BRPI0902022A2 - motorcycle - Google Patents

Abstract

An exhaust pipe (20) into which an exhaust gas from a single cylinder engine (50) flows is provided with a three way catalyst (90). The exhaust pipe includes a first pipe (42) inserted into a muffler (30) and a second pipe (44) extending toward the downstream side from the first pipe (42) within the muffler (30). A narrowed portion (47) having an inner diameter smaller than that of a cylindrical portion (46) of the first pipe (42) is provided in a downstream-end opening of the first pipe (42). The narrowed portion (47) is inserted into an upstream-end opening of the second pipe (44). A first expansion chamber (70) that integrally encloses the outer periphery and the downstream-end opening of the second pipe (44) is formed within the muffler (30). A plurality of holes (45) are formed in a distributed manner in a region, except a downstream region, of a peripheral surface of the second pipe (44). The length in the axial direction of the downstream region is not less than 1/3 times the inner diameter of the second pipe (44).

Description

"MOTORCYCLE"

This application claims the priority of Japanese Patent Application No. 2008-174408, filed July 3, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to motorcycles including stripping devices.

2. Description of the Prior Art

To date, a number of silencers have been developed to reduce the exhaust sounds caused by exhaust exhaust from car engines (see JP-B-60-37287, for example).

The silencer disclosed in JP-B-60-37287 has a perforated barrel and an outer cylinder. The perforated pipe is inserted into the outer cylinder. A resonant chamber is formed between the outer peripheral surface of the perforated barrel and the inner peripheral surface of the outer cylinder. An expansion chamber is formed on the downstream side of the resonant chamber within the outer cylinder. The resonant chamber and the expansion chamber are separated by a dividing plate. The internal space of the perforated barrel communicates with the resonant chamber through holes of the perforated barrel. In addition, a downstream end of the perforated pipe is opened within the expansion chamber.

The end on the downstream side of the exhaust pipe is narrowed down to form a small diameter portion. The end of the exhaust pipe is mounted on the perforated pipe. Exhaust gas discharged from the exhaust pipe is introduced into the expansion chamber through the perforated pipe, and is also introduced into the atmosphere through the discharge pipe. At this point, the exhaust sound is reduced by the function of the resonant chamber and the expansion chamber.

Meanwhile, mufflers are also fitted on motorcycles. Motorcycle mufflers need to reduce exhaust sounds caused by high-pressure, high-temperature exhaust exhaust. In addition, the rotational speeds of motorcycle engines amount to no less than 8000 rpm. Therefore, mufflers used on motorcycles need to have the desired engine performance by adjusting the engine exhaust exhaust flows.

In the case of multi-cylinder engines, a plurality of exhaust pipes communicate, so that the pressure fluctuation in each exhaust pipe is absorbed by the other exhaust pipe. Therefore, the pressure fluctuation in each of the exhaust pipes is relatively small. In contrast, in the case of single cylinder engines, the pressure fluctuation in a tailpipe is large.

In recent years, motorcycles, in which exhaust systems are supplied with catalysts to clean exhaust gases, have also been developed. In this case, the exhaust gas temperatures rise by the catalysts. This causes sound speeds to increase, causing high frequency components of exhaust sounds to increase. As a result, metallic exhaust sounds including high frequency components are produced when the catalysts are used for single cylinder engine exhaust systems.

In addition, mufflers that are thinner and shorter than these nasmotorcycles are necessary because of space limitations on motorcycles.

When motorcycle muffler structures are used for motorcycle-powered catalysts, it is impossible to sufficiently reduce the high frequency components of the exhaust sounds without increasing the size of the mufflers.

Particularly on motorcycles including single cylinder engines, it is desired that the engine output performances be sufficiently presented by small size silenced while small exhaust sounds that are synchronized with engine combustion are obtained.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a motorcycle in which the output performance of an engine is sufficiently presented while the high frequency exhaust sound components are sufficiently reduced.

