JP7327232B2 - Pipe joining method and pipe joining structure - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a pipe joining method and a pipe joining structure, and more particularly to a technique suitable for joining exhaust pipes through which exhaust gas flows.

Conventionally, as an exhaust gas aftertreatment device for an internal combustion engine, nitrogen contained in the exhaust gas is oxidized using ammonia, which is produced by hydrolyzing the urea water injected from the urea water injector with the heat of the exhaust gas and water vapor in the exhaust gas, as a reducing agent. A vehicle equipped with a selective catalytic reduction (hereinafter referred to as SCR catalyst) that reduces and purifies substances (hereinafter referred to as NOx) is known.

For example, Patent Literatures 1 and 2 disclose an inner pipe through which urea water is injected from a urea water injector and an outer pipe that covers the outer circumference of the inner pipe. An exhaust pipe structure is disclosed in which a swirling flow is generated in the inner pipe by allowing the fluid to flow tangentially into the interior of the inner pipe from the opening of the inner pipe.

JP 2008-215286 A JP 2013-104395 A

In the above exhaust pipe structure, the outer pipe that is not exposed to urea water or the like is made of stainless steel suitable for processing, and the inner pipe that is exposed to urea water or ammonia is made of high corrosion-resistant stainless steel containing a large amount of chromium (Cr). It may be made of Cr stainless steel. When the outer tube and the inner tube made of such dissimilar metals are joined by arc welding or the like using a filler (welding rod), a back bead with a diluted Cr content is formed on the inner peripheral surface of the inner tube by melting. It may be formed in the circumferential direction.

For this reason, for example, the urea water injected into the inner pipe from the urea water injector is hit against the inner peripheral surface of the inner pipe by the swirling flow of the exhaust gas, and the corrosive substance generated in the process of generating ammonia from the urea water is behind it. If it adheres to the bead, there is a problem that the corrosion of the back bead progresses, resulting in deterioration of durability.

The technique of the present disclosure has been made in view of the circumstances described above, and aims to effectively improve the durability of a joint structure between an inner tubular member and an outer tubular member.

The method of the present disclosure includes an inner tube member made of a predetermined metal material, and a metal material different from the metal material having a larger inner tube inner diameter than the inner tube member. When joining the outer tube member surrounding at least a part of the outer periphery and the intermediate member interposed between the inner tube member and the outer tube member and formed of the same metal material as the metal material, the The outer tubular member and the intermediate member are joined by welding, and the inner tubular member and the intermediate member are joined by welding without using a filler material.

In addition, the inner tube member, the intermediate member, and the outer tube member are made of stainless steel, and the inner tube member and the intermediate member have a Cr mass% content higher than that of the outer tube member. High is preferred.

The inner pipe member is an exhaust pipe through which exhaust gas flows, and an injector for injecting urea water into the pipe of the inner pipe member is provided at one end of the inner pipe member in the pipe axis direction, It is preferable that the intermediate member is joined to a portion of the outer peripheral surface of the inner tubular member where the urea water injected from the injector adheres to the inner peripheral side thereof.

A pipe joint structure according to the present disclosure is characterized by being joined by the pipe joining method.

According to the technique of the present disclosure, it is possible to effectively improve durability in the joint structure between the inner tubular member and the outer tubular member.

1 is a schematic overall configuration diagram showing an exhaust system of an engine according to an embodiment; FIG. 1 is a schematic perspective view showing an exhaust post-treatment device according to this embodiment; FIG. FIG. 4 is a schematic cross-sectional view for explaining the joining structure of the second chamber (outer pipe member) and the first connection exhaust pipe (inner pipe member) according to the present embodiment; (A) is a schematic cross-sectional view showing a joint structure according to the present embodiment, and (B) is a schematic cross-sectional view showing a joint structure of a comparative example. It is a flowchart explaining the procedure of the pipe joining method which concerns on this embodiment. It is a schematic diagram which shows the junction structure which concerns on other embodiment.

Hereinafter, a pipe joint method and a pipe joint structure according to this embodiment will be described based on the accompanying drawings. The same parts are given the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[overall structure]
FIG. 1 is a schematic overall configuration diagram showing an exhaust system of an engine 10 according to this embodiment.

As shown in FIG. 1, an engine 10 includes an engine body 11 including a cylinder head, a cylinder block in which a plurality of cylinders are formed, and the like. The cylinder head of the engine main body 11 is provided with an exhaust manifold 12 that collects exhaust gas discharged from each cylinder. An upstream exhaust pipe 13, an exhaust aftertreatment device 20, a downstream exhaust pipe 15, a muffler (not shown), and the like are connected to the exhaust manifold 12 in this order from the exhaust upstream side.

The exhaust aftertreatment device 20 includes, in order from the exhaust upstream side, a front casing 21 , a mixer chamber 50 , an aqueous urea injection device 30 , a connection exhaust pipe 60 , and a rear casing 41 .

Inside the front casing 21, an oxidation catalyst 22 and a filter 23 are housed in this order from the exhaust upstream side.

The oxidation catalyst 22 is formed, for example, by carrying catalyst components and the like on the surface of a ceramic carrier such as a cordierite honeycomb structure. The oxidation catalyst 22 oxidizes the unburned fuel (hydrocarbon: HC) supplied by the post-injection of the engine 10 or the exhaust pipe injection of the exhaust pipe injector (not shown) to raise the temperature of the exhaust gas.

The filter 23 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. . The filter 23 collects the particulate matter (Particulate Matter: hereinafter referred to as PM) in the exhaust gas on the pores and surface of the partition wall, and when the amount of accumulated PM reaches a predetermined amount, the filter is forcedly regenerated to burn and remove it. is carried out.

The mixer chamber 50 has its upstream end connected to the downstream end of the pre-stage casing 21 . Further, the upstream side of the connecting exhaust pipe 60 is inserted and fixed in the mixer chamber 50 . The urea water injector 35 of the urea water injection device 30 is provided at the upstream end of the connecting exhaust pipe 60 , and the urea water injected from the urea water injector 35 is stirred and mixed with the exhaust gas flowing from the mixer chamber 50 . It has become.

The urea water injection device 30 includes a urea water tank 31 that stores urea water, a strainer 32 that is immersed in the urea water in the urea water tank 31 to remove foreign matter, a supply pipe 33 connected to the strainer 32, a supply A urea water pump 34 is provided in the pipe 33 and pumps up the urea water from the urea water tank 31 , and a urea water injector 35 injects the urea water supplied from the supply pipe 33 into the connection exhaust pipe 60 .

The urea water injected from the urea water injector 35 is hydrolyzed by exhaust heat and water vapor in the exhaust gas to produce ammonia (NH3), which is supplied to the downstream SCR catalyst 48 as a reducing agent.

The connection exhaust pipe 60 is formed in a substantially cylindrical shape and connects the mixer chamber 50 and the upstream end of the rear casing 41 . The upstream end of the connection exhaust pipe 60 is inserted and fixed into the mixer chamber 50, into which urea water is injected from the urea water injector 35 in the axial direction.

An SCR catalyst 48 (an example of a reduction catalyst of the present disclosure) is housed inside the rear casing 41 . The SCR catalyst 48 is formed, for example, by supporting zeolite or the like on a porous ceramic carrier. The SCR catalyst 48 adsorbs ammonia supplied as a reducing agent from the urea water injector 35, and selectively reduces and purifies NOx from the passing exhaust gas with the adsorbed ammonia.

[Exhaust aftertreatment device]
FIG. 2 is a perspective view showing the exhaust post-treatment device 20 according to this embodiment.

As shown in FIG. 2, the front casing 21 and the rear casing 41 are cylindrical, arranged in parallel so that their axes are parallel to each other, and are connected by a connection exhaust pipe 60 arranged between them. . The connection exhaust pipe 60 includes a cylindrical first connection exhaust pipe 61 (the inner pipe member of the present disclosure), and the axis of the connection exhaust pipe 61 is parallel to the axes of the front casing 21 and the rear casing 41. is distributed to

The mixer chamber 50 includes a first chamber 51 arranged at the exhaust downstream end of the front casing 21 and having an arcuate side surface, and a second chamber 52 having an arcuate side surface extending from the side surface of the first chamber 51 toward the rear casing 41 side (this chamber is the main chamber). Disclosed outer tubular member). The first chamber 51 is arranged coaxially with the front casing 21 . Also, the diameter of the second chamber 52 is smaller than the diameter of the first chamber 51, and the boundary between the two is curved in an arc shape. Annular flanges are provided at the exhaust downstream end of the front casing 21 and the exhaust upstream end of the first chamber 51, and both flanges are fastened with bolts and nuts.

The connecting exhaust pipe 60 includes a cylindrical first connecting exhaust pipe 61 connected to the second chamber 52 and a second connecting exhaust pipe 62 connecting the first connecting exhaust pipe 61 and the exhaust upstream end of the rear casing 41 . and The first connection exhaust pipe 61 has its upstream end side inserted into the second chamber 52 and is arranged coaxially with the injection axis of the urea water injector 35 .

The second connection exhaust pipe 62 is an elbow pipe, and has a disk-shaped exhaust downstream end. The straight portion of the second connecting exhaust pipe 62 is arranged coaxially with the first connecting exhaust pipe 61, and annular flanges are provided between the exhaust downstream end of the first connecting exhaust pipe 61 and the exhaust upstream end of the second connecting exhaust pipe 62. is provided, and both flanges are fastened with bolts and nuts. Annular flanges are provided at the exhaust downstream end of the second connection exhaust pipe 62 and the exhaust upstream end of the rear casing 41, and both flanges are fastened with bolts and nuts.

The urea water injector 35 is provided at the upstream end of the first connection exhaust pipe 61 inserted and fixed in the second chamber 52 . The injection axis of the urea water injector 35 is aligned with the axial center of the first connecting exhaust pipe 61 , and the urea water injector 35 injects (sprays) the urea water into the first connecting exhaust pipe 61 .

In the first connecting exhaust pipe 61, the urea water injected from the urea water injector 35 and the exhaust gas flowing from the mixer chamber 50 to the rear casing 41 are mixed, and the urea water is hydrolyzed by exhaust heat to produce ammonia (NH3). is generated. The generated ammonia is supplied to the SCR catalyst 48 on the downstream side of the exhaust gas by the exhaust gas flow.

[Joint structure]
FIG. 3 is a schematic cross-sectional view illustrating the joining structure of the second chamber 52 and the first connecting exhaust pipe 61 according to this embodiment. In the following description, the second chamber 52 is simply referred to as the outer pipe member 52 and the first connection exhaust pipe 61 is simply referred to as the inner pipe member 61 .

The outer tube member 52 is formed to have a diameter larger than that of the inner tube member 61, and includes a substantially arc-shaped outer peripheral wall portion 53 surrounding the outer periphery of the inner tube member 61, a first side wall portion 54, and a second side wall portion 55. and

The first side wall portion 54 is provided with a through hole having substantially the same diameter as the outer diameter of the inner pipe member 61, and a first flange portion 56 is formed around the periphery of the through hole. The upstream end side outer periphery of the inner pipe member 61 is joined to the first flange portion 56 by welding or the like.

The second side wall portion 55 is provided with a through hole having a diameter larger than the outer diameter of the inner pipe member 61, and a second flange portion 57 is formed around the periphery of the through hole. The outer periphery of the inner pipe member 61 is welded to the second flange portion 57 via an intermediate member 68 .

The intermediate member 68 has a substantially annular or cylindrical shape, and has an inner diameter that is substantially the same as the outer diameter of the inner pipe member 61 and an outer diameter that is substantially the same as the inner diameter of the second flange portion 57 . diameter. Also, the thickness of the intermediate member 68 is preferably equal to or thicker than the inner tubular member 61 . Further, intermediate member 68 is preferably made of the same metallic material as inner tubular member 61 . The details of these joining methods will be described later.

In this embodiment, the outer pipe member 52 is made of stainless steel containing a standard amount of chromium (Cr), which is used for exhaust system parts, and the outer pipe member 52 can be easily processed into a complicated shape. It is possible.

The inner pipe member 61 is formed in a substantially cylindrical shape, and its upstream opening is closed with a circular lid member 63 . A urea water injector 35 is fixed to the lid member 63 . A substantially rectangular opening 64 for introducing exhaust gas from the outer pipe member 52 is formed in the peripheral wall portion of the inner pipe member 61 positioned between the first side wall portion 54 and the second side wall portion 55 . . Exhaust gas that flows into the opening 64 from a substantially tangential direction flows downstream while spiraling in the inner pipe member 61 in a substantially helical shape. The urea water injector 35 injects urea water toward the spirally swirling exhaust gas.

In this embodiment, the inner tube member 61 is preferably made of high-Cr stainless steel containing a predetermined mass % or more of Cr. As a result, the corrosion resistance of the inner tubular member 61 can be effectively improved against corrosive substances generated in the process of generating ammonia from urea water.

Here, as shown in the comparative example of FIG. 4B, when the second flange portion 570 of the outer tubular member 520 is directly joined to the outer periphery of the inner tubular member 610 by arc welding or the like using a filler, these The melted back bead B may be exposed on the inner peripheral surface of the inner tubular member 610 and formed in the circumferential direction. Since the inner tube member 610 is made of high-Cr stainless steel and the outer tube member 520 is made of stainless steel, the back bead B melted by them has a lower Cr content than the inner tube member 61 . Therefore, when corrosive substances generated from the urea water adhere to the back bead B as the exhaust gas flows, the corrosion of the back bead B progresses, which causes deterioration in durability.

In contrast, in the present embodiment shown in FIG. 4A, the inner tube member 61 and the intermediate member 68 are made of the same high Cr stainless steel. Also, the outer tubular member 52 is made of stainless steel different from the inner tubular member 61 and the intermediate member 68 .

In joining such pipe members together, in the present embodiment, the inner pipe member 61 and the intermediate member 68 formed of the same high Cr stainless steel are joined by non-filler welding without using a filler (welding rod/filler material). Join by (fillerless welding). That is, the weld bead B1 in which the inner pipe member 61 and the intermediate member 68 are melted by non-filler welding is formed from the material of the inner pipe member 61 and the intermediate member 68, and the Cr content value is not diluted. Even if a corrosive substance generated from the urea water adheres to (joint portion), corrosion of the joint portion can be effectively prevented.

Further, in the present embodiment, the inner tube member 61 and the outer tube member 52 made of different metal materials are not directly joined, but an intermediate member 68 is inserted between the members 61 and 52, and these intermediate members 68 and The outer tube member 52 is joined by arc welding or the like using a filler (welding rod). That is, even if the weld bead B2 whose Cr content value is diluted by melting different metal materials and fillers passes through the intermediate member 68 interposed between the members 61 and 52, it is retained within the inner tubular member 61 and is corrosion resistant. It is possible to effectively prevent the weld bead B2, which is inferior in strength, from being exposed on the inner peripheral surface of the inner tubular member 61. As shown in FIG. This makes it possible to effectively improve the durability of the pipe joint.

Further, by making the pipe joint part a three-layer structure of the inner pipe member 61, the intermediate member 68, and the outer pipe member 52, it is possible to effectively improve the structural strength.

As steps of these joining methods, as shown in FIG. 5, a first step (S100) of joining the inner tubular member 61 and the intermediate member 68 by non-filler welding, A second step (S110) of joining by arc welding or the like using a filler (welding rod) may be performed in order. If the outer tubular member 52 is welded after the inner tubular member 61 and the intermediate member 68 are welded in advance, welding can be performed in the same process as before the addition of the intermediate member 68, and workability can be improved.

[others]
It should be noted that the present disclosure is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the gist of the present disclosure.

For example, in the case of a pipe joint structure to which corrosive substances generated from urea water can adhere, as shown in FIG. It is also possible to apply the present disclosure to the pipe joint structure. In this case also, the intermediate member 68 of the present disclosure may be interposed between the outer circumference of the downstream end of the exhaust pipe 80 and the inner circumference of the upstream end of the casing 81 .

In addition, the metal materials forming the inner tube member 61, the intermediate member 68, and the outer tube member 52 are not limited to the above-described embodiments. Other materials can be applied as appropriate, as long as they are different metal materials.

Further, the intermediate member 68 does not have to be substantially annular or cylindrical, and may be a plate member having a curved surface along the outer peripheral surface of the inner tubular member 61 and the inner peripheral surface of the outer tubular member 52. A plurality of them may be arranged side by side.

In addition, the application of the present disclosure is not limited to the exhaust system of the engine 10, and is widely applicable to the joining of ducts in the intake system and EGR (exhaust gas recirculation) system as long as the pipe joint structure is exposed to corrosive substances. It is possible to

REFERENCE SIGNS LIST 10 engine 20 exhaust aftertreatment device 30 aqueous urea injection device 35 aqueous urea injector 41 post-stage casing 48 SCR catalyst (reduction catalyst)
50 mixer chamber 51 first chamber 52 second chamber (outer tubular member)
57 Second flange portion 60 Connection exhaust pipe 61 First connection exhaust pipe (inner pipe member)
64 opening 68 intermediate member

Claims (4)

An inner pipe member made of a predetermined metal material and a metal material different from the metal material having an inner diameter larger than that of the inner pipe member, and at least part of the outer circumference of the inner pipe member When joining the surrounding outer tube member and an intermediate member interposed between the inner tube member and the outer tube member and formed of the same metal material as that of the inner tube member ,
A method for joining pipes, wherein the outer pipe member and the intermediate member are joined by welding, and the inner pipe member and the intermediate member are joined by welding without using a filler material. The inner tube member, the intermediate member, and the outer tube member are made of stainless steel,
2. The pipe joining method according to claim 1, wherein the inner pipe member and the intermediate member have a higher mass % of Cr contained in the members than the outer pipe member. The inner pipe member is an exhaust pipe through which exhaust gas flows,
An injector for injecting urea water into the tube of the inner tube member is provided at one end of the inner tube member in the tube axis direction,
The pipe joining method according to claim 1 or 2, wherein the intermediate member is joined to a portion of the outer peripheral surface of the inner pipe member to which urea water injected from the injector adheres to the inner peripheral side thereof. A pipe joint structure characterized by being joined by the pipe joint method according to any one of claims 1 to 3.

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