Exhaust pipe

Abstract

To provide an exhaust pipe of an internal combustion engine having an addition valve for adding urea water to exhaust gas and having a stepped part in which an inner diameter is reduced downstream of the addition valve, and capable of suppressing progress of corrosion caused by urea.SOLUTION: An exhaust pipe includes: a pipe body including an upstream pipe and a downstream pipe having an outer diameter smaller than that of the upstream pipe and connected to a downstream-side inner peripheral surface of the upstream pipe; an addition valve for adding urea water to exhaust gas in the pipe body; a stepped part located downstream of the addition valve and formed by an upstream-side end surface of the downstream pipe, in which an inner diameter of the pipe body decreases; and a plate-shaped member fixed to an inner peripheral surface of the downstream pipe and extending upstream while forming a gap between the plate-shaped member and the inner peripheral surface of the upstream pipe beyond the stepped part.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an exhaust pipe, and more particularly to an exhaust pipe having an addition valve that adds urea water to exhaust gas from an internal combustion engine. [Background technology]

[0002] Generally, an exhaust purification device is provided in the exhaust path of an internal combustion engine. The exhaust purification device is, for example, an SCR device (selective catalytic reduction device) that purifies nitrogen oxides (NOx) contained in the exhaust. The SCR device purifies the nitrogen oxides by reducing them using ammonia gas. To generate ammonia gas, a urea addition valve is provided in the exhaust path upstream of the SCR device. When urea (specifically, urea water) is added to the exhaust gas by the urea addition valve, ammonia gas is generated by hydrolysis of the urea.

[0003] A dispersion plate may be arranged between the urea addition valve and the SCR device so that urea flows evenly (i.e., in a well-dispersed state) into the upstream end face of the SCR device. For example, in the exhaust pipe structure described in Patent Document 1, a cylindrical member that holds the dispersion plate together with a mixer is arranged inside the exhaust pipe. This exhaust pipe structure suppresses an increase in pressure loss while improving the dispersion of urea (reducing agent) flowing into the SCR device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-84312 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described exhaust pipe structure, the outer peripheral surface of the bracket for fixing the tubular member inside the exhaust pipe is fixed to the inner peripheral surface of the exhaust pipe. Therefore, a "step" is formed at the upstream end of the bracket, where the inner diameter of the exhaust path is reduced by the thickness of the bracket. If urea accumulates in the step, corrosion of the wall surface of the exhaust pipe may progress.

[0006] More specifically, a highly corrosion-resistant material (e.g., stainless steel) is generally used in a section of the exhaust pipe where urea is likely to adhere. However, even if a highly corrosion-resistant material is used, if urea and / or products derived from urea remain in the exhaust pipe for a long period of time, corrosion may occur from the inner circumferential surface of the exhaust pipe, and the corrosion may progress to the outer circumferential surface.

[0007] However, the above exhaust pipe structure does not take into consideration the prevention of corrosion at the stepped portion, and there is room for improvement. The present invention has been devised in view of this point, and an object of the present invention is to provide an exhaust pipe that can suppress the progression of corrosion caused by urea (urea corrosion) in an exhaust pipe formed with a stepped portion. [Means for solving the problem]

[0008] In order to solve the above problems, an exhaust pipe according to a first aspect of the present invention is an exhaust pipe for an internal combustion engine, and comprises a pipe body including an upstream pipe and a downstream pipe having an outer diameter smaller than that of the upstream pipe and connected to the downstream inner circumferential surface of the upstream pipe, an addition valve that adds urea water to the exhaust gas in the pipe body, a step portion that is located downstream of the addition valve and is formed by the upstream end face of the downstream pipe, and that reduces the inner diameter of the pipe body, and a plate-like member that is fixed to the inner circumferential surface of the downstream pipe and extends upstream beyond the step portion while forming a gap between it and the inner circumferential surface of the upstream pipe.

[0009] A second aspect of the present invention is an exhaust pipe according to the first aspect of the present invention, wherein the inner circumferential surface of the downstream pipe is annular, and the plate-like member is provided in one or both of left and right regions of the inner circumferential surface of the downstream pipe that extend from the center of the inner circumferential surface in a horizontal direction perpendicular to the vertical direction.

