JP3641668B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a purification device including a filter disposed in an exhaust system of an internal combustion engine.
[0002]
[Prior art]
As this type of exhaust purification device, for example, there is a configuration described in Japanese Patent Publication No. 7-106290. In this configuration, a catalyst comprising a mixture of a platinum group metal and an alkaline earth metal oxide is provided on the filter wall. Based on the configuration described above, exhaust gas from a diesel engine containing fine particles (particulates) is purified.
[0003]
[Problems to be solved by the invention]
However, in this type of exhaust gas purification apparatus, the alkaline earth metal oxide for particulate removal carried on the filter moves from the exhaust upstream side to the exhaust downstream side by the flow of the exhaust gas. This gradually reduces the amount of alkaline earth metal oxide supported on the exhaust gas upstream side of the filter, and in some cases, almost no alkaline earth metal oxide is supported on the exhaust upstream side to purify the exhaust gas. There was a risk that this area would be narrowed and hindered exhaust purification.
[0004]
The present invention has been made paying attention to such problems existing in the prior art. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress a reduction in the amount of catalyst carried on the exhaust upstream side with the use of a filter and can purify exhaust gas well over a long period of time. It is to provide.
[0005]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  The invention according to claim 1 is an exhaust gas purification apparatus for an internal combustion engine provided with a filter disposed in an engine exhaust system, wherein the filter is provided with a collecting wall for collecting impurities,sameOn the collecting wallA catalyst for purifying the impurities, which is easy to move by exhaust flowProviding a carrier layer,sameCarrier layerThen the same catalystThis is characterized in that the amount of the carbon is increased toward the exhaust upstream side of the collecting wall.
[0006]
  Therefore, according to the first aspect of the present invention, as the filter is used, the flow of exhaust gas causes the flow on the collecting wall.Catalyst for purifying impurities that is easy to move by exhaust flowEven when the exhaust gas is moved from the exhaust upstream side to the exhaust downstream side,Same catalystIt is possible to suppress the amount of the supported amount from being reduced more than necessary. In other words, the amount of the catalyst can be averaged over the entire catalyst support layer, and even if the exhaust gas purification device is used for a long period of time, the exhaust gas can be purified well over the entire catalyst support layer.
[0007]
  Invention of Claim 2According to,In an exhaust gas purification apparatus for an internal combustion engine provided with a filter disposed in an engine exhaust system,A reversing means for reversing the exhaust upstream side and the exhaust downstream side of the filter;The filter is provided with a collecting wall for collecting impurities, and the collecting wall is provided with a catalyst layer for purifying the impurities, which carries a catalyst that is easily moved by the exhaust flow, sameCarrier layerThen the catalystLoading amountTheThe intermediate portion between the exhaust upstream side and the exhaust downstream side of the collecting wall is characterized in that it is increased.
[0008]
  Therefore, the direction of the exhaust gas flowing through the filter is appropriately reversed by the reversing means.
The purification function can be recovered by reversing the exhaust flow. In this way, even if the exhaust flow direction is forward and reverse,A catalyst for purifying impurities that is easy to move in the exhaust stream.Middle partInSince the supported amount is increased, the amount of the catalyst is averaged in the entire catalyst supporting layer by the exhaust flow, and the exhaust gas can be purified well in the entire catalyst supporting layer over a long period of time.
[0009]
  According to a third aspect of the present invention, in the first or second aspect of the present invention, the catalyst is fine particle oxidation removal capable of oxidizing and removing fine particles.With agentis there.
  Therefore, exhaust gas containing particulates can be effectively purified, and is particularly effective as an exhaust gas purification device for diesel engines.
[0010]
The invention according to claim 4 is the invention according to claim 3, wherein the fine particle oxidation removing agent is made of at least one metal selected from alkali metals, alkaline earth metals, rare earths and transition metals.
Therefore, the exhaust gas containing fine particles can be suitably purified by these metals, and is extremely effective as an exhaust gas purification device for a diesel engine.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the exhaust emission control device of this embodiment includes a switching unit 11, a filter 13, and a filter 13 that are connected to the downstream side of an exhaust manifold in a diesel engine (not shown) via an exhaust pipe 12. A first connection part 14 that connects one side of the filter and the switching part 11, a second connection part 15 that connects the other side of the filter 13 and the switching part 11, and an exhaust passage 16 downstream of the switching part 11. It has.
