Exhaust pipe structure

Abstract

To provide an exhaust pipe structure capable of promoting the vaporization of a reductant introduced into an exhaust pipe.SOLUTION: An exhaust pipe structure 1 to be connected to an internal combustion engine of a vehicle includes an exhaust pipe 10, an injector 50 for introducing a reductant into the exhaust pipe 10, and a dispersion plate 25 arranged in the exhaust pipe 10 on the downstream side of the injector 50. At least a portion of the exhaust pipe 10 including the downstream side of the dispersion plate 25 is a multiplex structure area P with an inner pipe 95, and an outer pipe 96 covering the inner pipe 95 to form a clearance area S6 between the inner pipe 95 and itself. The multiplex structure area P is provided with a lead-in part 98 for leading part of exhaust gas circulating in the inner pipe 95 into the clearance area S6.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to an exhaust pipe structure. [Background technology]

[0002] An example of a conventional exhaust pipe structure is an exhaust purification device for an internal combustion engine described in Patent Document 1. This conventional exhaust purification device includes an exhaust pipe, a selective reduction type NOx catalyst provided in the exhaust pipe via a support member, and a reducing agent addition valve arranged in the exhaust pipe upstream of the NOx catalyst. The exhaust pipe has a bent portion between the addition valve and the NOx catalyst to block the reducing agent added from the addition valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-167843 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional exhaust purification device, it is intended that the reducing agent blocked at the bent portion is evaporated by the high-temperature exhaust gas when the internal combustion engine is in a high-load operating state. However, in reality, it is considered that the temperature of the exhaust gas does not rise to the intended temperature, and the reducing agent blocked at the bent portion subsequently reaches the NOx catalyst in a mist state.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an exhaust pipe structure that can promote evaporation of a reducing agent introduced into the exhaust pipe. [Means for solving the problem]

[0006] An exhaust pipe structure according to one aspect of the present disclosure is an exhaust pipe structure connected to an internal combustion engine of a vehicle, and includes an exhaust pipe, an injector that introduces a reducing agent into the exhaust pipe, and a dispersion plate arranged downstream of the injector in the exhaust pipe, wherein a portion of the exhaust pipe including at least the downstream side of the dispersion plate is a multi-layered structure portion consisting of an inner pipe and an outer pipe that covers the inner pipe so that a gap portion is formed between the inner pipe and an outer pipe, and the multi-layered structure portion is provided with an intake portion that draws a portion of the exhaust gas flowing through the inner pipe into the gap portion.

[0007] In this exhaust pipe structure, the reducing agent introduced into the exhaust pipe from the injector is diffused into the exhaust gas by the dispersion plate. At this time, the reducing agent that has passed through the dispersion plate without being gasified is evaporated by the exhaust pipe heated by the exhaust gas. In this exhaust pipe structure, at least a portion including a downstream side of the dispersion plate is a multi-layered structure portion consisting of an inner pipe and an outer pipe that covers the inner pipe so that a gap portion is formed between the inner pipe and the outer pipe. In addition, the multi-layered structure portion is provided with a drawing portion that draws a part of the exhaust gas flowing through the inner pipe into the gap portion. The multi-layered structure of the exhaust pipe increases the insulation of the exhaust pipe, and further, the drawing portion draws the exhaust gas into the gap portion between the inner pipe and the outer pipe, so that the temperature of the inner pipe that the reducing agent touches is maintained at a high temperature. This can promote evaporation of the reducing agent. Promotion of evaporation of the reducing agent prevents the reducing agent in a mist state from reaching the NOx catalyst, and can suppress the occurrence of problems such as peeling of the catalyst coating.

[0008] The gap portion may be a closed space upstream of the multi-layered structure portion, and the inlet portion may be provided downstream of the multi-layered structure portion. In this case, a portion of the exhaust gas flowing through the inner pipe is drawn from the downstream side to the upstream side of the multi-layered structure portion by the inlet portion. Therefore, it is possible to prevent the inlet portion from obstructing the flow of the exhaust gas.

[0009] The intake section is configured by terminating the downstream portion of the inner pipe upstream of the downstream portion of the outer pipe, and the downstream portion of the outer pipe may have a smaller diameter than the main portion of the outer pipe. In this case, the smaller diameter portion of the outer pipe functions as a guide when drawing the exhaust gas into the gap. Therefore, it is possible to draw the exhaust gas into the gap efficiently.

[0010] A wire mesh may be disposed in the gap. In this case, the wire mesh can enhance the heat retention effect of the exhaust gas in the gap, thereby more effectively promoting the evaporation of the reducing agent.