[0010] A third aspect of the present invention is an exhaust pipe according to the first aspect of the present invention, which has an inner cylindrical portion fixed to the downstream pipe and including blade-shaped portions extending inward, and a gap is formed between the outer peripheral surface of the inner cylindrical portion and the inner peripheral surface of the plate-shaped member. [Effects of the Invention]

[0011] According to the first aspect of the present invention, the movement of urea caused by the exhaust flow near the step is changed by the plate-like member extending upstream beyond the step, which increases the likelihood that the amount of urea remaining in the step will decrease. Therefore, the plate-like member suppresses the progression of urea corrosion in the area where urea would have remained if the plate-like member had not been present.

[0012] In the second aspect of the present invention, the plate-shaped member is disposed in the left and / or right regions of the exhaust pipe. In other words, the plate-shaped member can be disposed at a position corresponding to "a region in the exhaust pipe where urea corrosion would progress as a result of urea rising from the bottom surface due to the exhaust flow in the absence of the plate-shaped member."

[0013] In the third aspect of the present invention, the blade-like portions of the inner cylindrical portion of the pipe diffuse the urea, while a gap is formed between the inner cylindrical portion of the pipe, located inside the plate-like member, and the plate-like member. Because the exhaust gas flows into this gap, a decrease in the flow velocity of the exhaust gas near the plate-like member is suppressed. Therefore, the amount of urea remaining between the inner circumferential surface of the upstream pipe and the outer circumferential surface of the plate-like member is reduced, further increasing the possibility of suppressing the progression of urea corrosion. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram (cross-sectional view) of an internal combustion engine to which an exhaust pipe according to an embodiment is applied. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 2 is a perspective view of a downstream pipe included in the exhaust pipe. [Figure 5] FIG. [Figure 6] FIG. 4 is a schematic diagram showing a movement of urea water on the inner circumferential surface of an upstream pipe included in the exhaust pipe. [Figure 7] 10 is a graph (time chart) showing that the progress of urea corrosion (amount of wall thinning) in an exhaust pipe changes depending on whether or not a plate-shaped member is included in the downstream pipe. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described with reference to Figures 1 to 7. The same symbols (reference numerals) used in the description refer to the same elements having the same functions, although duplicated descriptions will not be given. An exhaust pipe 33 according to this embodiment forms part of an exhaust path in an internal combustion engine 1. The internal combustion engine 1 is mounted on a vehicle (not shown) as a driving force source. The internal combustion engine 1 is a compression-ignition multi-cylinder diesel engine. The internal combustion engine 1 is controlled by an ECU 11 (electronic control unit).

[0016] Intake air is introduced into an engine body 12 of the internal combustion engine 1 (more specifically, a plurality of combustion chambers formed in the engine body 12) via an intake pipe 21, a compressor 13a of the turbocharger 13, an intake pipe 22, and an intake manifold 23. A fuel injection valve 14 is disposed in each combustion chamber. The fuel injection valve 14 injects fuel into the combustion chamber in response to an instruction from the ECU 11 (more specifically, power supply). Combustion gas (exhaust gas) generated in the combustion chamber is discharged via an exhaust manifold 31, an exhaust pipe 32, a turbine 13b of the turbocharger 13, and an exhaust pipe 33.

[0017] The exhaust pipe 33 includes exhaust pipes 33a to 33c. A fuel addition valve 41, a first oxidation catalyst 42, a DPF 43, and a urea addition valve 44 are disposed in the exhaust pipe 33a. The exhaust pipe 33b will be described later. An SCR 45 and a second oxidation catalyst 46 are disposed in the exhaust pipe 33c.

[0018] The first oxidation catalyst 42 is a diesel oxidation catalyst (DOC) that oxidizes and purifies carbon monoxide (CO), hydrocarbons (HC), etc. contained in the exhaust gas. The DPF 43 is a well-known particulate matter trap that collects (traps) particulate matter (PM) contained in the exhaust gas.

