Exhaust pipe structure of vehicle

Abstract

To provide an exhaust pipe structure capable of reducing exhaust sound while suppressing pressure loss of exhaust gas.SOLUTION: An exhaust pipe structure of a vehicle includes: an inner pipe 22 in which exhaust gas flows; and an outer pipe 20 which is arranged outside the inner pipe 22 and forms an auxiliary chamber 28 between itself and the inner pipe 22. A plurality of communication holes 30 for communicating the inner pipe 22 with the auxiliary chamber 28 are formed on a peripheral surface of the inner pipe 22, and an edge wall 32 on an upstream side of the communication hole 30 protrudes in an inclination direction in such a manner of going to an outer side in a radial direction of the inner pipe 22 as going to a downstream side in an exhaust direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present specification discloses an exhaust pipe structure through which exhaust from a vehicle flows. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in order to reduce exhaust noise from a vehicle, many exhaust pipe structures have been proposed that attenuate exhaust noise during the exhaust process.

[0003] For example, Patent Document 1 discloses a sub-muffler that includes an inner pipe having a plurality of holes in the pipe wall, and an outer pipe that is connected to the inner pipe and covers the perforated portion with a gap. In this sub-muffler, the downstream end of the inner pipe is blocked. In the case of such a sub-muffler, exhaust gas expands in the process of flowing out from the holes of the inner pipe to the outer pipe. This expansion attenuates the acoustic energy of the exhaust, reducing the exhaust noise.

[0004] However, in the case of the technology of Patent Document 1, the exhaust gas loses pressure in the process of flowing from the inner pipe to the outer pipe, so the technology of Patent Document 1 has room for improvement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-113706 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, this specification discloses an exhaust pipe structure that can reduce exhaust noise while suppressing the pressure loss of exhaust gas. [Means for solving the problem]

[0007] The vehicle exhaust pipe structure disclosed in this specification comprises an inner pipe through which exhaust gas flows, and an outer pipe arranged outside the inner pipe and forming an auxiliary chamber between the inner pipe and the outer pipe, the circumferential surface of the inner pipe is formed with a plurality of communication holes which connect the inner pipe with the auxiliary chamber, and the upstream edge wall of the communication holes protrudes in an inclined direction so as to progress radially outward of the inner pipe as it progresses downstream in the exhaust direction. Effect of the Invention

[0008] With this configuration, it is possible to reduce exhaust noise while suppressing pressure loss of the exhaust gas. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view and a partially enlarged view of a silencer employing an exhaust pipe structure; [Diagram 2] 4A to 4C are cross-sectional views of the double tube portion cut from various directions. [Diagram 3] FIG. 11 is a cross-sectional view showing another example of the inner tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The exhaust pipe structure will be described below with reference to the drawings. Fig. 1 is a perspective view and a partially enlarged view of a silencer 10 that employs the exhaust pipe structure according to the present application. Fig. 2 is a cross-sectional view of a double pipe portion, which will be described later, cut from various directions. Note that the arrows F in each figure indicate the exhaust direction of the exhaust gas.

[0011] This silencer 10 is a device mounted on a vehicle, which guides exhaust gas output from an engine to the outside of the vehicle and attenuates sound during the exhaust process. As shown in Fig. 1(a), this silencer 10 has an upstream exhaust pipe 16, a sub-muffler 12, a main muffler 14, and a downstream exhaust pipe 18. The upstream exhaust pipe 16 has an upstream end connected to an engine and a downstream end connected to the main muffler 14. In addition, the sub-muffler 12 is attached midway through the upstream exhaust pipe 16. Both the sub-muffler 12 and the main muffler 14 are components that reduce exhaust sound by temporarily expanding the exhaust gas, etc.