[0011] The thickness of the inner pipe may be smaller than that of the outer pipe. By making the thickness of the inner pipe smaller than that of the outer pipe, the heat capacity of the inner pipe is suppressed. Therefore, the heat of the exhaust gas is less likely to be taken away by the inner pipe, and the temperature of the inner pipe is easily increased by the exhaust gas, so that the evaporation of the reducing agent captured at the bent portion can be more effectively promoted. In addition, by making the thickness of the outer pipe larger than that of the inner pipe, the strength of the exhaust pipe can be sufficiently secured.

[0012] The exhaust pipe may have a bent portion that captures the reducing agent downstream of the dispersion plate, and at least the portion including the bent portion may be a multi-layered structure portion. In this case, the reducing agent that has passed through the dispersion plate without being gasified can be captured by the bent portion. The reducing agent captured by the bent portion comes into contact with the inner pipe that is maintained at a high temperature by the exhaust gas drawn into the gap, and the evaporation of the reducing agent can be more effectively promoted.

[0013] The bent portion may have an arched shape with one side of the pipe protruding and the other side recessed, and the amount of protrusion of the bent portion may be equal to or less than the diameter of the exhaust pipe. With this configuration, the degree of curvature of the exhaust pipe at the bent portion is gentle. The gentle degree of curvature at the bent portion makes it possible to avoid an increase in pressure loss in the exhaust pipe. In addition, when the exhaust pipe structure is mounted on a vehicle, it is possible to avoid the exhaust pipe interfering with other components on the vehicle.

[0014] A heat insulator that covers the outer pipe may be provided at least in a portion of the exhaust pipe that includes the bent portion. This further improves the heat insulation of the exhaust pipe, making it easier to maintain the temperature of the inner pipe at a high temperature. This further ensures that the evaporation of the reducing agent captured by the bent portion can be promoted. Effect of the Invention

[0015] According to the present disclosure, evaporation of the reducing agent introduced into the exhaust pipe can be promoted. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a side view showing the upstream side of the exhaust pipe structure according to the embodiment of the present disclosure. [Diagram 2] 2 is a perspective view showing the downstream side of the exhaust pipe structure shown in FIG. 1. [Diagram 3] FIG. 4 is an enlarged perspective view showing the exhaust pipe structure in the vicinity of the dispersion plate. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 4 is a partial cross-sectional view showing the exhaust pipe structure in the vicinity of a bent portion. [Figure 6] FIG. 4 is a partial cross-sectional view showing an exhaust pipe structure upstream of a bent portion. [Figure 7] FIG. 4 is a partial cross-sectional view showing the exhaust pipe structure downstream of a bent portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A preferred embodiment of an exhaust pipe structure according to one aspect of the present disclosure will be described in detail below with reference to the drawings. For ease of explanation, the terms "upper" and "lower" are used below based on the state in which the exhaust pipe is attached to the vehicle. In addition, the terms "upper" and "downstream" are used below based on the flow direction of exhaust gas in the exhaust pipe.

[0018] FIG. 1 is a side view showing the upstream side of an exhaust pipe structure according to an embodiment of the present disclosure. FIG. 2 is a perspective view showing the downstream side of the exhaust pipe structure shown in FIG. 1. As shown in FIGS. 1 and 2, the exhaust pipe structure 1 is a structure in which an exhaust pipe 10 is insulated by a first heat insulator 20 and a second heat insulator 30. As shown in FIG. 1, the exhaust pipe 10 has a protruding region 19 that protrudes vertically downward due to bending or swelling of the exhaust pipe 10. The first heat insulator 20 is disposed so as to cover the exhaust pipe 10 upstream of the protruding region 19. The second heat insulator 30 is disposed so as to cover the exhaust pipe 10 downstream of the protruding region 19.

[0019] The exhaust pipe 10 is connected to an internal combustion engine mounted on a vehicle, and constitutes an exhaust passage that discharges exhaust gas generated by combustion in a combustion chamber of the internal combustion engine. When connected to the internal combustion engine, the exhaust pipe 10 extends, for example, along the front-rear direction of the vehicle. An example of the internal combustion engine is a diesel engine. Examples of vehicles to which the exhaust pipe structure 1 is applied include passenger cars, pickup trucks, buses, dump trucks, and the like.

[0020] On the upstream side of the exhaust pipe 10, for example, a turbocharger, a DOC (Diesel Oxidation Catalyst), a DPF (Diesel Particulate Filter), etc. are provided. On the downstream side of the exhaust pipe 10, for example, an SCR (Selective Catalytic Reduction) is provided. In the example of FIG. 1, an injector 50 for injecting a reducing agent (e.g., urea water) into the SCR is disposed in the exhaust pipe 10. The injector 50 is attached to a wall of the exhaust pipe 10 so as to face the upstream side of the exhaust pipe 10.

