Title of Invention

AN EXHAUST SYSTEM FOR AN ENGINE

Abstract

A muffler 21 has an outer cylinder 30 and an inner cylinder 31 disposed in the outer cylinder 30, and is separated into a plurality of expansion chambers A and B. A communicative passage 40 for communicatively connecting the expansion chambers A and B together is formed between the outer cylinder 30 and the inner cylinder 31. Both edge parts 31e, 31e of the communicative passage 40 contact the outer cylinder 30 and welded thereto.

Full Text

EXHAUST SYSTEM FOR AN ENGINE AND MOTORCYCLE INCLUDING THE EXHAUST SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for an engine including an exhaust pipe connected to the engine and a muffler connected to the exhaust pipe, and a motorcycle including the exhaust system. 2. Description of the Related Art It is required for an exhaust system for a motorcycle that an exhaust sound is reduced as mush as possible. To meet this request, it is effective to separate the inside of a muffler into a plurality of expansion chambers and communicatively connect the expansion chambers by a plurality of communicative pipe, and thereby damps exhaust energy and reduces an exhaust sound. However, there is a problem that with the construction such that a plurality of communicative pipes is disposed in a muffler, a weight of the muffler increases as a number of the pipes, and it deteriorates a traveling performance. In consideration of the problem, JP-A-6-264741 suggests a muffler for a motorcycle in which a space is formed by disposing an inner cylinder with a small 1 diameter in an outer cylinder, a small pipe part is formed in a manner such that the small pipe concaves inside in the inner cylinder, and a sound absorbing member such as glass wool fills the space. In the above conventional construction, a weight of the muffler can be reduced. However, because the space is communicatively connected to the small pipe part, glass wool filled in the space scatters outside by passing through the small pipe part, and exhaust gas enters the space from the small pipe part. Exhaust sound tends to leak outside from there, and thus a silencing effect may not be obtained satisfactorily. SUMMARY OF THE INVENTION The present invention is made in consideration of the foregoing circumstance. The object of the present invention is to provide an exhaust system for an engine such that a weight of a muffler can be reduced and a silencing effect can be assured to prevent leak of exhaust sound, and a motorcycle including the exhaust system. The aspects of the present invention provide an exhaust system for an engine, including: an engine; an exhaust pipe connected to the engine; and a muffler connected to the exhaust pipe, in which the muffler has 2 an outer cylinder and an inner cylinder disposed in the outer cylinder, and is separated into a plurality of expansion chambers, a communicative passage for communicatively connecting the expansion chambers is formed between the outer cylinder and the inner cylinder, and both edge parts of a part constructing the communicative passage of the inner cylinder contact the outer cylinder and are welded thereto. Here, disposing the inner cylinder in the outer cylinder includes both cases that the inner cylinder is disposed in the outer cylinder with a space between them, and that the inner cylinder is disposed in the outer cylinder in a manner such that the inner cylinder abuts against or firmly contacts an inner peripheral surface of the outer cylinder. In the exhaust system according to the present invention, a communicative passage for communicatively connecting the expansion chambers is formed between the outer cylinder and the inner cylinder. Both the edge parts of the part of the inner cylinder constructing the communicative passage contact the outer cylinder and are welded thereto. Consequently, exhaust gas flowing in the communicative passage does not enter the space between the inner cylinder and the outer cylinder. Therefore, an exhaust sound does not leak outside from the space 3 between both the cylinders, and a silencing effect can be assured. The communicative passage formed between the outer cylinder and the inner cylinder communicatively connects the expansion chambers. Thus, a communicative pipe conventionally used is not necessary, and a weight of the muffler and a cost for the muffler can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a motorcycle in which an exhaust system for an engine according to a first embodiment of the present invention is disposed; FIG. 2 is a rear view of the exhaust system; FIG. 3 is a plan view of the exhaust system; FIG. 4 is a cross sectional view of a muffler of the exhaust system; FIG. 5 is a cross sectional view of the muffler (a cross sectional view taken along line V-V of FIG. 1); FIGs. 6 are cross sectional views of the muffler (cross sectional views taken along lines Vla-VIa, VIb-Vib, and VIc-VIc of FIG. 4); FIG. 7 is a cross sectional view of a muffler according to a second embodiment of the present invention; and FIG. 8 is a cross sectional view of the muffler (a 4 cross sectional view taken along a line VIII-VIII of FIG. 7) . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the attached drawings hereinafter. FIGs. 1 through 6 are drawings for describing an exhaust system for an engine according to the first embodiment of the present invention. Here, front, rear, right, and left in this embodiment mean the front, the rear, the right, and the left in the view of a driver sitting on a seat. In the figure, a reference numeral 1 shows a motorcycle including the exhaust system according to this embodiment. This motorcycle 1 includes a diamond-shaped vehicle body frame 2, an engine 3 mounted on the vehicle body frame 2, and an exhaust system 50 connected to the engine 3. A front fork 5 is supported steerably in the transverse direction by a head pipe 4 disposed at a front end of the vehicle body frame 2. A front wheel 6 is disposed at a bottom end of the front fork 5. Steering handlebars (not shown) are disposed at a top end of the front fork 5. 5 A rear arm 7 is supported swingably in the vertical direction at a lower part of a rear end of the vehicle frame 2. A rear wheel 8 is disposed at a rear end of the rear arm 7. A fuel tank 9 is disposed above the engine 3 of the vehicle body frame 2. A straddle type seat 10 is disposed on a rear side of the fuel tank 9. The vehicle body frame 2 has a down tube 11 extending obliquely downward from a lower part of the head pipe 4, an upper tube 12 having a tank rail part 12a extending rearward form an upper part of the head pipe 4 and a rear arm supporting part 12b curvedly extending rearward from a rear end of the tank rail part 12a, and a seat rail 13 extending obliquely upward and rearward from the rear arm supporting part 12b. The engine 3 is an air-cooled four cycle single cylinder engine mounted on with its cylinder axis inclining forward, laid over the down tube 11 and the upper tube 12 and connected there, and constructs a part of the vehicle body frame 2. An intake system is connected to the engine 3. The intake system has an intake pipe 16 connected to a rear wall 15a of a cylinder head 15 of the engine 3, a throttle body 17 containing a throttle valve 17a connected to the intake pipe 16 inside, an air cleaner 6 (not shown) connected to the throttle body 17. The exhaust system 50 has an exhaust pipe 20 connected to a front wall 15b of the cylinder head 15 of the engine 3, and a muffler 21 connected to a downstream end of the exhaust pipe 20. The exhaust pipe 20 is disposed on a right side of the vehicle body frame 2. The exhaust pipe 20 has an exhaust pipe main body 20', and bifurcating branches 20d, 20d connected to a rear end of the exhaust pipe main body 20' . Viewing from the lateral side of the vehicle, the exhaust pipe main body 20' has an upstream exhaust part 20a extending downward from the front wall 15b of the cylinder head 15, a downstream exhaust part 20b extending rearward from a rear end of the upstream exhaust part 20a passing through a part below the engine 3, and a rear inclining part 20c extending obliquely upward and rearward from a rear end of the downstream exhaust part 20b. The rear inclining part 20c (downstream end) bifurcates up and down into the bifurcating branches 20d, 20d. A metal honeycomb type catalyst 22 for cleaning up exhaust gas is disposed in the rear inclining part 20c. The muffler 21 has two muffler main bodies 23, 23 arranged in parallel with the upper and the lower bodies. The bifurcating branches 20d, 20d are inserted in the 7 respective upper and lower muffler main bodies 23, 23, and fixed there. A protector 25 functioning as a thermal insulation member covers a part positioned outside in vehicle's width direction through an upper part of the upper muffler main body 23. The rear inclining part 20c of the exhaust pipe 20, the upper and lower bifurcating branches 20d, 20d, and a part where each bifurcating branch 20d connects to the muffler main body 23 are disposed outside in vehicle's width direction, and a generally triangular protector 26 functioning as a thermal insulation member covers them. The upper and lower muffler main bodies 23, 23 are united into one body by a bracket 24 disposed inside in vehicle's width direction. An attachment part 24a protruding upward from the upper muffler main body 23 is formed on the bracket 24. This attachment part 24a is fixed by bolting to a tandem foot bracket 25 mounted on a bottom surface of the seat rail 13. A center of gravity G of the exhaust system 50 according to this embodiment is positioned at a front edge part of the muffler 21. An attachment part 24a of the bracket 24 is disposed to be in a vicinity of the rear part of this center of gravity G (see FIG. 1). The muffler 21 is disposed to be placed on a front 8 side in a vehicle from a perpendicular line (a) passing through a rotational center 8a of the rear wheel 