ES2373260T3 - EXHAUST SYSTEM FOR A MOTORCYCLE AND MOTORCYCLE THAT INCLUDES THE SAME. - 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

Exhaust system for a motorcycle and motorcycle comprising the same

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an exhaust system for a motorcycle and to a motorcycle that includes such an exhaust system.

Description of the background of the technique

Conventionally, various silencers have been developed in order to reduce the exhaust sounds caused by the discharge of exhaust gases from automobile engines (see JP 60-37287 B, for example).

The silencer disclosed in JP 60-37287 B has a perforated tube and an external cylinder. The perforated tube is inserted into the outer cylinder. A resonant chamber is formed between an outer peripheral surface of the perforated tube and an 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 partition plate. An internal space of the perforated tube communicates with the resonant chamber through holes in the perforated tube. In addition, one end downstream of the perforated tube opens inside the expansion chamber.

One end on the downstream side of the exhaust pipe narrows downwards, to form a small diameter part. The end of the exhaust pipe fits into a perforated tube. Exhaust gas discharged from the exhaust pipe is introduced into the expansion chamber through the perforated tube, and is further introduced into the atmosphere through an exhaust terminal tube. At this time, the exhaust sound is reduced by the function of the resonant chamber and the expansion chamber.

Meanwhile, motorcycle silencers are also planned. Silencers used on motorcycles are required to reduce exhaust sounds caused by high pressure and high temperature exhaust gas discharges. In addition, the rotation speeds of motorcycle engines amount to no less than 8000 rpm. Therefore, mufflers used in motorcycles are required to achieve desired engine performance by adjusting the exhaust gas flows discharged from the engines.

In the case of multi-cylinder engines, a plurality of exhaust pipes communicate with each other, so that a pressure fluctuation in each of the exhaust pipes 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 an exhaust pipe is large.

In recent years, motorcycles have also been developed in which exhaust systems are provided with catalysts to purify exhaust gases. In this case, the temperatures of the exhaust gases are increased by the catalysts. This increases the speed of the sound, causing the high frequency components of the exhaust sounds to increase. As a result, metallic exhaust sounds are produced that include high frequency components when catalysts are used for exhaust systems in single cylinder engines.

In addition, mufflers that are thinner and shorter than those of cars are required due to space limitations on motorcycles.

When the structures of automobile silencers are used for motorcycles with catalysts, it is impossible to sufficiently reduce the high frequency components of the exhaust sounds without increasing the sizes of the silencers.

Particularly on motorcycles that include single-cylinder engines, it is desired to achieve sufficient output performances of the engines by means of small silencers while obtaining low exhaust sounds that are synchronized with the combustion of the engines.

Document DE 10 2006 056 414 A1 describes an exhaust silencer for an internal combustion engine. The exhaust silencer has an outer tube, an inner tube arranged on the inner side of the outer tube and having one end arranged to receive the exhaust gas from the internal combustion engine and another end opposite the first end to discharge the gas from escape in the environment. The inner tube has two openings that are arranged between the two ends. An intermediate tube is disposed between the outer tube and the inner tube. A chamber is disposed between the intermediate tube and the inner tube, so that the exhaust gas leaves the inner tube through the first opening inside the chamber and leaves the chamber through the second opening inside the inner tube .

US 2006/000205 A1 describes a method of operating a dynamic exhaust system of a motorcycle engine. The method includes providing a valve in the exhaust system that can be moved to direct the exhaust gases between a first flow path through the exhaust system and a second flow path through the exhaust system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an exhaust system for a motorcycle that allows sufficient output performance of an engine to be achieved while reducing the high frequency components of an exhaust sound.

This object is achieved by an exhaust system according to claim 1.

(1) According to one aspect of the present invention, an exhaust system for a motorcycle includes an exhaust pipe, and a silencer that discharges the exhaust gas flowing out from the exhaust pipe to the outside, in which the Exhaust pipe includes a first tube that has an opening in the downstream end inserted into the muffler, and a second tube that has an opening in the upstream end and an opening in the downstream end and that extends to the water side down from the first tube into the silencer, a narrowed part having an internal diameter smaller than that of the first tube is provided in the opening at the downstream end of the first tube, and is inserted into the opening at the upstream end of the second tube, a first expansion chamber is formed that completely encloses the outer periphery and the opening at the downstream end of the second tube inside the silencer, and a plurality of holes are formed It is distributed in a region, except for a region at a downstream end, of a peripheral surface of the second tube, and the length in the axial direction of the region at the downstream end is not less than 1/3 times the internal diameter of the second tube

Embodiments of the invention relate to a motorcycle that includes the exhaust system. In a motorcycle of this type, the exhaust gas from the engine of a single cylinder provided in the bodywork flows into the exhaust pipe. At this time, the exhaust gas can be purified by a catalyst while entering a high temperature state. This increases the speed of sound, causing the high frequency components of the exhaust sound to increase.

The high temperature exhaust gas flows outwardly into the first expansion chamber in the silencer through the first tube and the second tube in the exhaust pipe. At this time, the exhaust gas is expelled into the second tube while it is compressed through the narrowed part of the first tube so that the exhaust gas pressure (exhaust gas pressure) increases. This prevents mixed gas from burning out in a period of engine overlap. This results in improvements in engine torque generated by the engine in a low speed area and a medium speed area.

In this case, a part of the exhaust gas inside the second tube expands as it flows outwardly into the first expansion chamber through the holes. In addition, the rest of the exhaust gas inside the second tube expands as it flows outwardly into the first expansion chamber from the opening at the downstream end. In this case, the first expansion chamber completely and continuously encloses the outer periphery and the opening at the downstream end of the second tube.

The plurality of holes are formed in the region, except for the region at the downstream end, of the peripheral surface of the second tube. The length in the axial direction of the region at the downstream end is set not to be less than 1/3 times the internal diameter of the second tube. Therefore, the fluctuation of the pressure of the exhaust gas flowing out of the second tube through the holes and the fluctuation of the pressure of the exhaust gas flowing out from the opening at the downstream end of the second tube respectively They have high frequency components of different phases. Therefore, the high frequency components of different phases cancel each other out. As a result, the high frequency components of the exhaust sound are reduced.

In addition, the compressed exhaust gas through the narrowed part of the first tube expands step by step in the second tube and the first expansion chamber. This causes a pressure wave to be released that can be generated by the rapid expansion of the exhaust gas. This results in the inhibition of the production of a sound caused by the pressure wave.

In addition, the first expansion chamber fully encloses the outer periphery and the opening at the downstream end of the second tube within the silencer. Therefore, it is possible to ensure that the volume of the first expansion chamber that serves as the space of equal pressure 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 cross-sectional area of the silencer.

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

(2)

 The second tube can be attached to the first tube in a position on the upstream side of the narrowed part.

In this case, the second tube is reliably fixed to the first tube in a cantilever state without using a support element. This prevents vibration and oscillation of the second tube. This results in the production of a sound being prevented due to vibration or oscillation of the second tube.

(3)

 The narrowed part may include a part of decreasing section that has an internal diameter that gradually decreases. In this case, it is possible to prevent the production of a flow noise due to the disturbance of the exhaust gas flow.

(4)

 A second expansion chamber may be additionally formed on the downstream side of the first expansion chamber within the silencer, the first expansion chamber and the second expansion chamber may be separated by a partition plate, and a connection tube may be provided. to penetrate the dividing plate.

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

(5)

 The volume of the first expansion chamber may be greater than the volume of the second expansion chamber. In this case, the first expansion chamber completely encloses the outer periphery and the opening at the downstream end of the second tube. Therefore, 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 diameter of the silencer. 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 can be held in the silencer, and the second pipe cannot be held in the silencer.

In this case, there is no support element on the side of the outer periphery of the second tube, so that the flow of the exhaust gas flowing out of the plurality of holes in the second tube is not disturbed. This can prevent the production of a flow noise due to the disturbance of the flow of the exhaust gas.

According to the present invention, sufficient output performance of the engine is achieved while the high frequency components of the exhaust sound are sufficiently reduced.

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

BRIEF DESCRIPTION OF THE 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 an exhaust device seen from above;

Figure 3 is a perspective view of the appearance of an exhaust device seen from the side;

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

Figure 5 is an enlarged sectional view of an exhaust pipe shown in Figure 4;

Figure 6 is a cross-sectional view of a silencer in a comparative example 1;

Figure 7 is a diagram showing the respective measurement results of the damping properties of a silencer in an example of the invention and the silencer in comparative example 1; Y

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

DESCRIPTION OF THE EMBODIMENTS

Referring to the drawings, embodiments of the present invention will be described in reference to the drawings. In the following description, the upstream side and the downstream side will be defined based on the flow of an exhaust gas.

(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 body 80 composed of a body frame and a frame cover. A main tube (not shown) is provided on the front of the body 80, and a handlebar 81 is provided on an upper end of the main tube. A front fork 82 is attached to a lower end of the main tube. In this state, the front fork 82 can rotate within a predetermined angular range using the axis of the main tube as the center. A front wheel 83 is rotatably supported at a lower end of the front fork 82. A rear wheel 84 is rotatably supported at the rear of the body 80. A single cylinder engine 50 is provided in the center of the body 80. The rear wheel 84 is rotated by a rotation force of the engine 50 .

An exhaust device 10 that introduces an exhaust gas to the outside is connected to a cylinder head 51 of the engine 50. The exhaust device 10 includes an exhaust pipe 20 and a silencer 30. The exhaust pipe 20 extends rearward from the cylinder head 51 of the engine 50. The muffler 30 extends to the side of the rear wheel 84 from an end downstream of the exhaust pipe 20.

(2) Configuration of the exhaust device 10

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

An exhaust port connector 22 is provided at one end upstream of the exhaust pipe 20. An opening on the upstream side of the exhaust pipe 20 is connected to an exhaust port of the cylinder head 51 of the engine 50 shown in Figure 1 by the exhaust port connector 22. The downstream end 24 of the exhaust pipe 20 is inserted into an upstream end (an inlet) of the silencer 30. The outer periphery at the upstream end of the silencer 30 is secured by a mounting element 26 so that the silencer 30 It is fixed to the exhaust pipe 20.

The end 24 downstream of the exhaust pipe 20 is connected to an upstream end of an exhaust pipe 40 within the muffler 30. A three-way catalyst 90 is provided within the exhaust pipe 40. Note that the exhaust pipe 20 and the exhaust pipe 40 may be formed in a integral manner. Alternatively, the exhaust pipe 20 and the exhaust pipe 40 may be connected to each other through another element. Covers 31a and 31b are attached to an outer peripheral surface of the silencer 30.

An exhaust gas generated by burning an air-fuel mixture in the engine 50 shown in Figure 1 is fed to the silencer 30 through the exhaust pipe 20. The exhaust gas is discharged into the atmosphere through the silencer 30. Therefore, an exhaust path of the engine 50 includes the exhaust port of the cylinder head 51, the exhaust pipe 20, and the silencer 30 in the order from the upstream side to the downstream side.

The silencer 30 has an attenuation function to reduce an exhaust sound before discharging the exhaust gas into the atmosphere. In the present embodiment, the interior of the silencer 30 has a structure of a type of multiphase expansion, which is described below. That is, the interior of the silencer 30 is divided into a plurality of expansion chambers, so that the exhaust gas expands as it passes through the plurality of expansion chambers. This causes the exhaust gas to depressurize.

(3) Internal structure of the silencer 30

The internal structure of the silencer 30 will then be described in reference to Figure 4. Figure 4 is a cross-sectional view taken along the line IV-IV of the silencer 30 shown in Figure 2. Figure 5 is a view in enlarged section of the exhaust pipe 40 shown in figure 4.

As shown in Figure 4, the silencer 30 includes a conical head 32, a hollow cylindrical body 34, and a dome-shaped terminal part 37. The head 32 fits into an opening on the upstream side of the body 34. The terminal part 37 fits into an opening on the downstream side of the body 34.

Division plates 36 and 38 are arranged with a predetermined separation in the order from the upstream side in positions close to a downstream end of the body 34. Thus, an internal space of the silencer 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 are aligned in order from the upstream side to the downstream side in the longitudinal direction of the silencer 30.

A connection tube 62 penetrates the division plate 36, a connection tube 64 penetrates the division plate 38, and an exhaust terminal tube 66 penetrates the terminal part 37.

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

The exhaust pipe 40 includes a first tube 42 on the upstream side and a second cylindrical tube 44 on the downstream side. The first tube 42 has a cylindrical part 46 on the upstream side and a part 47 narrowed on the downstream side. The narrowed part 47 has a part 48a of decreasing section and a part 48b of small diameter. The small diameter part 48b has an external diameter and an internal diameter respectively smaller than the external diameter and the internal diameter of the cylindrical part 46. The external diameter and the internal diameter of the part 48a of decreasing section gradually decrease from an external diameter and an internal diameter that are the same as those of the cylindrical part 46 towards an external diameter and an internal diameter that are the same as those of the part 48b of small diameter. Therefore, the cross-sectional area of a flow path of the narrowed portion 47 gradually decreases from the upstream side to the downstream side.

The internal diameter R2 of the second tube 44 is equal to the external diameter of the cylindrical part of the first tube 42. The narrowed portion 47 of the first tube 42 is inserted into an opening at the upstream end of the first tube 42 so that a water end above the second tube 44 overlaps the cylindrical part in a position on the upstream side of the narrowed part 47 of the first tube 42. In this state, an outer peripheral surface of the cylindrical part of the first tube 42 and an inner peripheral surface of the second tube 44 are welded so that the second tube 44 is attached to the cylindrical part. Therefore, the second tube 44 is held in the first tube 42 in a cantilever state. In addition, a cylindrical gap is formed between the inner peripheral surface of the second tube 44 and the narrowed part 47. The part 48a of decreasing section opens into the second tube 44.

The first tube 42 is attached to an inner surface of the head 32 through a support cross member 35 to be located in the center of the head 32 and the body 34.

The internal diameter R0 of the small diameter part 48b of the narrowed part 47 is smaller than the internal diameter R1 of the cylindrical part 46 (R0 <R1). The internal diameter R2 of the second tube 44 is larger than the internal diameter R0 of the small diameter part 48b of the narrowed part 47 and is smaller than the internal diameter R3 of the first expansion chamber 70 (R0 <R2 <R3). This allows a pressure fluctuation created by a rapid expansion of the exhaust gas flowing out of the first tube 42 into the first expansion chamber 70 to be released.

In this case, it is preferable that the internal diameter R2 of the second tube 44 is not too close to the internal diameter R3 of the expansion chamber 70 and is not too close to the internal diameter R0 of the small diameter part 48b. This allows a pressure wave caused by the rapid expansion of the exhaust gas to be sufficiently released by the second tube 44.

It is preferable that the internal diameter R2 of the second tube 44 is approximately equal to the internal diameter R1 of the cylindrical part of the first tube 42. In the present embodiment, the internal diameter R2 of the second tube 44 is equal to the external diameter of the cylindrical part of the First tube 42. Therefore, the internal diameter R2 of the second tube 44 is approximately equal to the internal diameter R1 of the cylindrical part 46 of the first tube 42. This allows the pressure wave to be effectively released.

Note that a length L from an opening 49 at the downstream end of the narrowed portion 47 to an opening 43 at the downstream end of the second tube 44 is not particularly limited and is determined such that a low frequency component of the sound Exhaust does not disappear and the resistance of the second tube 44 secured in a cantilever state is guaranteed.

As shown in Figure 5, the second tube 44 includes an upstream RU region in which a plurality of holes 45 and a downstream RD region are provided in which substantially holes in the order towards the water side are not provided down. The plurality of holes 45 are spaced uniformly in the upstream RU region. The plurality of holes 45 are drill holes, for example. The plurality of holes 45 penetrate the second tube 44 from its outer peripheral surface towards its inner peripheral surface. In the present embodiment, the shape of each of the holes 45 is circular.

The downstream RD region has a length D towards the upstream side from the opening 43 at the downstream end of the second tube 44. The length D of the downstream RD region is not less than 1/3 times the internal diameter R2 of the second tube 44.

The downstream RD region may be provided with one or more holes so that it has an openings ratio that is not greater than one third of the openings in the upstream RU region. The ratio of openings of the upstream region RU means the ratio of the sum of the open areas of the plurality of holes 45 with respect to the area of the upstream region RU. The relationship of openings of the RD region downstream means the ratio of the sum of the open areas of the one or more holes with respect to the area of the RD region downstream. In this case, the one

or more holes provided in the RD region downstream hardly affect the effect of reducing the high frequency components, described below. Therefore, the fact that the downstream RD region is provided with one or more holes so that it has the ratio of openings not exceeding one third of the openings ratio of the upstream RU region means that substantially holes are not provided. in the RD region downstream.

Although the ratio of the sum of the open areas of the plurality of holes 45 with respect to the cross-sectional area of the flow path of the second tube 44 (hereinafter referred to as the area ratio of the plurality of holes 45) is not particularly limited, it is preferable that the area ratio of the plurality of holes 45 is not less than 0.5 or greater than 2.0, for example, approximately 1.0.

Note that the internal diameter of each of the holes 45 and the passage between the holes 45 (the distance between the centers of the adjacent holes 45) can be adjusted as necessary, such that the aforementioned sound reduction effect can achieved satisfactorily. In this case, the internal diameter of each of the holes 45 and the passage between the holes 45 can be selected so that the sound reduction effect is effectively obtained while limiting a loss of pressure.

(4) Operation of the exhaust device 10

The operation of the exhaust device 10 according to the present embodiment will then be described.

An exhaust gas from the exhaust port of the engine 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 time, the exhaust gas is purified by means of the three-way catalyst 90 while entering a high temperature state. This increases the speed of sound, causing the high frequency components of an exhaust sound to increase.

The high temperature exhaust gas flows outwardly into the first expansion chamber 70 in the silencer 30 through the first tube 42 and the second tube 44 in the exhaust pipe 40. At this time, the exhaust gas is expelled into the second tube 44 while it is compressed by the narrowed portion 47 of the first tube 42 so that the exhaust gas pressure (exhaust gas pressure) increases. This prevents an unburned mixed gas from leaving in an overlapping period (a period during which both a suction valve and an exhaust valve are open) of the engine 50. This results in improvements in the torque generated by the 50 engine in a low speed area and a medium speed area.

The compressed exhaust gas through the narrowed portion 47 expands as it flows outwardly into the second tube 44. As shown in Figure 5, an exhaust gas E1 that is part of the exhaust gas within the second tube 44 expands as it flows outwardly into the first expansion chamber 70 through the holes 45. In addition, the challenge of the exhaust gas E2 expands by flowing outwardly into the first expansion chamber 70 from the opening 43 at the downstream end of the second tube 44. In this case, the first expansion chamber 70 fully encloses the outer periphery continuously and the opening 43 at the downstream end of the second tube 44.

The holes 45 are formed in the upstream RU region, except in the downstream RD region, as described above. Therefore, the fluctuation of the pressure of the exhaust gas E1 flowing out of the second pipe 44 through the holes 45 and the fluctuation of the pressure of the exhaust gas E2 flowing out from the opening 43 at the water end below the second tube 44 respectively have high frequency components of different phases. Therefore, the high frequency components of the fluctuation of the pressure of the exhaust gas E1 and the high frequency components of the fluctuation of the pressure of the exhaust gas E2 cancel each other in the space of equal pressure. The results of the considerations provided by the inventors of the present invention show that the high frequency components effectively cancel each other out when the length D of the RD region downstream is not less than 1/3 times the internal diameter R2 of the second tube 44. This causes the high frequency components of the exhaust sound to be reduced.

In addition, the exhaust gas compressed by the narrowed portion 47 of the first tube 42 expands step by step in the second tube 44 and the first expansion chamber 70. This causes a pressure wave to be released that can be generated by the rapid expansion of the exhaust gas. This results in the inhibition of the production of a sound due to the pressure wave (particularly a metallic sound that includes the high frequency components).

The exhaust gas inside the first expansion chamber 70 expands as it flows outwardly into the second expansion chamber 72 through the connecting tube 62. The exhaust gas inside the second expansion chamber 72 expands as it flows outwardly into the third expansion chamber 74 through the connection tube 64. The exhaust gas inside the third expansion chamber 74 is discharged to the outside through the exhaust terminal tube 66 and released into the atmosphere.

If the distance between the opening 43 at the downstream end of the second tube 44 and the opening at the upstream end of the connecting tube 62 is too small, an attenuation effect is reduced. If the distance between the opening 43 at the downstream end of the second tube 44 and the dividing plate 36 is too small, the torque generated by the motor 50 is reduced. Therefore, the length D of the downstream RD region is preferably not more than three times and more preferably not more than twice the internal diameter R2 of the second tube 44.

(5) Effects of the preferred embodiment

In the motorcycle 100 according to the present embodiment, the exhaust gas introduced into the exhaust pipe 40 from the engine 50 of a single cylinder through the exhaust pipe 20 is compressed by the narrowed portion 47 of the first pipe 42. This prevents the unburned mixed gas leaves the engine 50. This results in improvements in the torque generated by the engine 50 in the low speed area and the medium speed area.

In addition, the exhaust gas compressed by the narrowed portion 47 of the first tube 42 expands step by step in the second tube 44, the first expansion chamber 70, the second expansion chamber 72, and the third mode expansion chamber 74 that the exhaust gas pressure decreases towards atmospheric pressure step by step. This causes the exhaust sound to be reduced.

In this case, the exhaust gas E1 inside the second tube 4 flows outwardly into the first expansion chamber 70 through the holes 45, and the rest of the exhaust gas E2 flows outwardly into the interior of the first expansion chamber 70 from the opening 43 at the downstream end. Therefore, the high frequency components of the fluctuation of the pressure of the exhaust gas E1 and the high frequency components of the fluctuation of the pressure of the exhaust gas E2 cancel each other within the first expansion chamber 70 which serves as The space of equal pressure. This causes the high frequency components of the pressure fluctuation increased by the three-way catalyst 90 to be reduced. Therefore, the high frequency components of the exhaust sound are reduced sufficiently. As a result, it is possible to obtain an intermittent low exhaust sound that is synchronized with the combustion of the engine 50 of a single cylinder while inhibiting the production of the metallic sound that includes the high frequency components.

In addition, the second tube 44 is fixed to the first tube 42 in a cantilever state at its upstream end. Therefore, there is no support element on the side of the outer periphery of the second tube 44, and the first expansion chamber 70 integrally and continuously encloses the outer peripheral surface and the opening 43 at the downstream end of the second tube 44. Therefore, it is possible to ensure that the volume of the first expansion chamber 70 serving as the space of equal pressure 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 silencer

30. In addition, this may prevent the production of a flow noise due to the disturbance of the exhaust gas flow.

Since the second tube 44 is connected to the first tube 42 in a position on the upstream side of the narrowed portion 47, the second tube 44 is stably fixed to the outer peripheral surface of the first tube 42 with high strength. This prevents the vibration and oscillation of the second tube 44 from occurring. This results in the production of a sound having a natural vibration frequency or the oscillation of the second tube 44 and a continuous sound caused by the vibration being prevented. or the oscillation of the second tube 44.

(6) Other embodiments

Although the narrowed part 47 has the part 48a of decreasing section and the part 48b of small diameter in the aforementioned embodiment, the narrowed part 47 may have a step structure unless the flow of the exhaust gas is disturbed. In such a case, the exhaust pressure on the narrowed part 47 also increases.

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

Furthermore, although the plurality of holes 45 are uniformly spaced apart in the upstream RU region, except in the downstream RD region, the plurality of holes 45 can be arranged randomly.

Although the first tube 42 and the second tube 44 respectively have circular cross sections in the aforementioned embodiment, the present invention is not limited thereto. For example, the first tube 42 and the second tube 44 may respectively have elliptical cross sections. In this case, the length of the long axis of an ellipse is taken as the internal diameter. Therefore, the length D of the RD region downstream of the second tube 44 is set such that it is not less than 1/3 times the length of the long axis of the ellipse and preferably not more than three times and more preferably not more than twice the internal diameter R2 of the second tube 44. In addition, the first tube 42 and the second tube 44 may respectively have polygonal cross sections. In this case, the length of the longest diagonal line of a polygon is taken as the internal diameter. Therefore, the length D of the RD region downstream of the second tube 44 is set not to be 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 tube 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 reducing, respectively, high frequency components of exhaust sounds by silencers in an example of the invention and in comparative examples 1 and 2 were examined. In the example of the invention the silencer 30 shown in Figure 4 was used.

Figure 6 is a cross-sectional view of the silencer in comparative example 1. The silencer 30a shown in Figure 6 differs from the silencer 30 shown in Figure 4 in that the silencer 30a shown in Figure 6 does not have the second tube 44 The configuration of the other parts of the silencer 30a shown in Figure 6 is the same as the configuration of the silencer 30 shown in Figure 4.

In the silencer 30 in the example of the invention and the silencer 30a in comparative example 1, the internal diameter R0 of the narrowed portion 47 is 16.1 mm, and the internal diameter R1 of the first tube 42 is 23.6 mm In addition, the internal diameter and the length of the connecting tube 62 are respectively 28.6 mm and 50 mm, the internal diameter and the length of the connecting tube 64 are respectively 22.2 mm and 50 mm, and the internal diameter and the length of the exhaust terminal tube 66 are respectively 22.2 mm and 30 mm.

In the silencer 30 in the example of the invention, the internal diameter R2 of the second tube 44 is 27.4 mm, the internal diameter of the holes 45 is 5 mm, and the passage between the holes 45 is 7.5 mm The diameter of the holes 45 is 5 mm, and the length L from the opening 49 at the downstream end of the narrowed portion 47 to the opening 43 at the downstream end of the second tube 44 is 42 mm. The length D of the RD downstream region is 9.5 mm.

The respective damping properties of the exhaust sounds were measured by the silencer 30 in the example of the invention and the silencer 30a in comparative example 1.

Figure 7 is a diagram showing the respective results of the measurement of the damping properties of the silencer 30 in the example of the invention and the silencer 30a in comparative example 1. In Figure 7, the horizontal axis represents a frequency ( Hz), and the vertical axis represents a sound pressure level (dB). On the same frequency, the lower the sound pressure level, the lower the noise value.

In Fig. 7, the damping properties of the silencer 30 in the example of the invention are indicated by a thick continuous line L0, and the damping properties of the silencer 30s in comparative example 1 are indicated by a thin continuous line L1.

In regions indicated by arrows B1 and B2, the sound pressure levels of high frequency components in the silencer 30 in the example of the invention became sufficiently lower than the sound pressure levels thereof in the silencer 30a in comparative example 1. The respective damping properties of a low frequency component of less than 2000 Hz in the silencer 30 in the example of the invention and the silencer 30a in comparative example 1 were substantially the same.

Therefore, the use of the silencer 30 in the example of the invention caused the sound pressure levels of high frequency components not less than 2000 Hz to be reduced sufficiently. Therefore, it was found that the use of the silencer 30 in the An example of the invention can inhibit the production of a metallic exhaust sound that includes high frequency components.

Figure 8 is a cross-sectional view of the silencer in comparative example 2. The silencer 30b shown in Figure 8 differs from the silencer 30 shown in Figure 4 in the following aspects. In the silencer 30b shown in Figure 8, the plurality of holes 45 are uniformly formed in the entire second tube

44. The configuration of the other parts of the silencer 30a shown in Figure 8 is the same as the configuration of the silencer 30 shown in Figure 4.

