Engine silencer

Abstract

The present invention provides a muffling device (1) for an engine, comprising an exhaust pipe(10) which includes a main pipe (11) into which exhaust gas from an engine is introduced through a base end (E1) thereof and a branch pipe (12) branched from the main pipe (11) at a branch part (B), and a muffler (20) which includes a resonance chamber (21), wherein a second pipe axial direction (D2) of the main pipe (11) at the exit of the branch part (B) is along a first pipe axial direction (D1) of the main pipe (11) at the entrance of the branch part (B), a third pipe axial direction (D3) of the branch pipe (12) at the exit of the branch part (B) is different from the first pipe axial direction (D1), and the front end (E2) of the main pipe (11) is connected to the resonance chamber (21).

Description

Engine silencer

[0001] The present invention relates to an engine silencer.

[0002] In a muffler for an automobile engine, three chambers are arranged side by side, each separated in the direction of the exhaust pipe, and the exhaust pipe passes through the three chambers. A branch pipe from the exhaust pipe connects to one of the three chambers, and the chamber to which the branch pipe is connected is connected to the chamber at the other end via a communicating pipe, making the chambers at both ends of the three chambers resonance chambers, and a number of small holes are provided in the exhaust pipe of the central chamber, making the central chamber a resonance chamber or expansion chamber (Patent Document 1).

[0003] Special Publication No. 3-45208

[0004] However, in the above-mentioned conventional technology, there are cases where plane wave sound waves traveling straight through the exhaust pipe are output directly from the muffler (hereinafter also referred to as a silencer) without entering the branch pipe, which creates the problem that the desired silencing effect cannot be obtained in the resonance chambers at both ends of the three parallel chambers.

[0005] An object of the present invention is to provide an engine silencer that can suppress a decrease in the silencing effect in the resonance chamber of the silencer.

[0006] The present invention solves the above problem by connecting the tip of the main pipe to the resonance chamber of the muffler using an exhaust pipe that includes a main pipe into which engine exhaust gas is introduced from the base end and a branch pipe that branches off from the main pipe at a branching section, wherein the pipe axis direction of the main pipe at the outlet of the branching section is in the same direction as the pipe axis direction of the main pipe at the inlet of the branching section, and the pipe axis direction of the branch pipe at the outlet of the branching section is in a different direction from the pipe axis direction of the main pipe at the inlet of the branching section.

[0007] According to the present invention, it is possible to suppress a decrease in the silencing effect in the resonance chamber of the silencer.

[0008] 6 is a plan view showing an example of a silencer according to the present invention. FIG. 6 is a plan sectional view of the exhaust pipe of FIG. 1. FIG. 6 is a plan sectional view of the silencer of FIG. 1. FIG. 6 is a plan sectional view showing the flow of exhaust gas and sound waves in the silencer of FIG. 1. FIG. 6 is a plan sectional view of a main part showing the flow of exhaust gas in the branch pipe of FIG. 1. FIG. 6 is a plan sectional view of another example of a silencer according to the present invention. FIG. 6 is an end view of a main part showing a front view of a connection part where the main pipe and the branch pipe are connected to each other in FIG. 6. FIG. 6 is a plan sectional view of a main part showing the flow of exhaust gas in the branch pipe of FIG. 6. FIG. 6 is a plan sectional view of yet another example of an exhaust pipe according to the present invention. FIG. 6 is a plan sectional view of an example of a silencer according to a comparative example of the present invention.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] Fig. 1 is a plan view showing an example of a silencer 1 according to the present invention. The silencer 1 is a device for reducing exhaust noise from an internal combustion engine (hereinafter also referred to as an engine) mounted on an automobile, motorcycle, etc., and the engine in question includes a hybrid engine that combines an internal combustion engine with an electric motor. Fig. 1 is a plan view of the silencer 1 mounted on an automobile. As shown in Fig. 1, the silencer 1 includes an exhaust pipe 10, a silencer 20, and a tail pipe 30.