8. The muffler 21 is disposed obliquely upward to extend generally along the seat rail 13 on a right side of the rear wheel 8. Viewing from the lateral side of the vehicle, the muffler 21 is disposed in a manner such that a major part of the muffler 21 falls in a projection area of the rear wheel 8. In other words, a top edge part 21a of a rear end of the muffler 21 generally corresponds to the perpendicular line (a) in a top rim part of the rear wheel 8. A top edge part 21b of a front end generally corresponds to a front rim part of the rear wheel 8. The upper and lower muffler main bodies 23, 23 have respective cylindrically shaped outer cylinders 30, and also cylindrically shaped inner cylinders inserted into the outer cylinders. An upstream opening 30a of the outer cylinder 30 is blocked with a generally plate-shaped partition 32. The bifurcating branch 20d passes through the partition 32 and extends to a vicinity of a center part inside the outer cylinder 30. A downstream end opening 30b is blocked with a generally bowl-shaped partition 33. A double wall tail cap 34 is removably fixed to a rear part of the partition 33 by a plurality of bolts 35. Two spaces b, b formed 9 between the tail cap 34 and the partition 33 inhibit an increase of temperature of the tail part. A tail pipe 36 for communicatively connecting an inside of the muffler main body 23 with an outside is disposed to pass through the partition 33 and fixed there. This tail pipe 36 is disposed to be generally horizontal in a state that it is mounted on the vehicle, passes through the tail cap 34, and opens rearward. The inner cylinder 31 is disposed at a center part except for a front end and a rear end in an axis direction of the outer cylinder 30, and contacts with an inner peripheral surface of the outer cylinder 30. An upstream end opening 31a of the inner cylinder 31 opens to communicatively connect with a front part of the outer cylinder 30. A downstream end opening 31b is blocked with a generally plate-shaped partition 38. A punched partition 39 is disposed at a center in an axis direction inside the inner cylinder 31. A large number of through holes 39a for communicatively connecting spaces inside the inner cylinder 31 is formed on the punched partition 39 (see FIG. 6(b)). The partition 38 of the inner cylinder 31 divides an inside of the muffler main body 23 into a first expansion chamber (A) on a front side of the partition 38 and a second expansion chamber (B) on a rear side of the 10 partition 38. A communicative passage 40 for communicatively connecting the first expansion chamber (A) and the second expansion chamber (B) is formed between the outer cylinder 30 and the inner cylinder 31. The communicative passage 40 is formed in a manner such that a bottom part 31c of the inner cylinder 31 is concaved from the inner peripheral surface of the outer cylinder 30 in a direction to a center (e) of the outer cylinder. Specifically, the bottom part 31c is an arc- shaped part with a radius of curvature R larger than a radius of curvature r of the outer cylinder 30. Thereby, a horizontal cross section of the communicative passage 40 has an arc shape. A large number of weight reducing holes 31d is formed by punching (see FIG. 4) over a generally entire surface of a contacting part c where the inner cylinder 31 except for the bottom part 31c contacts the outer cylinder 30 (see FIG. 6(a)) . Contacting parts 40a, 40a where right and left edge parts 31e, 31e of the bottom part 31c of the inner cylinder 31, which structures the communicative passage 40, contact with the inner peripheral surface of the outer cylinder 30 are welded over an entire length in the axis direction by spot welding or arc welding. 11 Exhaust gas exhausted from the engine 3 flows inside the exhaust pipe 20, and is cleaned up when it flows through the catalyst 22 of the rear inclining part 20c. From here, the gas separately flows into the top and bottom bifurcating branches 20d, 20d and flows in each of the muffler main bodies 23, 23. Exhaust gas flowed into the first expansion chamber A of each muffler main body 23, 23 passes through the punched partition 39 inside the inner cylinder 31, meets the partition 38 positioned at a rear end, and there makes a U-turn frontward. The gas flows inside the communicative passage 40 rearward from the front end of the outer cylinder 30, and then flows into the second expansion chamber B. The gas is discharged outside by passing through the tail pipe 36 (see the arrows in FIG. 4) . In this embodiment, the muffler main body 23 is constructed with the outer cylinder 30 and the inner cylinder 31 contacting the inner peripheral surface of the outer cylinder 30. The communicative passage 40 for communicatively connecting the first expansion chamber A and the second expansion chamber B together is formed between the inner cylinder 31 and the outer cylinder 30. Also, the right and left edge parts 31e, 31e of the part of the inner cylinder 31, which