[0021] As shown in Fig. 1, a connection part 11 and bent parts 12, 13, and 14 are provided on the upstream side of the exhaust pipe 10. Another exhaust pipe arranged on the upstream side (internal combustion engine side) of the exhaust pipe 10 is connected to the connection part 11. A straight part 15 extending from the connection part 11 is inclined downward toward the injector 50 in accordance with the piping path of the upstream exhaust pipe. The bent part 12 bends the exhaust pipe 10 such that the downward inclination of a straight part 16 extending downstream from the bent part 12 is smaller than the downward inclination of the straight part 15. The extension direction of the straight part 15 downstream of the bent part 12 is more aligned with the direction of the injector 50 than the straight part 15.

[0022] The bent portion 13 is provided near the base end of the injector 50. The bent portion 13 bends the exhaust pipe 10 so that the downward inclination of a straight portion 17 downstream of the bent portion 13 is greater than the downward inclination of the straight portion 16. The straight portion 17 downstream of the bent portion 13 extends downward toward the attachment position of the injector 50. The bent portion 14 bends the exhaust pipe 10 immediately downstream of the bent portion 13 so that the straight portion 18 downstream of the injector 50 extends generally along the axial direction of the injector 50. The straight portion 18 downstream of the injector 50 extends at a slight upward inclination with respect to the horizontal plane.

[0023] These bent portions 12, 13, and 14 allow the piping path of the exhaust pipe 10 to avoid interference with, for example, the lower structure of the vehicle (such as a cross member of the suspension). Also, by using an injector 50 attached so as to inject the reducing agent toward the rear of the vehicle, the reducing agent can be injected downstream inside the exhaust pipe 10.

[0024] The exhaust pipe 10 has a protruding region 19 that protrudes due to bending of the bent portion 14. That is, in the exhaust pipe 10, a certain range downstream of the bent portion 14 becomes the protruding region 19 that is formed by bending the bent portion 14. As an example, the protruding region 19 is a region that includes the point located vertically most downward (the point with the smallest height above ground) in the exhaust passage including the exhaust pipe 10. In the protruding region 19, a dispersion plate 25 is arranged inside the exhaust pipe 10.

[0025] The dispersion plate 25 has a plurality of fins 25a that swirl the exhaust gas flowing inside the exhaust pipe 10 in the circumferential direction. The dispersion plate 25 is disposed inside the exhaust pipe 10 so as to face the injector 50. The dispersion plate 25 has a function of suppressing variations in the exhaust oxygen concentration inside the exhaust pipe 10, as well as a function of stirring and mixing the reducing agent introduced from the injector 50 into the exhaust pipe 10 with the exhaust gas.

[0026] As shown in FIG. 2, a connection portion 80 (see FIG. 7) and bent portions 81 and 82 are provided on the downstream side of the exhaust pipe 10. The connection portion 80 is a portion that is connected to the SCR described above. A flange 84 used for connection to the SCR is provided on the outer periphery of the connection portion 80. The bent portions 81 and 82 are portions that capture the reducing agent downstream of the dispersion plate 25. The bent portion 81 bends the exhaust pipe 10 so that the upward inclination of a straight portion 85 extending downstream of the bent portion 81 is greater than the upward inclination of the straight portion 18.

[0027] At bent portion 82, the inclination direction of straight portion 86 extending downstream of bent portion 82 is reversed relative to straight portion 85. That is, at the position of bent portion 82, exhaust pipe 10 forms an arch shape with one side of exhaust pipe 10 protruding and the other side recessed. The inclination angle of straight portion 86 with respect to straight portion 18 and the inclination angle of straight portion 86 with respect to straight portion 18 may be equal to each other or may be different from each other.

[0028] FIG. 3 is an enlarged perspective view showing the exhaust pipe structure in the vicinity of the dispersion plate. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3. As shown in FIG. 3 and FIG. 4, the first heat insulator 20 has a pair of heat shield plates 21, 22 provided along the outer surface of the exhaust pipe 10 upstream of the protruding region 19. The second heat insulator 30 has a pair of heat shield plates 31, 32 provided along the outer surface of the exhaust pipe 10 downstream of the protruding region 19. The first heat insulator 20 has a left-right split structure with the heat shield plates 21, 22 when viewed from the axial direction of the exhaust pipe 10. Similarly, the second heat insulator 30 has a left-right split structure with the heat shield plates 31, 32 when viewed from the axial direction of the exhaust pipe 10.

[0029] The heat shield 21 is disposed on one side in the horizontal direction of the first heat insulator 20. The heat shield 22 is disposed on the other side in the horizontal direction of the first heat insulator 20. The heat shield 31 is disposed on one side in the horizontal direction of the second heat insulator 30. The heat shield 32 is disposed on the other side in the horizontal direction of the second heat insulator 30. The heat shields 21, 22, 31, and 32 are formed, for example, by pressing or the like, and each has a substantially semicircular cross section. The heat shields 21, 22, 31, and 32 can be made of, for example, stainless steel or the like.

