JP2009008089A - Exhaust system of motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust system for a motorcycle engine including a muffler assembly. <P>SOLUTION: The muffler assembly includes: a downstream attenuation portion adapted to be positioned substantially rearward of the motorcycle engine and having a first height; an upstream portion adapted to be positioned substantially forward of the motorcycle engine and having a second height; and an intermediate attenuation portion between the downstream attenuation portion and the upstream portion. The intermediate attenuation portion is adapted to be positioned substantially below the motorcycle engine and has a third height lower than half the first height. In an embodiment, a motorcycle is provided, in which the motorcycle engine is positioned substantially within a recess part of the muffler assembly to a depth greater than the third height. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  This application claims priority to US patent application serial number 11 / 770,051, filed June 28, 2007, the entire contents of which are incorporated herein by reference.

  The present invention relates to a muffler assembly for a motorcycle engine. More particularly, the present invention relates to a muffler assembly having a specific component configuration and overall shape.

  In one embodiment, the present invention provides a muffler assembly for a motorcycle engine. The muffler assembly has a first height, a downstream damping portion configured to be positioned substantially on the rear side of the motorcycle engine, and a second height, and the muffler assembly has a second height. An upstream portion configured to be positioned substantially on the front side, and an intermediate attenuation portion between the downstream attenuation portion and the upstream portion are included. The intermediate damping portion has a third height smaller than half of the first height, and is configured to be positioned substantially below the engine of the motorcycle.

  In another embodiment, the present invention relates to an engine, a transmission coupled to the engine and configured to receive an output from the engine, and coupled to the transmission, the output of the engine being transmitted through the transmission. A motorcycle includes a rear wheel configured to receive and a muffler assembly coupled to the engine and in communication with the engine to receive exhaust gas from the engine. The muffler assembly includes a downstream-side damping portion disposed between the transmission and the rear wheel, and an intermediate damping portion disposed on the front side of the downstream-side damping portion. The intermediate damping part extends along the underside of the engine.

  In yet another embodiment, the present invention is directed to an engine, two wheels defining a central axis of the motorcycle, and substantially positioned along the central axis to receive exhaust gas from the engine. There is provided a motorcycle including a muffler assembly in communication with the engine. The muffler assembly includes a downstream damping portion, an upstream portion, an intermediate damping portion positioned substantially below the engine, and a recess at least partially defined by the downstream damping portion and the intermediate damping portion. including. The recess has a depth greater than the height of the intermediate damping portion, and the engine is disposed substantially inside the recess.

  Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

  Before detailed description of embodiments of the present invention, it should be understood that the present invention is limited in its application to the details of the structure and arrangement of parts illustrated in the drawings or given the following description. Not. The invention is capable of other embodiments and of being practiced or carried out in various ways. It should also be understood that the terminology or terminology used herein is for the purpose of explanation and should not be regarded as limiting. “Including”, “having” and variations thereof are used to include additional items as well as the items previously listed and their equivalents. Unless otherwise specified or limited, the terms “mounted”, “connected”, “supported” and “coupled” and variations thereof are used in a broad sense, and are directly and indirectly mounted. Connection, support and coupling. Further, “connected” and “coupled” are not limited to physical or mechanical connections or couplings.

  FIG. 1 shows a motorcycle 10 having a twin-cylinder engine 14. The motorcycle 10 includes a front wheel 15, a rear wheel 16, and a transmission 17 coupled to the engine 14 for receiving output from the engine. The rear wheel 16 is driven by the output of the engine 14 via a transmission 17 (and a driving member such as a belt). The air / fuel mixture is ignited in a combustion chamber (not shown) for each cylinder of the engine 14. Following combustion in a combustion chamber, exhaust gas (a mixture of combustion reaction and some residue, unreacted components) is expelled through the exhaust port into the motorcycle exhaust system 18.

