plurality of cell walls,
The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein a cell wall thickness of the first porous body is smaller than a cell wall thickness of the second porous body. The exhaust gas purification apparatus according to any one of claims 1 to 6, wherein the first porous body and the second porous body are disposed in a single casing. The exhaust gas purification apparatus according to any one of claims 1 to 7, wherein the first porous body has a porosity of 70% or more. The exhaust gas purifying apparatus according to any one of claims 1 to 8, wherein the second porous body has a porosity of 55% or less.

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