[0030] Each of the pair of heat shield plates 21, 22 constituting the first heat insulator 20 includes arc portions 21a, 22a, lower end portions 21b, 22b, and upper end portions 21c, 22c. The overlapping portions of the lower end portions 21b, 22b are joined together, and the overlapping portions of the upper end portions 21c, 22c are joined together, so that the first heat insulator 20 is formed into a cylindrical shape. The lower end portions 21b, 22b and the upper end portions 21c, 22c are joined together by spot welding or the like, for example, at joining positions that take into consideration vibration suppression of the entire first heat insulator 20.

[0031] Each of the pair of heat shield plates 31, 32 constituting the second heat insulator 30 includes arc portions 31a, 32a, lower end portions 31b, 32b, and upper end portions 31c, 32c. The second heat insulator 30 is formed into a cylindrical shape by joining the overlapping portions of the lower end portions 31b, 32b and the upper end portions 31c, 32c together. The lower end portions 31b, 32b and the upper end portions 31c, 32c are joined by spot welding or the like at joining positions that take into consideration the overall vibration suppression of the second heat insulator 30.

[0032] The downstream end 20a of the first heat insulator 20 and the upstream end 30a of the second heat insulator 30 have an overlapping portion R such that gaps S3, S4 are formed along the circumferential direction of the exhaust pipe 10 and communicate with the outside. In this embodiment, the overlapping portion R is located downstream of the dispersion plate 25. Also, in this embodiment, the upstream end 30a of the second heat insulator 30 has an expanded diameter at the overlapping portion R and is disposed so as to be on the outer side in the radial direction of the exhaust pipe 10 relative to the downstream end 20a of the first heat insulator 20.

[0033] As shown in FIG. 4, in the overlapping portion R, the pair of heat shield plates 21, 22 are provided with step portions 23, 24 that bulge outward in the radial direction. The step portion 23 of the heat shield plate 21 is formed by one bent portion provided between the arc portion 21a and the lower end portion 21b, and one bent portion provided between the arc portion 21a and the upper end portion 21c. The step portion 24 of the heat shield plate 22 is formed by one bent portion provided between the arc portion 22a and the lower end portion 22b, and one bent portion provided between the arc portion 22a and the upper end portion 22c. As a result, between the first heat insulator 20 and the exhaust pipe 10, a gap portion S1 located between the step portions 23, 24 on the lower end portions 21b, 22b side and the exhaust pipe 10, and a gap portion S2 located between the step portions 23, 24 on the upper end portions 21c, 22c side and the exhaust pipe 10 are formed.

[0034] As shown in Fig. 4, in the overlapping portion R, the pair of heat shield plates 31, 32 are provided with stepped portions 33, 34 that bulge outward in the radial direction. The stepped portion 33 of the heat shield plate 31 is composed of two bent portions provided between the arc portion 31a and the lower end portion 31b, and two bent portions provided between the arc portion 31a and the upper end portion 31c. The stepped portion 34 of the heat shield plate 32 is composed of two bent portions provided between the arc portion 32a and the lower end portion 32b, and two bent portions provided between the arc portion 32a and the upper end portion 32c. As a result, between the first heat insulator 20 and the second heat insulator 30, a gap portion S3 is formed between the step portions 23, 24 on the lower end portions 21b, 22b side and the step portions 33, 34 on the lower end portions 31b, 32b side, and a gap portion S4 is formed between the step portions 23, 24 on the upper end portions 21c, 22c side and the step portions 33, 34 on the upper end portions 31c, 32c side.

[0035] 3 and 4, a wire mesh 40 is disposed in the gap at least in the portion on the extension direction side (here, the vertically downward side) of the extension region 19. The wire mesh 40 is formed of, for example, stainless steel. The wire mesh 40 allows liquids such as water to pass through while capturing foreign matter such as dead grass.

[0036] In this embodiment, the wire mesh 40 is disposed around the entire circumferential direction of the exhaust pipe 10, including the gap portions S3 and S4. The wire mesh 40 is disposed with a substantially constant thickness in the gap portions S3 and S4. The wire mesh 40 is disposed in a compressed state between the arc portions 21a and 22a of the heat shield plates 21 and 22 of the first heat insulator 20 and the arc portions 31a and 32a of the heat shield plates 31 and 32 of the second heat insulator 30.