(1) In accordance with one aspect of the present invention, a motorcycle includes a vehicle chassis, a single cylinder engine provided in the vehicle chassis, a tailpipe into which an engine exhaust gas flows, a supplied nocano exhaust catalyst and a muffler that discharges exhaust gas flowing out of the exhaust pipe, wherein the exhaust pipe includes a first pipe having a downstream end opening inserted into the silencer, and a second pipe having an upstream end opening and a opening at the downstream end and extending downstream of the first barrel within the silent, a narrow portion having an inner diameter smaller than that of the first barrel is provided at the downstream end opening of the first barrel and is inserted into the upstream end opening of the second pipe, a first expansion chamber which completely surrounds the outer periphery and the opening at the downstream of the second pipe is formed within the muffler and a plurality of holes are formed in a way distributed in one region except one region at a downstream end, a peripheral surface of the second pipe and the length in the axial direction of the downstream end region Not less than 1/3 times the inside diameter of the second pipe.

In the motorcycle, the single cylinder engine exhaust gas provided in the vehicle chassis flows into the exhaust pipe. At this time, the exhaust gas is cleaned by the catalyst while entering a state of high temperature. This induces the speed of sound to increase, causing the high frequency components of the exhaust sound to increase.

The high temperature exhaust gas exits into the first nozzle expansion chamber via the first pipe and the second pipe in the exhaust pipe. At this time, the exhaust gas is extruded into the second pipe while being compressed by the narrow portion of the first pipe. so that the exhaust gas pressure (exhaust gas pressure) increases. This prevents an unburnt mixed gas from exiting in a period of engine overlap. This results in improved engine-generated torques in a low speed area and a medium speed area.

In this case, a portion of the exhaust gas within the second pipe expands outwardly into the first expansion chamber through the holes. In addition, the exhaust gas remaining within the second pipe expands fluid into the first expansion chamber from the downstream end opening. In this case, the first expansion chamber completely and continuously surrounds the outer periphery and the opening of the downstream end of the second pipe.

A plurality of holes are formed in the region, except the region at the downstream end, of the peripheral surface of the second pipe. The length in the axial direction of the downstream region is adjusted to not less than 1/3 times the inside diameter of the second pipe. Thus, the fluctuation of the exhaust gas pressure out of the second pipe through the holes and the fluctuation of the exhaust gas pressure flowing out of the downstream end opening of the second pipe, respectively, have high frequency components of different phases. Therefore, high frequency components of different phases are canceled by each other. As a result, the high frequency components of the exhaust sound are reduced.

Moreover, the exhaust gas compressed by the narrow portion of the first chuck expands step by step in the second pipe and first expansion chamber. This causes a pressure wave that can be generated by the rapid expansion of the exhaust gas to be relieved. This results in the inhibition of sound production caused by the high pressure.

Moreover, the first expansion chamber fully surrounds the outer periphery and the opening at the downstream end of the second pipe within the muffler. Therefore, it is possible to ensure that the volume of the first expansion chamber serving as the same pressure space is sufficiently large. As a result, it is possible to sufficiently reduce the high frequency components of the exhaust sound by increasing the length and cross-sectional area of the muffler.

These results show that the output performance of the single cylinder engine is sufficiently presented while the high frequency components of the exhaust sound are sufficiently reduced.

(2) The second barrel may be joined to the first barrel in a position on the bulging side of the narrow portion.

In this case, the second pipe is securely fixed to the first pipe in a swing state without using a support element. This prevents vibration and rocking of the second pipe from being generated. This results in the prevention of sound production due to vibration or swaying of the second pipe.

(3) The narrow portion may include a conical portion having an inner diameter that gradually decreases. In this case, it is possible to avoid the production of a flow noise due to the exhaust gas flow disturbance.

(4) A second expansion chamber may also be formed on the downstream side of the first expansion chamber within the muffler, the first expansion chamber and the second expansion chamber may be separated by a split plate, and a connecting plug may be provided. to penetrate the split plate.

In this case, the exhaust gas compressed by the narrow portion of the first tube expands step by step in the second pipe, the first expansion chamber and the second expansion chamber. This causes a pressure wave that can be generated by the rapid expansion of the exhaust gas to be effectively relieved. This results in sufficient inhibition of sound production due to the pressure wave.

(5) The volume of the first expansion chamber may be larger than the volume of the second expansion chamber. In this case, the first expansion chamber completely surrounds the outer periphery and the opening of the downstream end of the second pipe. Thus, it is possible to make the volume of the first expansion chamber larger than the volume of the second expansion chamber without increasing the length and length of the second expansion chamber. diameter of the muffler.