constructs the 12 communicative passage, are welded to the contacting parts 40a, 40a on the outer cylinder 30. As a result, exhaust gas flowing in the communicative passage 40 does not enter the space between the inner cylinder 31 and the outer cylinder 30. Therefore, an exhaust sound does not leak from the space between both the cylinders 30 and 31, and thereby a silencing effect can be assured. The first and second expansion chambers A, B are communicatively connected together by the communicative passage 40 formed between the outer cylinder 30 and the inner cylinder 31. Thus, a conventional communicative pipe is not necessary, and a weight of the muffler and a cost for the muffler can be reduced. In this embodiment, the communicative passage 40 is formed in a manner such that a bottom part 31c of the inner cylinder 31 is concaved from the inner peripheral surface of the outer cylinder 30 in a direction to a center (e) of the outer cylinder 30. Therefore, without processing the outer cylinder 30, the communicative passage 40 can be formed with a simple structure such that the bottom part 31c of the inner cylinder 31 is only deformed inside. This results in a prevention of cost increase and deterioration of an appearance. In this embodiment, the communicative passage 40 is constructed in a manner such that the bottom part 31c of 13 the inner cylinder 31 is an arc-shaped part having the radius of curvature R larger than the radius of curvature r of the outer cylinder 30. That is, the bottom part 31c is not flat but arc-shaped. Therefore, a shell sound can be prevented while a necessary passage area can be assured. In this embodiment, a large number of the weight reducing holes 31d is formed on the contacting part c where the inner cylinder 31 except for the bottom part 31c contacts the outer cylinder 30, and thus a weight of the muffler main body 23 can be reduced more. In this embodiment, the muffler 21 has two muffler main bodies 23, 23 arranged in parallel with the upper and lower main bodies. Thereby, the vehicle has a powerful appearance although the engine is a single cylinder engine. The bifurcating branches 20d, 20d of the single exhaust pipe 20 are connected to the respective muffler main bodies 23, 23. Thereby, engine output in medium and high-speed ranges is maintained, and also engine output in low and medium speed ranges can be improved. In a performance simulation study, engine output is improved by 10% in a range between 2500 rpm and 4000 rpm comparing with an engine having one muffler main body. In this embodiment, the muffler 21 is disposed to be 14 on a front side in a vehicle from a perpendicular line (a) passing through a rotational center 8a of the rear wheel 8. Consequently, the center of gravity G of the exhaust system 50 can be positioned closer to a center of gravity of the vehicle, thereby, mass is concentrated, and operational stability can be improved. The attachment part 24a of the muffler 21 is disposed in the vicinity of the rear part of the center of gravity G. The exhaust system 50 can be attached to the vehicle body frame 2 at a single place. This can improve an assemblage characteristic and results in a cost reduction. FIGs. 7 and 8 are figures for describing the exhaust system according to a second embodiment of the present invention. In the figure, the reference numerals and symbols the same as in FIG. 4 show the same or equivalent parts. The exhaust system of this embodiment includes a muffler 45. The muffler 45 has the outer cylinder 30 and the inner cylinder 31 inserted in the outer cylinder 30 in a manner such that the inner cylinder 31 contacts the inner peripheral surface of the outer cylinder 30. An inside of the muffler 45 is separated into first, second, and third expansion chambers A, B, and C by two partitions 46 and 47. The first expansion chamber A and the second 15 expansion chamber B are communicatively connected together by a first communicative passage 48 formed between the outer cylinder 30 and the inner cylinder 31. The second expansion chamber B and the third expansion chamber C are communicatively connected together by a second communicative passage 49 formed between the outer cylinder 30 and the inner cylinder 31. A basic construction is generally the same as the first embodiment. The first communicative passage 48 and the second communicative passage 49 are formed in such a manner that a bottom part 31g and a side part 31f of the inner cylinder 31 are deformed to form arcs whose centers of curvatures d and d' , respectively, are positioned closer to the center e of the outer cylinder 30 than to the inner peripheral surface of the outer cylinder 31. In other words, those communicative passages are formed in a manner such that the bottom part 31g and the side part 31f are concaved so that each of them forms an arc inside. These bottom part 31g and side part 31f form a generally cylindrical ring part f. Both edge parts of the bottom part 31g and the