The exhaust sounds were compared in cases where silencer 30 was used in the example of the invention and silencer 30a in comparative example 2. The use of silencer 30 in the example of the invention sufficiently inhibited the production of a metallic sound that includes high frequency components. On the other hand, the use of the silencer 30b in comparative example 2 caused a metallic sound to be produced that includes the high frequency components.

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

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

Non-limiting examples of correspondences between various elements mentioned in the following claims and those described above with respect to various embodiments of the present invention are explained in the following paragraphs.

In the embodiments described above, the body 80 is an example of a body, the engine 50 is an example of an engine, the exhaust pipes 20 and 40 are examples of an exhaust pipe, the three-way catalyst 90 is an example of a catalyst, the silencer 30 is an example of a silencer, the first tube 42 is an example of a first tube, the second tube 44 is an example of a second tube, the narrowed part 47 is an example of a narrowed part, The first expansion chamber 70 is an example of a first expansion chamber, and the holes 45 are an example of a hole.

In addition, the second expansion chamber 72 is an example of a second expansion chamber, the division plate 36 is an example of a division plate, the connection tube 36 is an example of a connection tube, and part 48a of decreasing section is an example of a part of decreasing section.

Like each of the various elements mentioned in the claims, other various elements having the configurations or functions described in the claims can also be used.

Although embodiments of the present invention have been described above based on motorcycles having a catalyst, it is indicated that the exhaust system of the invention can also be used on motorcycles that do not have a catalyst.

Claims (8)

1. Exhaust system for a motorcycle comprising: an exhaust pipe (40); Y a silencer (30) that discharges the exhaust gas flowing out of the exhaust pipe (40) outwards, in which the exhaust pipe (40) includes a first tube (42) having an opening in the downstream end inserted in the silencer (30), and a second tube (44) having an opening at the upstream end and an opening (43) at the downstream end and extending to the downstream side from the first tube (41) inside the muffler (30), wherein a narrowed part (47) having an internal diameter smaller than that of the first tube (42) is provided in the opening at the downstream end of the first tube (42), and is inserted into the opening at the water end above the second tube (44), in which a first expansion chamber (70) is formed inside the silencer (30), and in which a plurality of holes (45) are formed distributed in a region (RU), except for a region (RD) at a downstream end, of a peripheral surface of the second tube (44), and the length in the axial direction of the region (RD) at the downstream end is not less than 1/3 times the internal diameter (R2) of the second tube (44), characterized because the first expansion chamber (70) completely encloses the outer periphery and the opening (43) at the downstream end of the second tube (44), and the opening (43) at the downstream end of the second tube (44) opens into the first expansion chamber (70) so that an exhaust gas (E1, E2) inside the second tube (44) flows outwardly into the first expansion chamber (70) through the holes (45) and through the opening (43) at the downstream end of the second tube (44). 2. Exhaust system according to claim 1, wherein the second tube (44) is attached to the first tube (42) in a position on the upstream side of the narrowed part (47).

3.

Exhaust system according to claim 1 or 2, wherein the narrowed part (47) includes a part (48a) of decreasing section having an internal diameter that gradually decreases.

Four.

Exhaust system according to any one of claims 1 to 3, wherein a second expansion chamber (72) is further formed on the downstream side of the first expansion chamber (70) within the muffler (30), being separated the first expansion chamber (70) and the second expansion chamber (72) by means of a partition plate (36), and a connection tube (62) is provided to penetrate the partition plate (36).

5.

Exhaust system according to claim 4, wherein the volume of the first expansion chamber (70) is greater than the volume of the second expansion chamber (72).

6.

Exhaust system according to any one of claims 1 to 5, wherein in the exhaust pipe (40), a part of the first pipe (42) is held in the silencer (30), and the second pipe (44) is held in the first tube (42) in a cantilever state.

7.

Motorcycle, comprising:

a body (80); a motor (50) of a single cylinder provided in the body (80); Y an exhaust system (10) according to any one of claims 1 to 6, wherein an exhaust gas from the engine (50) flows into the exhaust pipe (40) of the exhaust system. 8. Motorcycle according to claim 7, further comprising a catalyst (90) provided in the tube (40) exhaust.