Muffling device for engine

Abstract

A muffling device for an engine of the present invention includes: a first pipe (51) that has one end communicating with a chamber (X1) forming a closed space, and another end as an open end; and a second pipe (52) that has one end communicating with the chamber (X1), and another end as an open end, and that is disposed outside the first pipe (51) so as to include at least a portion of the first pipe (51), wherein a predetermined interval is provided between the first pipe (51) and the second pipe (52), and first holes (61-68) and second holes (71-78) are provided in the portion of the first pipe (51) included in the second pipe (52), the first holes (61-68) and the second holes (71-78) being separated from each other by a first predetermined distance (D1) in the axial direction of the first pipe (51).

Description

Engine silencer

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

[0002] A silencer is known in which a resonance chamber is separated by a partition plate provided with a resonance tube in which a long small diameter tube is inserted inside a short large diameter tube (Patent Document 1).

[0003] Japanese Utility Model Application Publication No. 60-173615

[0004] In the above-mentioned conventional technology, in order to increase the frequency of the exhaust noise to be silenced, it is necessary to increase the number of pipes, which results in an increase in the size of the muffler.

[0005] The problem to be solved by the present invention is to provide an engine silencer that can prevent the muffler from becoming too large.

[0006] The present invention solves the above problem by providing a first tube having one end connected to a chamber that forms a closed space and the other end being an open end, and a second tube having one end connected to the chamber and the other end being an open end and arranged outside the first tube so as to encompass at least a portion of the first tube, with a predetermined gap between the first tube and the second tube, and providing a first hole and a second hole in the portion of the first tube that is encompassed by the second tube, the first hole and the second hole being spaced from each other by a first predetermined distance in the axial direction of the first tube.

[0007] According to the present invention, it is possible to prevent the muffler from becoming too large.

[0008] FIG. 1B is a plan view showing an example of a silencer according to an embodiment of the present invention. FIG. 1C is a left side view of the silencer of FIG. 1A. FIG. 1D is a cross-sectional view taken along line A-A in FIG. 1B, showing the interior of the muffler of FIG. 1A. FIG. 2A is a cross-sectional view taken along line B-B in FIG. 2A, showing the interior of the muffler of FIG. 1A. FIG. 2D is a cross-sectional view taken along line C-C in FIG. 2A, showing the interior of the muffler of FIG. 1A. FIG. 2E is a perspective view showing a main portion of a hole formed in the first pipe of FIG. 2A. FIG. 3A is a cross-sectional view showing another example of a muffler according to an embodiment of the present invention. FIG. 3F is a perspective view showing a main portion of a hole formed in the first pipe of FIG. 3A. FIG. 3G is an enlarged cross-sectional view showing the operation of the silencer tube of FIG. 2A. FIG. 3H is an enlarged cross-sectional view showing the operation of the silencer tube when the first pipe is shorter than the second pipe in the silencer tube of FIG. 2A. FIG. 3H is an enlarged cross-sectional view showing the operation of the silencer tube of FIG. 3A.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For convenience of explanation, the front side of a vehicle engine is defined as the front side. In addition, in the drawings, "front" refers to the front of the vehicle, "rear" refers to the rear of the vehicle, "right" refers to the right side of the vehicle, "left" refers to the left side of the vehicle, "up" refers to the top of the vehicle, and "down" refers to the bottom of the vehicle.

[0010] [Configuration of silencer] Fig. 1A is a plan view showing an example of a silencer according to an embodiment of the present invention, and Fig. 1B is a left side view of the silencer shown in Fig. 1A. The silencer is a device that reduces exhaust noise from an engine 10, and includes an exhaust pipe 20, a muffler 30, and a tail pipe 40. The engine 10 may be an internal combustion engine that obtains output by combusting a combustible air-fuel mixture, or may be a hybrid engine that combines an internal combustion engine with an electric motor.