[0011] The exhaust pipe 10 is a pipe that introduces exhaust gases from an internal combustion engine, as well as exhaust sound waves, into the silencer 20. The exhaust gases and exhaust sound waves emitted from the engine are introduced to the base end of the exhaust pipe 10 via an exhaust manifold attached to the engine and an exhaust pipe routed under the floor of the vehicle. Note that the exhaust pipe routed under the floor may be a different exhaust pipe from the exhaust pipe 10, or may be the same exhaust pipe integrated with the exhaust pipe 10.

[0012] The exhaust pipe 10 is a circular pipe made of corrosion-resistant stainless steel (such as SUS409) or a titanium alloy. The exhaust pipe 10 is made, for example, by rolling a stainless steel or titanium alloy plate to a desired diameter. When combining multiple pipes, they are joined by, for example, welding. The exhaust pipe 10 can be bent as needed using, for example, a pipe bender. The exhaust pipe 10 is suspended below the floor of the vehicle by stays (not shown). The stays are fixed to the floor via rubber.

[0013] Figure 2 is a plan cross-sectional view of the exhaust pipe 10 shown in Figure 1. Specifically, it is a cross-sectional view of a cross section perpendicular to the height direction of the vehicle, including the central axes A1 to A3 (hereinafter also referred to as the pipe axis) of the exhaust pipe 10. As shown in Figure 2, the exhaust pipe 10 includes a main pipe 11 and a branch pipe 12 that branches off from the main pipe 11 at a branching point B. The pipe axis of the main pipe 11 is A1, and the pipe axes of the branch pipes 12 are A2 and A3. The diameter of the exhaust pipe 10 (main pipe 11 and branch pipe 12) can be set to an appropriate value within a range that allows engine exhaust gas to be appropriately introduced into the silencer 20.

[0014] The main pipe 11 has a base end E1 and a tip end E2. Engine exhaust gas and exhaust sound waves are introduced into the base end E1, and the tip end E2 is connected to the resonance chamber of the silencer 20 using a joining method such as welding. The main pipe 11 also has a branch portion B defined by dashed lines L1 to L3 in FIG. 2 . The dashed line L1 is a line parallel to the cross-sectional direction of the main pipe 11, and its position corresponds to position C1, one of the base ends of the branch pipe 12. Similarly, the dashed line L2 is a line parallel to the cross-sectional direction of the main pipe 11, and its position corresponds to position C2, the other of the base ends of the branch pipe 12. The dashed line L3 connects position C1 and position C2.

[0015] The branch pipe 12 has a base end E3 at a position corresponding to dashed line L3 and a tip end E4. The tip end E4 is connected to the expansion chamber of the silencer 20 using a joining method such as welding. Here, assuming that the position of dashed line L1 is the inlet of the branch section B and the positions of dashed lines L2 and L3 are the outlet of the branch section B, the positional relationship between the main pipe 11 and the branch pipe 12 before and after the branch section B is as follows: That is, the pipe axis direction D1 (hereinafter also referred to as the first pipe axis direction D1) of the main pipe 11 at the inlet of the branch section B (the position of dashed line L1) and the pipe axis direction D2 (hereinafter also referred to as the second pipe axis direction D2) of the main pipe 11 at the outlet of the branch section B (the position of dashed line L2) are parallel to each other. That is, the first pipe axis direction D1 and the second pipe axis direction D2 may be the same direction, or may form an angle (e.g., an angle greater than 0° and less than 10°) between the first pipe axis direction D1 and the second pipe axis direction D2. In contrast, the tube axis direction D3 (hereinafter also referred to as the third tube axis direction D3) of the branch pipe 12 at the outlet of the branch section B (position of the dashed line L3) is a direction different from the above-mentioned first tube axis direction D1, and the first tube axis direction D1 and the third tube axis direction D3 form a predetermined angle, for example, within a range of 10 to 90 degrees.