Therefore, the high frequency components of the exhaust sound can be effectively reduced in the first expansion chamber.

(6) In the exhaust pipe, a part of the first pipe may be kept silent, and the second pipe may not be kept silent.

In this case, no supporting element exists on the periphery side of the second pipe, so that the exhaust gas flow flowing out of the plurality of holes in the second pipe is not disturbed. This can prevent the production of a flow noise due to the disruption of the exhaust gas flow. According to the present invention, the engine output performance is sufficiently applied while the high frequency components of the exhaust sound are sufficiently reduced.

Other aspects, elements, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a side view of a motorcycle according to an embodiment of the present invention.

Figure 2 is a perspective view of the appearance of a stripping device when viewed from above,

Figure 3 is a perspective view of the appearance of a stripping device when viewed from the side,

Figure 4 is a cross-sectional view taken along line IV - IV of a silentman shown in Figure 2,

Figure 5 is an enlarged cross-sectional view of an exhaust pipe shown in Figure 4,

Figure 6 is a cross-sectional view of a muffler in comparative example 1,

Figure 7 is a diagram showing the respective results of measuring the damping properties of a muffler in an inventive example and the muffler in comparative example 1 and 2.

Figure 8 is a cross-sectional view of a muffler in a comparative example 2.

DESCRIPTION OF MODALITIES

With reference to the drawings, embodiments of the present invention will be described while referring to the drawings.

In the following description, the upstream side and downstream side will be defined with the flow of an exhaust gas used as a base.

(1) Motorcycle Configuration

Figure 1 is a side view of a motorcycle according to an embodiment of the present invention.

A motorcycle 100 shown in Figure 1 includes a vehicle chassis 80 composed of a vehicle chassis frame and a frame cover. A (not shown) front barrel is provided on the front of the vehicle chassis 80 and a handlebar 81 is provided at an upper end of the front barrel. A front fork 82 is secured to a lower end of the front barrel. In this state, the front fork 82 is rotatable within a predetermined angle range with the geometric axis of the front barrel used as its center. A front wheel 83 is rotatably supported on a lower end of the front fork 82. A rear wheel 84 is rotatably supported on the chassis of vehicle 80. A single cylinder engine 50 is provided at the center of vehicle 80. The wheel rear 84 is rotated by a rotary force of the engine 50.

An exhaust device 10 introducing an external exhaust gas is connected to a cylinder head 51 of the engine 50. The exhaust device 10 includes an exhaust pipe 20 and a muffler 30. Exhaust pipe 20 extends rearwardly. of cylinder head 51 of engine 50. Muffler 30 extends to rear wheel side 84 from a downstream end of exhaust pipe 20.

(2) Exhaust device configuration 10

Figure 2 is a perspective view of the appearance of the exhaust device when viewed from above. Figure 3 is a perspective view of the exhaust device appearance 10 when viewed from the side.

An exhaust port connector 22 is provided at one end of the exhaust pipe 20. An opening in the upstream side of the exhaust pipe 20 is connected to a cylinder head exhaust port 51 shown in Figure 1 by the connector of the exhaust port. Exhaust port 22. The downstream end 24 of the exhaust pipe 20 is inserted into an upstream (inlet) end of the silencer 30. The outer periphery at the upstream end of the silencer 30 is secured by a mounting member 26 so that the Muffler 30 is fixed to Exhaust Pipe 20.

Downstream end 24 of exhaust pipe 20 is connected at an upstream end of an exhaust pipe 40 within muffler 30. A three-way catalyst 90 is provided within exhaust pipe 40. Note that exhaust pipe 20 and pipe 40 may also be integrally formed. Alternatively, the exhaust pipe 20 and the exhaust pipe 40 may be connected to one another via another element. The covers 31a and 31b are secured to an outer peripheral surface of the muffler 30.

An exhaust gas generated by the combustion of an air-fuel mixture within the engine 50 shown in Figure 1 is fed into the muffler 30 through the exhaust pipe 20. The exhaust gas is discharged into the atmosphere through the muffler 30. Thus , an engine exhaust path 5035 includes cylinder head exhaust hole 51, exhaust pipe 20 and slack 30 in the upstream to downstream order.