[0037] When arranging the wire mesh all around the exhaust pipe 10 in the circumferential direction, including the gap portions S3 and S4, the wire mesh 40 can be joined in advance by spot welding to one of the downstream end 20a of the first heat insulator 20 and the upstream end 30a of the second heat insulator 30. In this state, the pair of heat shields 31 and 32 are arranged so as to cover the downstream end 20a of the first heat insulator 20, and the lower ends 31b and 32b and the upper ends 31c and 32c are joined by spot welding or the like, whereby the wire mesh 40 can be easily arranged all around the exhaust pipe 10 in the circumferential direction, including the gap portions S3 and S4.

[0038] 1 and 2, the exhaust pipe structure 1 is provided with a bracket 60 and a base portion 70 used for mounting the exhaust pipe 10 to a vehicle. In arranging the bracket 60 and the base portion 70, in this embodiment, an opening 35 is provided that exposes the exhaust pipe 10 from a part of the second heat insulator 30. The opening 35 has, for example, a rectangular shape with rounded corners in a plan view, and is provided along the circumferential surface of the second heat insulator 30. In this embodiment, the opening 35 and the base portion 70 are provided at a position that is above the exhaust pipe 10 when the exhaust pipe 10 is mounted to the vehicle.

[0039] The bracket 60 is made of, for example, stainless steel. As shown in Fig. 2, the bracket 60 has a base end 61 fixed to the base portion 70, a rising portion 62 rising from one edge of the base end 61, and a tip end 63 bent from the tip of the rising portion 62, and is generally C-shaped in side view. The tip end 63 extends longer than the other edge of the base end 61. The tip end 63 is provided with an insertion hole 64 through which a stud bolt is inserted.

[0040] A rubber member that serves as a suspension point for the exhaust pipe 10 relative to the vehicle is attached to the tip portion 63. The rubber member is fixed in advance to, for example, a frame on the vehicle side, and has bolt holes corresponding to stud bolts. The exhaust pipe 10 can be attached to the vehicle by inserting a stud bolt through an insertion hole 64 in the tip portion 63 and screwing it into the bolt hole of the rubber member.

[0041] The base 70 is formed of stainless steel, for example, like the pair of heat shield plates 31, 32 constituting the second heat insulator 30. As shown in FIG. 2, the base 70 has a box-shaped main body 71 with one side open, and a flange 72 provided around the entire periphery of the edge of the opening side of the main body 71. The top surface 71a of the main body 71 is an inclined surface such that the distance from the exhaust pipe 10 decreases toward the downstream side of the exhaust pipe 10. The base end 61 of the bracket 60 is fixed to the top surface 71a of the main body 71 by welding, for example. There is no particular limit to the height of the main body 71 from the exhaust pipe 10, but in this embodiment, the height is such that the entire top surface 71a is located outside the opening 35.

[0042] The flange portion 72 has a curved shape that follows the circumferential surface of the exhaust pipe 10. The flange portion 72 is fixed without any gaps to the circumferential surface of the exhaust pipe 10 exposed from the opening 35, for example by welding. By fixing the flange portion, an internal space V (see FIG. 6 ) that is sealed by the exhaust pipe 10 and the main body portion 71 is formed between the exhaust pipe 10 and the bracket 60. The internal space V is filled with air. The air in the internal space V functions as a heat insulating layer between the exhaust pipe 10 and the bracket 60.

[0043] By forming the opening 35, a gap portion S5 is formed between the exhaust pipe 10 and the second heat insulator 30. A wire mesh 90 (see FIG. 6) is arranged in this gap portion S5. The wire mesh 90 is made of, for example, stainless steel. Like the wire mesh 40 (see FIG. 4) arranged around the entire circumferential direction of the exhaust pipe 10 including the above-mentioned gap portions S3 and S4, the wire mesh 90 allows liquids such as water to pass through while capturing foreign matter such as dead grass.

[0044] The wire mesh 90 is disposed in the gap portion S5 between the exhaust pipe 10 and the second heat insulator 30, around the entire periphery of the edge of the opening 35. In this embodiment, the flange portion 72 of the base portion 70 extends to the gap portion S5, and the wire mesh 90 is disposed around the base portion 70 so as to fill the gap between the second heat insulator 30 and the flange portion 72.

[0045] Next, the configuration of the above-mentioned exhaust pipe 10 will be described in more detail. Fig. 5 is a partial cross-sectional view showing the exhaust pipe structure in the vicinity of the bent portion. Fig. 6 is a partial cross-sectional view showing the exhaust pipe structure upstream of the bent portion, and Fig. 7 is a partial cross-sectional view showing the exhaust pipe structure downstream of the bent portion.