[0016] The tube axis A1 of the main tube 11 at the branching portion B may be a straight line extending along the first and second tube axis directions (for example, a straight line parallel to the tube axis directions D1 and D2). The tube axis A1 of the main tube 11 may be curved between the base end E1 and the inlet of the branching portion B, and between the outlet of the branching portion B and the tip E2. The angle between the first tube axis direction D1 and the second tube axis direction D2 is smaller than the angle between the first tube axis direction D1 and the third tube axis direction D3.

[0017] The silencer 20 is a device that lowers the temperature of exhaust gas introduced from the exhaust pipe 10 and reduces the sound pressure (or volume) of the exhaust noise. The silencer 20 is a cylindrical hollow molded product made of corrosion-resistant stainless steel (e.g., SUS409) or a titanium alloy, and its cross-sectional shape may be circular, elliptical, rectangular, or the like. For example, the silencer 20 is produced in a desired shape by pressing and welding a stainless steel plate or a titanium alloy plate. The silencer 20 is suspended from the underside of the vehicle floor, for example, via stays (not shown) provided at both ends in the longitudinal and / or lateral directions. The stays are fixed to the underside of the floor via rubber.

[0018] 3 is a plan cross-sectional view of the silencer 20. Specifically, it is a cross-sectional view of a cross section perpendicular to the height direction of the vehicle, including the pipe axes A1-A3 of the exhaust pipe 10. The silencer 20 has a resonance chamber 21 and an expansion chamber 22, and the two chambers are separated by a partition 23. The partition 23 may be provided with a hole or a communication pipe that connects the resonance chamber 21 and the expansion chamber 22. Furthermore, the silencer 20 may have one or more resonance chambers 21 and one or more expansion chambers 22, and the number and arrangement of the resonance chambers 21, expansion chambers 22, and partitions 23 can be set as appropriate within the range in which the silencer 20 can exhibit the desired silencing effect.

[0019] The resonance chamber 21 is a section that attenuates exhaust sound waves introduced from the exhaust pipe 10 by causing them to interfere with sound waves having a waveform of the opposite phase. For example, sound waves introduced from the tip E2 of the main pipe 11 are attenuated by causing them to interfere with sound waves whose waveform has been reversed after being reflected at the fixed end within the resonance chamber 21. Furthermore, the presence of the resonance chamber 21 causes the air present between the outlet (position of dashed line L2) of the branch B shown in Figure 2 and the tip E2 to act as a spring, and sound waves having a certain frequency among the exhaust sound waves are attenuated by resonance.

[0020] The shape of the resonance chamber 21 can be set using a formula for calculating the resonance frequency of Helmholtz resonance, depending on the frequency of the sound waves to be attenuated by resonance. That is, the resonance frequency of the Helmholtz resonator consisting of the resonance chamber 21 and the portion of the main pipe 11 from the outlet of the branch B to the tip E2 (hereinafter also referred to as the neck portion) can be calculated from the length of the neck portion in the pipe axial direction, the cross-sectional area of ​​the main pipe 11, and the volume of the resonance chamber 21. Therefore, when the dimensions of the main pipe 11 are determined, the resonance chamber 21 can be shaped appropriately within a range that ensures a volume that achieves the desired resonance frequency.

[0021] The expansion chamber 22 is a compartment that expands the exhaust gas introduced from the branch pipe 12 to reduce its pressure and temperature. The expansion chamber 22 may be divided into multiple compartments by partitions 23 to expand the exhaust gas in stages. The expansion chamber 22 may also function as a resonance chamber different from the resonance chamber 21. The exhaust gas that expands in the expansion chamber 22 is discharged into the atmosphere through a tail pipe 30 connected to the expansion chamber 22. The tail pipe 30 is made of the same material and by the same method as the exhaust pipe 10, and is connected to the expansion chamber 22 by a joining method such as welding.