The muffler 30 has a sound muffling function to reduce the sound of the exhaust before discharging the exhaust gas into the atmosphere. In the present embodiment, the interior of the muffler 30 has a multistage expansion type structure described later. That is, the interior of muffler 30 is divided into a plurality of expansion chambers, so that exhaust gas expands through the plurality of expansion chambers. This induces the exhaust gas to be depressurized.

(3) Internal structure of muffler 30

The internal structure of muffler 30 will then be described while referring to figure 4. Figure 4 is a cross-sectional view taken along line IV - IV of the silent 30 shown in figure 2. Figure 5 is an enlarged sectional view of the barrel of the exhaust 40 shown in figure 4.

As shown in Figure 4, muffler 30 includes a tapered head 32, a hollow body cylindrical 34 and a bowl-shaped tail 37. Head 32 is mounted in an opening in the upstream side of body 34. Tail 37 is mounted in a opening in downstream side of body 34.

Split plates 36 and 38 are arranged with predetermined spacing in the upstream side at positions near a downstream end of the body 34. Thus an internal silencer space 30 is divided into a first expansion chamber 70, a second expansion chamber 72 and a third expansion chamber 74. The first expansion chamber 70, the second expansion chamber 72 and the third expansion chamber 74 align in the upstream to downstream order in the longitudinal direction of the muffler 30.

A connecting pipe 62 penetrates the splitting plate 36, a connecting pipe 64 penetrates the splitting plate 38 and a rear pipe 66 penetrates the tail 37.

Exhaust pipe 40 is inserted into head 32. A downstream portion of exhaust pipe 40 extends into first expansion chamber 70. Exhaust gas is introduced into first expansion chamber 70 through exhaust pipe 40.

Exhaust pipe 40 includes a first pipe 42 on the upstream side and a second cylindrical pipe 44 on the downstream side. First barrel 42 has a cylindrical portion 46 on the upstream side and a narrow portion 47 on the downstream side. The narrow portion 47 has a conical portion 48a and a small diameter portion 48b. The small diameter portion 48b has an outer diameter and an inner diameter respectively smaller than the outer diameter and the inner diameter of the cylindrical portion 46. The outer diameter and the inner diameter of the tapered portion 48a gradually decrease from an outer diameter and an inner diameter which are the same as those of cylindrical portion 46 for an outer diameter and an inner diameter which are the same as the small diameter portion 48b. Thus, the cross-sectional area of a flow path of the right portion 47 gradually decreases from upstream to downstream.

The inner diameter R2 of the second barrel 44 is equal to the outer diameter of the cylindrical portion 46 of the first barrel 42. The narrow portion 47 of the first barrel 42 is inserted into an opening in the upstream end of the first barrel 42 such that a bulging end of the second barrel 42. 44 is overlapped with the cylindrical portion 46 in a position upstream of the narrow portion 47 of the first barrel 42. In that state, an outer peripheral surface of the cylindrical portion 46 of the first barrel 42 and an inner peripheral surface of the second barrel 44 are welded together. that the second pipe 44 is joined at the cylindrical portion 46. Thus, the second pipe 44 is held on the first pipe 42 in a swing state. Furthermore, a cylindrical clearance is formed between the inner peripheral surface of the second pipe 44 and the narrow portion 47. The conical portion 48a is open into the second pipe 44.

The first barrel 42 is secured to an inner surface of the head 32 by a support shoulder 35 so that it is positioned in the center of the head 32 and body 34.

The inner diameter RO of the small diameter portion 48b of the narrow portion 47 is smaller than the inner diameter R1 of the cylindrical portion 46 (R0 <R1). The inner diameter R2 of the second barrel 44 is larger than the inner diameter RO of the small diameter portion 48b of the narrow portion 47 and is smaller than the inner diameter R3 of the first expanding chamber 70 (R0 <R2 <R3). This enables a pressure fluctuation created by the rapid expansion of the exhaust gas flowing out of the first pipe 42 into the first expansion chamber 70 to be relieved.

In this case, it is preferable that the inside diameter R2 of the second pipe 44 is not very close to the inside diameter R3 of the expansion chamber 70 and not too close to the inside diameter RO of the small diameter portion 48b. This allows a depression wave caused by the rapid expansion of the exhaust gas to be sufficiently relieved by the second pipe 44.