[0019] The fuel addition valve 41 injects (adds) fuel in response to an instruction from the ECU 11. The fuel injected from the fuel addition valve 41 flows into the first oxidation catalyst 42 and is oxidized. This causes the temperature of the first oxidation catalyst 42 to rise, and as a result, the exhaust gas that flows out of the first oxidation catalyst 42 and into the DPF 43 becomes hot. This causes the particulate matter trapped in the DPF 43 to be burned away. That is, the fuel injection from the fuel addition valve 41 executes a regeneration process for the DPF 43.

[0020] The urea addition valve 44 injects (adds) urea water to the SCR 45 in response to a command from the ECU 11. The SCR 45 is a selective catalytic reduction device (SCR device, SCR catalyst) that reduces and purifies nitrogen oxides (NOx) contained in the exhaust gas using ammonia gas produced by hydrolysis of the urea water injected from the urea addition valve 44. The second oxidation catalyst 46 oxidizes and purifies the residual ammonia gas discharged from the SCR 45.

[0021] The EGR pipe 51 connects the exhaust pipe 32 and the intake pipe 22. Therefore, a portion of the exhaust gas discharged from the combustion chamber flows (recirculates) into the combustion chamber as EGR gas. The EGR valve 52 is disposed in the EGR pipe 51. The EGR valve 52 adjusts the EGR opening degree Er, which is the opening degree of the EGR pipe 51, in response to a command from the ECU 11. That is, the ECU 11 controls the EGR valve 52, thereby adjusting the amount of recirculated EGR gas.

[0022] A throttle valve 53 is disposed in the intake pipe 22. The throttle valve 53 adjusts the throttle valve opening Tr, which is the opening of the intake pipe 22, in response to instructions from the ECU 11. That is, the ECU 11 controls the throttle valve 53, thereby adjusting the amount of fresh air flowing into the combustion chamber.

[0023] The ECU 11 is an electronic control unit including a CPU, ROM, RAM, and EEPROM. The CPU sequentially executes a predetermined program to read data, perform numerical calculations, and output the calculation results. The ROM stores the programs executed by the CPU and maps (look-up tables), etc. The RAM temporarily stores data referenced by the CPU. The EEPROM stores data referenced by the CPU and furthermore, retains the stored data even when the ECU 11 stops operating.

[0024] The exhaust pipe 33b will now be described. The exhaust pipe 33b is disposed between the urea addition valve 44 and the SCR 45 (see FIG. 1). The urea addition valve 44 injects urea water toward the exhaust pipe 33b (see FIG. 2). The exhaust pipe 33b disperses (diffuses) the urea water added by the urea addition valve 44. That is, the presence of the exhaust pipe 33b makes the concentration distribution of urea (liquid or gaseous) contained in the exhaust gas flowing into the SCR 45 more uniform. The exhaust pipe 33b is also referred to as a urea dispersion plate or a urea dispersion device.

[0025] In the following description, the direction opposite to the exhaust flow in the exhaust pipe 33 is also referred to as the "upstream side." In addition, the radial direction of the exhaust pipe 33b (more specifically, the cylindrical portion 61 described below) and the direction toward the central axis line (not shown) of the exhaust pipe 33b is also referred to as the "inner side."

[0026] The exhaust pipe 33b includes an outer pipe 6, an outer cylindrical portion 7, an inner cylindrical portion 8, and a plate-like member 9 (see FIG. 5 in particular). The outer pipe 6 includes a cylindrical portion 61 and three tabs 62-64 (claw-like portions). The outer peripheral surface of the cylindrical portion 61 at its upstream end is joined to the inner peripheral surface (downstream inner peripheral surface) at the downstream end of the exhaust pipe 33a (see FIGS. 2-3 and 6). The outer peripheral surface of the cylindrical portion 61 at its downstream end is joined to the inner peripheral surface at the upstream end of the exhaust pipe 33c (see FIGS. 2 and 6). The cylindrical portion 61 is joined to the exhaust pipes 33a and 33c by welding. The cylindrical portion 61, together with the exhaust pipes 33a and 33c, forms the exhaust path of the internal combustion engine 1. More specifically, as can be seen from FIG. 5, the inner peripheral surface of the cylindrical portion 61 (i.e., the outer pipe 6) is annular. Therefore, a substantially cylindrical exhaust path is formed by the downstream portion of the exhaust pipe 33a, the outer pipe 6, and the upstream portion of the exhaust pipe 33c.