[0012]
The switching unit 11 constitutes a reversing means for reversing the exhaust upstream side and the exhaust downstream side of the filter 13 and has a valve body 11a for switching the exhaust flow therein. As shown in FIG. 1, when the valve body 11a is switched to one switching position, the upstream side in the switching unit 11 communicates with the first connection unit 14 and the downstream side in the switching unit 11 is the first side. 2 is communicated with the connection 15. In this state, the exhaust gas flows from one side of the filter 13 to the other side as indicated by an arrow in FIG.
[0013]
On the other hand, as shown in FIG. 3, when the valve body 11a is switched to the other switching position, the upstream side in the switching unit 11 communicates with the second connection unit 15 and The downstream side communicates with the first connection portion 14. In this state, the exhaust gas flows from the other side of the filter 13 to one side as indicated by an arrow in FIG. Thus, by switching the valve body 11a, the direction of the exhaust gas flowing into the filter 13 can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the filter 13 can be reversed.
[0014]
The reverse operation between the exhaust upstream side and the exhaust downstream side of the filter 13 is performed, for example, every predetermined time, every predetermined travel distance of the vehicle, or the differential pressure between the exhaust upstream side and the exhaust downstream side of the filter 13 exceeds a set value. This is performed when the particulate accumulation amount of the filter 13 exceeds a set value.
[0015]
As described above, the exhaust gas purification apparatus can alternately reverse the exhaust upstream side and the exhaust downstream side of the filter 13 with a simple configuration. Further, in the filter, a large opening area is required for facilitating the inflow of exhaust gas. However, in this exhaust purification device, a filter having a large opening area is used without deteriorating the vehicle mountability. be able to.
[0016]
Next, the structure of the filter 13 will be described. As shown in FIGS. 4 to 6, the filter 13 is a wall flow type having a substantially oval front surface and a honeycomb structure made of a porous ceramic material such as cordierite, for example. It has a large number of axial spaces subdivided by a large number of partition walls 19 extending in the axial direction. In two adjacent axial spaces, one space is closed by the plug 20 on the exhaust downstream side or upstream side, and the other space is closed by the plug 20 on the exhaust upstream side or downstream side.
[0017]
Thus, one of the two adjacent axial spaces becomes the exhaust gas inflow passage 21 and the other becomes the exhaust gas outflow passage 22, and as shown in FIG. Will pass through the pores 17 of the partition walls 19 which are porous. In this case, the particulates (not shown) in the exhaust gas are very small compared to the size of the pores 17 of the partition wall 19, but as is clear from FIG. 6A, the exhaust upstream side of the partition wall 19. It collides on the surface and on the surface of the pore 17 in the partition wall 19 and is collected. Thus, each partition wall 19 functions as a collecting wall for collecting particulates.
[0018]
As shown in FIG. 7, a catalyst support layer 27 is applied on both side surfaces of each partition wall 19 of the filter 13 and on the surface of the pores 17 in each partition wall 19. In FIG. 7, for easy understanding, the pores of the partition walls 19 are omitted, the configuration is simplified, and the catalyst support layer 27 is drawn exaggerated thickly. A precious metal catalyst 23 and a particulate oxidation removing agent 24 as a catalyst are supported on the catalyst supporting layer 27 using alumina 25 or the like. Thereby, the particulates collected by each partition wall 19 of the filter 13 are oxidized and removed. The fine particle oxidation removing agent promotes the oxidation of particulates by releasing active oxygen. Preferably, oxygen is taken in and retained when excess oxygen is present in the surroundings, and the oxygen concentration in the surroundings is increased. Oxygen retained when it is lowered is released in the form of active oxygen.
[0019]
As the noble metal catalyst 23, platinum Pt is usually used. Further, as the fine particle oxidation removing agent 24, alkaline metal such as potassium K, sodium Na, lithium Li, cesium Cs, rubidium Rb, alkaline earth metal such as barium Ba, calcium Ca, strontium Sr, lanthanum La, yttrium At least one metal selected from rare earths such as Y and transition metals is used. Also, the particulate oxidation removing agent 24 is NO._XAlso functions as an absorbent. Therefore, thereafter, the particulate oxidation removing agent 24 is NO._XAbsorbent and SO_XWhen explaining the case of functioning as an absorbent,_XThe absorbent 24 will be described.
[0020]
This NO_XThe absorbent 24 is NO when the air-fuel ratio in the nearby atmosphere is lean._XWhen the air-fuel ratio becomes stoichiometric or rich, the absorbed NO_XAs a result, NO_XPerforms absorption and release action.
[0021]
This absorption / release action is considered to be performed by the mechanism shown in FIG. This mechanism will be described by taking as an example the case where platinum Pt is supported as the noble metal catalyst 23 of the catalyst support layer 27 and barium Ba is supported as the fine particle oxidation removing material 24, but other noble metals, alkali metals, alkaline earths, and rare earths are used. Is the same mechanism.