It is preferred that the inside diameter R2 of the second barrel 44 is approximately equal to the inside diameter R1 of the cylindrical portion 46 of the first barrel 42. In this embodiment, the inside diameter R2 of the second barrel 44 is equal to the outside diameter of the cylindrical portion 46 of the first barrel 42. Therefore, the inside diameter R2 of the second barrel44 is approximately equal to the inside diameter R1 of the cylindrical portion 46 of the first barrel42. This enables the pressure wave to be effectively relieved.

Note that the length L of an opening at the downstream end 49 of the narrow portion 47 to an opening at the downstream end 43 of the second pipe 44 is not particularly limited and is determined such that a low frequency exhaust dosing component does not disappear and the resistance of the second pipe 44 kept in a swing state is guaranteed.

As shown in Figure 5, the second pipe 44 includes an upstream region RU where a plurality of holes 45 are produced and a downstream region RD where no holes are substantially produced in the downstream order. The plurality of holes 45 are equally spaced in the upstream region RU. The plurality of holes 45 are drill holes, for example. The plurality of holes 45 penetrates the second barrel 44 from its outer peripheral surface to its inner peripheral surface. In the present embodiment, the shape of each of the holes 45 is circular.

The downstream region RD has an upstream length D from the downstream end opening 43 of the second pipe 44. The length D of the downstream region RD is not less than 1/3 times the inside diameter R2 of the second pipe 44.

The downstream region RD may be provided with one or more holes to have an aperture ratio that is not greater than one third of the opening ratio of the bulking region RU. The opening ratio of the upstream region RU means the ratio of the sum of the open areas of the plurality of holes 45 to the area of the upstream region RU. The reason for the opening of the downstream region RD means the ratio of the sum of the open areas at one or more holes to the area of the downstream region RD. In this case, the one or more holes produced in the downstream region RD hardly affect the reducing effect of the high frequency components described later. Therefore, the fact that the downstream region RD is produced with one or more holes so that the opening ratio is not greater than one third of the opening ratio of the upstream region RU means that no hole is substantially produced in the downstream region. downstream RD.

Although the ratio of the sum of the open areas of the plurality of holes 45 to the cross-sectional area of the second pipe flow path 44 (hereinafter referred to as the area ratio of the plurality of holes 45) is not particularly limited, it is preferable that the ratio the area of the plurality of holes 45 is not less than 0.5 nor greater than 2.0, for example approximately 1.0.

Note that the internal diameter of each of the holes 45 and the spacing between the holes 45 (the distance between the centers of the adjacent holes 45) can be adjusted as necessary so that the above mentioned sound reduction effect can be satisfactorily achieved. In this case, the inside diameter of each of the holes 45 and the spacing between the holes 45 may be selected to efficiently obtain the sound reducing effect while restricting pressure loss.

(4) Exhaust device operation 10

Operation of the exhaust device 10 according to the present embodiment will be described below. An exhaust gas from the engine exhaust hole 50 shown in figure 1 is introduced into the exhaust pipe 40 through the exhaust pipe 20 shown in figures 2 and 3. At this point, the exhaust gas is cleaned by the three way catalyst 90 while entering a high temperature state. This induces an increase in sound velocity, causing an increase in the high frequency components of the exhaust sound.

The high temperature exhaust gas flows into the first expansion chamber 70 in muffler 30 via the first pipe 42 and the second pipe 44 in the exhaust pipe 40. At that time, the exhaust gas is extruded into the second pipe 44 while being compressed. by the narrow portion 47 of the first pipe 42, so that the exhaust gas pressure (exhaust gas pressure) increases. This prevents an unburned blended gas from exiting a period of overlap (a period during which both a suction valve and an exhaust valve are open) from engine 50. This results in improved torques generated by engine 50 in a slow speed area. and a medium speed area.

The exhaust gas compressed by the narrow portion 47 expands flowing into the second pipe 44. As shown in Figure 5, an exhaust gas E1 which is a part of the exhaust gas within the second pipe 44 expands flowing into the first expansion chamber 70 through Further, the remaining exhaust gas E2 expands by flowing into the first expansion chamber 70 from the opening of the downstream end 43 of the second pipe 44. In this case, the first expansion chamber 70 completely and continuously surrounds the periphery. opening and opening at the downstream end 43 of the second barrel 44.

