JP2006257920A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily raise the temperature of exhaust gas flowing in a DPF to a degree capable of natural combustion of deposited PM. <P>SOLUTION: This exhaust emission control device has an exhaust gas circulating means 4 for arranging an oxidation catalyst 1 on the exhaust gas upstream side, arranging a filter body 2 of a wall flow structure on its downstream side and supplying at least a part of outlet gas from the oxidation catalyst 1 in the exhaust gas on the exhaust gas upstream side of the oxidation catalyst 1 from between the oxidation catalyst 1 and the filter body 2. Since at least a part of the outlet gas of the oxidation catalyst 1 passes again through the oxidation catalyst 1 by the exhaust gas circulating means 4, the temperature of the exhaust gas flowing in the filter body 2 increasingly becomes the high temperature, and the NO<SB>2</SB>concentration increases, to thereby promote oxidation and natural combustion of the PM deposited on the filter body 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification device that purifies exhaust gas containing particulates such as exhaust gas from a diesel engine.

  As for gasoline engines, toxic components in exhaust gas are steadily decreasing due to strict regulations on exhaust gas and technological advances that can cope with it. However, for diesel engines, gasoline engines have a unique situation in which harmful components are discharged as particulates (particulate matter: carbon fine particles, sulfur fine particles such as sulfate, high molecular weight hydrocarbon fine particles, etc., hereinafter referred to as PM). Different coping techniques are required.

  As an exhaust gas purification device for diesel engines that has been developed so far, a trap type exhaust gas purification device (wall flow) represented by a ceramic plug-type honeycomb body (diesel PM filter (hereinafter referred to as DPF)) is available. Mainstream. This DPF is formed by alternately sealing both ends of the openings of the cells of the ceramic honeycomb structure, for example, in a checkered pattern, and is adjacent to the inflow side cells and the inflow side cells clogged on the exhaust gas downstream side. It consists of an outflow side cell clogged upstream of the exhaust gas and a cell partition partitioning the inflow side cell and the outflow side cell. The exhaust gas is filtered through the pores of the cell partition wall to collect PM, thereby suppressing emissions. To do.

  However, in DPF, pressure loss increases due to PM accumulation, so it is necessary to periodically remove and regenerate PM accumulated by some means. Thus, conventionally, when pressure loss increases, DPF is regenerated by burning PM accumulated by heating with a burner or an electric heater or circulating high temperature exhaust gas. However, in this case, the higher the amount of PM deposited, the higher the temperature during combustion, and the resulting thermal stress may damage the DPF. In addition, since the system performs a regeneration process after detecting that the pressure loss has increased to a predetermined value, a rapid response becomes difficult when the pressure loss suddenly increases, and the engine output may be adversely affected. Furthermore, since the exhaust gas from diesel engines is in a relatively low temperature range, there is also a problem that it is difficult to reach a high temperature of about 600 ° C. or higher at which PM spontaneously burns.

Therefore, it is desirable to regenerate DPF before the amount of accumulated PM becomes so large. In addition, it is desirable to spontaneously combust PM deposited by the heat of exhaust gas without using a burner or an electric heater. Thus, for example, Japanese Patent Application Laid-Open No. 10-159552 proposes an exhaust gas purification device in which an oxidation catalyst body is disposed on the exhaust gas upstream side of DPF. According to this exhaust gas purification device, the exhaust gas heated by the reaction heat in the oxidation catalyst body flows into the DPF, so that the spontaneous combustion of PM is promoted. Also, NO in the exhaust gas is oxidized by the oxidation catalyst body to produce NO ₂ with high oxidation activity, which flows into the DPF and oxidizes the deposited PM. Therefore, it is possible to regenerate the DPF before the amount of accumulated PM increases, that is, before the pressure loss increases so much.

However, at the time of start-up or in winter, the exhaust gas temperature is extremely low, so that there is no reaction in the oxidation catalyst body. As a result, it is difficult to produce NO ₂ and PM cannot be oxidized. When the amount of reaction heat in the oxidation catalyst body is small, the exhaust gas cannot be heated to a temperature at which PM can spontaneously combust.

Further, the exhaust gas flowing through the exhaust pipe has a temperature distribution in which the inner peripheral portion has a higher temperature and the outer peripheral portion has a lower temperature. For this reason, in the DPF, the PM deposits on the outer periphery greatly affect the pressure loss because PM is less likely to spontaneously combust and accumulate more easily. In addition, the oxidation catalyst body disposed on the upstream side also has a problem that the oxidation reaction at the outer peripheral portion is less likely to occur, and the amount of generated NO ₂ or the amount of reaction heat becomes insufficient.

  Japanese Patent Laid-Open No. 2003-120260 proposes an exhaust gas purification apparatus having a return path for heating the outer periphery of the DPF with the exhaust gas that has passed through the DPF. According to this apparatus, since the temperature rise of the outer peripheral portion of the DPF is promoted by the return exhaust gas, the combustion of PM is promoted and the regeneration of the DPF can be performed more reliably.

However, in DPF, oxidation reaction does not usually occur, so the temperature of the outgas is often lower than the temperature of the input gas, and even if it is returned, the temperature rise effect on the outer periphery is small. Therefore, a large effect cannot be expected from the above apparatus particularly in a low temperature region.
JP-A-10-159552 JP2003-120260

  The present invention has been made in view of the above circumstances, and an object to be solved is to easily raise the temperature of the exhaust gas flowing into the DPF to such an extent that the accumulated PM can be spontaneously combusted.

The feature of the exhaust gas purification apparatus of the present invention that solves the above problems is an oxidation catalyst body arranged on the exhaust gas upstream side,
An inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and a porous material that partitions the inflow side cell and the outflow side cell and has many pores A filter body having a wall flow structure, which is disposed on the exhaust gas downstream side of the oxidation catalyst body,
And an exhaust gas circulation means for supplying at least a part of the output gas from the oxidation catalyst body into the exhaust gas upstream of the oxidation catalyst body from between the oxidation catalyst body and the filter body.

  At least the oxidation catalyst body is disposed in a hollow tube having a double tube structure in the exhaust gas upstream portion, the double tube structure portion includes an opening that opens toward the inlet gas side end surface of the oxidation catalyst body, and the exhaust gas circulation means includes: It is preferable to discharge at least a part of the output gas from the oxidation catalyst body from the opening through the double pipe structure. In this case, it is desirable that the opening is opened toward the cell opening in the outer peripheral portion of the oxidation catalyst body.

According to the exhaust gas purification apparatus of the present invention, the exhaust gas that has passed through the oxidation catalyst body flows into the filter body. That is, the exhaust gas that is heated by the reaction heat in the oxidation catalyst body and contains NO ₂ having high oxidation activity flows into the filter body. Furthermore, since at least a part of the outgas of the oxidation catalyst body passes through the oxidation catalyst body again by the exhaust gas circulation means, the exhaust gas temperature flowing into the filter body becomes higher and the NO ₂ concentration increases. Therefore, the oxidation and spontaneous combustion of PM deposited on the filter body are promoted, and the filter body can be continuously regenerated while suppressing an increase in pressure loss. Further, as the temperature of the oxidation catalyst body is further increased, the oxidation activity is further improved and the purification rate of HC and CO is improved.

If a hollow tube having a double pipe structure is used in the exhaust gas upstream portion, the exhaust gas that has passed through the oxidation catalyst body is discharged from an opening formed at an arbitrary position of the double pipe structure. By adjusting, the exhaust gas can be supplied to an arbitrary position of the end surface on the gas entering side of the oxidation catalyst body. Therefore, for example, high-temperature exhaust gas can be supplied to the outer peripheral portion of the oxidation catalyst body, the temperature of the exhaust gas flowing into the filter body can be further increased, and the NO ₂ concentration in the exhaust gas is further increased. Thereby, continuous regeneration of the filter body can be performed more reliably.

  The exhaust gas purification apparatus of the present invention includes an oxidation catalyst body, a filter body, and exhaust gas circulation means. As the oxidation catalyst body, a material composed of a base material having an exhaust gas flow path and a catalyst layer formed on the surface of the base material can be used. As the substrate, a straight flow structure having a honeycomb passage, a foam structure, a pellet structure, or the like can be used, and the material is conventionally used, such as a heat-resistant ceramic such as cordierite or a metal. Can be used.

The catalyst layer is formed by supporting a catalyst metal on a porous oxide carrier, and is formed on the surface of a substrate by a wash coat method or the like. As the porous oxide serving as the carrier, alumina, titania, zirconia, ceria, silica, or a composite oxide composed of a plurality of types selected from these can be used. The catalyst metal may be any metal having oxidation activity, and may be a noble metal such as Pt, Rh, Pd, or Ir or a base metal such as Fe, Co, Ni, or W. Depending on the application, a NO _x storage material such as alkali metal or alkaline earth metal may be further supported.

The amount of catalyst metal supported is preferably 0.1 to 20 g per liter of the substrate volume. If the loading amount is less than this, the activity is too low to be practical, and if the loading amount exceeds this range, the activity is saturated and the cost is increased. The amount of the NO _x storage material supported is preferably in the range of 0.05 to 0.45 mol per liter of the substrate volume. If the loading amount is less than this, the activity is too low and there is no meaning of loading. If the loading amount is more than this range, the catalytic metal is covered and the activity decreases.

  The filter body is divided into an inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and a large number of pores dividing the inflow side cell and the outflow side cell. A wall flow structure having a porous cell partition wall having the structure is used. This filter body can be manufactured from heat-resistant ceramics such as cordierite and silicon carbide. For example, a clay-like slurry containing cordierite powder as a main component is prepared, and the slurry is formed by extrusion or the like and fired. Instead of cordierite powder, powders of alumina, magnesia and silica can be blended so as to have a cordierite composition. Thereafter, the cell opening on one end face is sealed in a checkered pattern with the same clay-like slurry, and the cell opening of the cell adjacent to the cell sealed on the one end face is sealed on the other end face. Thereafter, the filter body can be manufactured by fixing the sealing material by firing or the like.

  In order to form pores in the cell partition walls of the filter body, a combustible powder such as carbon powder, wood powder, starch, or resin powder is mixed in the slurry, and the combustible powder disappears upon firing. Thus, pores can be formed, and by adjusting the particle size and addition amount of the combustible powder, the distribution of the surface vacancies and the diameters of the internal pores and the opening area can be controlled.

  It is also preferable to form a catalyst layer in which a catalyst metal is supported on an oxide carrier on the surface of the cell partition wall and the surface in the pores. Thereby, the oxidation activity of PM is remarkably improved, and regeneration from a lower temperature range is possible. As the oxide carrier, an oxide such as alumina, ceria, zirconia, titania, or a composite oxide composed of a plurality of these can be used. As the catalyst metal, it is preferable to use one or more selected from platinum group noble metals such as Pt, Rh, Pd, Ir and Ru. The amount of the catalyst metal supported is preferably 0.1 to 5 g per liter volume of the filter body. If the loading amount is less than this, the activity is too low and there is no meaning of loading, and even if the loading is larger than this range, the activity is saturated and the cost is increased.

The catalyst layer preferably contains a NO _x storage material selected from alkali metals, alkaline earth metals and the like. When the NO _x storage material is included in the catalyst layer, NO ₂ generated by oxidation with the catalyst metal can be stored in the NO _x storage material, so that the NO _x purification activity is further improved. Loading amount of _the NO _x storage material, it is preferable that the volume per liter 0.05 to 0.45 mols of the filter body. If the loading amount is less than this, the activity is too low and there is no meaning of loading. If the loading amount is more than this range, the catalytic metal is covered and the activity decreases.

  To form a catalyst layer on the filter body, oxide powder or composite oxide powder is made into a slurry together with a binder component such as alumina sol and water, and the slurry is attached to the cell partition wall and fired, and then the catalyst metal is supported. do it. A slurry can also be prepared from a catalyst powder in which a catalyst metal is previously supported on an oxide powder or a composite oxide powder. A normal dipping method can be used to attach the slurry to the cell partition walls. However, the slurry is forcibly filled into the pores of the cell partition walls by air blowing or suction, and the excess slurry contained in the pores is filled. It is desirable to remove things.

  In the exhaust gas purification apparatus of the present invention, the oxidation catalyst body is disposed on the exhaust gas upstream side, and the filter body is disposed on the exhaust gas downstream side of the oxidation catalyst body. The distance between the two is not particularly limited, but it is preferable to arrange them as close as possible in order to prevent the temperature of the exhaust gas flowing into the filter body from decreasing.

  The exhaust gas circulation means that characterizes the present invention supplies at least a part of the output gas from the oxidation catalyst body between the oxidation catalyst body and the filter body into the exhaust gas upstream of the oxidation catalyst body. Although it is possible to circulate only with the kinetic energy of the exhaust gas itself, it is desirable to use auxiliary power such as a pump. The exhaust gas circulation means may supply at least a part of the output gas from the oxidation catalyst body into the exhaust gas upstream of the exhaust gas of the oxidation catalyst body. You may supply in the waste gas of an upstream side.

  For example, a bypass passage that connects the upstream exhaust passage and the downstream exhaust passage of the oxidation catalyst body and bypasses the oxidation catalyst body is formed, and exhaust gas is sent from the downstream side to the upstream side in the bypass passage. By arranging a pump or the like, exhaust gas circulation means can be formed. In this case, the output gas from the oxidation catalyst body is supplied into the exhaust gas passage on the exhaust gas upstream side of the oxidation catalyst body, but the portion where the supplied exhaust gas flows into the oxidation catalyst body is indefinite.

Therefore, at least an oxidation catalyst body is arranged in a hollow tube having a double-pipe structure in the exhaust gas upstream part, and an opening is formed in the double-pipe structure part that opens toward the gas-side end face of the oxidation catalyst body. deep. It is desirable that at least a part of the gas emitted from the oxidation catalyst body supplied from the exhaust gas circulation means is discharged from the opening through the double pipe structure. By doing so, the exhaust gas can be supplied to any position on the inlet gas side end face of the oxidation catalyst body by adjusting the position of the opening. Therefore, for example, it becomes possible to supply high-temperature exhaust gas to the outer peripheral portion of the oxidation catalyst body, the temperature of the exhaust gas flowing into the filter body can be further increased, and the NO ₂ concentration in the exhaust gas is further increased. Continuous reproduction can be performed more reliably. Moreover, since the temperature of the oxidation catalyst body can be raised quickly, the purification rate of HC and CO in a low temperature region is improved.

  At least the oxidation catalyst body is disposed in the hollow tube, but it is also preferable to dispose the filter body in the same hollow tube on the downstream side of the oxidation catalyst body. By doing so, the heat retention effect in the hollow tube is enhanced by the exhaust gas flowing through the double-pipe structure, and the efficiency of PM oxidation or spontaneous combustion in the filter body is further improved.

  The exhaust gas circulation means can be always driven, but it is desirable to control the driving according to the operating condition of the engine. For example, the exhaust gas circulation means can be driven only when PM is accumulated to some extent and the filter body is regenerated. Also, in situations where the oxidation activity of the oxidation catalyst body is not manifested, such as during startup, driving the exhaust gas circulation means does not make much sense, and the exit gas temperature of the oxidation catalyst body is greater than the temperature entering the oxidation catalyst body. It is desirable to drive the exhaust gas circulation means only when the value is high. As an index of this control, the difference between the temperature of the gas entering the oxidation catalyst body and the temperature of the oxidation catalyst body, the concentration of HC in the gas entering the oxidation catalyst body and the concentration of HC in the gas exiting the oxidation catalyst body Or the like can be used.

  When the filter body is regenerated using the exhaust gas purification apparatus of the present invention, it is desirable to supply an HC source such as light oil into the exhaust gas upstream of the oxidation catalyst body. When the supplied HC source is oxidized by the oxidation catalyst body, a large amount of heat is generated, and the PM deposited on the filter body can be efficiently burned by the heat. By providing the exhaust gas circulation means, unburned HC can be supplied again to the oxidation catalyst body and combusted, so that the utilization efficiency of the HC source is improved and the purification rate of HC is improved. Further, the amount of catalyst metal supported on the oxidation catalyst body can be reduced to reduce the cost. Further, by improving gas diffusibility, the combustion of light oil becomes uniform, and stable heat supply to the oxidation catalyst body becomes possible.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1
FIG. 1 shows an exhaust gas purification apparatus of this embodiment. In this exhaust gas purifying apparatus, an oxidation catalyst body 1 and a filter catalyst body 2 are disposed in the catalytic converter 3 adjacent in this order from the exhaust gas upstream side to the downstream side. Between the oxidation catalyst body 1 and the filter catalyst body 2, a downstream pipe 40 having one end opened toward the center of the output gas side end face of the oxidation catalyst body 1 and the other end penetrating the peripheral wall of the catalytic converter 3. Is arranged. Further, on the upstream side of the oxidation catalyst body 1, an upstream pipe 41 having one end opened toward the center of the inlet gas side end face of the oxidation catalyst body 1 and the other end penetrating the peripheral wall of the cone portion 30 of the catalytic converter 3 is disposed. Has been. The downstream pipe 40 and the upstream pipe 41 are connected to each other outside the catalytic converter 3, and a pump 42 that sends exhaust gas from the downstream pipe 40 to the upstream pipe 41 is disposed at the connection portion. That is, the exhaust gas circulation means 4 is formed by the downstream pipe 40, the upstream pipe 41 and the pump 42.

  Further, an injector 5 for adding light oil to the exhaust gas is disposed upstream of the catalytic converter 3, and an A / F sensor 50 is disposed in the exhaust pipe between the injector 5 and the catalytic converter 3. A temperature sensor 10 and a temperature sensor 11 for detecting the exhaust gas temperature are disposed upstream and downstream of the oxidation catalyst body 1. Detection signals from the A / F sensor 50, the temperature sensor 10, and the temperature sensor 11 are input to the control device 6, and the control device 6 controls the driving of the pump 42 in accordance with these input signals.

  Hereinafter, the manufacturing method of the oxidation catalyst body 1 and the filter catalyst body 2 will be described, and a detailed description of these configurations will be given.

A honeycomb substrate made of cordierite with a straight flow structure was prepared. This honeycomb substrate has cell partition walls of 400 / inch ² , a diameter of 130 mm, a thickness of 0.1 mm, and a volume of 1 liter.

  Next, a mixed slurry in which each powder of alumina, titania, zirconia and ceria was dispersed in water was prepared, and a coating layer of 150 g / L was formed on the cell partition wall surface of the honeycomb substrate by a wash coat method. Thereafter, 2 g / L of Pt was supported by a water absorption supporting method and then calcined at 500 ° C. to prepare an oxidation catalyst body 1.

On the other hand, a honeycomb structure having a wall flow structure made of cordierite was prepared. This honeycomb structure has a volume of 2 liters, has cell partition walls of 200 / inch ² and a thickness of 0.3 mm. Further, both end faces are alternately sealed one cell at a time.

  Next, a slurry similar to that used in the preparation of the oxidation catalyst body 1 was used, and a coating layer of 150 g / L was formed on the cell partition wall surface and the pore surface inside the cell partition wall. Thereafter, 2 g / L of Pt was supported by a water absorption supporting method, and then calcined at 500 ° C. to prepare a filter catalyst body 2.

(Example 2)
The exhaust gas purifying apparatus of this embodiment shown in FIGS. 2 and 3 is the same as that of Embodiment 1 except that the structure of the catalytic converter 3 and the structure of the upstream pipe 41 are different.

  In the catalytic converter 3, a double cone portion 32 having a double tube structure having a hollow portion 31 in the upstream cone portion is formed, and one end of the upstream pipe 41 is connected from the outer peripheral side of the double cone portion 32 to the hollow portion 31. Communicate. A plurality of openings 33 are formed on the inner peripheral surface of the double cone portion 32 so as to open toward the outer peripheral portion of the inlet gas side end surface of the oxidation catalyst body 1 and communicate with the hollow portion 31. Therefore, the exhaust gas supplied from the exhaust gas circulation means 4 is discharged from the opening 33 through the hollow portion 31 of the double-contained portion 32 and discharged toward the outer peripheral portion of the inlet gas side end surface of the oxidation catalyst body 1.

(Comparative Example 1)
The exhaust gas purification apparatus of this comparative example shown in FIG. 4 is the same as that of Example 1 except that it does not have the exhaust gas circulation means 4, the A / F sensor 50, the temperature sensor 10, the temperature sensor 11, and the control device 6.

<Test and evaluation>
In the exhaust gas purifying apparatuses of the first and second embodiments, the control shown in FIG. 5 is performed. In step 100, the detection signal of the A / F sensor 50 is compared with the predetermined value X, and when the atmosphere of the exhaust gas to the oxidation catalyst body 1 is rich with oxygen deficiency, that is, when light oil is added from the injector 5. The process proceeds to step 101. If no light oil has been added, the drive of the pump 42 is stopped in step 103 and the process returns to step 100.

  In step 101, the detection signals of the temperature sensor 10 and the temperature sensor 11 are compared, and the process proceeds to step 102 only when the gas output temperature from the oxidation catalyst body 1 is higher than the gas input temperature. If the temperature of the gas emitted from the oxidation catalyst body 1 is equal to or lower than the incoming gas temperature, it is determined that no oxidation reaction has occurred in the oxidation catalyst body 1, the drive of the pump 42 is stopped in step 103, and the processing is step 100. Return to.

  When both step 100 and step 101 are satisfied, that is, when light oil is added and the temperature of the gas emitted from the oxidation catalyst body 1 is higher than the gas temperature, the pump 42 is driven in step 102 to circulate the exhaust gas. A part of the gas emitted from the oxidation catalyst body 1 is returned to the exhaust gas upstream of the oxidation catalyst body 1 by the means 4. The process of step 102 continues as long as both step 100 and step 101 are satisfied.

  Therefore, while the light oil is added and the oxidation reaction in the oxidation catalyst body 1 occurs, a large reaction heat is generated due to the oxidation of the light oil in the oxidation catalyst body 1, and the exhaust gas heated thereby becomes the filter catalyst body. Flows into 2. Furthermore, since part of the heated exhaust gas passes through the oxidation catalyst body 1 again by the exhaust gas circulation means 4, the temperature of the exhaust gas passing through the oxidation catalyst body 1 further increases, and the oxidation reaction in the oxidation catalyst body 1 is further promoted. The Moreover, since unburned HC passes through the oxidation catalyst body 1 again and is burned, the HC purification rate is also improved.

  Since the exhaust gas whose temperature is greatly increased by the above action flows into the filter catalyst body 2, the oxidation activity of the filter catalyst body 2 is improved and the combustion of the accumulated PM is promoted. Is played.

  The exhaust gas purifying apparatuses of Examples 1 and 2 and Comparative Example 1 were respectively attached to the exhaust system of a diesel engine, 10 g of PM was deposited on each filter catalyst body 2 by steady operation, and then the gas entering the oxidation catalyst body 1 The operation was performed for 5 minutes under the condition that the temperature was 300 ° C., and then the operation was performed for 5 minutes while adding light oil from the injector 5 under the condition of 2 g / min. Since light oil is added and the catalyst bed temperature of the oxidation catalyst body 1 is about 300 ° C., both the conditions of Step 100 and Step 101 are satisfied, and in Example 1 and Example 2, the exhaust gas circulation means 4 is set to 5 minutes. Driven during driving.

  Table 1 shows the results of measuring the PM amount remaining in the filter catalyst body 2 and calculating the PM removal rate after the end of the above test.

  On the other hand, the exhaust gas purifiers of Examples 1 and 2 and Comparative Example 1 were installed in the exhaust system of the diesel engine, respectively, and the HC purification rate and the CO purification rate in 11 mode driving were respectively added without adding light oil from the injector 5. It was measured. The results are shown in Table 1. In each example, step 100 was not performed. That is, the pump 42 was driven when the temperature of the gas emitted from the oxidation catalyst body 1 was higher than the gas temperature.

  From Table 1, it can be seen that the exhaust gas purifying apparatus of each Example showed a higher PM removal rate than that of Comparative Example 1, and the accumulated PM was burned efficiently. This is clearly the effect of driving the exhaust gas circulation means 4.

  In addition, the exhaust gas purification apparatus of each example shows higher HC purification rate and CO purification rate than Comparative Example 1, and this is when the temperature of the outgas from the oxidation catalyst body 1 is higher than the incoming gas temperature during 11-mode running. This is an effect obtained by driving the exhaust gas circulation means 4.

  Further, it is clear from the comparison between Example 1 and Example 2 that the exhaust gas purifying apparatus of Example 2 shows superior results. That is, by supplying a part of the output gas from the oxidation catalyst body 1 to the outer peripheral portion of the oxidation catalyst body 1, the oxidation activity is also improved at the outer peripheral portion of the oxidation catalyst body 1, thereby improving the purification rate of HC and CO. It is considered that PM combustion in the filter catalyst body 2 was promoted as well as improved.

It is explanatory drawing which shows the exhaust gas purification apparatus of one Example of this invention. It is explanatory drawing which shows the exhaust gas purification apparatus of the 2nd Example of this invention. It is the side view which looked at the double cone part in the exhaust gas purification apparatus of the 2nd Example of this invention from the inner peripheral side. It is explanatory drawing which shows the exhaust gas purification apparatus of a comparative example. It is a flowchart which shows the control content in the exhaust gas purification apparatus of the Example of this invention.

Explanation of symbols

1: oxidation catalyst body 2: filter catalyst body (filter body) 3: catalytic converter 4: exhaust gas circulation means 5: injector 6: control device
10: Temperature sensor 11: Temperature sensor 42: Pump
50: A / F sensor

Claims (3)

An oxidation catalyst body disposed upstream of the exhaust gas;
An inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, the inflow side cell and the outflow side cell are partitioned, and a large number of pores are formed. A filter body having a wall flow structure, which has a porous cell partition wall, and is disposed on the exhaust gas downstream side of the oxidation catalyst body;
Exhaust gas circulating means for supplying at least a part of the output gas from the oxidation catalyst body into the exhaust gas upstream of the oxidation catalyst body from between the oxidation catalyst body and the filter body. Exhaust gas purification device. At least the oxidation catalyst body is disposed in a hollow tube having a double tube structure upstream of the exhaust gas,
The double pipe structure includes an opening that opens toward an inlet gas side end surface of the oxidation catalyst body,
The exhaust gas purification device according to claim 1, wherein the exhaust gas circulation means discharges at least a part of the output gas from the oxidation catalyst body from the opening through the double pipe structure. The exhaust gas purification device according to claim 2, wherein the opening portion opens toward a cell opening in an outer peripheral portion of the oxidation catalyst body.

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