[0022]
Regardless of low-temperature combustion or normal combustion, when combustion is performed with the air-fuel ratio being lean, the oxygen concentration in the exhaust gas is high. At this time, as shown in FIG. O₂Is O₂ ^-Or O^2-It adheres to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas is O on the surface of platinum Pt.₂ ^-Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). Then the generated NO₂As shown in FIG. 9 (a), a part of is absorbed in the absorbent while being oxidized on platinum Pt and combined with barium oxide BaO._Three ^-NO in the form of_XIt diffuses into the absorbent 24. In this way NO_XIs NO_XAbsorbed in the absorbent 24. As long as the oxygen concentration in the ambient atmosphere is high, NO on the surface of platinum Pt₂Is generated and NO_XNO in absorbent 24_XUnless the absorption capacity is saturated, NO₂Is absorbed into the absorbent and nitrate ion NO._Three ^-Is generated.
[0023]
On the other hand, when the air-fuel ratio of the nearby atmosphere is made rich, the oxygen concentration decreases, and as a result, NO on the surface of platinum Pt₂The production amount of is reduced. NO₂When the amount of produced decreases, the reaction proceeds in the reverse direction (NO_Three ^-→ NO₂) And thus NO_XNitrate ion NO in absorbent 24_Three ^-Is NO₂NO in the form of_XReleased from the absorbent 24. NO at this time_XNO released from the absorbent 24_XAs shown in FIG. 9 (b), it is reduced by reacting with HC, CO, etc. contained in the nearby atmosphere. In this way, NO on the surface of platinum Pt.₂NO when no longer exists_XNO from the absorbent 24 one after another₂Is released. Therefore, when the air-fuel ratio of the nearby atmosphere is made rich, NO is quickly reached._XNO from absorbent 24_XIs released, and this released NO_XIs reduced in the atmosphere because NO is reduced_XWill not be discharged.
[0024]
NO_XNO in absorbent 24_XThere is a limit to the absorption capacity of NO, NO_XNO in absorbent 24_XBefore the absorption capacity is saturated, NO_XNO from absorbent 24_XNeed to be released. That is, NO_XNO absorbed by the absorbent 24_XAmount of NO_XNO before reaching storage capacity_XNeed to be regenerated to reduce and purify. To that end, NO_XThe amount of absorption is estimated using a means such as a map, and when it reaches an allowable amount, low-temperature combustion at the stoichiometric or rich air-fuel ratio is performed, or a filter 13 is connected from a fuel supply device (not shown). Supply fuel upstream. Based on this, the atmosphere in the vicinity of the filter 13 is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio. For this reason, as mentioned above, NO_XNO from absorbent 24_XIs released, and this released NO_XIs reduced and NO_XThe absorbent 24 is regenerated
In addition, the fuel of the internal combustion engine contains sulfur, and the SO_XIs generated. SO_XIs said NO_XNO in the form of sulfate by the same mechanism as_XAbsorbed by the absorbent 24. Since sulfate is a stable substance, it is difficult to be released from the filter even if the surrounding atmosphere has a rich air-fuel ratio, and the occlusion amount gradually increases. NO_XThe amount of nitrate or sulfate that can be stored in the absorbent 24 is finite, NO._XIf the storage amount of sulfate in the absorbent 24 increases (hereinafter referred to as SO_X(Referred to as poisoning), the amount of nitrate that can be stored decreases, and finally SO_XCannot absorb.
[0025]
In this case, NO_XSO of absorbent 24_XPoisoning is restored. First, SO_XIt is determined whether it is time to recover from poisoning. This determination is made based on the accumulated amount of consumed fuel or the like. Further, in the NOx purification process, the air-fuel ratio on the upstream side of the exhaust of the filter is made rich. During the above regeneration, reducing substances such as HC are released from the released NO._XTherefore, the air-fuel ratio on the downstream side of the filter 13 is close to the stoichiometric air-fuel ratio. However, when the regeneration is completed, the air-fuel ratio on the downstream side of the filter 13 becomes almost equal to the rich air-fuel ratio on the upstream side. If playback time is detected using this, SO_XThe recovery time of poisoning can be determined. That is, SO_XIf poisoning is in progress, NO during the regeneration period_XIs absorbed by a sensor (not shown) or the like.
[0026]
Based on this, fuel is supplied to the filter 13 by the fuel supply device. Thus, sufficient oxygen and fuel are supplied to the filter 13, and this fuel starts to burn well by the catalyst carried therein mainly at the exhaust inlet of the filter 13. The heat obtained by the combustion propagates to the downstream side of the catalyst along with the flow of the exhaust gas, and therefore the temperature on the downstream side becomes higher than the upstream side of the catalyst.