[0011] The exhaust pipe 20 is a pipe that introduces exhaust gas (hereinafter simply referred to as "exhaust gas") from the engine 10 and sound waves (hereinafter simply referred to as "sound waves") from the exhaust sound of the engine 10 into the muffler 30, and is routed under the floor of the vehicle. For example, the exhaust pipe 20 is made by welding together multiple circular pipes made of corrosion-resistant stainless steel (such as SUS409), and is attached to the vehicle by stays that are fixed to the floor via rubber. The base end of the exhaust pipe 20 is attached to the exhaust manifold (not shown) of the engine 10, and the exhaust gas and sound waves are introduced from the engine 10. Meanwhile, the end of the exhaust pipe 20 is attached to the muffler 30 and communicates with the chamber of the muffler 30.

[0012] The muffler 30 is a device that reduces the temperature of exhaust gases introduced from the exhaust pipe 20 and the sound pressure level of exhaust noise, and has at least one chamber. For example, the muffler 30 is a cylindrical hollow molded product made of corrosion-resistant stainless steel, and its cross-sectional shape may be circular, elliptical, rectangular, or the like. A muffler 30 having a desired shape is manufactured, for example, by pressing and welding a stainless steel plate. The muffler 30 is suspended from the underside of the vehicle floor, for example, via stays provided at both ends in the longitudinal and / or lateral directions. The stays are fixed to the underside of the floor via rubber.

[0013] The tail pipe 40 is a pipe that discharges exhaust gas and sound waves outside the muffler 30 (for example, into the atmosphere). The tail pipe 40 is made of the same material as the exhaust pipe 20, and is attached to the muffler 30 using a joining method such as welding. The shape of the tail pipe 40 is not particularly limited. When the muffler 30 is connected to a different subsequent muffler, the tail pipe 40 discharges the exhaust gas and sound waves that are introduced into the different muffler outside the housing of the muffler 30.

[0014] [Configuration of muffler] The configuration of the muffler 30 shown in Fig. 1A will be described using Figs. 2A to 2D. Fig. 2A is a cross-sectional view showing the interior of the muffler 30 shown in Fig. 1A, taken along line A-A in Fig. 1B (a cross-sectional view perpendicular to the up-down direction). As shown in Fig. 2A, the muffler 30 comprises a housing 31 that houses the devices that make up the muffler 30, and partition plates 32 and 33 that separate the interior of the housing 31. The shape of the housing 31 is not particularly limited, but may be, for example, a substantially rectangular parallelepiped.

[0015] The interior of the housing 31 is divided into three chambers by partition plates 32 and 33. That is, the muffler 30 has a first chamber X1 separated by the partition plate 32, a second chamber X2 separated by the partition plates 32 and 33, and a third chamber X3 separated by the partition plate 33. The first chamber X1 is defined by the housing 31 and the partition plate 32, the second chamber X2 is defined by the housing 31 and the partition plates 32 and 33, and the third chamber X3 is defined by the housing 31 and the partition plate 33. The second chamber X2 communicates with the engine 10 via the exhaust pipe 20, and the third chamber X3 communicates with the outside of the muffler 30 via the tailpipe 40. The second chamber X2 and the third chamber X3 also communicate with each other via a hole 33a in the partition plate 33.

[0016] In the muffler 30 shown in FIG. 2A , exhaust gas is introduced from the exhaust pipe 20 into the second chamber X2 (arrow Y1), moves from the second chamber X2 to the third chamber X3 through the holes 33a (arrow Y2), and is discharged from the tailpipe 40 to the outside of the muffler 30 (arrow Y3). Similarly, sound waves introduced from the exhaust pipe 20 into the second chamber X2 propagate through the second chamber X2 and the third chamber X3, and are discharged to the outside of the muffler 30 through the tailpipe 40. The sound pressure level of the sound waves decreases when they pass through the holes 33a due to an expansion effect, etc. The size (opening area) of the holes 33a can be set as appropriate within a range that allows the exhaust gas to move appropriately and the sound waves to propagate appropriately.

