Vehicle exhaust system

An exhaust system for a vehicle, such as a motorcycle or other straddle-type vehicle, that achieves miniaturization while providing advantageous noise reduction characteristics. The exhaust system is associated with an engine of a vehicle and includes an exhaust pipe connected to the engine and a silencer. A conical member is positioned within the silencer and includes an upstream end and a downstream end. At least a portion of a side wall of the conical member includes a plurality of through-holes. The conical member is oriented such that a radial dimension of the conical member increases in a direction from the upstream end to the downstream end.

RELATED APPLICATIONS

This application is related to, and claims priority from, Japanese Patent Application No. 2007-031099, filed Feb. 9, 2007 and Japanese Patent Application No. 2006-092334, filed Mar. 29, 2006, the entireties of which are hereby incorporated by reference herein and made a part of the present specification. Application Ser. Nos. 11/692,824; 11/692,783; and 11/692,814, entitled VEHICLE EXHAUST SYSTEM, all filed on Mar. 28, 2007, are also incorporated by reference herein in their entireties and made a part of the present specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an exhaust system for a vehicle. More particularly, the present invention relates to an exhaust system for a straddle-type vehicle and a straddle-type vehicle incorporating such an exhaust system.

2. Description of the Related Art

A exhaust system used in a straddle-type vehicle (for example, a motorcycle) is requested to meet two demands, that is, an exhaust efficiency, at which exhaust gases discharged from an engine should be efficiently discharged, and reduction of exhaust noise, which accompanies discharge of exhaust gases of high pressure and high temperature.

In particular, the demand for noise reduction or noise elimination has increased as noise regulations have been made more rigorous. Accordingly, it is increasingly desired that noise reduction or noise elimination be attained, while at the same time maintaining exhaust efficiency.

SUMMARY OF THE INVENTION

When design of an exhaust system is considered only in terms of exhaust efficiency, a muffler (exhaust system) is preferably extended straight. However, such an exhaust system is not well accommodated in a vehicle body of a motorcycle. Accordingly, in order to lessen an exhaust resistance, the exhaust system is extended toward the rear of a vehicle body in an attempt to avoid tight radius bends, which is difficult in many cases because of the front wheel of the motorcycle and a bank angle of the combustion chamber(s). Normally, a muffler having an ideal length in terms of engine performance is only seldom accommodated intact in a configuration of a motorcycle and, as compared with design of a muffler for four-wheel passenger cars, the design of a motorcycle exhaust system to meet both performance and physical constraints is significantly more challenging. That is, it is difficult in the context of a motorcycle exhaust system to achieve a length of the exhaust system that will both provide desired performance attributes and be accommodated within the space constraints of a motorcycle while maintaining a configuration that is as smooth as possible.

Also, not only an exhaust efficiency, but also a weight of a an exhaust system has a significant influence on the handling characteristics of a motorcycle. That is, because a motorcycle is relatively lightweight, even a weight of about one (1) kg has a great influence on the motorcycle. Moreover, because certain components of the exhaust system (e.g., the silencer) are usually located at a distance from a center of gravity of the motorcycle, the adverse influence of excess weight of the exhaust system on the handling characteristics of the motorcycle is increased.

On the other hand, in spite of any contrivance on a construction of the exhaust system, a certain silencer (or muffler) volume is needed to some extent to provide a noise reducing effect. In order to conform to regulations on noise, which are made increasingly rigorous, a silencer cannot but be made larger in many cases. Moreover, when a metallic sheet from which the silencer is constructed is thin, it vibrates thereby increasing noise. To avoid such a situation, the silencer is by all means liable to be relatively large in weight. An increase in the weight of the silencer results in undesired handling characteristics of the associated motorcycle.

In this manner, since a structure of an exhaust system for motorcycles is determined in terms of a variety of interrelated factors, it has been extremely difficult to realize an exhaust system in which miniaturization is achieved and a desired exhaust efficiency and noise-reduction characteristics are met.

At least some of the preferred embodiments of the present invention provide an exhaust system for straddle-type vehicles, such as motorcycles, in which miniaturization is achieved while a demand for noise reduction characteristics are met.