[0012] A downstream exhaust pipe 18 is connected to both ends of the main muffler 14 in the longitudinal direction. The downstream exhaust pipe 18 is a pipe body that guides exhaust gas discharged from the main muffler 14 to the outside of the vehicle. FIG. 1(b) is an enlarged view of the downstream end of the downstream exhaust pipe 18. Also, FIG. 2(a) is a cross-sectional view taken along line BB in FIG. 1. As is clear from these drawings, the downstream end of the downstream exhaust pipe 18 has a double pipe structure having an inner pipe 22 and an outer pipe 20.

[0013] Fig. 1(c) is a perspective view of only the inner pipe 22. As is clear from Fig. 1(c) and Figs. 2(a) and (b), the inner pipe 22 forms an exhaust passage 26 through which exhaust gas flows. A plurality of communication holes 30 are formed in the circumferential surface of the inner pipe 22. In this example, as shown in Fig. 1(c), the plurality of communication holes 30 are formed in an array around the entire circumference of the inner pipe 22. The specific configuration of the communication holes 30 will be described later.

[0014] The outer pipe 20 is a pipe disposed outside the inner pipe 22 and concentrically with the inner pipe 22. As shown in FIG. 2(a), the outer pipe 20 has a diameter sufficiently larger than that of the inner pipe 22. Therefore, a predetermined gap is formed between the inner pipe 22 and the outer pipe 20. Hereinafter, this gap space is referred to as the "auxiliary chamber 28." Both the upstream end and the downstream end of the auxiliary chamber 28 are closed. The aforementioned communication hole 30 communicates the auxiliary chamber 28 with the exhaust passage 26.

[0015] The auxiliary chamber 28 is filled with sound-absorbing material 24 (e.g., glass cloth, etc.) for attenuating sound. The sound that flows into the auxiliary chamber 28 is attenuated as it travels through the sound-absorbing material 24. This reduces the exhaust sound.

[0016] Next, the communication hole 30 formed in the inner pipe 22 will be described. FIG. 2(b) is an enlarged view of part C in FIG. 2(a), and FIG. 2(c) is a DD cross-sectional view in FIG. 2(b). As is clear from these figures, in this example, the upstream edge wall 32 of the communication hole 30 is protruded in an inclined direction that proceeds radially outward as it proceeds downstream in the exhaust direction. Also, when viewed from the exhaust direction, as shown in FIG. 2(c), this edge wall 32 protrudes radially outward from the general surface 34 of the inner pipe 22. At this time, the rising angle at which the edge wall 32 rises from the general surface 34 of the inner pipe 22 is smaller than 90 degrees. In other words, the rising portion of the edge wall 32 from the general surface 34 is inclined with respect to the normal line La of the general surface 34. This makes the corner portion 33 of the edge wall 32 an obtuse angle.

[0017] The reason for protruding the edge wall 32 radially outward in this manner will be explained. In order to sufficiently reduce exhaust noise, it is necessary to output as much sound as possible to the auxiliary chamber 28. To address this issue, it is conceivable to enlarge the communication hole 30, but if the communication hole 30 is enlarged, the exhaust gas itself will also flow into the auxiliary chamber 28, resulting in pressure loss and, in some cases, a change in engine performance.

[0018] On the other hand, in this example, the edge wall 32 on the upstream side of the communication hole 30 protrudes in an inclined direction that progresses radially outward as it progresses downstream. With this configuration, more sound is guided to the sub-chamber 28. The thick dashed line in Fig. 2(b) shows the flow of sound spreading from a certain point P. Also, the two-dot chain line in Fig. 2(b) shows the case where the edge wall 32 does not protrude in the inclined direction.

[0019] If the edge wall 32 does not protrude in the inclined direction, the only sound that can reach the auxiliary chamber 28 from point P is the sound that can reach the communication hole 30 directly from point P. In other words, if the edge wall 32 does not protrude, only sounds within the range of angle β in Figure 2(b) can reach the auxiliary chamber 28.