[0017] In order to suppress the sound pressure level of relatively low-frequency exhaust noise, such as muffled noise, the muffler 30 shown in FIG. 2A includes a pipe 50 (hereinafter also referred to as a "silencer pipe") that communicates with a first chamber X1 that forms a space closed off from the outside. The silencer pipe 50 is a double pipe that includes a first pipe 51 and a second pipe 52 that is disposed outside the first pipe 51 so as to encompass at least a portion of the first pipe 51. The second pipe 52 encompassing the first pipe 51 means that the first pipe 51 is located radially inside the second pipe 52 between both ends of the second pipe 52. In the first pipe 51 shown in FIG. 2A, the second pipe 52 encompasses the portion of the second pipe 52 that corresponds to the open end 52a to the portion that corresponds to the open end 52b of the second pipe 52.

[0018] The first tube 51 and the second tube 52 are arranged so that a predetermined distance is provided between them. The predetermined distance can be set to an appropriate value within a range in which sound waves can be appropriately propagated between the first tube 51 and the second tube 52, and is, for example, 10 to 150% of the diameter (inner diameter) of the first tube 51. In the silencer tube 50 shown in FIG. 2A , the first tube 51 and the second tube 52 are arranged so that the distance between the first tube 51 and the second tube 52 is approximately equal to the inner diameter of the first tube 51.

[0019] The support members for supporting the first pipe 51 and the second pipe 52 are not particularly limited and may be plates, beams, stays, clamps, etc. The first pipe 51 shown in Fig. 2A is supported by annular stays 53 and 54, and the second pipe 52 is supported by the annular stays 53 and 54 and the partition plates 32 and 33.

[0020] The first pipe 51 and the second pipe 52 have open ends at both ends, one end of which communicates with a chamber that forms a closed space, and the other end of which communicates with a chamber different from the chamber that the one end communicates with. The chamber that forms a closed space is a chamber that communicates with the outside only via the silencer pipe 50 (specifically, the first pipe 51 and the second pipe 52), and no members (pipes, etc.) other than the silencer pipe 50 are connected to the inside of the chamber, and no holes are provided that communicate with members other than the silencer pipe 50.

[0021] The first tube 51 shown in Fig. 2A has open ends 51a and 51b at both ends, with the open end 51a communicating with the first chamber X1 and the open end 51b communicating with the third chamber X3. Similarly, the second tube 52 shown in Fig. 2A has open ends 52a and 52b at both ends, with the open end 52a communicating with the first chamber X1 and the open end 52b communicating with the third chamber X3. Sound waves are introduced into the first chamber X1 only through the silencer tube 50 (specifically, the first tube 51 and the second tube 52), and no other components are provided that introduce sound waves into the first chamber X1. In other words, the first chamber X1 forms a closed space apart from the silencer tube 50.

[0022] The structure of the muffler 30 will be further described using Figures 2B and 2C. Figure 2B is a cross-sectional view taken along line B-B in Figure 2A, showing the interior of the muffler 30 as viewed from the left side (from the first chamber X1 side). The cross-sectional view in Figure 2B shows a cross-section of the housing 31 taken along line B-B, the partition plate 32, a cross-section of the tail pipe 40 taken along line B-B, the first pipe 51, the second pipe 52, and the stay 53. The stay 53 has eight holes 53a to 53h to prevent the second pipe 52 from being blocked. The shape, opening area, and number of holes provided in the stay 53 are not particularly limited as long as sound waves can propagate between the first chamber X1 and the third chamber X3 via the second pipe 52. Also, as shown in Figure 2B, the cross-sectional view of Figure 2A (cross-sectional view along line AA) is a cross-section passing through the center of the tail pipe 40, the center of the first pipe 51, and the center of the second pipe 52.

[0023] 2C is a cross-sectional view taken along line CC in FIG. 2A, illustrating the interior of the muffler 30 as viewed from the right side (from the third chamber X3 side). The cross-sectional view in FIG. 2C shows a cross section of the housing 31 taken along line CC, the partition plate 33, the tail pipe 40, the first pipe 51, the second pipe 52, and the stay 54. The partition plate 33 has a circular hole 33a that connects the second chamber X2 and the third chamber X3. The stay 54 has eight holes 54a to 54h, similar to the stay 53. The shape, opening area, and number of holes provided in the stay 54 are not particularly limited as long as sound waves can propagate between the first chamber X1 and the third chamber X3 via the second pipe 52.