A preferred embodiment of the present invention provides an exhaust system associated with an engine of a vehicle. The exhaust system includes an exhaust pipe connectable to the engine and a silencer connected to the exhaust pipe. A conical member is provided within the silencer. The conical member has an upstream end, a downstream end and a side wall extending between the upstream end and the downstream end. At least a portion of the sidewall includes a plurality of through-holes formed therein. The conical member is oriented so that a radial dimension of the conical member increases in a direction from the upstream end toward the downstream end.

In a preferred embodiment of the exhaust system described above, the conical member is arranged proximate a junction of the exhaust pipe and the silencer. In some arrangements, the conical member is positioned toward an upstream end of the silencer.

In a preferred embodiment of the exhaust system described above, a plurality of the conical members is provided in the silencer. In some arrangements, the silencer comprises an outer housing and an inner core accommodated in the outer housing, and the conical member is mounted to the inner core of the silencer.

In a preferred embodiment of the exhaust system described above, the silencer comprises an outer housing and an inner core accommodated in the outer housing. A tail pipe is connected to the inner core of the silencer. Multiple conical members are provided, including a first conical member connected to the tail pipe and a second conical member connected to the inner cylinder. In some arrangements, at least one of the first conical member and the second conical member is open at an upstream end thereof. In some arrangements, the second conical member is arranged to overlap at least an upstream end of the first conical member. In some arrangements, the first conical member is arranged near an upstream end of the silencer and the second conical member is located proximate a junction of the exhaust pipe and the silencer.

A preferred embodiment involves a straddle-type vehicle, such as a motorcycle, including an exhaust device as described above. In some arrangements, a downstream end of the inner core of the silencer is located forward of the axis of an axle shaft of a rear wheel provided on the straddle-type vehicle. In some arrangements, the straddle-type vehicle includes a four-stroke engine. The straddle-type vehicle can be an off-road motorcycle, or other type of motorcycle.

In accordance with some embodiments of the invention, because a conical member is positioned in the silencer and at least a portion of a side wall of the conical member includes a plurality of through-holes, energy of exhaust gases, which are introduced into the silencer from the exhaust pipe, can be consumed or dissipated through the through-holes of the conical member, so that it is possible to absorb exhaust noise. In addition, because a radial dimension of the conical member increases in a direction from the upstream end toward the downstream end, it is possible to appropriately adjust a ventilation resistance in the silencer whereby it is possible to reduce exhaust noise. Accordingly, even with a small-sized muffler or silencer, it is possible to produce sufficient noise reduction without an increase in a lengthwise dimension of the silencer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While an exhaust system for a motorcycle is designed under various restrictions, conventional design philosophy is that a noise reducing effect cannot be actually produced unless the silencer is increased in volume. On the other hand, it is not possible to avoid a phenomenon in which an increase in volume of the silencer brings about an adverse affect on the handling characteristics of the motorcycle. In a muffler in, for example, present four-stroke motocross motorcycles (in particular, sports vehicles), a silencer is increased in volume whereby noise reduction and running performance are met, so that the muffler is large and heavy.

The present inventors have realize an exhaust device (muffler), which is small-sized and light while meeting performance criteria (exhaust property) and a noise characteristics. Embodiments of the invention are described below with reference to the drawings. In addition, the invention is not limited to the following embodiment

FIG. 1illustrates a motorcycle1000, on which an exhaust system having certain features, aspects and advantages of an embodiment of the invention is mounted. The exhaust system100is connected to the engine50. The exhaust system100includes an exhaust pipe20and a silencer10. In addition, the exhaust system100including the silencer10is in some cases referred to as a “muffler” in the specification of the present application for the sake of convenience.

The muffler100according to the embodiment includes the exhaust pipe20connectable to the engine50of the motorcycle1000, and the silencer10connected to the exhaust pipe20. With a construction shown inFIG. 1, a tail pipe30is connected to the silencer10.

A state, in which the muffler100is removed from the motorcycle1000, is shown inFIG. 2(a). The exhaust pipe20and the silencer10of the muffler100shown inFIG. 2(a) are formed with members for mounting to a vehicle body. The muffler100according to the embodiment is configured for use with a four-stroke engine and the motorcycle1000shown inFIG. 1is an off-road vehicle. However, the muffler100may be used with, or adapted for use with, other types of motorcycles or other vehicles, as well. In addition, a cylinder head exhaust port22communicates with an upstream end of the exhaust pipe20shown inFIG. 2(a), which is connectable to the engine50.