  The exhaust system 18 includes a bracket 20 for mounting on the motorcycle 10, as shown in FIGS. The exhaust system 18 includes a pair of header pipes (or “headers”) 22, a collector section 26, a catalytic converter 30 and a silencer section 34. The header 22 is an exhaust conduit that leads directly from the engine 14. The silencing section 34 includes a first silencing (“attenuation”) portion 34A and a second silencing (“attenuation”) portion 34B. The collector section 26, the catalytic converter 30, the first silencing (“attenuation”) portion 34 </ b> A and the second silencing (“attenuation”) portion 34 </ b> B collectively form a muffler assembly 35. In the illustrated embodiment, the muffler assembly 35 is located substantially along the central axis of the motorcycle 10 (defined by the front wheels 15 and the rear wheels 16). Each of the first attenuating portion 34A and the second attenuating portion 34B is measured along a single axis (for example, the central axis) or an individual axis portion that follows the general surface (outer surface shape) of the muffler assembly 35. It occupies at least 20% of the entire length of the muffler assembly 35 at that time. Preferably, each of the first attenuation portion 34 </ b> A and the second attenuation portion 34 </ b> B occupies about 1/3 of the entire length of the muffler assembly 35. The portion of the muffler assembly 35 in front of the second damping portion 34B also occupies at least 20% of the total length of the muffler assembly 35, and preferably occupies about one third of the total length of the muffler assembly 35.

  The upstream end 36 </ b> A of each header 22 is coupled to the engine 14 for receiving exhaust gas from a respective exhaust port of the engine 14. The headers 22 define separate exhaust flow paths, and each header 22 routes exhaust gas directly from the exhaust port of the engine 14 to downstream exhaust components. The downstream end 36 </ b> B of each header 22 enters the upstream end 35 </ b> A of the muffler assembly 35, more specifically, the collector section 26. The illustrated collector section 26 defines a 2-in-1 exhaust path that integrates the two separate exhaust paths of the header 22 into a single, larger exhaust path near the catalytic converter. It is an exhaust conduit. Therefore, the exhaust gas from both combustion chambers is processed by the catalytic converter.

  The second attenuation portion 34B defines an intermediate portion 35C of the muffler assembly 35 between the upstream end 35A and the downstream end 35B of the muffler assembly 35 along the lower side of the engine 14. The first attenuation portion 34 </ b> A disposed at the substantially downstream end 35 </ b> B is disposed substantially on the rear side of the engine 14. A muffler shell or casing 35D (generated by one or more pieces) extends from the upstream end 35A to the downstream end 35B and defines the outer surface of the muffler assembly 35. Although the casing 35D can be assembled from multiple pieces in one embodiment, the casing 35D has a substantially continuous outer surface that does not have a sudden transition from one part of the muffler assembly 35 to the next. Define.

  On the downstream side of the catalytic converter 30, the exhaust gas flows through the intermediate portion 35C to the first attenuation portion 34A at the downstream end 35B. As described above, the intermediate portion 35 </ b> C extends in the longitudinal direction below the engine 14, but alternative shapes and positions of the exhaust components of the motorcycle 10 are arbitrary. As described in detail below, the exhaust gas from the catalytic converter 30 is directed substantially straight to the first attenuation portion 34A via the intermediate portion 35C, and at least a portion of the exhaust gas is at the pair of outlets 35E. Before exiting the muffler assembly 35, the first damping portion 34A flows back into the second damping portion 34B.

Here, to return to the processing of the exhaust gas at the upstream end 35A, the catalytic converter 30 uses one or more known catalytic materials (hereinafter simply referred to as the catalyst 38) contained in the catalytic converter 30 from the engine 14. Improve emission quality of exhaust gas. The catalyst 38 reacts with undesired exhaust gas components to produce more desirable product before being discharged into the atmosphere via outlet 35E. Specifically, carbon monoxide (CO) can be converted to carbon dioxide (CO ₂ ) while converting nitrogen oxide (NOx) to nitrogen (N ₂ ) and oxygen (O ₂ ).

  The temperature of the catalyst 38 affects its performance. To obtain the desired level of performance from the catalytic converter 30 to efficiently change undesirable exhaust gas components as described above, it is necessary to warm or “light off” the catalyst 38 above the minimum threshold temperature. is there. From a cold start of the engine 14, the catalyst 38 is generally below the minimum threshold temperature, and therefore it is desirable to heat the catalyst as quickly as possible to obtain sufficient or optimal performance. One way to obtain a quicker light-off of the catalyst 38 is to place the catalytic converter 30 near the engine 14 which is a heat source via hot exhaust gas flowing through the header 22 to the catalytic converter 30. .