[0024] Returning to FIG. 2A , a portion of the first tube 51 enclosed within the second tube 52 is provided with a first hole and a second hole spaced a first predetermined distance apart in the axial direction of the first tube 51. FIG. 2D is a perspective view of a main portion showing the holes provided in the first tube 51 of FIG. 2A . As shown in FIG. 2D , the first tube 51 is provided with holes 61-68 and holes 71-78. In this case, holes 61-68 correspond to first holes, and holes 71-78 correspond to second holes. While the number of first holes and second holes is not particularly limited, in order to synchronize the pressures inside the first tube 51 and the second tube 52 without phase delay, it is preferable to provide a plurality of first holes and second holes on one circumference of the first tube 51, such as holes 61-68 and 71-78 shown in FIG. 2D . It is more preferable to provide a plurality of first holes and / or second holes symmetrically about the central axis of the first tube 51.

[0025] The first tube 51 shown in FIG. 2A has first holes 61-68 and second holes 71-78 in a portion corresponding to the area between both ends of the second tube 52. The distance between the first holes 61-68 and the second holes 71-78 in the axial direction of the first tube 51 is a first predetermined distance D1. The opening area (shape) of the first holes, the opening area (shape) of the second holes, and the first predetermined distance D1 can be set to any appropriate value within a range in which the air between the first holes and the second holes functions as a spring. The first predetermined distance D1 is, for example, 0.1 to 50% of the diameter (inner diameter) of the first tube 51. Furthermore, as long as the predetermined distance between the first tube 51 and the second tube 52 is appropriately maintained, the first tube 51 shown in FIG. 2A may be divided at the positions of the first holes 61-68 or at the positions of the second holes 71-78.

[0026] Although the first tube 51 and the second tube 52 shown in FIG. 2A are circular tubes, the first tube 51 and the second tube 52 may each be an elliptical tube or a rectangular tube. The first tube 51 and the second tube 52 may each be straight or curved. The cross-sectional areas perpendicular to the axial direction of the first tube 51 and the second tube 52 can be set to appropriate values ​​within a range in which sound waves can be appropriately propagated. The cross-sectional shapes perpendicular to the axial direction of the first tube 51 and the second tube 52 may differ depending on the axial position. The lengths of the first tube 51 and the second tube 52 are not particularly limited as long as at least a portion of the first tube 51 is encompassed by the second tube 52.

[0027] A third hole may be provided in the portion of the first pipe 51 enclosed by the second pipe 52, the third hole being a second predetermined distance away from the second holes 71-78 in the axial direction of the first pipe 51 and in a direction away from the first holes 61-68. FIG. 3A is a cross-sectional view showing a muffler 30 in which a third hole is provided in the first pipe 51 of the silencer tube 50, and shows a cross section taken along line A-A, similar to FIG. 2A . The muffler 30 shown in FIG. 3A is similar to the muffler 30 shown in FIG. 2A except for the third hole being provided in the first pipe 51. FIG. 3B is a perspective view of a main portion showing the holes provided in the first pipe 51 of FIG. 3A . As shown in FIG. 3B , the first pipe 51 is provided with holes 61-68, holes 71-78, and holes 81-88. In this case, the holes 61 to 68 correspond to the first holes, the holes 71 to 78 correspond to the second holes, and the holes 81 to 88 correspond to the third holes.

[0028] 3A, first holes 61-68, second holes 71-78, and third holes 81-88 are provided in the first tube 51 in a portion corresponding to the area between both ends of the second tube 52. The distance between the second holes 71-78 and the third holes 81-88 in the axial direction of the first tube 51 is a second predetermined distance D2. The opening area (shape) of the third holes and the second predetermined distance D2 can be set to appropriate values ​​depending on the target frequency at which the sound pressure level is to be suppressed by the silencer tube 50.

[0029] Although the number of third holes is not particularly limited, in order to synchronize the pressure inside the first pipe 51 and the pressure inside the second pipe 52 without phase delay, it is preferable to provide multiple third holes on one circumference of the first pipe 51, such as holes 81 to 88 shown in FIG. 3B , and it is more preferable to provide multiple third holes symmetrically about the central axis of the first pipe 51. Furthermore, when the first predetermined distance D1 and the second predetermined distance D2 are the same length, the first predetermined distance D1 may be set shorter than the second predetermined distance D2 in order to focus on muffling exhaust noise of one frequency and to aim at muffling exhaust noise of a wide range of frequencies. In the first pipe 51 shown in FIG. 3A , the first predetermined distance D1 is shorter than the second predetermined distance D2, and the first predetermined distance D1 is approximately half of the second predetermined distance D2. Furthermore, as long as the predetermined distance between the first tube 51 and the second tube 52 is properly maintained, the first tube 51 shown in FIG. 3A may be divided at the positions where the third holes 81 to 88 are provided.

[0030] [Function of the Silencer Tube] The function of the muffler 30 according to the embodiment of the present invention will be described using Figures 4 to 6. Figure 4 is an enlarged cross-sectional view of the silencer tube 50 in the cross-sectional view of Figure 2A. Sound waves introduced from the exhaust pipe 20 in Figure 2A into the second chamber X2 and propagated to the third chamber X3 via the hole 33a are introduced into the silencer tube 50 from the open ends 51b and 52b and propagate to the first chamber X1 via the first tube 51 and the second tube 52. The air in the first chamber X1, which forms a closed space, functions as a spring for the sound waves introduced from the open ends 51a and 52a, and the air in the silencer tube 50 functions as a mass for the spring, causing the air in the silencer tube 50 to vibrate. When sound waves having a certain frequency are introduced into the first chamber X1 from the open ends 51 a, 52 a, the air inside the silencer tube 50 vibrates, and the air vibrations are in opposite phase to the introduced sound waves, reducing the sound pressure level of the introduced sound waves. In this way, the silencer tube 50 shown in Figure 2A functions as a resonator that suppresses the sound pressure level of the exhaust sound in the muffler 30, together with the first chamber X1.

[0031] The resonator consisting of the silencer tube 50 and first chamber X1 shown in Fig. 2A can be expressed as a mass-spring system shown in Fig. 4. In the mass-spring system shown in Fig. 4, the air in the first chamber X1, which forms a closed space, functions as a spring, so the part corresponding to the first chamber X1 becomes spring S1. Furthermore, because springs and masses appear alternately, the air between the open ends 51a and 51b of the first tube 51 becomes mass M1, and the air between the open ends 52a and 52b of the second tube 52 becomes mass M2. Furthermore, in the first tube 51 and the second tube 52, the air between the positions where the first holes 61 to 68 are provided and the positions where the second holes 71 to 78 are provided functions as springs S2 and S3, so that the air between the open end 51 a of the first tube 51 and the positions where the first holes 61 to 68 are provided becomes mass M3, the air between the open end 51 b of the first tube 51 and the positions where the second holes 71 to 78 are provided becomes mass M4, the air between the open end 52 a of the second tube 52 and the positions where the first holes 61 to 68 are provided becomes mass M5, and the air between the open end 52 b of the second tube 52 and the positions where the second holes 71 to 78 are provided becomes mass M6. Note that the positions where the first holes are provided are positions in the axial direction of the silencer tube 50, and the same applies to the second and third holes.

[0032] For example, when sound waves having a frequency corresponding to mass M1 are introduced into the silencer tube 50, the introduced sound waves excite mass M1, and the vibrated mass M1 vibrates spring S1, resulting in a resonance phenomenon between mass M1 and spring S1. If the vibration of mass M1 amplified by this resonance phenomenon is in the opposite phase to the introduced sound waves, the sound waves introduced into the silencer tube 50 are canceled out. The same is true for the other masses M2 to M6. When sound waves having frequencies corresponding to each of masses M2 to M6 are introduced into the silencer tube 50, the corresponding masses M2 to M6 are vibrated, and the vibrated masses M2 to M6 vibrate the adjacent springs S1 to S3, resulting in a resonance phenomenon between masses M2 to M6 and springs S1 to S3. If the vibration of masses M2 to M6 amplified by this resonance phenomenon is in the opposite phase to the introduced sound waves, the sound waves introduced into the silencer tube 50 are canceled out. Therefore, the resonator consisting of the silencer tube 50 and the first chamber X1 shown in FIG. 2A can suppress the sound pressure level of six frequencies among the sound waves of the exhaust sound.

[0033] In contrast, in a double pipe that does not have the first and second holes, the springs S2 and S3 between the first and second holes are not formed, so the sound pressure level can only be suppressed for two frequencies of the exhaust sound waves. In other words, in the muffler 30 according to the embodiment of the present invention, by providing the first holes 61-68 and the second holes 71-78 in the first pipe 51, the number of frequencies at which the sound pressure level can be suppressed can be increased.

[0034] Figure 5 is an enlarged cross-sectional view showing a mass-spring system when the first tube 51 is shorter than the second tube 52. The silencer tube 50 shown in Figure 5 is similar to the silencer tube 50 shown in Figure 4 except that the stay 54 is not present and the open end 51b is enclosed by the second tube 52. In the resonator consisting of the silencer tube 50 shown in Figure 5 and the first chamber X1, a mass-spring system similar to that shown in Figure 4 is formed. That is, a mass-spring system is formed that includes springs S1 to S3 similar to those in FIG. 4, a mass M1a which is air between the open ends 51a and 51b of the first tube 51, a mass M2a which is air between the open ends 52a and 52b of the second tube 52, a mass M3 which is air between the open end 51a of the first tube 51 and the positions where the first holes 61 to 68 are provided, a mass M4a which is air between the open end 51b of the first tube 51 and the positions where the second holes 71 to 78 are provided, a mass M5 which is air between the open end 52a of the second tube 52 and the positions where the first holes 61 to 68 are provided, and a mass M6a which is air between the open end 52b of the second tube 52 and the positions where the second holes 71 to 78 are provided. The resonator shown in FIG. 5, which is made up of the silencer tube 50 and the first chamber X1, can suppress the sound pressure level of six frequencies of the exhaust sound waves, similar to the resonator shown in FIG.

[0035] Figure 6 is an enlarged cross-sectional view showing a mass-spring system when a third hole is provided in the first tube 51. The silencer tube 50 shown in Figure 6 is similar to the silencer tube 50 shown in Figure 4 except that a third hole is provided in the first tube 51. In the resonator consisting of the silencer tube 50 and the first chamber X1 shown in Figure 6, in addition to the springs S1 to S3 and masses M1 to M6 shown in Figure 4, a mass-spring system is formed that includes a mass M7 of air between the positions of the second holes 71 to 78 and the positions of the third holes 81 to 88 in the first tube 51, and a mass M8 of air between the positions of the second holes 71 to 78 and the positions of the third holes 81 to 88 in the second tube 52. This is because, by providing the third holes 81-88 in the first tube 51, the air in the first tube 51 and the air in the first holes 61-68, second holes 71-78, and third holes 81-88 each have the characteristics of a spring and a mass in each section, and two masses M4 and M7 can be formed between the positions where the second holes 71-78 are provided and the open end 51b, and two masses M6 and M8 can be formed between the positions where the second holes 71-78 are provided and the open end 52b. As a result, the resonator consisting of the silencer tube 50 provided with the third holes 81-88 and the first chamber X1 can suppress the sound pressure level for eight frequencies of the sound waves in the exhaust sound.

[0036] Note that in Figures 4 to 6, the sizes of the springs and masses are appropriately modified for the purpose of explanation, but the sizes of the springs and masses shown do not represent the characteristics of the springs and masses. For example, the spring S2 shown in Figure 4 and the spring S2 shown in Figure 6 have different display sizes, but have the same characteristics as a spring. Similarly, the mass M4 shown in Figure 4 and the mass M4 shown in Figure 6 have different display sizes, but have the same characteristics (mass) as a mass.