[0027] For convenience, the exhaust pipe 33a is also referred to as the "upstream pipe." The outer pipe 6 connected to the downstream inner circumferential surface of the exhaust pipe 33a is also referred to as the "downstream pipe." As shown in Figures 2 and 3, the outer diameter of the exhaust pipe 33b is smaller than that of the exhaust pipe 33a. For convenience, the exhaust pipe 33a and the outer pipe 6 are also collectively referred to as the "pipe body."

[0028] Furthermore, because the inner diameter of the cylindrical portion 61 is smaller than the inner diameter of the exhaust pipe 33a, a step Ga is formed at the upstream end of the cylindrical portion 61, where the inner diameter of the exhaust path is reduced (see FIG. 6). More specifically, the step Ga is formed by the upstream end face 61a of the cylindrical portion 61 (see FIGS. 4 and 5). That is, at the step Ga, the inner diameter of the exhaust path is reduced by the plate thickness of the cylindrical portion 61 (particularly, the upstream end face 61a). Note that the reference numerals for the upstream end face 61a and the step Ga are omitted in FIG. 3.

[0029] The tabs 62 to 64 each include a joint portion 62a to 64a extending upstream and inward relative to the cylindrical portion 61 (see FIG. 5). In particular, the joint portion 64a extends further in the circumferential direction. That is, the joint portion 64a is wider than the joint portions 62a to 63a.

[0030] As shown in FIG. 5, the outer tubular portion 7 includes outer tubular members 71-72. Each of the outer tubular members 71-72 includes an outer cylindrical portion 7a and four downstream fins 7b (wing-shaped portions). Each of the outer tubular members 71-72 is formed by bending a plate material. More specifically, the outer cylindrical portions 7a of the outer tubular members 71-72 form a substantially cylindrical shape. That is, the outer tubular portion 7 has a half-split structure (divided structure) including the outer tubular members 71-72. Each of the downstream fins 7b of the outer tubular members 71-72 is bent inward in a stepwise manner (see FIG. 3). Note that only a portion of the downstream fins 7b is shown in FIGS. 3 and 5.

[0031] The outer tubular portion 7 is fixed to the outer pipe 6 by welding. More specifically, as can be seen from Figures 4 and 5, the inner circumferential surface of the joint portion 62a of the tab 62 is joined to the outer circumferential surface of the outer tubular member 71. The inner circumferential surface of the joint portion 63a of the tab 63 is joined to the outer circumferential surface of the outer tubular member 72. The inner circumferential surface of the joint portion 64a of the tab 64 is joined to the outer circumferential surfaces of the outer tubular members 71 and 72. Gaps 7c1 and 7c2 are formed between the outer tubular member 71 and the outer tubular member 72. For convenience, the outer tubular portion 7 is also referred to as the "inner-pipe cylindrical portion."

[0032] As shown in FIG. 5, the inner cylindrical portion 8 includes an inner cylindrical portion 8a and three upstream fins 8b (wing-shaped portions). The inner cylindrical portion 8 is formed by bending a plate material. More specifically, the inner cylindrical portion 8a is formed into a substantially cylindrical shape. Each of the upstream fins 8b is bent inward in a stepwise manner. The inner cylindrical portion 8 is fixed to the outer cylindrical portion 7 by welding. More specifically, the outer peripheral surface of the inner cylindrical portion 8a is joined to the inner peripheral surfaces of the outer cylindrical portions 7a of the outer cylindrical members 71-72.

[0033] 5, the plate-shaped member 9 includes a base portion 9a extending in the circumferential direction and an upstream extending portion 9b extending upstream from the base portion 9a. The plate-shaped member 9 is fixed to the outer pipe 6 by welding. More specifically, the outer peripheral surface of the downstream region of the base portion 9a is joined to the inner peripheral surface of the outer pipe 6.