  However, disposing the catalytic converter 30 at the downstream end 36 of the header 22 has an undesirable effect on the dynamics of the exhaust gas pressure compared to a configuration further downstream. This undesirable effect can be somewhat reduced by using multiple catalytic converters in parallel. However, the use of multiple catalytic converters 30 results in an undesirable increase in catalyst light-off time (in addition to increased cost, size and weight). Regardless of its location within the exhaust system 18, the catalyst 38 is a substantial obstruction in the flow path and therefore causes a rapid increase in flow resistance at its upstream end. This produces a positive exhaust wave or pulse that is reflected back to the engine 14 via the header 22. The exhaust gas coming from the engine 14 and the dynamics of the reflected waves moving toward the engine affect the engine performance (ie, horsepower, torque output).

  Under certain operating conditions, the reflected exhaust pulses hinder the exhaust scavenging process as well as the ability to fill the cylinder with fresh intake air (which also adversely affects fuel input into the cylinder). If exhaust waves reflected by catalyst 38 arrive in either combustion chamber during valve overlap (when both intake and exhaust valves are open), significant performance loss due to reduced volumetric efficiency There is. The high exhaust gas pressure downstream of the combustion chamber reduces the net pressure differential that draws fresh air into the cylinder. Therefore, less air and fuel fill the cylinder, resulting in poor volumetric efficiency and creating “holes” in horsepower and torque output. Reduced output occurs over a range of engine speeds where positive exhaust waves return during valve overlap. In general, a long distance between the cylinder and the catalyst 38 results in power loss at low engine speeds, and a short distance between the cylinder and the catalyst 38 results in power loss at high engine speeds.

  In the illustrated exhaust system 18, the catalytic converter 30 is located within the first half of the overall exhaust gas flow length between the engine 14 and the outlet 35E. Further, as shown in FIGS. 2-4, at least a portion of the collector section 26 is disposed within a resonator chamber 42 that substantially surrounds or surrounds the catalytic converter 30. In the illustrated embodiment, the catalytic converter 30 is entirely surrounded in the resonator chamber 42 over the entire length of the catalytic converter. In some embodiments, the resonator chamber 42 does not generally surround or surround the catalytic converter, but is in the vicinity of or partially surrounds the catalytic converter 30. The one or more holes or openings 46 define a perforated section 50 that communicates the exhaust flow path of the collector section 26 to the resonator chamber 42 and thus provides an expansion to the flow path at the perforated section 50. As shown in FIGS. 2 to 4, the openings 46 are circular and are equally spaced around the outer periphery of the collector section 26. The openings 46 may have other shapes and / or other directions in other embodiments.

  The resonator chamber 42 functions as an expansion volume of a “bag path” in that only the passage to the resonator chamber 42 and the passage from the resonator chamber 42 are openings 46. Accordingly, any exhaust gas that enters the resonator chamber 42 through the opening 46 eventually flows out of the resonator chamber 42 through the opening 46 and subsequently passes through the catalytic converter 30. On the other hand, the exhaust gas that does not enter the resonator chamber 42 can pass directly into the catalytic converter 30. The flow to the catalytic converter 30 is unobstructed in that there is no physical obstacle that hinders the flow of exhaust through the catalytic converter 30 straight from the header 22, and only the flow resistance characteristics of the catalytic converter itself.

  In the illustrated embodiment, the collector section 26 does not form a substantial length of the exhaust system 18. This is in contrast to an exhaust system with a long collector section that typically runs from the side or front of the engine to a position behind the engine. Rather, the collector section 26 of the illustrated exhaust system 18 is such that the perforated section 50 and catalytic converter 30 are within approximately the first 40% of the total flow length between the engine exhaust port and the outlet 35E of the header 22. The exhaust gas flow path of the header 22 is integrated over a short length in a manner located at or near each downstream end 36. For example, the length from the rear cylinder exhaust port to the perforation section 50 is about 612 millimeters, and the length from the perforation section 50 to the outlet 35E is about 950 millimeters.

  The above description highlights some of the difficulties of simply taking the catalytic converter from a downstream position and moving it to a much upstream position for faster light-off. The resonator chamber 42 and perforated section 50 of the present invention allow both fast light off and satisfactory power output of the engine 14.