[0037] [Embodiment of the Invention] According to this embodiment, there is provided an engine silencer comprising: a first pipe 51 having one end communicating with a chamber forming a closed space and the other end being an open end; and a second pipe 52 having one end communicating with the chamber and the other end being an open end and arranged outside the first pipe 51 so as to encompass at least a portion of the first pipe 51, a predetermined distance being provided between the first pipe 51 and the second pipe 52; and first holes 61-68 and second holes 71-78 spaced a first predetermined distance from each other in the axial direction of the first pipe 51 in the portion of the first pipe 51 encompassed by the second pipe 52. As a result, the frequency of exhaust noise at which the sound pressure level can be suppressed increases compared to when a conventional double pipe is used, and the size of the muffler 30 can be suppressed.

[0038] In the engine silencer of this embodiment, the first pipe 51 is provided with a plurality of the first holes 61 to 68 on one circumference of the first pipe 51. This allows the pressure inside the first pipe 51 and the pressure inside the second pipe 52 to be synchronized without any phase delay.

[0039] In the engine silencer of this embodiment, the first pipe 51 is provided with a plurality of the second holes 71 to 78 on one circumference of the first pipe 51. This allows the pressure inside the first pipe 51 and the pressure inside the second pipe 52 to be synchronized without any phase delay.

[0040] In the engine silencer of this embodiment, third holes 81 to 88 are provided in the portion of the first pipe 51 that is enclosed within the second pipe 52, the third holes 81 to 88 being spaced a second predetermined distance from the second holes 71 to 78 in the axial direction and in a direction away from the first holes 61 to 68. This makes it possible to further increase the frequencies of exhaust noise whose sound pressure level can be suppressed.

[0041] In the engine silencer of this embodiment, the first pipe 51 is provided with a plurality of the third holes on one circumference of the first pipe 51. This allows the pressure inside the first pipe 51 and the pressure inside the second pipe 52 to be synchronized without any phase delay.

[0042] In the engine silencer of this embodiment, the first predetermined distance is shorter than the second predetermined distance, which makes it possible to silence exhaust noise over a wide range of frequencies.

[0043] DESCRIPTION OF SYMBOLS 10... Engine 20... Exhaust pipe 30... Muffler 31... Housing 32, 33... Partition plate 33a... Hole 40... Tail pipe 50... Pipe (silencer pipe) 51... First pipe 51a, 51b... Open end 52... Second pipe 52a, 52b... Open end 53, 54... Stays 53a, 53b, 53c, 53d, 53e, 53f, 53g, 53h, 54a, 54b, 54c, 54d, 54e, 54f, 54g, 54h... Holes 61, 62, 63, 64, 65, 66, 67, 68, 71, 72, 73, 74, 75, 76, 77, 78, 81, 82, 83, 84, 85, 86, 87, 88... Holes D1...first predetermined distance, D2...second predetermined distance M1, M1a, M2, M2a, M3, M4, M4a, M5, M6, M6a, M7, M8...masses S1, S2, S3...springs X1...first chamber, X2...second chamber, X3...third chamber Y1, Y2, Y3...arrows

Claims

1. An engine soundproofing device comprising: a first pipe having one end communicating with a chamber forming a closed space and the other end being an open end; and a second pipe having one end communicating with the chamber and the other end being an open end and arranged outside the first pipe so as to encompass at least a portion of the first pipe, a predetermined distance being provided between the first pipe and the second pipe, and a first hole and a second hole being spaced from each other by a first predetermined distance in the axial direction of the first pipe in the portion of the first pipe encompassed by the second pipe.

2. The engine silencer according to claim 1, wherein the first pipe is provided with a plurality of the first holes on one circumference of the first pipe.

3. An engine silencer as set forth in claim 1 or 2, wherein the first pipe is provided with a plurality of the second holes on one circumference of the first pipe.

4. An engine silencer as described in any one of claims 1 to 3, wherein a third hole is provided in the portion of the first pipe enclosed within the second pipe, the third hole being a second predetermined distance away from the second hole in the axial direction and in a direction away from the first hole.

5. The engine silencer according to claim 4, wherein the first pipe is provided with a plurality of the third holes on one circumference of the first pipe.

6. An engine silencer as set forth in claim 4 or 5, wherein the first predetermined distance is shorter than the second predetermined distance.

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