The exhaust pipe20connects to an exhaust port opening of the engine50as shown inFIG. 2(b) to lead exhaust gases from the engine50to the silencer10. In an example as shown, the cylinder head exhaust port22of the exhaust pipe20is connected to the engine50. The silencer10has a noise reducing function to discharge exhaust gases led from the exhaust pipe20to the environment. In the case where the tail pipe30is connected to the silencer10, exhaust gases are discharged from the tail pipe30. In addition, as shown inFIG. 2(c), an expansion chamber21can be further provided in the exhaust pipe20. In this case, exhaust gases from the engine50pass through the chamber21and are then led to the silencer10to be discharged to the environment.

FIGS. 3(a) to3(c) are cross sectional views showing a cross sectional structure of the silencer10, into which exhaust gases are introduced. The silencer10comprises an outer housing, or cylinder10a, and an inner core, or cylinder10b, accommodated in the outer cylinder10a. The term “cylinder” as used herein is a broad term that is not limited to extruded shapes having a circular cross-sectional shape, but may include any closed, extruded shape, such as an oval cross-sectional shape, for instance. Also, the tail pipe30is connected to the silencer10to lead exhaust gases to the external environment or atmosphere. A plurality of through-holes, or punched holes13, are formed in at least a portion (here, a region P) of the inner cylinder10bof the silencer10. Although referred to as “punched holes” herein, the holes13may be formed by any suitable method. The punched holes13are small holes formed in the silencer10(here, the inner cylinder10b) and serve to enable energy of exhaust gases, which are introduced from the exhaust pipe20, to be led to the outer cylinder10athrough the small holes.

In an example shown inFIG. 3, a sound absorbing material15is positioned between an inner surface of a wall of the outer cylinder10aand an outer surface of a wall of the inner cylinder10bin a manner to come into close contact therewith. The sound absorbing material15is a material capable of absorbing sound waves and can use, for example, glass wool, stainless steel wool (SUS wool), aluminum wool, ferrite, asbestos, etc. In this example, glass wool is used as the sound absorbing material15. The sound absorbing material15fairly absorbs a high frequency sound (that is, exhaust noise in a high frequency range).

Further, the silencer10adopts a structure in which at least one conical member, generally32, is arranged therein. The conical member32comprises at least one member having a generally cone-shaped portion31(or pyramidal-shaped portion) made of, for example, stainless steel. The cone-shaped portion31may be selectively formed on a part of the conical member32, or the whole conical member32may comprise a cone-shaped portion. In this embodiment, the whole conical member32comprises the cone-shaped portion31. Also, in an example as shown, conical members32are provided in two locations (32a,32b) in the silencer10. Thus, the illustrated arrangement includes a pair of conical members32a,32b. Through-holes14or “punched holes” are formed within a side wall of the cone-shaped portion31(here, the whole conical member32).

The punched holes14are a plurality of small holes (through-holes) formed in the side wall of the cone-shaped portions31of the conical member32. Although referred to herein as “punched holes,” the holes14may nonetheless be formed by any suitable method. The punched holes14serve to enable energy of exhaust gases, which are introduced from the exhaust pipe20, to be consumed through the through-holes. That is, energy of sound is consumed by viscous damping (that is, viscous damping caused by movements of an air on inner walls of the holes14) and pressure loss damping (that is, pressure loss damping caused by the ventilation resistance in the holes14portions) when exhaust noise is transmitted in the punched holes14). Thereby, it is possible to decrease the exhaust noise (noise reducing effect). In addition, while energy consumption due to pressure loss damping enables reducing the exhaust noise in the whole frequency range (that is, the whole frequency range from a low frequency range to a high frequency range), energy consumption due to viscous damping can produce a noise reducing effect especially in a high frequency range.