[0046] 5 to 7, in the exhaust pipe structure 1, a portion of the exhaust pipe 10 including at least the bent portions 81, 82 is a multiple-structure portion P made up of an inner pipe 95 and an outer pipe 96. In this embodiment, the entire exhaust pipe 10 is a multiple-structure (here, a double structure) made up of the inner pipe 95 and the outer pipe 96, except for a portion corresponding to an overlapping portion R between the downstream end 20a of the first heat insulator 20 and the upstream end 30a of the second heat insulator 30.

[0047] As described above, in this embodiment, the bent portions 81 and 82 are formed in a mountain shape with one side of the pipe protruding and the other side recessed. The protruding amount of the bent portions 81 and 82 is equal to or less than the pipe diameter of the exhaust pipe 10, as shown in FIG. 5. Specifically, when the highest point of the outer pipe 96 in the straight portion 18 before the bent portion 81 is P1, the highest point of the outer pipe 96 in the bent portion 82 is P2, and the outer diameter of the outer pipe 96 is D, D≧P2-P1 is satisfied. Also, when the lowest point of the outer pipe 96 in the straight portion 18 before the bent portion 81 is Q1, the lowest point of the outer pipe 96 in the bent portion 81 is Q2, and the outer diameter of the outer pipe 96 is D, D≧Q2-Q1 is satisfied.

[0048] Exhaust gas from the internal combustion engine and a reducing agent introduced by the injector 50 flow through the inside of the inner pipe 95. The thickness T1 of the inner pipe 95 is smaller than the thickness T2 of the outer pipe 96. The ratio of the thickness T1 of the inner pipe 95 to the thickness T2 of the outer pipe 96 is not particularly limited, but for example, the thickness T1 of the inner pipe 95 is half or less of the thickness T2 of the outer pipe 96. The outer pipe 96 has a larger diameter than the inner pipe 95 and is disposed so as to cover the inner pipe 95. A gap portion S6 based on the difference between the outer diameter of the inner pipe 95 and the inner diameter of the outer pipe 96 is provided between the inner pipe 95 and the outer pipe 96. The gap portion S6 corresponds to a portion where the exhaust pipe 10 has a multiple structure, and extends along the pipe axis direction of the exhaust pipe 10.

[0049] As shown in FIG. 6, the upstream portion 95a of the inner pipe 95 and the upstream portion 96a of the outer pipe 96 are joined to each other by welding or the like at a position corresponding to the overlapping portion R. As a result, the gap portion S6 is a closed space on the upstream portion 95a side of the inner pipe 95 and the upstream portion 96a side of the outer pipe 96. The upstream portion 95a of the inner pipe 95 has a reduced diameter portion 97 that is gradually reduced in diameter relative to the upstream portion 96a of the outer pipe 96 downstream of the joint portion. The reduced diameter portion 97 prevents the flow of exhaust gas passing through the overlapping portion R toward the downstream side from being obstructed by the upstream portion 95a of the inner pipe 95, even when the upstream side of the gap portion S6 is a closed space.

[0050] 7, the downstream portion 95b of the inner pipe 95 and the downstream portion 96b of the outer pipe 96 are not joined to each other on the downstream side of the exhaust pipe 10. As a result, the gap portion S6 is an open space on the downstream portion 95b side of the inner pipe 95 and the downstream portion 96b side of the outer pipe 96. The downstream portion 95b of the inner pipe 95 terminates upstream of the downstream portion 96b of the outer pipe 96, thereby forming an inlet portion 98 for exhaust gas into the gap portion S6. In the inlet portion 98, a part of the exhaust gas flowing inside the inner pipe 95 turns around to the outside of the downstream portion 95b of the inner pipe 95 just before the connection portion 80 and is drawn into the gap portion S6.

[0051] The downstream portion 96b of the outer pipe 96 has a reduced diameter portion 99 that gradually reduces in diameter relative to the main body of the outer pipe 96, downstream of the terminal position of the downstream portion 95b of the inner pipe 95. In the example of Fig. 7, the inner diameter of the reduced diameter portion 99 is approximately the same as the outer diameter of the inner pipe 95. The reduced diameter portion 99 of the outer pipe 96 functions as a guide when drawing the exhaust gas from the drawing-in portion 98 into the gap portion S6, and supports the flow of a portion of the exhaust gas flowing inside the inner pipe 95 into the gap portion S6.

[0052] In this embodiment, as shown in Fig. 7, a wire mesh 100 is disposed in the gap portion S6. The wire mesh 100 is formed of, for example, stainless steel, similar to the wire meshes 40 and 90. The wire mesh 100 is disposed around the entire circumferential direction of the gap portion S6, for example, at a position closer to the lead-in portion 98 of the gap portion S6. The wire mesh 100 itself has a certain heat capacity, which enhances the heat retention effect of the exhaust gas drawn into the gap portion S6.