Holes 45 are formed in the upstream region RU, except in the downstream region RD, as described above. Therefore, the exhaust gas pressure fluctuation E1 flowing out of the second pipe 44 through the holes 45 and the exhaust gas pressure fluctuation E2 flowing out of the opening at the downstream end 43 of the second plane 44, respectively, have high components. frequency of different phases. Thus, the high frequency exhaust gas pressure fluctuation components and the high frequency exhaust gas pressure fluctuation components are balanced by each other within the same pressure space. The results of the considerations given by the inventors of the present invention show that the high frequency components are effectively canceled by each other when the length L of the downstream region RD is not less than 1/3 times the inner diameter R2 of the second pipe44. This induces a reduction in the high frequency components of the exhaust sound. Furthermore, the exhaust gas compressed by the narrow portion 47 of the first pipe 42 expands step by step in the second pipe 44 and the first expansion chamber 70. This causes a pressure wave that can be generated by the rapid expansion of the exhaust gas is relieved. This results in the inhibition of sound production due to the pressure wave (particularly a metallic sound including high frequency components).

The exhaust gas within the first expansion chamber 70 expands into the second expansion chamber 72 via the connecting pipe 62. The exhaust gas within the second expansion chamber 72 expands by flowing into the third expansion chamber 74 through the expansion pipe. port 64. The exhaust gas inside the third expansion chamber 74 is discharged outward through the canotras 66 and is released into the atmosphere.

If the distance between the downstream end opening 43 of the second pipe 44 and the upstream end opening of the connecting pipe 62 is too small, the dampening effect of the sound is reduced. If the distance between the downstream end opening 43 of second pipe 44 and split plate 36 is too small, the torque generated by motor 50 is reduced. Therefore, the length D of the downstream region RD preferably is not more than three times and more preferably no more than two times the inner diameter R2 of the second pipe 44.

(5) Effects of preferred mode

In motorcycle 100 according to the present embodiment, exhaust gas introduced into exhaust pipe 40 from single cylinder engine 50 through exhaust pipe 20 is compressed by narrow portion 47 of first pipe 42. This prevents the unburnt mixed gas exit engine 50. This results in improved nostocks generated by engine 50 in the low speed and medium speed area.

Furthermore, the exhaust gas compressed by the narrow portion 47 of the first pipe 42 expands step by step in the second pipe 44, the first expansion chamber 70, the second expansion chamber 72 and the third expansion chamber 74, so that the pressure of the exhaust gas decreases to atmospheric pressure step by step. This induces a reduction in the exhaust sound.

In this case, the exhaust gas E1 within the second pipe 44 flows into the first expansion chamber 70 through the holes 45, and the remaining exhaust gas E2 flows into the first expansion chamber 70 from the opening at the downstream end 43. Thus , the high frequency components of the exhaust gas depression fluctuation E1 and the high frequency components of the exhaust gas depression fluctuation E2 are canceled by each other within the first expansion chamber 70 serving as the same pressure space. This causes the high frequency components of the increased pressure fluctuation increased by the three-way catalyst 90 to be reduced. Therefore, the high frequency components of the exhaust sound are sufficiently reduced. As a result, it is possible to obtain an intermittent low exhaust sound that is synchronized with the combustion of the single cylinder motor 50 while preventing metallic sound including the high frequency components from being produced.

Moreover, the second barrel 44 is fixed to the first barrel 42 in a wrapping state at its upstream end. Thus, no supporting element exists on the outer periphery of the second barrel 44, and the first expansion chamber 70 completely and continuously surrounds the outer peripheral surface and the opening in the downstream end 43 of the second barrel 44. Therefore, it is possible to ensure that the volume of the first expansion chamber 70 serving as the same pressure space is sufficiently large. As a result, it is possible to sufficiently reduce the high frequency components of the exhaust sound without increasing the length and diameter of the muffler 30. In addition, this may prevent the production of a flow noise due to the exhaust gas flow disturbance.