[0027]
With the supplied fuel, the temperature of the entire filter 13 including the exhaust inlet can be gradually raised. SO_XNitrate, which is a source of poisoning, is a stable substance. However, if the filter 13 is at a high temperature of about 600 ° C., the oxygen concentration is lowered by setting the ambient atmosphere as the theoretical air-fuel ratio or rich air-fuel ratio, thereby reducing SO_XCan be released as Therefore, SO_XIn order to recover poisoning, it is necessary to raise the temperature of the entire filter 13 to about 600 ° C. However, as described above, the heat obtained by combustion propagates downstream of the catalyst along with the flow of exhaust gas. Since heat is released from the downstream side of the catalyst, it takes a long time to raise the catalyst temperature.
[0028]
For this reason, the valve body 11a is switched at regular intervals to reverse the exhaust upstream side and the exhaust downstream side of the filter 13. This predetermined time is, for example, several tens of seconds to several minutes. Therefore, when the valve element 71a is switched, the heat radiated from the downstream side of the catalyst is propagated to the center side of the catalyst by the flow of exhaust gas from the reverse side, so that it is not necessary to throw away the heat. The temperature can be raised in a short time.
Thus, if the temperature of the filter 13 is raised to 600 ° C., the fuel is supplied, so that the atmosphere in the vicinity of the filter 13 results in the theoretical air fuel ratio, or preferably the rich air fuel ratio. As a result, SO 13_XRelease of this SO_XIs reduced and purified. And when predetermined time passes, the valve body 71a will be switched and the exhaust upstream side and downstream side of the filter 13 will be reversed. As described above, since the temperature of the catalyst is mainly low on the upstream side, the SO stored in the upstream side is mainly used._XHowever, by reversing the upstream side and the downstream side of the catalyst, the upstream side where it is difficult to release is now located on the downstream side where the temperature is high._XCan be reduced and purified. Thus, NO_XSO of the entire storage reduction catalyst unit_XThe poisoning recovery can be completed in a short time.
[0029]
Next, for example, an air-fuel ratio sensor (not shown) is provided in each of the first connection portion 72a and the second connection portion 72b, and it is determined whether or not the outputs of these air-fuel ratio sensors are substantially equal. That is, it is determined whether or not the air-fuel ratio on the exhaust upstream side of the filter 13 is substantially equal to the air-fuel ratio on the exhaust downstream side. When this judgment is affirmed, reducing substances such as HC_XThat is not used for reduction purification of SO, ie SO_XThe poisoning recovery is complete. However, immediately after switching the valve body, the air-fuel ratio on the exhaust downstream side remains rich, and detection of the air-fuel ratio is performed immediately before switching the valve body or after a while after switching the valve body. It is preferable to do.
[0030]
Next, regarding how the collected particulates are oxidized and removed by the filter 13 carrying the particulate oxidation removing agent 24, platinum Pt is used as the noble metal catalyst 23, and the particulate oxidation removing agent 24 is used. A case where potassium K is used will be described as an example. Even when another noble metal is used as the noble metal catalyst 23, or when another alkali metal, alkaline earth metal, rare earth, or transition metal is used as the fine particle oxidation removing agent 24, the same particulate removing action is performed.
[0031]
As described above, in a diesel engine, combustion is usually performed under an excess of air, so that the exhaust gas contains a large amount of excess air. That is, when the ratio of air and fuel supplied to the intake passage and the combustion chamber is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio is lean. Further, since NO is generated in the combustion chamber, the exhaust gas contains NO. Further, the fuel contains sulfur S, which reacts with oxygen in the combustion chamber to react with SO.₂Therefore, in the exhaust gas, SO₂It is included. Therefore, excess oxygen, NO and SO₂The exhaust gas containing the gas flows into the exhaust upstream side of the filter 13.
[0032]
As described above, since a large amount of excess air is contained in the exhaust gas, when this exhaust gas comes into contact with the exhaust gas contact surface of the filter 13, as shown in FIG.₂Is O^{2 -}Or O^{2 -}And adheres to the surface of the particles of the noble metal catalyst 23 made of platinum Pt. On the other hand, NO in the exhaust gas is O on the surface of the noble metal catalyst 23 made of platinum Pt.^{2 -}Or O^{2 -}Reacts with NO₂(2NO + O₂→ 2NO₂).