[0053] As described above, in the exhaust pipe structure 1, the reducing agent introduced into the exhaust pipe 10 from the injector 50 is diffused into the exhaust gas by the dispersion plate 25. At this time, the reducing agent that has passed through the dispersion plate 25 without being gasified is evaporated by the exhaust pipe 10 that is heated by the exhaust gas. In the exhaust pipe structure 1, at least a portion including a downstream side of the dispersion plate 25 is a multi-layered structure portion P made of the inner pipe 95 and the outer pipe 96. In addition, the multi-layered structure portion P is provided with a drawing-in portion 98 that draws in a part of the exhaust gas flowing through the inner pipe 95 into the gap portion S6. The multi-layered structure of the exhaust pipe 10 enhances the heat insulation of the exhaust pipe 10, and further, the drawing-in portion 98 draws the exhaust gas into the gap portion S6 between the inner pipe 95 and the outer pipe 96, so that the temperature of the inner pipe 95 that the reducing agent comes into contact with is maintained at a high temperature. This can promote evaporation of the reducing agent. By promoting the evaporation of the reducing agent, the reducing agent in a mist state is prevented from reaching the NOx catalyst, thereby suppressing the occurrence of problems such as peeling of the catalyst coating.

[0054] In the exhaust pipe structure 1, the gap portion S6 is a closed space upstream of the multi-structure portion P, and the inlet portion 98 is provided downstream of the multi-structure portion P. With this configuration, a portion of the exhaust gas flowing through the inner pipe 95 is drawn by the inlet portion 98 from the downstream side to the upstream side of the multi-structure portion P. Therefore, it is possible to prevent the inlet portion 98 from obstructing the flow of exhaust gas.

[0055] In the exhaust pipe structure 1, the intake section 98 is configured by terminating a downstream section 95b of the inner pipe 95 upstream of a downstream section 96b of the outer pipe 96. In addition, the downstream section 96b of the outer pipe 96 has a reduced diameter section 99 that is smaller in diameter than the main body of the outer pipe 96. With this configuration, the reduced diameter section 99 of the outer pipe 96 functions as a guide when drawing the exhaust gas into the gap section S6. Therefore, it is possible to efficiently draw the exhaust gas into the gap section S6.

[0056] In the exhaust pipe structure 1, a wire mesh 100 is disposed in the gap portion S6. By disposing the wire mesh 100 in the gap portion S6, the heat retention effect of the exhaust gas in the gap portion S6 can be improved. Therefore, the evaporation of the reducing agent can be promoted more effectively.

[0057] In the exhaust pipe structure 1, the thickness T1 of the inner pipe 95 is smaller than the thickness T2 of the outer pipe 96. Because the thickness T1 of the inner pipe 95 is smaller than the thickness T2 of the outer pipe 96, the heat capacity of the inner pipe 95 is reduced. Therefore, the heat of the exhaust gas is less likely to be taken away by the inner pipe 95, and the inner pipe 95 is more likely to be heated by the exhaust gas, so that the evaporation of the reducing agent K captured at the bent portions 81, 82 can be more effectively promoted. In addition, because the thickness T2 of the outer pipe 96 is larger than the thickness T1 of the inner pipe 95, the strength of the exhaust pipe 10 can be sufficiently ensured.

[0058] In the exhaust pipe structure 1, the exhaust pipe 10 has bent portions 81, 82 that capture the reducing agent downstream of the dispersion plate 25, and the portion including at least the bent portions 81, 82 is the multiple structure portion P. With this configuration, the reducing agent K that has slipped through the dispersion plate 25 without being gasified is captured by the bent portions 81, 82 of the exhaust pipe 10 (see FIG. 5). The reducing agent K captured by the bent portions 81, 82 comes into contact with the inner pipe 95, which is maintained at a high temperature by the exhaust gas drawn into the gap portion S6, thereby more effectively promoting evaporation of the reducing agent.

[0059] In the exhaust pipe structure 1, the bent portions 81, 82 form an arch shape with one side of the pipe protruding and the other side recessed. The amount of protrusion of the bent portions 81, 82 is equal to or less than the pipe diameter of the exhaust pipe 10. This means that the degree of curvature of the exhaust pipe 10 at the bent portions 81, 82 is gentle. The gentle degree of curvature at the bent portions 81, 82 makes it possible to avoid an increase in pressure loss in the exhaust pipe 10. In addition, when the exhaust pipe structure 1 is mounted on a vehicle, it is possible to avoid the exhaust pipe 10 interfering with other components on the vehicle side.