Since the second pipe 44 is connected to the first pipe 42 in a position upstream of the narrow portion 47, the second pipe 44 is fixedly fixed to the outer peripheral surface of the first pipe 42 with high strength. This prevents vibration and balance of second pipe 44 from being produced. This results in the prevention of sound production having a natural frequency of vibration or swaying of the second drum 44 and a continuous sound caused by vibration or swaying of the second pipe 44.

(6) Other Modalities

Although the narrow portion 47 has the conical portion 48a and the small diameter 48b portion in the above-mentioned embodiment, the narrow portion 47 may have a step structure unless the flow of the exhaust gas is disturbed. In such a case, the exhaust pressure is also increased by the narrow portion 47.

Although the shape of the plurality of holes 45 is circular in the above mentioned embodiment, the present invention is not limited thereto. For example, the plurality shape of holes 45 may be elliptical or polygonal.

Moreover, although the plurality of holes 45 are equally spaced in the upstream region RU, except in the downstream region RD, the plurality of holes 45 may be randomly arranged.

Although first barrel 42 and second barrel 44 have, respectively, circular cross-sections in the aforementioned embodiment, the present invention is not limited thereto. For example, first barrel 42 and second barrel 44 may have elliptical cross sections, respectively. In this case, the long eixogeometric length of an ellipse is taken as an inner diameter. Therefore, the length D of the downstream region RD of the second barrel 44 is adjusted to not less than 1/3 times the length of the long ellipse axis and preferably no more than three times and more preferably no more than twice the inner diameter. R2 of the second barrel 44. Moreover, the first barrel 42 and the second barrel 44 may have respectively polygonal cross sections. In this case, the length of the longest diagonal line of a polygon is taken as an inner diameter. Therefore, the length D of the downstream region RD of the second pipe 44 is adjusted to not less than 1/3 times the length of the longest diagonal line of the polygon and preferably not more than three times and more preferably not more than twice the internal diameter. R2 of the second pipe 44.

Although the three-way catalyst 90 is used in the aforementioned embodiment, the present invention is not limited thereto. The three-way catalyst 90 may be replaced by an oxidation catalyst or a reduction catalyst, for example.

(7) Examples

The effects of respectively reducing the high frequency components of muffler escape sounds in an inventive example and comparative examples 1 and 2 were examined. In the inventive example, muffler 30 shown in figure 4 was used.

Figure 6 is a cross-sectional view of the muffler in comparative example1. The muffler 30a shown in figure 6 differs from the muffler 30 shown in figure 4 in that the muffler 30a shown in figure 6 does not have the second barrel 44. The configuration of the other portions of muffler 30a shown in figure 6 is the same as the muffler configuration 30 shown in figure 4.

In muffler 30 in the inventive example and muffler 30a in comparative example1, the inner diameter RO of the narrow portion 47 is 16.1 mm, and the inner diameter R1 of the first barrel 42 is 23.6 mm. In addition, the inside diameter and length of the disconnect pipe 62 are 28.6 mm and 50 mm respectively, the inside diameter and the length of the connecting pipe 64 respectively 22.2 mm and 50 mm, and the inner diameter and length of rear barrel 66 are, respectively, 22.2 mm and 30 mm.

In muffler 30 in the inventive example, the inside diameter R2 of the second pipe 44 is 27.4 mm, the inside diameter of the holes 45 is 5 mm, and the spacing between the holes 45 is 7.5 mm. The diameter of the holes 45 is 5 mm, and the length L of the opening at the downward end 49 of the narrow portion 47 to the opening at the downstream end 43 of second second 44 is 42 mm. The length D of the downstream region RD is 9.5 mm.

The respective damping properties of the muffler exhaust sounds 30 in the inventive example and the muffler 30a in the comparative example 1 were measured.

Figure 7 is a diagram showing the respective results of measuring the damping properties of muffler 30 in the inventive example and muffler 30year comparative example 1. In figure 7, the horizontal geometry axis represents a frequency (Hz) and the vertical geometry axis represents a level. sound pressure (dB). Frequency names, the lower the sound pressure level, the lower the noise value.

In Figure 7, the damping properties of muffler 30 in the inventive example are indicated by a thick solid line L0 and the muffler damping properties of 30a in comparative example 1 are indicated by a thin solid line L1.