[0034] 3, the plate-like member 9 is disposed on the right side surface of the exhaust pipe 33b (i.e., the right region of the top, bottom, left, and right regions of the exhaust pipe 33b). In other words, the plate-like member 9 is disposed in a region extending rightward from the center of the inner circumferential surface of the outer pipe 6 (i.e., the axis of the exhaust path formed by the inner circumferential surface of the cylindrical portion 61). Here, the rightward direction can also be said to be one of the horizontal directions (i.e., the left-right direction) perpendicular to the vertical direction.

[0035] In addition, the plate-shaped member 9 extends upstream beyond the upstream end face 61a (i.e., the step portion Ga). Furthermore, as can be seen from FIGS. 4 and 5, the upstream extension portion 9b faces the gap 7c1 associated with the outer tubular portion 7. In addition, as shown in FIG. 3, a gap 9c is formed between the inner circumferential surface of the plate-shaped member 9 and the outer circumferential surface of the outer tubular portion 7. As will be described later, by including the plate-shaped member 9 in the exhaust pipe 33b, urea corrosion in the exhaust pipe 33 is suppressed.

[0036] As described above, the urea addition valve 44 injects urea water into the SCR 45. The urea water injected by the urea addition valve 44 flows into the exhaust pipe 33b and then into the SCR 45. Because the tips of the upstream fins 8b extend to the vicinity of the central axis of the exhaust pipe 33a, most of the urea water injected from the urea addition valve 44 along this central axis collides with the upstream fins 8b and is dispersed. That is, atomization and vaporization of the urea water are promoted. Furthermore, the downstream fins 7b disperse (agitate) the exhaust gas containing urea. As a result, the concentration distribution of urea contained in the exhaust gas flowing into the SCR 45 becomes more uniform.

[0037] The exhaust pipe 33a, the outer pipe 6, the exhaust pipe 33c, etc. are made of a highly corrosion-resistant material (a corrosion-resistant material, for example, stainless steel) to prevent corrosion caused by adhesion of urea (or urea-derived products such as biuret and cyanuric acid). However, the inventors have noticed that even if the exhaust pipe 33a is made of a corrosion-resistant material, corrosion by urea (urea corrosion) may occur at the above-mentioned step portion Ga.

[0038] 3 and 6 (i.e., the area near the stepped portion Ga in the exhaust pipe 33a and located on the right side) if the exhaust pipe 33b does not have the plate-shaped member 9. In other words, in the exhaust pipe 33, the area Rc in the exhaust pipe 33a (and the area near the area Rc in the exhaust pipe 33b) is the location where urea corrosion progresses most rapidly if the exhaust pipe 33b does not have the plate-shaped member 9.

[0039] The dashed line La in Fig. 7 shows the results of an experiment that measured the progress of urea corrosion in the region Rc when the exhaust pipe 33b does not have the plate-like member 9. The dashed line La indicates the amount of wall thinning Ca in the region Rc of the exhaust pipe 33a when the amount of urea added (g / hour) by the urea addition valve 44, the flow rate (g / second) of exhaust gas flowing into the exhaust pipe 33b, and the temperature (°C) continue to be predetermined values ​​(i.e., predetermined measured values ​​that represent specific operating states of the internal combustion engine 1). The predetermined measured values ​​are set to correspond to the respective parameters (e.g., the amount of fuel injected by the fuel injection valve 14, the EGR opening degree Er, and the throttle valve opening degree Tr) when the internal combustion engine 1 is operating at a high load and a high rotation speed.

[0040] As can be seen from the dashed line La, the amount of metal loss Ca increases as the elapsed time Tp from the reference time t0 increases. In other words, urea corrosion progresses as the internal combustion engine 1 continues to operate. In addition, when the amount of metal loss Ca exceeds the thickness cf at the elapsed time t1a, the rate of increase in the amount of metal loss Ca (i.e., the slope of the dashed line La) increases. The thickness cf is equal to the thickness of the film formed on the surface of the material (i.e., the corrosion-resistant material) that constitutes the exhaust pipe 33a. In other words, when the film on the exhaust pipe 33a is lost due to urea corrosion of the exhaust pipe 33a, the rate of progress of urea corrosion increases. Thereafter, the amount of metal loss Ca reaches the thickness ct of the exhaust pipe 33a at the elapsed time t2a. In other words, a hole is formed in the exhaust pipe 33a due to urea corrosion.