side part 31f of the inner cylinder 31, which form the first and second communicative passages 48 and 49, contact the inner peripheral surface of the outer cylinder 30 at 16 contacting parts 48a, 48a and 49a, 49a. These contacting parts 48a, 48a and 49a, 49a are welded over an entire length in an axis direction by spot welding or arc welding. Exhaust gas passes through inside the exhaust pipe 20 and flows into the first expansion chamber A in the muffler 45. The gas meets the partition 46 and there makes a U-turn frontward. Then, the gas flows rearward in the communicative passage 48 and flows into the second expansion chamber B. Form here, the gas flows frontward inside the second communicative passage 49 and flows into the third expansion chamber C. The gas flows out from the third expansion chamber C passing through the tail pipe 36, and is discharged outside (see the arrows in FIG. 7) . According to this embodiment, the muffler 45 is constructed with the outer cylinder 30 and the inner cylinder 31 contacting the inner peripheral surface of the outer cylinder 30. The first communicative passage 48 for communicatively connecting the first and second expansion chambers A and B, and the second communicative passage 49 for communicatively connecting the second and third expansion chambers B and C are formed between the inner cylinder 31 and the outer cylinder 30. The first and second communicative passages 48 and 49 are formed in 17 a manner such that the contacting parts 48a and 49a where the inner cylinder 31 contactes the outer cylinder 30 are welded. Thereby, a silencing function can be assured while reducing a weight. Therefore, an effect generally equivalent to the first embodiment can be obtained. 18 WE CLAIM: 1. An exhaust system for an engine, comprising: an engine; an exhaust pipe connected to the engine; and a muffler connected to the exhaust pipe, wherein: the muffler has an outer cylinder and an inner cylinder disposed in the outer cylinder, and is separated into a plurality of expansion chambers; a communicative passage for communicatively connecting the expansion chambers is formed between the outer cylinder and the inner cylinder; and both edge parts of a part constructing the communicative passage of the inner cylinder contact the outer cylinder and are welded thereto. 2. The exhaust system for an engine as claimed in claim 1, wherein the inner cylinder contacts an inner peripheral surface of the outer cylinder, and the communicative passage is formed in a manner such that a part of the inner cylinder is concaved from the inner peripheral surface of the outer cylinder in a direction to a center of the outer cylinder. 3. The exhaust system for an engine as claimed in claim 2, wherein the communicative passage includes an 19 arc-shaped part formed by setting a radius of curvature of a part of the inner cylinder larger than a radius of curvature of the outer cylinder. 4. The exhaust system for an engine as claimed in claim 2, wherein the communicative passage includes a part of the inner cylinder being a ring part with its center positioned closer to the outer cylinder than to the inner peripheral surface of the outer cylinder. 5. The exhaust system for an engine as claimed in claim 2, wherein a large number of weight reducing holes are formed in a contacting part where the inner cylinder except for a part constructing the communicative passage contacts the outer cylinder. 6. The exhaust system for an engine as claimed in claim 1, wherein the exhaust pipe has an exhaust pipe main body connected to the engine and a bifurcating part such that the exhaust pipe main body is bifurcated into two pipes in its downstream, the muffler has a pair of muffler main bodies arranged in parallel, and each of the muffler main bodies is connected to a bifurcating branch of the bifurcating part. 20 7. A motorcycle comprising: a vehicle body frame; an engine mounted on the vehicle body frame; and an exhaust system connected to the engine and as claimed in any one of claims 1 through 6. 21 8. The motorcycle as claimed in claim 7, wherein the muffler is attached to the vehicle body frame to be positioned on a front side in a vehicle from a perpendicular line passing through a rotational center of a rear wheel. 9. The motorcycle as claimed in claim 7, wherein a center of gravity of the exhaust system is positioned in a vicinity of a part where the exhaust pipe and the muffler connect together, and a vicinity of the center of gravity of the exhaust system is mounted on the vehicle body frame. A muffler 21 has an outer cylinder 30 and an inner cylinder 31 disposed in the outer cylinder 30, and is separated into a plurality of expansion chambers A and B. A communicative passage 40 for communicatively connecting the expansion chambers A and B together is formed between the outer cylinder 30 and the inner cylinder 31. Both edge parts 31e, 31e of the communicative passage 40 contact the outer cylinder 30 and welded thereto.