In addition, the punched holes14can be appropriately regulated in hole diameter and pitch between respective holes so as to favorably achieve the noise reducing effect described above. That is, while pressure loss, which possibly influences the muffler performance (typically, the exhaust performance) is suppressed as far as possible, hole diameter and pitch between respective holes can be selected so as to efficiently produce the noise reducing effect. For example, with the same numerical aperture (a ratio of an area occupied by the punched holes to a total area of conical side walls of the conical members), as the hole diameter and the pitch decrease (that is, a state, in which the small holes14are spaced more closely), a large ventilation resistance worsens the exhaust performance but a great noise reducing effect is produced.

The cone-shaped portions31of the conical members32are in the form of a cone with a tip end (upstream end) opened, and opening holes of the cone-shaped portions31of the punched cones have an opening diameter at an upstream end thereof, which is smaller than an opening diameter at a downstream end thereof. That is, the cone-shaped portions31of the conical members32are formed to have an inside diameter R (R1and R2) increasing from an upstream side to a downstream side. Although described as having diameters, it will be understood that in non-circular cross-sectional embodiments of the conical members, that a radial dimension (rather than a diameter) of the conical members will increase from an upstream end to a downstream end along any particular longitudinal plane passing through the conical member. In this manner, by forming the cone-shaped portions31of the conical members32so that an inside diameter R thereof increases from an upstream side to a downstream side, the cone-shaped portions31of the conical members32are gradually enlarged in cross sectional area in a direction, in which exhaust gases flow out. Thereby, it is possible to suitably regulate that degree (ventilation resistance), in which flow of the exhaust gases are resisted in the silencer10, thus producing a noise reducing effect of the muffler100due to pressure loss (that is, energy consumption of exhaust gases caused by the ventilation resistance).

In this manner, the exhaust device100can consume energy of exhaust noise through the punched holes14of the cone-shaped portions31of the conical members32formed in the silencer10. Thereby, it is possible to reduce the exhaust noise (noise reducing effect). This noise reducing effect is especially effective for exhaust noise in a high frequency range.

Furthermore, because the cone-shaped portions31of the conical members32are formed to have an inside diameter R increasing from an upstream side to a downstream side, it is possible to suitably regulate the ventilation resistance in the silencer10, thereby regulating a noise reducing effect on exhaust noise. This noise reducing effect is effective for exhaust noise in a whole frequency range.

In addition, the conical members32can be preferably used for a typical, small-sized muffler, which achieves miniaturization and lightening. “Small-sized muffler” referred to herein is the muffler100arranged forward of an axle shaft72of a rear wheel70like the motorcycle1000shown inFIG. 1. In this example, a downstream end10dof the silencer10is positioned forward of a perpendicular line A extended from an axis of the axle shaft72of the rear wheel70in a vertical direction. In this manner, a muffler, in which a downstream end of a silencer is positioned forward of an axle shaft of a rear wheel, involves a problem that a space, in which a sound absorbing material is filled, cannot be ensured to be adequately sized so that a desired noise reducing effect by the sound absorbing material alone can be achieved.

In contrast, when the conical members32according to the preferred embodiments are adopted, even the small-sized muffler as shown inFIG. 1can absorb exhaust noise effectively and a so-called “directly transmitting” sound can be suppressed. That is, a sufficient noise reducing effect can be produced without an increase in lengthwise dimension of the silencer.

In addition, the downstream end10dof the silencer10more specifically means a downstream end of the inner cylinder10bprovided in the silencer. Accordingly, for example, even when a part of the tail pipe30connected to the silencer10is positioned rearwardly of the axle shaft72of the rear wheel70, the structure corresponds to “small-sized muffler” referred herein to. Also, the conical members32according to the embodiment are not limited to the muffler of the type shown inFIG. 1but can be preferably used in a muffler of a so-called “cruiser” type motorcycle.

In addition, while the cone-shaped portions31of the conical members32according to the embodiment are in the form of a cone, a cross sectional shape thereof is not limited thereto but may be shaped otherwise (for example, any closed shape may be utilized, including flat oval, elliptical, polygonal, etc.). With the form of a cone, an inside diameter is increased from an upstream side to a downstream side, but a cross sectional area is increased from an upstream side to a downstream side in the case where the cross section is other than circular in shape. Or, in other words, as described above, a radial dimension of the generally conical member increases in the upstream to downstream direction.