[0033]
Then the generated NO₂Part of the catalyst is oxidized on the noble metal removal agent 24 while being oxidized on the noble metal catalyst 23 made of platinum Pt, and combined with potassium K, as shown in FIG.^3-In the form of particulate oxidation remover 24 and potassium nitrate KNO_ThreeIs generated. Thus, in this embodiment, harmful NO contained in the exhaust gas._XCan be absorbed by the filter 13 and the amount released into the atmosphere can be greatly reduced.
[0034]
On the other hand, as described above, the exhaust gas contains SO.₂Is included, so this SO₂Is absorbed into the fine particle oxidation removing agent 24 by the same mechanism as in the case of NO. That is, as described above, oxygen O₂Is O^2-Or O^2-And adheres to the surface of the particles of the noble metal catalyst 23 made of platinum Pt, and the SO in the exhaust gas.₂Is O on the surface of the noble metal catalyst 23 made of platinum Pt.^2-Or O^2-Reacts with SO_ThreeIt becomes.
The generated SO is then_ThreeA part of the catalyst is further oxidized on the noble metal catalyst 23 made of platinum Pt and absorbed into the fine particle oxidation remover 24, and is combined with potassium K, and sulfate ions SO4.^2-In the form of particulate oxidation remover 24 and potassium sulfate K₂SO_FourIs generated. In this way, in the fine particle oxidation removing agent 24, potassium nitrate KNO._ThreeAnd potassium sulfate K₂SO_FourIs generated.
[0035]
Further, the particulates in the exhaust gas adhere to the surface of the particulate oxidation removing agent 24 carried on the filter 13 as indicated by reference numeral 26 in FIG. At this time, the oxygen concentration decreases at the contact surface between the particulate 26 and the fine particle oxidation removing agent 24. For this reason, a concentration difference occurs between the contact surface portion and the fine particle oxidation remover 24 having a high oxygen concentration, so that the oxygen in the fine particle oxidation remover 24 is changed between the particulate 26 and the fine particle oxidation remover 24. Try to move towards the part of the contact surface.
[0036]
As a result, potassium nitrate KNO formed in the particulate oxidation removing agent 24_ThreeIs decomposed into potassium K, oxygen O, and NO, and oxygen O is released toward the contact surface between the particulate 26 and the particulate oxidation removing agent 24. At the same time, NO is released from the particulate oxidation removing agent 24 to the outside. The NO released to the outside is oxidized on the noble metal catalyst 23 made of platinum Pt on the downstream side and is again absorbed in the fine particle oxidation removing agent 24.
[0037]
At this time, potassium sulfate K formed in the particulate oxidation removing agent 24₂SO4 is also potassium K, oxygen O, SO₂The oxygen O is released toward the contact surface between the particulate 26 and the particulate oxidation removing agent 24. At the same time, SO₂Is released to the outside from the particulate oxidation removing agent 24. SO released to the outside₂Is oxidized on the noble metal catalyst 23 made of platinum Pt on the downstream side, and is again absorbed into the fine particle oxidation removing agent 24. However, potassium sulfate K₂SO_FourIs stabilized, potassium nitrate KNO_ThreeIt is difficult to release active oxygen compared to.
[0038]
On the other hand, the oxygen O toward the contact surface between the particulate 26 and the particulate oxidation removing agent 24 is potassium nitrate KNO._ThreeAnd potassium sulfate K₂SO_FourIt is oxygen decomposed from a compound such as Thus, oxygen O decomposed from the compound has high energy and has extremely high activity. That is, the oxygen directed toward the contact surface between the particulate 26 and the particulate oxidation removing agent 24 is active oxygen O. Therefore, when this active oxygen O comes into contact with the particulates 26, the particulates 26 are oxidized without generating a luminous flame.
[0039]
When the amount of active oxygen is insufficient to oxidize all the particulates 26, as shown in FIG. 12A, when the particulates 26 adhere on the fine particle oxidation removing agent 61, the particulates 26 Particulate portions 63 that are only partially oxidized and not sufficiently oxidized remain on the exhaust upstream surface of the filter 13. Next, when the state where the amount of active oxygen is insufficient continues, the particulate portion 63 that has not been oxidized from one to the next remains on the exhaust upstream surface, and as a result, FIG. 6 (a) and FIG. 12 (b). As shown in FIG. 5, the exhaust upstream surface of the partition wall 19 of the filter 13 is covered with the residual particulate portion 63.