  When an exhaust valve (not shown) of one cylinder opens, a high pressure wave propagates down the associated header pipe 22. When this wave reaches the perforation section 50, its pressure is relieved by the expansion of the resonator chamber 42. The secondary wave (the remaining component of the original high-pressure wave) hits the catalyst 38. Part of the secondary wave of the exhaust gas passes through the catalytic converter 30 and proceeds to the first attenuation unit 34A. The portion of the secondary wave that does not pass through the catalytic converter 30 is reflected by the catalyst 38 and returns toward the engine 14. The reflected wave pressure is further reduced by the expansion that occurs when the reflected wave encounters the perforated section 50 before propagating to the upstream end 36 A of the header 22. Therefore, the reflected wave that eventually returns toward the engine 14 is dissipated by expansion in the perforated section 50 (in addition to the portion that passes through the catalytic converter 30). In addition to dissipation, wave cancellation effects occur under certain operating conditions and are at least partially adjusted by the size of the volume in the resonator chamber 42 and the number of openings 46. When wave cancellation occurs, two waves going in opposite directions are incident on each other and at least one wave is canceled. For example, fresh exhaust gas waves from the engine 14 can counteract the effects of reflected waves coming from the collector section 26 toward the engine 14.

  In the illustrated twin-cylinder engine 14 in which both cylinders supply a single catalytic converter 30, the reflected waves from the catalyst 38 are separated by the collector section 26 and continue to rise on both header pipes 22. In any exhaust configuration with multiple header pipes feeding a single catalytic converter, the reflected waves at the catalyst are separated at the collector in the header pipe. Thus, the combination of perforated section 50 and resonator chamber 42 provides particularly good performance in a twin cylinder shared exhaust configuration, such as in the motorcycle 10 of FIG. Although an exhaust system 18 is shown and primarily described for operation in a 2-in-1 configuration, it is also useful for single cylinder engines, multi-cylinder engines with separate or common exhaust systems. It is.

  5 and 6 illustrate the improved performance provided by the features of the exhaust system 18. FIG. 5 is a computer-simulated graph showing the relationship between crankshaft angle of engine 14 and exhaust pressure (at the port) while operating at relatively high engine speeds, such as 800 RPM. One pressure plot in FIG. 5 is for a basic configuration comprising a catalytic converter arranged in a manner similar to the catalytic converter 30 in the muffler assembly 35 of the illustrated exhaust system 18. The basic configuration shown in solid lines does not include the perforated section 50 or the resonator chamber 42, but is otherwise identical to the exhaust system 18 shown. The second pressure plot in FIG. 5, indicated by the dashed line, is for an engine 14 with an exhaust system 18 that includes a perforated section 50 and a resonator chamber 42. Each plot of the graph of FIG. 5 shows the effect of the reflected exhaust wave arriving at the exhaust port during valve overlap about TDC (360 degrees as shown in FIG. 5). The exhaust system 18 with the perforated section 50 and the resonator chamber 42 experiences very low exhaust pressure during valve overlap. The relatively high exhaust pressure during valve overlap relative to the basic configuration results in reduced volumetric efficiency and reduced engine power as described above. Due to the position of the catalytic converter 30 in the vicinity of the downstream end 36 of the header 22 (short exhaust length between the engine 14 and the catalyst 38), the reflected exhaust waves are subject to valve overlap at these relatively high engine speeds. Present in the exhaust port.

  FIG. 6 is a computer-simulated graph illustrating the final power loss for an engine operating at the rate at which exhaust waves reflected at the exhaust port arrive during the valve overlap. The solid line in the graph of FIG. 6 represents the engine 14 having the above-described theoretical basic configuration that serves as a basis for comparison. The dashed line represents the engine 14 with the illustrated exhaust system 18 including the perforated section 50 and the resonator chamber 42. Between 5500 rpm and 9000 rpm, the perforated section 50 and the resonator chamber 42 of the exhaust system 18 allow the engine to generate a horsepower that is greater by between 2 and 4 horsepower. This represents an increase of about 5% in power (measured at about 6000 rpm).

  Next, the structure of the downstream side of the catalytic converter 30 and the exhaust flow will be described. The first passage 60 (that is, the pipe) shown in FIGS. 2 to 4 receives the exhaust gas from the catalytic converter 30. The first passage 60 is disposed in the chamber 62 of the second attenuation portion 34B. However, the exhaust gas in the first passage 60 is not allowed to communicate with the chamber 62 of the second attenuation portion 34B directly. The first passage 60 extends through the first and second chambers 64 and 68 of the first attenuation portion 34A and opens into the third chamber 72 of the first attenuation portion 34A. The first, second, and third bulkheads 74A, 74B, 74C are coupled to the outer casing 35D to provide first, second, and third separate chambers 64, 68, 72 is defined. The first passage 60 is perforated at a position passing through the first and second chambers 64 and 68 of the first attenuation portion 34A, and extends from the first passage 60 to the first and second chambers 64 and 68. On the contrary, the exhaust gas can be communicated.