Further, while the punched holes14in the embodiment are circular in shape, they are not limited thereto but can be shaped otherwise (for example, flat oval, elliptical, polygonal, etc.). Further, the punched holes14may be varied in diameter (or area) with locations of formation, or all the plurality of punched holes14as formed may be the same in diameter (or area).

In addition, “upstream” side and “downstream” side referred to in the specification of the present application mean an upstream side and a downstream side, respectively, in a direction, in which exhaust gases in the muffler flow. In other words, “upstream” side is that side, on which an engine is arranged, and “downstream” side is that side, on which exhaust gases are discharged to the environment.

A construction of an exhaust device according to a further embodiment is described below with reference toFIGS. 4 and 5.FIG. 4is a perspective view showing an outward appearance with a part of a constituent member being cut out so that an internal construction of a silencer10, into which exhaust gases are introduced, is conveniently shown.

With the silencer10shown inFIG. 4, conical members32are provided in two locations (32a,32b) on an inner cylinder10band an upstream end of a tail pipe30. Here, a first cone32aconnected to the tail pipe30and a second cone32bconnected to the inner cylinder10bare included. Specifically, the first cone32ais welded or otherwise secured at the upstream end of the tail pipe30and the second cone32bis welded or otherwise secured to an inner surface of the wall of the inner cylinder10bthrough a stay portion33. The stay portion33serves to hold the second cone32bin the inner cylinder10b.

FIG. 5schematically shows a cross sectional structure of the silencer10shown inFIG. 4. As shown inFIG. 5, circular-shaped, punched holes14are formed on side walls (a region Q1, a region Q2) of the respective cones (32a,32b). Also, the respective cones (32a,32b) are formed to have an inside diameter R (R1and R2) increasing from an upstream side to a downstream side. Further, the second cone32bis provided in a manner to cover an upstream end of the first cone32a. That is, the first cone32aand the second cone32bare arranged so as to overlap each other.

In this manner, a plurality (32a,32b) of the conical members32are provided in the silencer whereby it is possible to effectively regulate that degree (ventilation resistance), in which the flow of exhaust gases is resisted, therefore enabling a further noise reduction effect due to pressure loss.

FIGS. 4 and 5show a modification of the example shown inFIG. 3, in which the conical members32shaped with an upstream end closed are included. That is, while the first cone32ahas a shape (opened shape) with an upstream end34aopened, the second cone32bhas a shape with an upstream end34bclosed. The upstream ends of the respective cones (32a,32b) are not especially limitative in shape but may be open, or closed, and a directly transmitting sound can be suppressed irrespective of the shape. However, it is preferred that one of the upstream ends of the respective cones (32a,32b) be open and the other be closed. Thereby, that degree (ventilation resistance), in which the flow of the exhaust gases are resisted, can be further enhanced, so that it is possible to produce a desired noise reduction effect.

For example, when the upstream ends of all of the respective cones (32a,32b) are closed, the ventilation resistance may become undesirably large and a decrease in exhaust efficiency may result. However, when two cones, one having an open upstream and one having a closed upstream end, are combined together as shown in this example, the ventilation resistance is desirably regulated to reduce or prevent a directly transmitting sound, thus enabling the realization of a muffler, which provides desired levels of both exhaust efficiency and noise damping characteristics. In addition, the upstream ends of the conical members32can be appropriately changed in shape according to that performance (for example, exhaust performance, damping characteristic, etc.), which is demanded of a particular muffler. For example, as shown inFIG. 6, the first cone32amay be closed in shape at the upstream end and the second cone32bmay be open in shape at the upstream end.

Also, in an example shown inFIG. 5, the second cone32bis provided in a manner to cover the first cone32a(that is, the first cone32aand the second cone32boverlap each other), but this arrangement is not limitative and the first cone32aand the second cone32bmay be arranged so as not to overlap one another, as shown inFIG. 7. In addition,FIG. 7(a) shows an example, in which the first cone32ais closed in shape at the upstream end and the second cone32ais opened in shape at the upstream end.FIG. 7(b) shows an example, in which the first cone32ais opened in shape at the upstream end and the second cone32ais closed in shape at the upstream end.