[0041] The holes formed in the exhaust pipe 33a are located on the right side of the exhaust pipe 33a (i.e., in the region Rc). The reason why the holes are formed on the side (rather than below) the exhaust pipe 33a is considered as follows. Each of the dashed arrows shown in FIG. 6 represents the manner in which the urea water moves on the inner circumferential surface of the exhaust pipe 33a when the exhaust pipe 33b does not have the plate-like member 9 and the predetermined measurement value is achieved in the internal combustion engine 1. The manner in which the urea water moves represented by the dashed arrows in FIG. 6 is based on fluid analysis (specifically, CFD simulation).

[0042] More specifically, a portion of the urea water injected from the urea addition valve 44 accumulates on the bottom surface of the exhaust pipe 33a (i.e., the inner circumferential surface on the vertically lower side of the exhaust pipe 33a). The portion of the urea water that accumulates on the bottom surface of the exhaust pipe 33a moves on the inner circumferential surface of the exhaust pipe 33a due to the exhaust flow and reaches a position corresponding to the region Rc, causing urea corrosion.

[0043] More specifically, the urea water accumulated on the bottom surface of the exhaust pipe 33a dissolves water contained in the exhaust gas. As the urea water rises along the inner circumferential surface, the water evaporates, increasing the urea concentration. The urea water reaches the region Rc with an increased urea concentration, and as a result, urea corrosion progresses in the region Rc. In the region above the region Rc on the inner circumferential surface of the exhaust pipe 33a (the upper region), the urea concentration further increases, but the amount of urea water reaching the upper region decreases (compared to the region Rc). Therefore, urea corrosion progresses faster in the region Rc than in the regions below or above the region Rc.

[0044] On the other hand, the results of an experiment measuring the progress of urea corrosion in the region Rc when the exhaust pipe 33b has the plate-like member 9 are shown by the solid line Lb in Fig. 7. Similar to the dashed line La, the solid line Lb indicates the amount of wall thinning Ca in the region Rc of the exhaust pipe 33a when the state in which the predetermined measurement value is achieved in the internal combustion engine 1 continues.

[0045] As can be seen from the solid line Lb, when the amount of metal loss Ca exceeds the thickness cf at elapsed time t1b (longer than elapsed time t1a), the rate of increase in the amount of metal loss Ca increases. Thereafter, at elapsed time t2b (longer than elapsed time t2a), the amount of metal loss Ca reaches the thickness ct. In other words, the exhaust pipe 33b has the plate-shaped member 9, which suppresses the increase in the amount of metal loss Ca. In other words, the rate of progression of urea corrosion decreases.

[0046] More specifically, each of the solid arrows shown in Fig. 6 represents the manner in which the urea water moves on the inner circumferential surface of the exhaust pipe 33a when the exhaust pipe 33b has the plate-shaped member 9 and the predetermined measurement value is achieved in the internal combustion engine 1. As can be seen from Fig. 6, the amount of urea water that reaches the region Rc is reduced because the exhaust pipe 33b has the plate-shaped member 9. This is thought to suppress the progress of urea corrosion in the region Rc.

[0047] As described above, according to the exhaust pipe 33 (particularly, the exhaust pipe 33b including the plate-like member 9), the movement of the urea water in the exhaust pipe 33a is changed by the plate-like member 9 having the upstream extending portion 9b. This increases the possibility of suppressing the progression of corrosion caused by the urea water injected from the urea addition valve 44 (particularly, corrosion in the region Rc near the step portion Ga in the exhaust pipe 33a).