  The flow of the exhaust gas changes its direction in the third chamber 72 of the first attenuation portion 34A and enters the second passage 76 (for example, a pipe). The second passage 76 passes through the first and second chambers 64 and 68 of the first attenuation portion 34A and opens into the chamber 62 of the second attenuation portion 34B. The second passage 76 is perforated at a position passing through the first and second chambers 64 and 68 of the first attenuation portion 34A, and extends from the first passage 60 to the first and second chambers 64 and 68. The reverse exhaust gas communication is possible. The second passage 76 has substantially the same cross-sectional size as the first passage 60.

  The exhaust gas enters the chamber 62 of the second attenuating portion 34B, which includes a perforated plate 80 (FIGS. 2 and 4) that divides the chamber 62 into a plurality of sub chambers that communicate with each other via the perforated plate 80. The chamber 62 and the perforated plate 80 of the second attenuation unit 34B function as a quarter wavelength tuner for erasing a specific range of sound waves generated by the engine 14. Part of the flow of exhaust gas from the second passage 76 flows from the resonator chamber 42 to the end plate 84 that separates the chamber 62 of the second attenuation portion 34B via the perforated plate 80. That portion of the exhaust gas flow can then be reflected by the end plate 84 and act on the pulse of exhaust gas flowing in the opposite direction to erase all or part of the sound energy.

  From the chamber 62 of the second attenuation section 34B, the exhaust gas passes through the first and second chambers 64 and 68 of the first attenuation section 34A, respectively, and the pair of outlet passages 88 (shown in FIGS. 2 to 4). Exit the muffler assembly 35 through a pipe, for example. The outlet passage 88 is perforated at a position passing through the first and second chambers 64 and 68 of the first attenuation portion 34A, and exhausts from the outlet passage 88 to the first and second chambers 64 and 68 and vice versa. Allows gas communication.

The muffler assembly 35 is configured to substantially surround the engine 14 along the longitudinal central axis of the motorcycle 10 defined by the front wheels 15 and the rear wheels 16. The catalytic converter 30 and the resonator chamber 42 extend substantially upright on the front side of the engine 14, and the first damping portion 34A fits between the rear wheel 16 of the motorcycle 10 and the engine 14 (FIG. 1). The muffler assembly 35 has a substantially flat lower surface 96 defined by an outer casing 35D. First damping portion 34A has a height H ₁ from the lower surface 96 to its highest point. The resonator chamber 42 has a height H ₂ from the lower surface 96 to its highest point. Second damping portion 34B has a respective height _H 1, the minimum height _{H 3} less than half of _{H 2} first damping portion 34A and the resonator chamber 42. In an embodiment, the height H ₃ of the second attenuation portion is about 1/3 (or about 33%) of the height H ₁ of the first attenuation portion 34A, and the height H _{2 of the} resonator chamber 42 is. About 40%.

  Even in a small space for operation (below the engine 14), the muffler assembly 35 is configured to effectively utilize the space by utilizing the intermediate portion 35C as the second damping portion 34B. Similarly, in a place where there is not enough space by the motorcycle (immediately before and after the engine 14), the muffler assembly 35 passes through the catalytic converter 30, the resonator chamber 42, and the first damping portion 34A. Configured for effective use. The first damping portion 34A not only extends behind the engine 14, but also the first damping portion 34A is disposed substantially between the transmission 17 and the rear wheel 16 in a manner such that the first damping portion 34A is disposed between the transmission 17 and the rear wheel 16. It extends upward on the lower edge 17A. In some embodiments, the engine 14 and the transmission 17 are partially or wholly housed within a common housing (eg, a common cast part that includes at least the engine crankcase portion and the transmission case portion).

The muffler assembly 35 defines a depression or recess 100 that is imparted with an outer shape to receive the lower portion of the engine 14 and substantially conforms to the outer shape of the lower edge 14A of the engine 14. . The depth of the recess 100 is equal to the height _{H 1} of the first damping portion 34A minus the height _{H 3} of the second damping portion 34B. Thus, the engine 14 is received in the recess 100 to approximately 2 times the depth of the height _{H 3} of the second damping portion 34B.

  Accordingly, the present invention provides, among other things, a compact muffler assembly 35 having a dampening 34B below the engine 14 and a recess 100 configured to receive a substantial portion of the engine 14. Various features and advantages of the invention are set forth in the appended claims.