[0060] In the exhaust pipe structure 1, a heat insulator (here, the second heat insulator 30) covering the outer pipe 96 is provided in a portion of the exhaust pipe 10 including at least the bent portions 81, 82. This further improves the thermal insulation of the exhaust pipe 10, making it easier to maintain the temperature of the inner pipe 95 at a high temperature. Therefore, the evaporation of the reducing agent K captured by the bent portions 81, 82 can be promoted more reliably.

[0061] The present disclosure is not limited to the above embodiment. For example, in the above embodiment, the gap portion S6 is a closed space upstream of the multi-structure portion P, and the inlet portion 98 is provided downstream of the multi-structure portion P. However, conversely, the gap portion S6 may be a closed space downstream of the multi-structure portion P, and the inlet portion 98 may be provided upstream of the multi-structure portion P. In this case, the inlet portion 98 faces the flow direction of the exhaust gas, so that it is possible to increase the speed at which the exhaust gas is drawn into the gap portion S6.

[0062] The lead-in portion 98 does not necessarily have to be located at the end of the multi-layered structure portion P. For example, an opening may be formed in the wall of the inner pipe 95 in the middle of the multi-layered structure portion P, and the opening may serve as the lead-in portion 98. In this case, the shape of the opening constituting the lead-in portion 98 is not particularly limited, and various shapes such as a circle, an ellipse, or a rectangle may be used. In the case of a shape having a major axis direction such as an ellipse, the major axis direction may be aligned with the extension direction of the multi-layered structure portion P (the flow direction of the exhaust gas).

[0063] In the above embodiment, the thickness T1 of the inner pipe 95 is smaller than the thickness T2 of the outer pipe 96, but the relationship between the thicknesses T1 and T2 may be reversed. Also, the thickness T1 of the inner pipe 95 and the thickness T2 of the outer pipe 96 may be equal to each other.

[0064] In addition, in the above embodiment, the protruding amount of the bent portions 81, 82 is equal to or less than the pipe diameter of the exhaust pipe 10, but this is not limited thereto, and the protruding amount of the bent portions 81, 82 may be greater than the pipe diameter of the exhaust pipe 10. In this case, since the degree of bending at the bent portions 81, 82 becomes steep, the reducing agent that has passed through the distribution plate 25 without being gasified can be easily captured by the bent portions 81, 82. In addition, the bent portions 81, 82 may be provided in multiple locations downstream of the distribution plate 25. In this way, the capture of the reducing agent K and the promotion of evaporation can be more reliably performed. [Explanation of symbols]

[0065] 1...exhaust pipe structure, 10...exhaust pipe, 25...dispersion plate, 30...second heat insulator (heat insulator), 50...injector, 81, 82...bent portion, 95...inner pipe, 95b...downstream portion, 96...outer pipe, 96b...downstream portion, 98...inlet portion, 100...wire mesh, K...reducing agent, P...multiple structure portion, S6...gap portion.

Claims

1. An exhaust pipe structure connected to an internal combustion engine of a vehicle, Exhaust pipe and an injector that introduces a reducing agent into the exhaust pipe; a dispersion plate disposed downstream of the injector in the exhaust pipe, the exhaust pipe has a connection portion that is connected to a catalyst to which the reducing agent is supplied, a portion of the exhaust pipe downstream of the dispersion plate and upstream of the connection portion is a multi-layered structure portion including an inner pipe and an outer pipe covering the inner pipe such that a gap is formed between the inner pipe and an outer pipe, An exhaust pipe structure in which the multiple structure portion is provided with an intake portion that draws a portion of the exhaust gas flowing through the inner pipe into the gap portion, and the remainder of the exhaust gas is guided to the connection portion.

2. The gap portion is a closed space upstream of the multiple structure portion, The exhaust pipe structure according to claim 1 , wherein the inlet portion is provided downstream of the multiple structure portion.

3. the lead-in portion is configured by a downstream portion of the inner pipe terminating upstream of a downstream portion of the outer pipe, 3. The exhaust pipe structure according to claim 2, wherein the downstream portion of the outer pipe has a smaller diameter than the main body portion of the outer pipe.

4. The exhaust pipe structure according to any one of claims 1 to 3, wherein a wire mesh is disposed in the gap portion.

5. 5. The exhaust pipe structure according to claim 1, wherein the thickness of the inner pipe is smaller than the thickness of the outer pipe.

6. The exhaust pipe has a bent portion that captures the reducing agent downstream of the dispersion plate, and at least a portion including the bent portion is the multiple structure portion.

7. The bent portion is formed in a convex shape with one side of the tube protruding and the other side recessed, 7. The exhaust pipe structure according to claim 6, wherein the protruding amount of the bent portion is equal to or smaller than a diameter of the exhaust pipe.

8. 8. The exhaust pipe structure according to claim 6, wherein a heat insulator covering the outer pipe is provided in at least a portion of the exhaust pipe including the bent portion.

Images