[0020] On the other hand, when the edge wall 32 protrudes in the inclined direction as in this example, the sound that can reach the auxiliary chamber 28 from the point P includes not only the sound that can reach the communication hole 30 directly from the point P, but also the sound that reaches the communication hole 30 by hitting the edge wall 32 and being reflected from the point P. That is, when the edge wall 32 protrudes, the sound in the range of the angle α (α>β) in FIG. 2(b) can reach the auxiliary chamber 28. That is, according to this example, more sound can be guided to the auxiliary chamber 28. Then, the sound that reaches the auxiliary chamber 28 is attenuated while traveling through the sound-absorbing material 24, and the sound level is reduced. As a result, according to this example, the exhaust sound can be reduced more effectively than when the edge wall 32 is not protruded.

[0021] Furthermore, the sound that has flowed into the auxiliary chamber 28 is repeatedly reflected (bent) as it travels through the sound-absorbing material 24. As a result, the sound may try to return to the exhaust passage 26 as it travels through the sound-absorbing material 24. However, in the case where the edge wall 32 is protruded in the inclined direction as in this example, the travel of the sound towards the exhaust passage 26 is blocked by the edge wall 32. As a result, it is possible to effectively prevent the sound from flowing back into the exhaust passage 26, and it is possible to more effectively reduce the exhaust noise.

[0022] In addition, in this example, the size of the communication hole 30 is the same as in the conventional example. Therefore, the main flow of the exhaust gas through the exhaust passage 26 remains almost the same as in the conventional example, and most of the exhaust gas does not pass through the sub chamber 28. As a result, pressure loss of the exhaust gas can be prevented, and the same engine performance as in the conventional example can be ensured.

[0023] As described above, in this example, the rising angle of the edge wall 32 from the general surface 34 is set to be less than 90 degrees, and the corners 33 of the edge wall 32 are set to be obtuse angles. This configuration effectively prevents the generation of vortexes at the corners 33. If vortexes are generated at the corners 33, the exhaust gas will be more likely to pass through the communication holes 30 due to the same principle as in the NACA duct. On the other hand, in this example, the generation of vortexes at the corners 33 is suppressed, so that the outflow of exhaust gas into the sub chamber 28 is effectively suppressed, and thus pressure loss can be effectively prevented.

[0024] Note that the configurations described so far are all examples, and other configurations may be changed as long as the configuration described in claim 1 is included. For example, in the description so far, the double pipe structure is provided at the downstream end of the downstream exhaust pipe 18, but the double pipe structure may be provided at other locations. For example, a part of the upstream exhaust pipe 16 (e.g., part E in FIG. 1(a) or the like) may have the above-mentioned double pipe structure.

[0025] Also, the shape of the communication hole 30 and the configuration of other edge walls may be changed as long as the upstream edge wall 32 protrudes in the inclined direction. For example, as shown in FIG. 3(a), the downstream edge wall 36 of the communication hole 30 may protrude in a radially inward direction as it advances upstream. As another configuration, as shown in FIG. 3(b), a convex portion 38 protruding radially inward may be provided at the base of the upstream edge wall 32. With such a configuration, the flow of exhaust gas toward the communication hole 30 is obstructed, so that the pressure loss can be reduced more effectively. [Explanation of symbols]

[0026] 10 silencer, 12 sub-muffler, 14 main muffler, 16 upstream exhaust pipe, 18 downstream exhaust pipe, 20 outer pipe, 22 inner pipe, 24 sound absorbing material, 26 exhaust passage, 28 sub-chamber, 30 communication hole, 32, 36 edge wall, 33 corner portion, 34 general surface, 38 convex portion.

Claims

[Claim 1] An exhaust pipe structure for a vehicle, comprising: An inner pipe through which exhaust gas flows; an outer tube disposed outside the inner tube and defining a sub-chamber between the outer tube and the inner tube; a plurality of communication holes are formed in a peripheral surface of the inner tube to communicate with the auxiliary chamber, an upstream edge wall of the communication hole protrudes in an inclined direction so as to progress radially outward of the inner pipe as it progresses downstream in the exhaust direction; An exhaust pipe structure characterized by:

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