[0040]
Such residual particulate portion 63 gradually changes to a carbonaceous material that is hardly oxidized. Further, when the exhaust upstream surface is covered with the residual particulate portion 63, NO and SO by platinum Pt.₂And the active oxygen release action by the fine particle oxidation removing agent 61 are suppressed. As a result, the residual particulate portion 63 can be gradually oxidized over time. However, as shown in FIG. 12C, another particulate 26 is formed on the residual particulate portion 63 from the next. When the particles are deposited next, that is, when the particulates 26 are deposited in a laminated form, these particulates 26 are, for example, the particulates 26 that are easily oxidized because they are separated from the platinum Pt and the particulate oxidation removing agent. However, it is not oxidized by active oxygen.
[0041]
Therefore, further particulates 26 are deposited on the particulates 26 one after another. That is, if the state in which the amount of discharged fine particles is larger than the amount of fine particles that can be removed by oxidation continues, the particulates 26 will be deposited on the filter 13 in a laminated form.
[0042]
Therefore, when the vehicle travel distance integrated value reaches the set travel distance, the travel distance integrated value is reset to 0, and then the valve body is switched to reverse the exhaust upstream side and the exhaust downstream side of the filter 13.
[0043]
While the vehicle travels the set travel distance, as shown in FIG. 6 (a), the exhaust upstream surface of the partition wall 19 where the exhaust gas mainly collides and the exhaust gas flow facing surface in the pore 17 are on one side. Particulates 26 are collided and collected as a collecting surface of the particles and oxidized and removed by the fine particle oxidation removing agent. However, the oxidation removal may be insufficient and the particulates 26 may remain. At this time, the exhaust resistance of the filter 13 does not adversely affect the vehicle running, but if the particulates 26 are further accumulated, problems such as a significant decrease in engine output occur. At this time, the exhaust upstream side and the exhaust downstream side of the filter 13 are reversed. Thereby, the particulates 26 are not further deposited on the particulate portion 63 remaining on one of the collecting surfaces of the partition wall 19, and the remaining particulate portion is not activated by the active oxygen released from one of the collecting surfaces. 63 is gradually oxidized and removed.
[0044]
Further, the residual particulate portion 63 is easily broken and subdivided by the exhaust gas flow in the reverse direction as shown in FIG. 6B, and flows mainly in the downstream side in the pores 17.
[0045]
As a result, many of the finely divided particulates are dispersed in the pores 17 of the partition walls 19 and directly contact with the fine particle oxidation removing agent 24 carried on the inner surfaces of the pores 17 of the partition walls 19 to be oxidized. There are more opportunities to be removed. In this way, by supporting the fine particle oxidation removing agent 24 in the pores 17 of the partition walls 19, the residual particulate portion 63 can be remarkably easily oxidized and removed. Further, in addition to this oxidation removal, the other collecting surface of the partition wall 19 that has become upstream due to the backflow of the exhaust gas, that is, the exhaust upstream surface and the pores 17 of the partition wall 19 where the exhaust gas mainly collides at present is present. In the exhaust gas flow facing surface (in the relationship opposite to one of the collecting surfaces), new particulates 26 in the exhaust gas adhere and are oxidized by the active oxygen released from the particulate oxidation removing agent 24. Removed.
[0046]
A part of the active oxygen released from the particulate oxidation removing agent 24 during the oxidation removal moves to the downstream side together with the exhaust gas, and the remaining particulates are oxidized and removed by the backflow of the exhaust gas.
[0047]
That is, the residual particulates 63 on one collection surface of the partition wall 19 include not only active oxygen released from the collection surface but also particulates on the other collection surface of the partition wall 19 due to the backflow of exhaust gas. The remaining active oxygen used for oxidation removal comes with the exhaust gas. As a result, even if particulates have accumulated to some extent on one collecting surface of the partition wall 19 at the time of switching of the valve body 11a, if exhaust gas flows backward, it will accumulate on the residual particulates 63. In addition to the arrival of active oxygen at the particulates 26, the particulates 26 are not further deposited, so that the deposited particulates 63 are gradually oxidized and removed, and there is a certain amount of time until the next backflow. In this case, it can be sufficiently removed by oxidation.
[0048]
Switching of the valve body 11a is performed at every set travel distance, and the valve body 11a is switched before the residual particulate 63 on the filter 13 is changed to a carbonaceous material that is hardly oxidized. Further, the oxidation removal of the particulate 63 before the large amount of particulate 63 is deposited prevents the problem that the large amount of accumulated particulate 63 is ignited and burned at a time and the filter 13 is melted by a large amount of combustion heat. Will also do.