1 is a side view of a motorcycle having an exhaust system embodying the present invention. FIG. 2 is a partially cutaway perspective view of the exhaust system of FIG. 1. FIG. 2 is a partially cut away top view of the muffler assembly of the exhaust system of FIG. 1. FIG. 2 is a partially cutaway side view of the muffler assembly of FIG. 1. The graph showing the relationship between a crank angle and exhaust pressure which shows the effect of the exhaust system of FIG. A graph showing the relationship between engine speed and engine output, showing the effect of the exhaust system. FIG. 2 is an enlarged side view of the transmission, engine, and muffler assembly of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motorcycle 14 Engine 17 Transmission 18 Exhaust system 22 Header 26 Collector section 30 Catalytic converter 34A 1st damping part 34B 2nd damping part 35 Muffler assembly 35D Casing 38 Catalyst 42 Resonator chamber 46 Opening 50 Perforated section 64, 68 chamber 100 recess

Claims (20)

A muffler assembly for a motorcycle engine,
A downstream damping portion having a first height and configured to be positioned substantially on the rear side of the motorcycle engine;
An upstream portion having a second height and configured to be positioned generally in front of the motorcycle engine;
Intermediate damping between the downstream damping part and the upstream part, having a third height less than half of the first height and configured to be located substantially below the motorcycle engine And a muffler assembly.   The muffler assembly according to claim 1, further comprising a shell surrounding the upstream portion, the downstream attenuation portion, and the intermediate attenuation portion.   The muffler assembly according to claim 1, wherein the upstream portion includes a catalytic converter.   The muffler assembly of claim 1, wherein the downstream attenuating portion includes first, second, and third bulkheads that at least partially define first, second, and third chambers.   The muffler assembly according to claim 1, wherein the intermediate damping portion includes a chamber configured to receive exhaust gas from the downstream damping portion.   The muffler assembly of claim 1, wherein the third height is about 33% of the first height and about 40% of the second height. Engine,
A transmission coupled to the engine and configured to receive power from the engine;
A rear wheel coupled to the transmission and configured to receive the output of the engine via the transmission;
A muffler assembly coupled to the engine and in communication with the engine to receive exhaust gas from the engine;
The muffler assembly is
A downstream damping portion disposed between the transmission and the rear wheel;
A motorcycle including an intermediate damping portion disposed on a front side of the downstream damping portion and extending along a lower side of the engine.   The exhaust system of claim 7, further comprising an upstream portion of the muffler assembly that includes a catalytic converter.   The exhaust system according to claim 8, wherein the downstream attenuation portion includes a plurality of chambers configured to receive exhaust gas from the upstream portion via a first passage.   The exhaust system according to claim 9, wherein the intermediate attenuation portion includes a chamber configured to receive exhaust gas from the downstream attenuation portion via a second passage.   The exhaust system according to claim 7, wherein the engine includes a crankcase, and the muffler assembly has a shape corresponding to a front portion, a bottom portion, and a rear portion of the crankcase.   The exhaust system according to claim 7, wherein a height of the intermediate attenuation portion is smaller than half of a height of the downstream attenuation portion.   The exhaust system according to claim 7, wherein a height of the intermediate damping portion is about 33% of a height of the downstream damping portion. A motorcycle,
Engine,
Two wheels defining the central axis of the motorcycle,
A muffler assembly positioned substantially along the central axis and in communication with the engine to receive exhaust gas from the engine;
The muffler assembly is
A downstream damping part;
Upstream,
An intermediate damping part located substantially below the engine and having a height;
A recess that is at least partially defined by the downstream damping portion and the intermediate damping portion, has a depth greater than the height of the intermediate damping portion, and in which the engine is disposed substantially internally. Motorcycle.   The motorcycle according to claim 14, further comprising a muffler shell that defines a substantially continuous outer surface of the muffler assembly and extends from the upstream portion to the downstream damping portion.   The motorcycle according to claim 15, wherein the muffler shell at least partially defines a plurality of chambers of the downstream damping portion and a chamber of the intermediate damping portion.   The motorcycle according to claim 15, wherein the upstream portion includes a catalytic converter.   The motorcycle according to claim 17, wherein the muffler shell at least partially defines an expansion chamber, and the catalytic converter is disposed in the expansion chamber.   The motorcycle according to claim 14, wherein a height of the intermediate damping portion is about half of a depth of the concave portion.   The motorcycle according to claim 19, wherein the recess has a surface shape that substantially matches a surface shape of a lower side of the engine.

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