[0022] Figure 4 is a plan cross-sectional view showing the flow of exhaust gas and exhaust sound waves in the silencer 1. The cross-section shown in Figure 4 is the same as the cross-sections shown in Figures 2 and 3. First, exhaust gas introduced from the base end E1 travels straight through the main pipe 11 and accumulates in the resonance chamber 21. Then, after the resonance chamber 21 and the neck portion of the main pipe 11 are filled with exhaust gas, the exhaust gas is introduced from the branch pipe 12 into the expansion chamber 22 along arrow G1 shown in Figure 4. The exhaust gas expands in the expansion chamber 22, reducing its temperature and pressure, and is then discharged into the atmosphere from the tail pipe 30 along arrow G2.

[0023] On the other hand, after being introduced from the base end E1, sound waves of exhaust noise travel straight through the main pipe 11 along arrow S1 shown in FIG. 4 . This is because sound waves propagating through the exhaust pipe 10 are plane waves and have the tendency to propagate straight along the pipe axis of the exhaust pipe 10. Some sound waves travel toward the branch pipe 12 at the branch point B and are introduced into the extension chamber 22 along arrow S4, while a relatively large portion of the sound waves travel straight through the branch point B and are introduced into the resonance chamber 21 along arrow S2. The sound waves introduced into the resonance chamber 21 interfere with sound waves whose waveforms are out of phase with each other after reverberating within the resonance chamber 21 (arrow S3), thereby reducing their sound pressure. This makes it easier for plane sound waves traveling straight through the main pipe 11 to be introduced into the resonance chamber 21 than into the branch pipe 12, thereby preventing a decrease in the silencing effect of the resonance chamber 21. The sound waves introduced into the extension chamber 22 are then output into the atmosphere from the tailpipe 30 along arrow S5.

[0024] In contrast, in a noise suppressor 1x according to a comparative example of the present invention shown in Fig. 10, the noise suppressor effect in the resonance chamber 21 is reduced. Fig. 10 is a plan cross-sectional view showing the noise suppressor 1x. The noise suppressor 1x differs from the noise suppressor 1 shown in Fig. 1 in that the main pipe 11 is connected to the extension chamber 22 and the branch pipe 12 is connected to the resonance chamber 21.

[0025] In the silencer 1x shown in FIG. 10 , exhaust gas introduced from the base end E1 is introduced from the main pipe 11 to the expansion chamber 22 along arrow Ga. The exhaust gas expands in the expansion chamber 22, reducing its temperature and pressure, and is then discharged into the atmosphere from the tailpipe 30 along arrow Gb. Meanwhile, exhaust sound waves are introduced from the base end E1 and then travel straight through the main pipe 11 along arrow Sa. Sound waves that travel straight through the branch B along arrow Sb are introduced into the expansion chamber 22. They are then output from the tailpipe 30 into the atmosphere along arrow Sc at a sound pressure exceeding a specified sound pressure, for example, as stipulated by law. The sound waves introduced into the resonance chamber 21 along arrow Sd are less than the sound waves that travel straight through the branch B and are introduced into the expansion chamber 22, resulting in a reduction in the noise reduction effect (arrow Se) due to interference from the resonance chamber 21.

[0026] FIG. 5 is a cross-sectional view of a main portion showing the flow of exhaust gas in the branch pipe 12. The cross section shown in FIG. 5 is the same as the cross section shown in FIG. 4. The pipe axis A2 of the branch pipe 12 shown in FIG. 5 is parallel to the third pipe axis direction D3 on the base end E3 side. In this case, the inner surface of the branch pipe 12 is also parallel to the third pipe axis direction D3, and such a smooth, uncurved inner surface promotes the growth of exhaust gas vortices. For example, if an exhaust gas vortex W1 is generated near the base end E3, the vortex W1 is subjected to a force f1 caused by the exhaust gas flow and a force f2 acting as a reaction force against the force f1 and exerted by the inner surface of the branch pipe 12. Because both forces f1 and f2 rotate the vortex W1 clockwise, the flow of exhaust gas promotes the rotation of the vortex W1, and the vortex W1 moves along the pipe axis A2 and grows into a larger vortex W2.

[0027] Since the force that promotes the rotation of the vortex is continuously applied to the generated vortex, as shown in Figure 5, forces f1 and f2 are also applied to vortex W2, promoting the rotation of vortex W2, which then moves along the tube axis A2 to become a larger vortex W3. Similarly, forces f1 and f2 are also applied to vortex W3, promoting the rotation of vortex W3, which then moves along the tube axis A2 to become a larger vortex W4.

[0028] When the growth of the vortex is accelerated and a large vortex is generated, a loud sound of a specific frequency is generated according to the size and rotation speed of the vortex. The sound caused by the vortex is a high-frequency sound like a whistle, and the sound pressure level of only some frequencies in the high-frequency range (e.g., 1000 Hz or higher) is increased. If the sound pressure level of only some frequencies in the high-frequency range is increased, the passengers of the vehicle will recognize it as an abnormal sound emitted by the engine. Therefore, in order to suppress the growth of the exhaust gas vortex in the branch pipe 12 and uniform the sound pressure level in the high-frequency range to achieve a pleasant high-pitched sound like that of a jet engine (hereinafter also referred to as jet sound), an exhaust pipe 10 having a branch pipe 12a with a shape shown in Figure 6 can be used.

[0029] Fig. 6 is a plan cross-sectional view of the silencer 1a, and the cross-section shown in Fig. 6 is the same as the cross-section shown in Fig. 4. The only difference between the silencer 1 and the silencer 1a is that the branch pipe 12 is replaced with a branch pipe 12a. The pipe axis of the branch pipe 12a is A4.

[0030] The branch portion B of the silencer 1a has an annular connection portion where the base end E3 of the branch pipe 12a and the main pipe 11 are connected. The annular connection portion is shown in FIG. 7 . FIG. 7 is a front end view of the main portion C3 where the main pipe 11 and the branch pipe 12a shown in FIG. 6 are connected. The left side of FIG. 7 is the base end E1 side of the main pipe 11, and the right side is the tip E2 side of the main pipe 11. In the case of the main pipe 11 and the branch pipe 12a shown in FIG. 6 , the connection portion C3 has an elliptical shape as shown in FIG. 7 . Here, when the connection portion C3 shown in FIG. 7 is viewed from the front from a direction along the third pipe axis direction D3 (e.g., the same direction as the third pipe axis direction D3), if a half of the connection portion C3 on the tip E4 side of the branch pipe 12a is designated as portion P, the surface formed by the inner surfaces of the main pipe 11 and the branch pipe 12a corresponding to portion P is a curved surface having a radius equal to or greater than a predetermined value in a cross section C4 perpendicular to the connection portion C3. When cross section C4 shown in Fig. 7 is viewed from viewpoint C5, the portion corresponding to portion P shown in Fig. 7 is portion Q shown in Fig. 6. That is, in the silencer 1a, the surface formed by the inner surfaces of the main pipe 11 and the branch pipe 12a at portion Q shown in Fig. 6 is a curved surface having a radius R equal to or greater than a predetermined value.

[0031] At portion Q shown in FIG. 6 , the surface formed by the inner surfaces of the main pipe 11 and the branch pipe 12a is a curved surface with a radius R equal to or greater than a predetermined value, so the flow of exhaust gas through the branch pipe 12a differs from the state shown in FIG. 5 . FIG. 8 is a cross-sectional view of a main portion showing the flow of exhaust gas through the branch pipe 12a. The cross section shown in FIG. 8 is the same as the cross section shown in FIG. 5 . If a vortex W5 of exhaust gas is generated near the base end E3, the vortex W5 is subjected to a force f1 caused by the flow of exhaust gas and a force f2, which is a reaction force to the force f1 exerted by the inner surface of the branch pipe 12a. However, because the inner surface of the branch pipe 12a is curved, the generated vortex W5 floats away from the inner surface of the branch pipe 12a. Then, the force f2, which is a reaction force from the inner surface of the branch pipe 12a, is no longer applied to the vortex W5, thereby suppressing the growth of the vortex W5.

[0032] The above-described effect also applies to the vortices W6 and W7 generated at different positions, resulting in the generation of multiple vortices with different sizes and rotational speeds within the branch pipe 12a. By suppressing the growth of the vortices and generating multiple different vortices in this way, it is possible to prevent the sound pressure level of only some frequencies from increasing in the high-frequency range (e.g., the range of 1000 Hz or higher). As a result, the sound pressure level can be made uniform throughout the high-frequency range, achieving a jet sound. The predetermined value of the radius, indicated as R in FIG. 8, can be set to any value within the range in which the growth of exhaust gas vortices can be suppressed, e.g., 5 mm or greater.

[0033] 7 , in addition to the portion P facing the flow of exhaust gas, a surface formed by the inner surfaces of the main pipe 11 and the branch pipe 12a, which corresponds to a half of the connection portion C3 on the base end E3 side of the branch pipe 12a when the connection portion C3 is viewed from the front in the direction along the third pipe axis D3, may be a curved surface having a radius R of a predetermined value or more in a cross section C4 perpendicular to the connection portion C3. In other words, the entire connection portion C3 may be a curved surface having a radius R of a predetermined value or more in a cross section C4 perpendicular to the connection portion C3.

[0034] Furthermore, instead of the branch pipe 12a shown in Fig. 6 , an exhaust pipe 10 having a branch pipe 12b shown in Fig. 9 may be used. The pipe axis A5 of the branch pipe 12b is curved from the base end E3 of the branch pipe 12b toward the tip E4. Specifically, the angle between the second pipe axis direction D2 and the pipe axis direction of the branch pipe 12b decreases as the pipe approaches the tip E4 of the branch pipe 12b. Alternatively, the angle between the second pipe axis direction D2 and the pipe axis direction of the branch pipe 12b may increase as the pipe approaches the tip E4 of the branch pipe 12b. In this case, the pipe axis A5 of the branch pipe 12b is curved in a direction away from the main pipe 11.

[0035] [Embodiments of the Invention] As described above, according to this embodiment, there is provided an engine silencer 1 including an exhaust pipe 10 including a main pipe 11 into which engine exhaust gas is introduced from a base end E1 and a branch pipe 12 branching from the main pipe 11 at a branch section B, and a silencer 20 including a resonance chamber 21, wherein a second pipe axis direction D2 of the main pipe 11 at an outlet of the branch section B is a direction along a first pipe axis direction D1 of the main pipe 11 at an inlet of the branch section B, and a third pipe axis direction D3 of the branch pipe 12 at the outlet of the branch section B is a direction different from the first pipe axis direction D1, and a tip E2 of the main pipe 11 is connected to the resonance chamber 21. This makes it possible to suppress a decrease in the silencing effect of the silencer 20 in the resonance chamber 21.

[0036] In the silencer 1 of this embodiment, the second pipe axis direction D2 may be the same as the first pipe axis direction D1. This allows the sound waves of the exhaust sound to be introduced more efficiently into the resonance chamber 21.

[0037] Furthermore, in the silencer 1 of this embodiment, the silencer 20 may include an expansion chamber 22 that expands the exhaust gas, and a tail pipe 30 that is connected to the expansion chamber 22 and that discharges the expanded exhaust gas into the atmosphere, and the tip E4 of the branch pipe 12 may be connected to the expansion chamber 22. This allows the exhaust gas to be discharged from the silencer 1 into the atmosphere while suppressing exhaust noise.