In the regions indicated by arrows B1 and B2, the sound pressure levels of the high frequency components in muffler 30 in the inventive example were significantly lower than their noise pressure levels in muffler 30a in comparative example 1. The respective damping properties of a component low frequencies of less than 2000 Hz in muffler 30 in inventive and nosilicious example 30a in comparative example 1 were substantially the same.

Thus, the use of muffler 30 in the inventive example has caused sound pressure levels of high frequency components of not less than 2000 Hz to be sufficiently reduced. Therefore, it was found that the use of muffler 30 in the inventive example could inhibit the production of a metallic exhaust sound including high frequency components.

Figure 8 is a cross-sectional view of the muffler in comparative example2. The muffler 30b shown in figure 8 differs from the muffler 30 shown in figure 4 in the following paragraphs. In muffler 30b shown in FIG. 8, the plurality of holes 45 are also formed in the second barrel assembly 44. The configuration of the other muffler portions 30a shown in FIG. 8 is the same as the configuration of muffler 30 shown in FIG. 4.

Leakage sounds in cases where muffler 30 in inventive example and silent 30a in comparative example 2 were used were compared. The use of the silent 30 in the inventive example sufficiently inhibited the production of a metallic sound including the high frequency components. On the other hand, the use of silencer 30b in comparative example 2 caused the production of a metallic sound including the high frequency components.

The results showed that the formation of the plurality of holes 45 in the RU mounting region, except in the RD downstream region, could inhibit the production of the metallic sound including the high frequency components.

(8) Correspondences between constituent elements in the claims and parts in the embodiments

In the following paragraphs, nonlimiting examples of correspondence to elements recited in the claims below and those described above with respect to the various embodiments of the present invention are explained.

In the embodiments described above, vehicle chassis 80 is an example of a vehicle chassis, engine 50 is an example of an engine, exhaust pipes 20 and 40 are examples of an exhaust pipe, three-way catalyst 90 is a example of a catalyst, muffler 30 is an example of a muffler, first pipe 42 is an example of a first pipe, second pipe 44 is an example of a second pipe, narrow appendage 47 is an example of a narrow portion, the first expansion chamber 70 is an example of a first expansion chamber and holes 45 are an example of a hole.

Furthermore, the second expansion chamber 72 is an example of a second expansion chamber, the splitter plate 36 is an example of a splitter plate, the connection plug 36 is an example of a plug pipe and the tapered portion 48a It is an example of a conical portion.

As each of the various elements recited in the claims, various other elements having configurations or functions described in the claims may also be used.

While embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined.

Claims (6)

1. Motorcycle, CHARACTERIZED by the fact that it comprises: a vehicle chassis, a single cylinder engine provided in the vehicle chassis, an exhaust pipe into which an engine exhaust gas flows, a catalyst provided in the exhaust pipe and a silencer which discharges exhaust gas flowing out of the exhaust pipe into which the exhaust pipe includes: a first pipe having a nozzle-inserted downstream end opening, and a second pipe having an upstream end opening and an opening downstream end and extending downstream of the first barrel within the silent, a narrow portion having an inner diameter smaller than that of the first barrel is provided at the downstream end opening of the first barrel and is inserted into the upstream end opening of the first barrel. second pipe, a first expansion chamber which integrally surrounds the outer periphery and the opening at the downstream end of the second Where a pipe is formed within the silent one, a plurality of holes are formed in a manner distributed in a region, except a region at a downstream end, of a peripheral surface of the second plane, and the length in the axial direction of the region at the downstream end is not. smaller than 1/3 times the inside diameter of the second pipe. Motorcycle according to claim 1, characterized in that the second pipe is joined to the first pipe in a position on the upstream side of the narrow portion. Motorcycle according to claim 1 or 2, characterized in that the narrow portion includes a conical portion having an inner diameter that is decreasing. Motorcycle according to any one of claims 1 to 3, characterized in that a second expansion chamber is also formed downstream of the first expansion chamber within the muffler, the first expansion chamber and the second expansion chamber. are separated by a split plate, and a connecting pipe is provided to penetrate the split plate. Motorcycle according to Claim 4, characterized in that the volume of the first expansion chamber is greater than the volume of the second expansion chamber. Motorcycle according to any one of claims 1 to 5, characterized in that, in the exhaust pipe, a portion of the first canoe is kept in the muffler, and the second barrel is not kept in the muffler.