In addition, it is also possible to provide only one conical member32instead of two in number and to provide three or more conical members. For example,FIG. 8shows an example, in which one conical member32is arranged in a silencer10. The conical member32is located toward an upstream end of the silencer10, and preferably within a forward half of the silencer10, to be welded to an inner surface of the wall of an inner cylinder10bthrough a stay portion33. Also, the conical member32is structured to have an inside diameter R increasing from an upstream side to a downstream side. In this manner, even when only one conical member is provided in a silencer, it is possible to obtain a reduction or prevention of a directly transmitting sound to a sufficient degree, provided that the inside diameter R of the punched cone32is enlarged in a direction, in which exhaust gases flow out. In addition, while the upstream end of the conical member32in the example as shown is closed in shape, it is not limited thereto but it is possible to select a preferable shape according to the performance (for example, exhaust performance, damping characteristic, etc. which are demanded) of a particular muffler.

In addition, while the conical member32shown inFIG. 8is arranged on an upstream side of the silencer10, a noise reducing effect can be produced irrespective of a position, in which the conical member32is mounted, provided that the inside diameter R of a cone-shaped portion31of the punched cone32increases from an upstream side to a downstream side.

For example, as shown inFIGS. 9(a) and9(b), it is possible to arrange a conical member32in the vicinity of an upstream end (that is, a junction or connection of an exhaust pipe20and a silencer10) of the silencer10. Here, the conical member32is welded to an upstream side (specifically, a diffuser) of an inner cylinder10bthrough a stay portion33. In this example, an upstream end34of the conical member32projects further toward a upstream side from the upstream end of the silencer but a noise reducing effect in a high frequency range can be produced even in such structure by making exhaust gases somewhat hard to flow. In addition,FIG. 9(a) shows an example, in which the upstream end of the conical member32is opened in shape andFIG. 9(b) shows an example, in which the upstream end of the conical member32is closed in shape.

FIGS. 10(a) and10(b) show an example, in which a conical member32is not welded to the wall of an inner cylinder10b, but to an upstream end of a tail pipe30. In this manner, the conical member32can be mounted also to the tail pipe30instead of the inner cylinder10b.

While the examples shown inFIGS. 8 to 10have been described with respect to a location of arrangement and a mount position in the case where the number of conical members is one, the same is with the case where a plurality of conical members32are provided. That is, even in case of a plurality of conical members32, a noise reducing effect in a high frequency range can be produced by making exhaust gases hard to flow provided that the inside diameter R of a cone-shaped portion31of the conical member32increases from an upstream side to a downstream side. Accordingly, positions, in which the conical member32are mounted, are not especially limitative.

For example, as shown inFIGS. 11(a) and11(b), a construction is possible, in which a first cone32ais mounted to a tail pipe30and a second cone32bis mounted to an upstream side (a diffuser) of an inner cylinder. In addition,FIG. 11(a) shows an example, in which the first cone32ais closed in shape at the upstream end and the second cone32ais opened in shape at the upstream end.FIG. 11(b) shows an example, in which the first cone32ais opened in shape at the upstream end and the second cone32ais closed in shape at the upstream end.

Also, whileFIGS. 3 to 11illustrate various examples of a muffler according to certain preferred embodiments of the invention, the mufflers according to all the embodiments are the same in that the inside diameter R of the cone-shaped portion31of the conical member32is enlarged in a direction, in which exhaust gases flow out of the silencer10, whereby the ventilation resistance in the silencer10can be appropriately regulated to thereby produce a noise reducing effect on exhaust noise due to pressure loss. It is possible to appropriately select positions in which the conical members32are located and the number of the conical members provided according to the desired performance characteristics of a particular muffler. That is, a noise reducing effect of the muffler100can be appropriately regulated according to positions, in which the conical members32are formed, and the number of the conical members.

An outflow path of exhaust gases in a silencer10is described with reference toFIG. 12.FIG. 12shows, as an example, an outflow path of exhaust gases in the silencer10shown inFIGS. 4 and 5.

Exhaust gases (arrow90) led into the silencer10from an exhaust pipe20can flow around (arrow91) a side of a second cone32b(which is closed at an upstream end). At this time, since an inside diameter of the second cone32bis enlarged in a direction, in which exhaust gases flow out, exhaust gases meet with a resistance so as to be damped in energy. As a result, it is possible to absorb an exhaust noise (in particular, a high frequency sound).