[0038] Furthermore, in the silencer 1 of this embodiment, the branch portion B has an annular connection portion C3 at which the base end E3 of the branch pipe 12 and the main pipe 11 are connected, and when the connection portion C3 is viewed from the front in a direction along the third pipe axis direction D3, in a portion P of the connection portion C3 which is a half on the tip E4 side of the branch pipe 12, the surface formed by the inner surfaces of the main pipe 11 and the branch pipe 12 may be a curved surface having a radius R of a predetermined value or more in a cross section C4 perpendicular to the connection portion C3. This suppresses the growth of vortices of the exhaust gas on the inner surface of the branch pipe 12, and makes it possible to achieve a jet sound with a uniform sound pressure level in a high frequency range.

[0039] In the silencer 1 of this embodiment, the pipe axis A2 of the branch pipe 12 may be curved from the base end E3 toward the tip E4 of the branch pipe 12. This suppresses the growth of vortices of the exhaust gas on the inner surface of the branch pipe 12, and realizes a jet sound with a uniform sound pressure level in a high frequency range.

[0040] Furthermore, in the silencer 1 of this embodiment, the angle formed by the second pipe axis direction D2 and the pipe axis direction of the branch pipe 12 may become larger or smaller as the angle approaches the tip E4 of the branch pipe 12. This suppresses the growth of vortices of the exhaust gas on the inner surface of the branch pipe 12, and realizes a jet sound with a uniform sound pressure level in a high frequency range.

[0041] DESCRIPTION OF SYMBOLS 1, 1a... silencer 1x... silencer (comparative example) 10... exhaust pipe 11... main pipe 12, 12a, 12b... branch pipe 20... silencer 21... resonance chamber 22... expansion chamber 30... tail pipe A1, A2, A3, A4, A5... central axis (pipe axis) B... branch section C1, C2... position C3... connection section C4... cross section C5... viewpoint D1, D2, D3... pipe axis direction E1, E3... base end E2, E4... tip f1, f2... force G1, G2, Ga, Gb... arrows L1, L2, L3... dashed line P, Q... part R... radius S1, S2, S3, S4, S5, Sa, Sb, Sc, Sd, Se... arrows W1, W2, W3, W4, W5, W6, W7...vortex

Claims

1. an exhaust pipe including a main pipe into which exhaust gas from an engine is introduced from a base end and a branch pipe branching off from the main pipe at a branching portion; a silencer including a resonance chamber; a second pipe axis direction of the main pipe at the outlet of the branching portion is a direction along a first pipe axis direction of the main pipe at the inlet of the branching portion, a third tube axis direction of the branch pipe at the outlet of the branching portion is different from the first tube axis direction; The tip of the main pipe is connected to the resonance chamber, The axis of the branch pipe is curved from the base end to the tip end of the branch pipe, An angle formed between the second pipe axis direction and the pipe axis direction of the branch pipe increases toward the tip of the branch pipe.

2. 2. The engine silencer according to claim 1, wherein the second pipe axis direction is the same as the first pipe axis direction.

3. The muffler includes an expansion chamber for expanding the exhaust gas, and a tail pipe connected to the expansion chamber for discharging the expanded exhaust gas into the atmosphere, 3. The engine silencer according to claim 1, wherein a tip of the branch pipe is connected to the expansion chamber.

4. the branch portion has an annular connection portion at which a base end of the branch pipe and the main pipe are connected, 4. The silencer for an engine according to claim 1, wherein, when the connection portion is viewed from the front in a direction along the third pipe axis direction, in a portion of the connection portion that is a half of the tip side of the branch pipe, a surface formed by inner surfaces of the main pipe and the branch pipe is a curved surface having a radius of a predetermined value or more in a cross section perpendicular to the connection portion.

5. 5. The engine silencer according to claim 1, wherein a pipe axis of the branch pipe is curved in a direction away from the main pipe.

6. the first tube axis direction and the second tube axis direction are the same direction, 6. The engine silencer according to claim 5, wherein a pipe axis of the main pipe is in the same direction as the first pipe axis direction between a base end of the main pipe and an inlet of the branching portion, and is in the same direction as the second pipe axis direction between an outlet of the branching portion and a tip end of the main pipe.