[0049]
Further, even if a large amount of particulates accumulates on one collecting surface of the partition wall 19 of the filter 13 at the time of switching of the valve body 11a due to some factor, if the valve body 11a is switched, the accumulated particulate 63 Are relatively easily broken and subdivided by the exhaust gas flow in the opposite direction. For this reason, some of the finely divided particulates that could not be oxidized and removed within the pores 17 of the partition wall 19 are discharged from the filter 13, but the exhaust resistance of the filter 13 is further increased, which adversely affects vehicle travel. The new particulates 26 can be collected by the other collecting surface of the filter 13.
[0050]
Thus, if the valve body 11a is switched for each set travel distance, it is possible to reliably prevent a large amount of particulates from being accumulated on the filter 13. The switching timing of the valve body 11a for this purpose is not limited for each set travel distance, and for example, may be set every set time or irregularly.
[0051]
In this embodiment, the filter 13 is configured such that the amount of the particulate oxidation removing agent 24 carried on each partition wall 19 increases toward the exhaust upstream side of the partition wall 19. That is, in this embodiment, since the upstream side and the downstream side of the exhaust of the filter 13 are switched in reverse by the switching of the valve body 11a of the switching unit 11, as shown by the solid line in FIG. In the initial state (immediately after manufacture), the amount of the gas is maximum at the intermediate portion of the partition wall 19 and gradually decreases toward both end portions on the exhaust downstream side of the intermediate portion. In FIG. 8, for ease of understanding, the curve of the loading amount of the particulate oxidation removing agent 24 is simplified and drawn linearly, but actually, it has a flat plateau and a skirt. A simple curve.
[0052]
As described above, in order to increase the carrying amount of the particulate oxidation removing agent 24 in the intermediate portion of the partition wall 19 in the exhaust flow direction, for example, the following manufacturing process is performed. That is, the filter 13 is immersed in the solution or slurry mixed with the particulate oxidation removing agent 24 from the exhaust upstream or downstream end to the central side, and from the exhaust upstream or downstream end to the central side. Apply the solution or slurry. Next, the filter 13 is turned upside down, and the filter 13 is immersed in a solution or slurry from the downstream or upstream end of the exhaust to the center, and the solution from the downstream or upstream end to the center of the solution. Or apply slurry. In this case, the application of the solution or slurry wraps at the center side.
[0053]
Therefore, the coating amount on the center side of the filter 13 is larger than that on the exhaust upstream side and downstream side, and the amount of the particulate oxidation removal agent 24 on the center side is increased. In addition, since platinum Pt does not move by the exhaust flow, it is not necessary to increase the carrying amount on the exhaust upstream side like the particulate oxidation removing agent 24.
[0054]
With the above-described configuration, even when the soft metal particulate removal agent 24 supported on the partition wall 19 is moved from the exhaust upstream side to the exhaust downstream side by the flow of the exhaust gas with the use of the filter 13, the particulate oxidation removal is performed. The application amount of the agent 24 is only averaged in the exhaust flow direction as shown by a solid line in FIG. Accordingly, it is possible to suppress the amount of the particulate oxidation removing agent 24 carried on the upstream side of the exhaust from being reduced.
[0055]
That is, in the switching state where the exhaust gas flows from one side of the filter 13 to the other side, the carrying amount of the particulate oxidation removing agent 24 changes to the other side of the partition wall 19. Further, when the exhaust gas is reversed so as to flow from the other side of the filter 13 to the one side, the amount of the particulate oxidation removing agent 24 changes to one side of the partition wall 19.
[0056]
As described above, the amount of the particulate oxidation removing agent 24 is alternately changed between one side and the other side of the partition wall 19 in accordance with the reverse switching between the exhaust upstream side and the exhaust downstream side of the filter 13. The maximum carrying portion of the particulate oxidation removing agent 24 in the intermediate portion is gradually broken down and replenished to both end portions of the partition wall 19. Therefore, the fine particle oxidation removing agent 24 becomes a chain line state from the state of the solid line in FIG. 8 so that the top portion is lowered and the base is increased, and the height is averaged. For this reason, the exhaust gas purification function can be satisfactorily maintained over a long period of time.
[0057]
Therefore, according to this embodiment, the following effects can be obtained.
(1) In this exhaust gas purification apparatus for an internal combustion engine, a filter 13 disposed in the engine exhaust system is provided, and the filter 13 is provided with a partition wall 19. Further, the particulate oxidation removing agent 24 is supported on the partition wall 19, and the amount of the particulate oxidation removing agent 24 supported is increased toward the exhaust upstream side of the partition wall 19.
[0058]
For this reason, even when the particulate oxidation removing agent 24 on the partition wall 19 is moved from the exhaust upstream side to the exhaust downstream side by the flow of the exhaust gas with the use of the filter 13, the particulate oxidation removing agent 24 on the upstream side of the exhaust gas is moved. It is possible to suppress the loading amount from being smaller than that on the downstream side. Therefore, the exhaust gas can be satisfactorily removed by oxidation over a long period of time.
[0059]
(2) In the exhaust gas purification apparatus for an internal combustion engine, the particulate oxidation removing agent 24 is made of alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, barium Ba, calcium Ca, and strontium Sr. And at least one metal selected from alkaline earth metals such as lanthanum La, rare earths such as yttrium Y, and transition metals. For this reason, the particulates collected in the filter 13 can be satisfactorily oxidized and removed by the action of the particulate oxidation removing agent 24 made of at least one of the metals.
[0060]
(3) The exhaust gas purification apparatus for an internal combustion engine is equipped with a switching unit 11 for reversing the exhaust upstream side and the exhaust downstream side of the filter 13. The particulate oxidation removing agent 24 is carried in an amount that is increased in the intermediate portion between the upstream side and the downstream side of the partition wall 19. For this reason, by reversing the exhaust upstream side and the exhaust downstream side of the filter 13, it is possible to satisfactorily remove particulates remaining in the filter 13 and prevent the filter 13 from being clogged. Further, it is possible to suppress a decrease in the amount of the particulate oxidation removing agent 24 carried on the upstream side of the partition wall 19 when the filter 13 is used on the upstream side and the downstream side.
[0061]
(Example of change)
In addition, this embodiment is not limited to said structure, You may change as follows.
[0062]
In the exhaust gas purification apparatus, the exhaust gas upstream side and the exhaust gas downstream side of the filter 13 are configured not to be reversed, and the particulates 19 move from the exhaust gas downstream side end of the filter 19 toward the exhaust upstream side end. It is formed so that the carrying amount of the oxidation removing agent 24 gradually increases.
[0063]
In the exhaust emission control device, the precious metal catalyst 23 and the particulate oxidation removing agent 24 carried on the filter 13 are different from the metal used in the embodiment.
[0064]
-The exhaust emission control device of the present invention is applied to a gasoline engine in addition to the diesel engine of the embodiment.
Even when configured in this manner, substantially the same operations and effects as those of the above-described embodiment can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine.
FIG. 2 is a front view of the exhaust emission control device of FIG.
3 is a partial plan view showing a switching state of a switching unit of the exhaust gas purification apparatus of FIG. 1. FIG.
FIG. 4 is a side view showing a configuration of a filter.
FIG. 5 is a sectional view of the same.
FIG. 6 is a partially enlarged cross-sectional view of a partition wall of a filter.
FIG. 7 is a sectional view of a filter partition wall.
FIG. 8 is a diagram for explaining the change in the amount of the particulate oxidation removing agent carried on the partition walls.
FIG. 9 NO_XExplanatory drawing which shows the absorption-and-release effect | action.
FIG. 10 is a diagram for explaining the oxidizing action of particulates.
FIG. 11 is also a diagram for explaining the oxidizing action of particulates.
FIG. 12 is a view for explaining the particulate deposition action.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Switching part which comprises reverse rotation means, 11a ... Valve body, 13 ... Filter, 19 ... Partition as collection wall, 24 ... Fine particle oxidation removal agent, 26 ... Particulate.

Claims (4)

In an exhaust gas purification apparatus for an internal combustion engine having a filter disposed in an engine exhaust system,
Wherein the filter is provided with collecting wall for collecting the impurities, the same collecting walls a catalyst for purifying the impurity, provided the carrier layer carrying the movement tends catalyst by the exhaust flow, An exhaust gas purification apparatus for an internal combustion engine, wherein the carrying amount of the catalyst is increased in the carrying layer toward the exhaust upstream side of the collecting wall. In an exhaust gas purification apparatus for an internal combustion engine having a filter disposed in an engine exhaust system,
Comprising a reversing means for reversing the exhaust downstream side and the exhaust upstream side of the filter, the same filter is provided with collecting wall for collecting the impurities, because the same collecting walls to purify the impurity of a catalyst, the carrier layer carrying the movement tends catalyst by the exhaust flow is provided, the carrying amount of the same supported layer the catalyst, as an intermediate portion between the exhaust upstream side of the collecting wall and the exhaust downstream side exhaust gas purification apparatus for an internal combustion engine you characterized in that as increases. The catalyst exhaust gas control apparatus according microparticles to claim 1 or 2 in particulate oxidation removal agent capable oxidized and removed. 4. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the particulate oxidation removing agent is made of at least one metal selected from alkali metals, alkaline earth metals, rare earths, and transition metals.

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