A part of exhaust gases going round the side of the second cone32bpasses through a wall of an inner cylinder10b, in which exhaust noise is absorbed by a sound absorbing material15(arrow92). Also, a part of exhaust gases flows into the second cone32bthrough punched holes14, in which exhaust noise is also absorbed (arrow93).

Thereafter, exhaust gases flow into, a first cone32afrom an opened, upstream end thereof (arrow94), go around a side of the first cone32a(arrow95), pass through the wall of the inner cylinder10b(arrow96), or flow into the first cone32athrough the punched holes14(arrow97), while exhaust noise is absorbed in respective locations, and finally pass through a tail pipe30(arrow98) to be then discharged outside the silencer (arrow99).

Accordingly, because the conical member32formed on a side thereof with the punched holes14is provided in the silencer10, at least a portion of the energy of exhaust gases introduced from the exhaust pipe20can be consumed through the through-holes14, and therefore, it is possible to absorb exhaust noise. In addition, since an inside diameter of the cone-shaped portion31of the conical member32increases from an upstream side to a downstream side, the ventilation resistance in the silencer10can be appropriately regulated whereby it is possible to produce a noise reducing effect on exhaust noise.

Further, a plurality (for example, two (the first cone32aand the second cone32b) of conical members32are provided in the silencer whereby it is possible to further effectively regulate that degree (ventilation resistance) in which the flow of exhaust gases is resisted, therefore enabling further heightening a damping effect due to pressure loss. At this time, a preferred muffler can be realized according to a requested performance (for example, exhaust performance, damping characteristic, etc.) by appropriately combining two cones, upstream ends of which are either closed or opened in shape (for example, appropriately combining two cones, at least one of which is opened in shape).

In addition, by appropriately changing a position, in which the conical member32is mounted (for example, arranging the conical member32on a connection of the exhaust pipe20and the silencer10as shown inFIG. 9, or arranging the conical member32on an upstream side of the silencer10as shown inFIG. 10), the ventilation resistance in the silencer10can be appropriately regulated whereby it is possible to produce a noise reducing effect on exhaust noise.

In addition, the conical member32can be preferably used in a small-sized muffler, in which typical miniaturization and lightening are achieved, (for example, a muffler arranged forwardly of the axle shaft72of the rear wheel70). Even such small-sized muffler can absorb an exhaust noise effectively and can suppress a so-called a directly transmitting sound. That is, it is possible to produce a sufficient noise reducing effect without an increase in lengthwise dimension of the silencer.

In addition, whileFIG. 1shows an off-road motorcycle as an example of the motorcycle1000, the motorcycle1000may be configured for on-road use. Also, “motorcycle” in the specification of the present application means a motorcycle and means a vehicle, which includes a bicycle with a motor (motorbike) and a scooter that can specifically turn with a vehicle body inclined. Accordingly, a three-wheeler, four-wheeler, at least one of a front wheel and a rear wheel of which has two or more wheels and which is three, four (or more) in the number of tires, can be included within the definition of a “motorcycle”. In addition, applicability is not limited to a motorcycle but to other vehicles capable of making use of the effect of the invention, for example, a so-called straddle-type vehicle, which includes a four-wheeled buggy, ATV (All Terrain Vehicle), and a snowmobile.

While the invention has been described with respect to preferred embodiments, such descriptions are not limitative but various modifications are of course possible. According to the various preferred embodiments of the invention, it is possible to provide a muffler for a straddle-type vehicle, which achieves miniaturization while meeting a demand for a noise reducing characteristic.

Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In particular, while the present exhaust system and vehicle incorporating the exhaust system have been described in the context of particularly preferred embodiments, the skilled artisan will appreciate, in view of the present disclosure, that certain advantages, features and aspects of the system may be realized in a variety of other applications, many of which have been noted above. Additionally, it is contemplated that various aspects and features of the invention described can be practiced separately, combined together, or substituted for one another, and that a variety of combination and subcombinations of the features and aspects can be made and still fall within the scope of the invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims.