JP2017155695A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation in performance of a catalyst as a whole even if the catalyst is poisoned by P (phosphorus).SOLUTION: An exhaust emission control device 100 of an internal combustion engine 1 is provided that has a plurality of catalysts 10 which are provided in series in an exhaust pipe 2. Engine oil containing phosphorus is circulated in the internal combustion engine. The catalyst 10a which is located at the most upstream side, of the plurality of the catalysts has an upstream-side portion 53 from an upstream-side end 51 up to a downstream-side portion spaced apart from each other at a prescribed distance L1, and a downstream-side portion 54 which is located at a position downstream from the upstream-side portion. The upstream-side portion and the downstream-side portion include catalyst metals, and a carrying amount of the catalyst metal per catalyst unit length of the upstream-side portion is smaller than that of the downstream-side portion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a plurality of catalysts provided in series with an exhaust pipe.

  Generally, a vehicle equipped with an internal combustion engine is provided with an exhaust gas purification device. The exhaust gas purification device is provided in series with the exhaust pipe and has a plurality of catalysts for purifying harmful substances in the exhaust gas.

JP 2002-309932 A

  The catalyst is poisoned by poisoning components such as S (sulfur), HC (hydrocarbon), and P (phosphorus) contained in the exhaust gas. Both of these poisoning components are derived from fuel and engine oil. S and HC are known to eliminate poisoning under high temperature conditions where the exhaust gas temperature is a predetermined temperature or higher. In other words, poisoning by S and HC is a temporary that can be recovered.

  However, poisoning by P is not eliminated even if the exhaust gas temperature becomes high. That is, P adhering to the catalyst is not desorbed from the catalyst even when the exhaust gas temperature becomes high. Therefore, poisoning by P is permanent and cannot be recovered. This leads to permanent deterioration of the catalyst. When P poisoning occurs, the catalyst purification ability inevitably decreases.

  Normally, P is contained in engine oil. When this engine oil burns and P is contained in exhaust gas, P adheres to the catalyst and causes P poisoning. In particular, when engine oil containing a relatively large amount of P, which is not recommended by the manufacturer, is used, catalyst deterioration due to P poisoning tends to proceed.

  On the other hand, as a result of intensive studies, the present inventor has found that a large amount of P adheres to a catalyst located on the most upstream side among a plurality of catalysts, particularly in the vicinity of the upstream end thereof. Therefore, a technique is desired that takes advantage of this characteristic and suppresses the performance degradation of the entire catalyst even if P poisoning occurs.

  Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can suppress a decrease in the performance of the entire catalyst even when P poisoning occurs.

According to one aspect of the invention,
An exhaust gas purification apparatus for an internal combustion engine having an exhaust pipe and a plurality of catalysts provided in series with the exhaust pipe,
In the internal combustion engine, engine oil containing phosphorus is circulated,
The catalyst located on the most upstream side of the plurality of catalysts has an upstream part from an upstream end to a downstream side by a predetermined distance, and a downstream part located downstream from the upstream part,
The exhaust gas purifying device for an internal combustion engine, wherein the upstream portion and the downstream portion include a catalyst metal, and the upstream portion has a smaller amount of catalyst metal supported per catalyst unit length than the downstream portion. Is provided.

According to another aspect of the invention,
An exhaust gas purification apparatus for an internal combustion engine having an exhaust pipe and a plurality of catalysts provided in series with the exhaust pipe,
In the internal combustion engine, engine oil containing phosphorus is circulated,
The catalyst located on the most upstream side of the plurality of catalysts has an upstream part from an upstream end to a downstream side by a predetermined distance, and a downstream part located downstream from the upstream part,
The exhaust gas purification apparatus for an internal combustion engine is provided, wherein the upstream portion and the downstream portion include a catalytic metal, and the upstream portion further includes barium.

  Preferably, the catalyst located on the most upstream side is an oxidation catalyst.

Preferably, the plurality of catalysts are provided in an aftertreatment unit provided in the middle of the exhaust pipe,
The post-processing unit is
A tubular first catalyst casing containing at least one catalyst;
A tubular second catalyst casing disposed in parallel to and downstream of the first catalyst casing and having at least one catalyst disposed therein;
A connecting pipe disposed at a position between the first catalyst casing and the second catalyst casing and connecting a downstream end of the first catalyst casing and an upstream end of the second catalyst casing; A connecting pipe having a folded portion that extends from the rear to the front along the U, and is folded back into a U shape and extends rearward.
An addition valve arranged to add urea water from the rear to the front from the upstream side of the folded portion toward the folded portion;
With
The catalyst located on the most upstream side is a catalyst located on the most upstream side in the first catalyst casing.

  According to the present invention, even when P poisoning occurs, an excellent effect is exhibited in that a decrease in performance of the entire catalyst can be suppressed.

It is a schematic structure figure showing an exhaust gas purification device concerning an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention.

  As shown in FIG. 1, the exhaust gas purification apparatus 100 includes an exhaust pipe 2 that allows exhaust gas of an internal combustion engine (engine) 1 to pass therethrough, and a plurality of catalysts 10 that are provided in the middle of the exhaust pipe 2 and purify the exhaust gas. The post-processing unit 3 and a casing 4 that houses the post-processing unit 3 are included.

  The internal combustion engine 1 is a multi-cylinder compression ignition internal combustion engine mounted on a vehicle (not shown), that is, a diesel engine. The internal combustion engine 1 is provided with an exhaust manifold 12 that collects exhaust gas discharged from each cylinder 11.

  The exhaust pipe 2 is a pipe that is connected to the exhaust manifold 12 and discharges exhaust gas from the exhaust manifold 12 in the downstream direction (direction indicated by arrow G) and releases it to the atmosphere.

  More specifically, the exhaust pipe 2 includes an upstream exhaust pipe 21 positioned upstream of the post-processing unit 3 and a downstream exhaust pipe 22 positioned downstream of the post-processing unit 3. The upstream exhaust pipe 21 has a flange 21a at its downstream end, and the downstream exhaust pipe 22 has a flange 22a at its upstream end.

  Next, the post-processing unit 3 will be described. The front-rear and left-right directions of the post-processing unit 3 are shown in FIG. In addition, the front-rear and left-right directions of the illustrated post-processing unit 3 are irrelevant to the front-rear, left-right directions of the vehicle, and are merely determined for convenience of explanation. In the present embodiment, the internal combustion engine 1 is placed vertically on the vehicle, and the left direction of the post-processing unit 3 coincides with the front direction of the vehicle.

  The aftertreatment unit 3 includes an exhaust gas inlet pipe 31, an exhaust gas outlet pipe 32, a first catalyst casing 33 in which at least one catalyst 10 is provided, a second catalyst casing 34 in which at least one catalyst 10 is provided, A connecting pipe 35 that connects the first catalyst casing 33 and the second catalyst casing 34 and an addition valve 36 that adds urea water are provided. Further, the post-processing unit 3 has a substantially symmetrical structure.

  The exhaust gas inlet pipe 31 is disposed at the front end and the left side of the post-processing unit 3, extends from the front to the rear, and the front end is connected to the downstream end of the upstream exhaust pipe 21. Further, the exhaust gas outlet pipe 32 is disposed at the front end and the right side of the post-processing unit 3, extends from the front to the rear, and the front end is connected to the upstream end of the downstream exhaust pipe 22.

  More specifically, a flange 31a is provided at the upstream end of the exhaust gas inlet pipe 31, and the flange 21a of the upstream exhaust pipe 21 is connected to the flange 31a. Similarly, a flange 32a is provided at the downstream end of the exhaust gas outlet pipe 32, and the flange 22a of the downstream exhaust pipe 22 is connected to the flange 32a. The flanges connected to each other are detachably fixed by fastening means such as bolts (not shown).

  The first catalyst casing 33 is formed in a tubular shape, extends rearward from the exhaust gas inlet pipe 31, and has a first side hole 33b on the right side surface of the downstream end portion 33a located at the rear end portion. Further, the first catalyst casing 33 is formed with a first enlarged-diameter portion 33c having a diameter larger than that of the exhaust gas inlet pipe 31 located on the upstream side and the connecting pipe 35 located on the downstream side.

  The first catalyst casing 33 has an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 10a and a particulate filter (hereinafter, referred to as “Diesel Oxidation Catalyst”) from the upstream side through a first heat insulating buffer member (mat) 37 at the position of the first enlarged diameter portion 33c. (Referred to as “DPF”) 10b.

  The oxidation catalyst 10a oxidizes and purifies unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas. The oxidation catalyst 10a has a function of heating and raising the temperature of exhaust gas with heat generated during oxidation of HC and CO. The oxidation catalyst 10a also has a function of oxidizing NO in the exhaust gas to NO2 and increasing the concentration of NO2 in the exhaust gas.

  The DPF 10b collects and removes particulate matter (PM) contained in the exhaust gas. In the present embodiment, a so-called wall flow type DPF 10b is used in which openings at both ends of a honeycomb-shaped heat-resistant substrate are alternately closed in a checkered pattern. However, any type of filter that physically captures PM can be used, such as a mesh-shaped foam shape.

  The DPF 10b is a so-called continuous regeneration type DPF with a catalyst in which a noble metal (catalyst metal) such as Pt is supported on the inner wall thereof. In this case, during normal operation of the engine, HC in the exhaust gas supplied to the DPF 10b is oxidized and burned by the catalytic action, and at this time, PM accumulated in the DPF 10b is simultaneously burned and removed. In addition, since DPF10b has a catalyst, DPF10b shall also be contained in the catalyst said to this invention here.

  The second catalyst casing 34 is formed in a tubular shape, extends rearward from the exhaust gas outlet pipe 32, and has a second side hole 34b on the left side of the upstream end 34a located at the rear end. Further, the second catalyst casing 34 is formed with a second diameter-expanded portion 34c having a diameter larger than that of the connecting pipe 35 positioned on the upstream side and the exhaust gas outlet pipe 32 positioned on the downstream side.

  In the second catalyst casing 34, the NOx catalyst 10c and the ammonia oxidation catalyst 10d are installed from the upstream side through the second heat insulating buffer member (mat) 38 at the position of the second enlarged diameter portion 34c.

  The NOx catalyst 10c is a catalyst for purifying nitrogen oxides NOx in the exhaust gas. The NOx catalyst 10c is composed of a selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) and can continuously reduce NOx by ammonia (NH3) generated by hydrolysis from urea water.

  The ammonia oxidation catalyst 10d is a catalyst that oxidizes excess ammonia (NH3) that has not been consumed by the NOx catalyst 10c to reduce NOx, thereby generating N2.

  In the present embodiment, the first catalyst casing 33 and the second catalyst casing 34 are arranged on the left and right in parallel with each other. Further, the first side hole 33b and the second side hole 34d are disposed at positions facing each other.

  The connecting pipe 35 is disposed at a position between the first catalyst casing 33 and the second catalyst casing 34 in the left-right direction, and connects the first side hole 33b and the second side hole 34b.

  More specifically, the connecting pipe 35 extends from the first side hole 33b toward the second side hole 34b (the right side in the figure) and bends forward, and the second side hole 34b extends to the first side hole 33b. A second portion 35b extending toward the side (the left side in the figure) and bent forward. Specifically, the first portion 35a corresponds to a portion from X1 to X2 in the drawing, and the second portion 35b corresponds to a portion from Y1 to Y2 in the drawing.

  The connecting pipe 35 has a third portion 35c that extends forward from the downstream end X2 of the first portion 35a, is folded back in a U-shape and extends rearward, and is connected to the upstream end Y2 of the second portion 35b. . By forming the connecting pipe 35 by being folded in a U shape in this way, the pipe length of the connecting pipe 35 becomes longer than connecting the first side hole 33b and the second side hole 34d linearly.

  The addition valve 36 is arranged so as to add urea water from the rear to the front from the bent part L of the first part 35a toward the folded part U of the third part 35c.

  The casing 4 is made of a box-type casing using a heat resistant material such as stainless steel, and covers the entire post-processing unit 3 in an airtight manner. A heat insulating material 5 such as glass wool is laid on almost the entire inner surface of the casing 4 to keep the post-processing unit 3 warm.

  On the rear surface 41 of the casing 4, a mounting portion 42 for attaching the addition valve 36 is formed at a portion located behind the bent portion L of the post-processing unit 3. The attachment portion 42 is formed to be recessed forward, and an outer insertion hole 43 is formed at the front end thereof. In addition, an inner insertion hole 35 d is formed coaxially with the outer insertion hole 43 on the rear end surface of the bent portion L of the post-processing unit 3. The addition valve 36 is inserted into both the outer insertion hole 43 and the inner insertion hole 35 d from the outside (rear) of the casing 4, and is fixed to the casing 4 by a boss portion 44 provided in the attachment portion 42.

  In the front surface 45 of the casing 4, an inlet hole 42 a through which the exhaust gas inlet pipe 31 of the post-processing unit 3 is inserted and an outlet hole 42 b through which the exhaust gas outlet pipe 32 is inserted are formed at the left and right positions.

  Thus, in the exhaust gas purification apparatus 100 according to the present embodiment, the exhaust pipe 2 is provided with a plurality of catalysts 10 (the oxidation catalyst 10a, the DPF 10b, the NOx catalyst 10c, and the ammonia oxidation catalyst 10d in order from the upstream side) in series. Yes. The oxidation catalyst 10a is located on the most upstream side.

  Engine oil containing P (phosphorus) is circulated in the engine 1 of the present embodiment. Therefore, the engine oil is burned simultaneously with the fuel in the cylinder 11, and the exhaust gas produced thereby contains P. The exhaust gas containing P is first supplied to the most upstream oxidation catalyst 10a. At this time, P adheres to the oxidation catalyst 10a, covers the noble metal (catalyst metal) of the oxidation catalyst 10a, and poisons the oxidation catalyst 10a. The degree of P poisoning increases as the use time of the oxidation catalyst 10a, specifically, the mileage of the vehicle increases.

  On the other hand, as a result of intensive studies, the present inventor has found that a large amount of P adheres near the upstream end of the oxidation catalyst 10a. Therefore, taking advantage of this characteristic, the present embodiment adopts the following configuration to minimize the performance degradation of the entire catalyst even when P poisoning occurs.

  As shown in FIG. 1, the oxidation catalyst 10a has an upstream end 51 located on the front side, a downstream end 52 located on the rear side, and a central axis C extending in the front-rear direction. The oxidation catalyst 10 a includes an upstream portion 53 from the upstream end 51 to the downstream side of the predetermined distance L <b> 1, and a downstream portion 54 that is located downstream of the upstream portion 53. The total length of the oxidation catalyst 10a is L, the length of the upstream portion 53 is L1, and the length of the downstream portion 54 is L2 (L = L1 + L2).

  The length L1 of the upstream portion 53 is set so as to include a region where the amount of deposited P is relatively large through experiments and the like. For example, it is set so as to include a region where the adhesion amount of P becomes a predetermined value or more at the time of a predetermined travel distance. Preferably, the length L1 is set to 5 to 38% of the total length L. It has been found that more P is attached to the upstream side.

  The oxidation catalyst 10a has a honeycomb-shaped carrier formed of a heat-resistant ceramic or metal such as cordierite, and a coat layer coated on the surface of the carrier. In the coating layer, a large number of fine particles of a noble metal (referred to as catalyst metal) such as Pt (platinum) as a main catalyst component are dispersedly arranged.

  Here, the catalyst metal is contained in the coat layers of both the upstream portion 53 and the downstream portion 54. However, the amount of catalyst metal supported per catalyst unit length is smaller in the upstream portion 53 than in the downstream portion 54. In addition, the said carrying amount can also be paraphrased as a carrying density.

  Regarding the production of the oxidation catalyst 10a, the carrier is immersed in a slurry (aqueous solution) in which fine particles of the catalyst metal are dispersed and containing a promoter component such as ceria (CeO2), and then the carrier is dried and calcined to form a surface of the carrier. A coat layer is formed (so-called wash coat method). At this time, two slurries with different catalyst metal concentrations are prepared, the support portion corresponding to the downstream portion 54 is immersed in the high concentration slurry, and the support portion corresponding to the upstream portion 53 is immersed in the low concentration slurry. To do. By doing so, it is possible to easily form the upstream portion 53 having a low carrying density and the downstream portion 54 having a high carrying density. Alternatively, in the latter case, the support portion corresponding to the downstream portion 54 is immersed twice in one slurry having a constant catalyst metal concentration, and the support portion corresponding to the upstream portion 53 is immersed once. The upstream portion 53 and the downstream portion 54 can also be easily formed by reducing the number of immersions of the above-mentioned ones than the former number of immersions.

  Next, based on FIG. 1, the effect of the exhaust gas purification apparatus 100 which concerns on this embodiment is demonstrated.

  The exhaust gas of the internal combustion engine 1 passes from the exhaust manifold 12 through the upstream exhaust pipe 21 and flows into the first catalyst casing 33 through the exhaust gas inlet pipe 31.

  The exhaust gas flowing into the first catalyst casing 33 passes through the oxidation catalyst 10a, whereby unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas are oxidized and purified.

  Next, the exhaust gas that has passed through the oxidation catalyst 10a flows into the DPF 10b, and particulate matter (PM) contained in the exhaust gas is collected and removed by the DPF 10b.

  The exhaust gas that has passed through the DPF 10b flows from the first side hole 33b located at the rear end of the first catalyst casing 33 to the first portion 35a of the connecting pipe 35, and moves forward 90 ° along the bent shape of the first portion 35a. The direction is changed to flow to the third portion 35c.

  The exhaust gas that has flowed to the third portion 35c turns 180 ° backward at the turn-up portion U, flows to the second portion 35b behind, and turns 90 ° along the bent shape of the second portion 35b. It flows into the second catalyst casing 34 through the side hole 34b.

  The addition valve 36 adds urea water from the rear to the front from the bent portion L toward the folded portion U. The exhaust gas mixed with the urea water is turned 180 ° rearward at the folded portion U, flows to the rear second portion 35b, is turned 90 ° along the bent shape of the second portion, and the second side. It flows into the second catalyst casing 34 through the hole 34b. In this process, the urea water is hydrolyzed to produce ammonia while being mixed with the exhaust gas and evaporating.

  Next, in the second catalyst casing 34, the exhaust gas containing at least one of urea water and ammonia passes through the NOx catalyst 10c. At this time, the NOx catalyst 10c reduces NOx with ammonia generated by hydrolysis of urea water.

  Excess ammonia that has not been consumed in the reduction of NOx by the NOx catalyst 10c is oxidized in contact with the ammonia oxidation catalyst 10d, and the release to the atmosphere is suppressed.

  The exhaust gas that has passed through the ammonia oxidation catalyst 10d is discharged to the downstream exhaust pipe 22 through the exhaust gas outlet pipe 32 and is released from the downstream exhaust pipe 22 to the atmosphere.

  By the way, the oxidation catalyst 10a is first supplied with exhaust gas containing P derived from P contained in the engine oil. A large amount of P contained in the exhaust gas adheres to the vicinity of the upstream end 51 of the oxidation catalyst 10a, and particularly adheres more in the upstream portion 53 than in the downstream portion 54. When P adheres, P covers the coating layer and the catalyst metal, reduces the catalytic action of the catalyst metal, and poisons the catalyst.

  However, since the upstream portion 53 has a smaller amount (supported density) of catalyst metal per catalyst unit length than the downstream portion 54, the degree of P poisoning of the oxidation catalyst 10a when viewed from the entire oxidation catalyst 10a. Can be reduced as compared with the case where both loading amounts are the same.

  That is, since the original performance (HC or CO purification rate) of the oxidation catalyst 10a when new is lower in the upstream portion 53 than in the downstream portion 54, P poisoning occurs in the upstream portion 53 having low performance. However, the influence (damage) on the entire oxidation catalyst 10a can be reduced. As a result, even when P poisoning occurs, it is possible to minimize the performance degradation of the entire catalyst.

  In addition, regarding the other advantage of the post-processing unit 3 of this embodiment, since the connection pipe 35 is formed in a U-shape, the first side hole 33b and the second side hole 34d are connected linearly. However, since the length of the connecting pipe 35 can be increased while the post-processing unit 3 can be made compact, it is advantageous for in-vehicle use.

  In the post-processing unit 3 of this embodiment, the urea water added from the addition valve 36 passes through this long and folded connection pipe 35. Thereby, the urea water can be sufficiently stirred and mixed with the exhaust gas, and the hydrolysis of the urea water is further promoted. As a result, ammonia is efficiently generated, which is advantageous for improving the NOx purification rate in the NOx catalyst 10c.

  As mentioned above, although embodiment of this invention was described in detail, the following other embodiment is also possible for this invention.

  (1) In the above embodiment, the amount of supported catalyst metal (supported density) per unit length of the catalyst is less in the upstream portion 53 than in the downstream portion 54. On the other hand, in addition or alternatively, Ba (barium) may be included in the upstream portion 53. According to the research result of the present inventor, it was found that when Ba is contained, the adhesion amount of P is reduced and the progress of P poisoning of the catalyst is delayed. Therefore, by including Ba in the upstream portion 53, the degree of P poisoning of the upstream portion 53 can be reduced and performance degradation in the entire oxidation catalyst 10a can be suppressed to a minimum.

  In addition, when Ba is included, as long as the catalyst metal is contained in the upstream part 53, the carrying density is arbitrary, and may be the same as the carrying density of the downstream part 54, for example. This is because the degree of P poisoning of the upstream portion 53 can be reduced even in this way. Regarding the production, Ba is mixed in advance in the slurry in which the carrier portion corresponding to the upstream portion 53 is immersed.

  (2) Embodiments including post-processing units other than those described above are possible. In addition, an embodiment without a post-processing unit is also possible.

  The configurations of the above-described embodiments can be combined partially or wholly unless there is a particular contradiction. The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust pipe 3 Aftertreatment unit 10 Catalyst 10a Oxidation catalyst 33 First catalyst casing 34 Second catalyst casing 35 Connection pipe 36 Addition valve 51 Upstream end 53 Upstream part 54 Downstream part 100 Exhaust gas purification device L1 Predetermined distance ( length)

Claims (4)

An exhaust gas purification apparatus for an internal combustion engine having an exhaust pipe and a plurality of catalysts provided in series with the exhaust pipe,
In the internal combustion engine, engine oil containing phosphorus is circulated,
The catalyst located on the most upstream side of the plurality of catalysts has an upstream part from an upstream end to a downstream side by a predetermined distance, and a downstream part located downstream from the upstream part,
The exhaust gas purifying device for an internal combustion engine, wherein the upstream portion and the downstream portion include a catalyst metal, and the upstream portion has a smaller amount of catalyst metal supported per catalyst unit length than the downstream portion. . An exhaust gas purification apparatus for an internal combustion engine having an exhaust pipe and a plurality of catalysts provided in series with the exhaust pipe,
In the internal combustion engine, engine oil containing phosphorus is circulated,
The catalyst located on the most upstream side of the plurality of catalysts has an upstream part from an upstream end to a downstream side by a predetermined distance, and a downstream part located downstream from the upstream part,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the upstream portion and the downstream portion include a catalytic metal, and the upstream portion further includes barium. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein the catalyst located on the most upstream side is an oxidation catalyst. The plurality of catalysts are provided in an aftertreatment unit provided in the middle of the exhaust pipe,
The post-processing unit is
A tubular first catalyst casing containing at least one catalyst;
A tubular second catalyst casing disposed in parallel to and downstream of the first catalyst casing and having at least one catalyst disposed therein;
A connecting pipe disposed at a position between the first catalyst casing and the second catalyst casing and connecting a downstream end of the first catalyst casing and an upstream end of the second catalyst casing; A connecting pipe having a folded portion that extends from the rear to the front along the U, and is folded back into a U shape and extends rearward.
An addition valve arranged to add urea water from the rear to the front from the upstream side of the folded portion toward the folded portion;
With
The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 3, wherein the catalyst located on the most upstream side is a catalyst located on the most upstream side in the first catalyst casing. .

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