Documents:

01353-kol-2007-abstract.pdf

01353-kol-2007-claims.pdf

01353-kol-2007-correspondence others 1.1.pdf

01353-kol-2007-correspondence others 1.2.pdf

01353-kol-2007-correspondence others.pdf

01353-kol-2007-description complete.pdf

01353-kol-2007-drawings.pdf

01353-kol-2007-form 1.pdf

01353-kol-2007-form 18.pdf

01353-kol-2007-form 2.pdf

01353-kol-2007-form 3.pdf

01353-kol-2007-form 5.pdf

01353-kol-2007-priority document.pdf

01353-kol-2007-translated copy of priority document.pdf

1353-KOL-2007-(08-02-2012)-ABSTRACT.pdf

1353-KOL-2007-(08-02-2012)-AMANDED CLAIMS.pdf

1353-KOL-2007-(08-02-2012)-DESCRIPTION (COMPLETE).pdf

1353-KOL-2007-(08-02-2012)-DRAWINGS.pdf

1353-KOL-2007-(08-02-2012)-EXAMINATION REPORT REPLY RECIEVED.pdf

1353-KOL-2007-(08-02-2012)-FORM 1.pdf

1353-KOL-2007-(08-02-2012)-FORM 2.pdf

1353-KOL-2007-(08-02-2012)-FORM 3.pdf

1353-KOL-2007-(08-02-2012)-OTHERS.pdf

1353-KOL-2007-(08-02-2012)-PETITION UNDER RULE 137.pdf

1353-KOL-2007-(28-08-2012)CORRESPONDENCE.pdf

1353-KOL-2007-CORRESPONDENCE 1.1.pdf

1353-KOL-2007-CORRESPONDENCE 1.2.pdf

1353-KOL-2007-CORRESPONDENCE OTHERS 1.3.pdf

1353-KOL-2007-CORRESPONDENCE.pdf

1353-KOL-2007-FORM 13.pdf

1353-KOL-2007-OTHERS.pdf

1353-KOL-2007-PA.pdf