[0048] In addition, exhaust gas containing urea water flows into a gap 9c formed on the inner peripheral surface of the plate-shaped member 9. If the inner peripheral surface of the plate-shaped member 9 were also joined to the outer peripheral surface of the outer cylinder portion 7, the flow velocity of the exhaust gas in the vicinity of the plate-shaped member 9 would decrease, increasing the likelihood that an increase in urea water would flow between the outer peripheral surface of the plate-shaped member 9 and the inner peripheral surface of the outer pipe 6. That is, in this case, urea corrosion in the region Rc may be more likely to progress.

[0049] Furthermore, if an attempt were made to suppress the progression of urea corrosion by tightly bonding a member to the inner circumferential surface of the exhaust pipe 33a corresponding to the region Rc, the member would need to have even higher corrosion resistance than the members that make up the exhaust pipe 33a, which could result in technical or cost difficulties. However, the plate-like member 9 according to this embodiment has the effect of changing the movement of the urea water without being in close contact with the inner circumferential surface of the exhaust pipe 33a, so that measures to suppress urea corrosion can be taken relatively easily.

[0050] Although the embodiments of the present invention have been described above with reference to the above structures, many modifications, improvements, and variations are possible without departing from the scope of the present invention. Therefore, the present invention includes all modifications, improvements, and variations that do not depart from the spirit and scope of the appended claims. The present invention is not limited to the specific structures described above, and modifications such as those described below are possible.

[0051] The plate-shaped member 9 was disposed on the right side surface of the exhaust pipe 33b. Additionally or alternatively, the plate-shaped member 9 may be disposed on the left side surface of the exhaust pipe 33b. That is, the position at which the plate-shaped member 9 is disposed can be adapted depending on the region where urea corrosion would progress if the plate-shaped member 9 were not present.

[0052] The outer cylindrical portion 7a of the outer cylinder 7 is made up of outer cylinder members 71 and 72 (i.e., two members) having a half-split structure. Alternatively, the outer cylindrical portion 7a may be made up of a single member. [Explanation of symbols]

[0053] 1...internal combustion engine, 11...ECU, 12...engine body 13... turbocharger, 13a... compressor, 13b... turbine, 14... fuel injection valve 21~22...Intake pipe 23...intake manifold, 31...exhaust manifold 32~33, 33a~33c...Exhaust pipe 41...fuel addition valve, 42...first oxidation catalyst, 43...DPF 44...Urea addition valve, 45...SCR, 46...Second oxidation catalyst 51...EGR pipe, 52...EGR valve, 53...throttle valve 6...Outer tube 61... cylindrical portion, 61a... upstream end surface, 62 to 64... tabs, 62a to 64a... joint portions 7...Outer cylinder 7a... outer cylindrical portion, 7b... downstream fin, 7c1 to 7c2... gap, 71 to 72... outer cylindrical member 8...inner cylindrical portion, 8a...inner cylindrical portion, 8b...upstream fin 9...plate-shaped member, 9a...base portion, 9b...upstream extension portion, 9c...gap Ga: step, Rc: region

Claims

1. An exhaust pipe of an internal combustion engine, a pipe body including an upstream pipe and a downstream pipe having an outer diameter smaller than that of the upstream pipe and connected to a downstream side inner circumferential surface of the upstream pipe; an addition valve that adds urea water to the exhaust gas in the pipe body; a step portion, which is located downstream of the addition valve and is formed by an upstream end surface of the downstream pipe, and in which the inner diameter of the pipe body is reduced; a plate-shaped member fixed to the inner peripheral surface of the downstream pipe and extending upstream beyond the step portion while forming a gap between the plate-shaped member and the inner peripheral surface of the upstream pipe.

2. 2. The exhaust pipe according to claim 1, an inner circumferential surface of the downstream pipe is annular, and the plate-like member is provided in one or both of left and right regions of the inner circumferential surface of the downstream pipe that extend from the center of the inner circumferential surface in a horizontal direction perpendicular to the vertical direction.

3. 2. The exhaust pipe according to claim 1, a cylindrical portion fixed to the downstream pipe and including an inwardly extending vane-like portion; An exhaust pipe, wherein a gap is formed between an outer peripheral surface of the inner cylindrical portion and an inner peripheral surface of the plate-like member.

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