U.S. patent application number 11/772507 was filed with the patent office on 2009-01-01 for motorcycle exhaust system.
This patent application is currently assigned to BUELL MOTORCYCLE COMPANY. Invention is credited to Erik Buell, Brian Freeh, Erick L. Gruber, Mike Johnson, Paul Pedersen, Michael D. Samarzja, Matthew J. Sheahan, Anthony D. Stefanelli, Ed Weston, Nick Zeidler.
Application Number | 20090000862 11/772507 |
Document ID | / |
Family ID | 40149273 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090000862 |
Kind Code |
A1 |
Buell; Erik ; et
al. |
January 1, 2009 |
MOTORCYCLE EXHAUST SYSTEM
Abstract
An exhaust system for a motorcycle engine includes a muffler
assembly. 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 upstream portion and the downstream attenuation
portion. The intermediate attenuation portion is adapted to be
positioned substantially below the motorcycle engine and has a
third height less than half the first height. In some embodiments,
a motorcycle is provided, in which the motorcycle engine is
positioned substantially within a recess of the muffler assembly to
a depth greater than the third height.
Inventors: |
Buell; Erik; (Mukwonago,
WI) ; Weston; Ed; (Cary, IL) ; Freeh;
Brian; (Elkhorn, WI) ; Sheahan; Matthew J.;
(Milwaukee, WI) ; Zeidler; Nick; (Wauwatosa,
WI) ; Samarzja; Michael D.; (Mukwonago, WI) ;
Johnson; Mike; (Wauwatosa, WI) ; Stefanelli; Anthony
D.; (Elkhorn, WI) ; Pedersen; Paul;
(Germantown, WI) ; Gruber; Erick L.; (Rubicon,
WI) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Assignee: |
BUELL MOTORCYCLE COMPANY
East Troy
WI
|
Family ID: |
40149273 |
Appl. No.: |
11/772507 |
Filed: |
July 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11770051 |
Jun 28, 2007 |
|
|
|
11772507 |
|
|
|
|
Current U.S.
Class: |
181/212 |
Current CPC
Class: |
F01N 2470/02 20130101;
F01N 2590/04 20130101; F01N 13/1805 20130101; F01N 1/083
20130101 |
Class at
Publication: |
181/212 |
International
Class: |
F01N 7/00 20060101
F01N007/00 |
Claims
1. A muffler assembly for a motorcycle engine, the muffler assembly
comprising: 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
upstream portion and the downstream attenuation portion, the
intermediate attenuation portion being adapted to be positioned
substantially below the motorcycle engine and having a third height
less than half the first height.
2. The muffler assembly of claim 1, further comprising a shell
encasing the upstream portion, the downstream attenuation portion,
and the intermediate attenuation portion.
3. The muffler assembly of claim 1, wherein the upstream portion
includes a catalytic converter.
4. The muffler assembly of claim 1, wherein the downstream
attenuation portion includes first, second, and third bulkheads at
least partially defining first, second, and third chambers.
5. The muffler assembly of claim 1, wherein the intermediate
attenuation portion includes a chamber configured to receive
exhaust gases from the downstream attenuation portion.
6. The muffler assembly of claim 1, wherein the third height is
about 33 percent of the first height and about 40 percent of the
second height.
7. A motorcycle comprising: an 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 engine
power through the transmission; and a muffler assembly coupled to
the engine and in communication therewith to receive exhaust gases
from the engine, the muffler assembly including a downstream
attenuation portion positioned between the transmission and the
rear wheel, and an intermediate attenuation portion positioned
forwardly of the downstream attenuation portion, the intermediate
attenuation portion extending along an underside of the engine.
8. The exhaust system of claim 7, further comprising an upstream
portion of the muffler assembly including a catalytic
converter.
9. The exhaust system of claim 8, wherein the downstream
attenuation portion includes a plurality of chambers configured to
receive exhaust gases from the upstream portion via a first
passage.
10. The exhaust system of claim 9, wherein the intermediate
attenuation portion includes a chamber configured to receive
exhaust gases from the downstream attenuation portion via a second
passage.
11. The exhaust system of claim 7, wherein the engine includes a
crankcase, the muffler assembly being shaped to conform to a front
portion, a bottom portion, and a rear portion of the crankcase.
12. The exhaust system of claim 7, wherein the intermediate
attenuation portion has a height less than half of a height of the
downstream attenuation portion.
13. The exhaust system of claim 7, wherein the height of the
intermediate attenuation portion is about 33 percent of the height
of the downstream attenuation portion.
14. A motorcycle comprising: an engine; two wheels defining a
central axis of the motorcycle; and a muffler assembly in
communication with the engine to receive exhaust gases from the
engine, the muffler assembly being positioned substantially along
the central axis and including a downstream attenuation portion, an
upstream portion, an intermediate attenuation portion positioned
substantially under the engine, the intermediate attenuation
portion having a height, and a recess at least partially defined by
the downstream attenuation portion and the intermediate attenuation
portion, wherein the recess has a depth greater than the height of
the intermediate attenuation portion, the engine being positioned
substantially within the recess.
15. The motorcycle of claim 14, further comprising a muffler shell
defining a substantially continuous outer surface of the muffler
assembly, the muffler shell extending from the upstream portion to
the downstream attenuation portion.
16. The motorcycle of claim 15, wherein the muffler shell at least
partially defines a plurality of chambers of the downstream
attenuation portion and a chamber of the intermediate attenuation
portion.
17. The motorcycle of claim 15, wherein the upstream portion
includes a catalytic converter.
18. The motorcycle of claim 17, wherein the muffler shell at least
partially defines an expansion chamber, the catalytic converter
being positioned within the expansion chamber.
19. The motorcycle of claim 14, wherein the height of the
intermediate attenuation portion is about half the depth of the
recess.
20. The motorcycle of claim 19, wherein the recess is formed by a
contour substantially matching a lower contour of the engine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. patent application
Ser. No. 11/770,051 filed Jun. 28, 2007, the entire contents of
which is incorporated herein.
BACKGROUND
[0002] The present invention relates to an exhaust system for a
motorcycle engine. More particularly, the invention relates to a
muffler assembly having a particular arrangement of parts and
overall shape.
SUMMARY
[0003] In one embodiment, the invention provides a muffler assembly
for a motorcycle engine. 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 upstream portion and the downstream
attenuation portion. The intermediate attenuation portion is
adapted to be positioned substantially below the motorcycle engine
and has a third height less than half the first height.
[0004] In another embodiment, the invention provides a motorcycle
including an 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 engine power through
the transmission, and a muffler assembly coupled to the engine and
in communication therewith to receive exhaust gases from the
engine. The muffler assembly includes a downstream attenuation
portion positioned between the transmission and the rear wheel and
an intermediate attenuation portion positioned forwardly of the
downstream attenuation portion. The intermediate attenuation
portion extends along an underside of the engine.
[0005] In yet another embodiment, the invention provides a
motorcycle including an engine, two wheels defining a central axis
of the motorcycle, and a muffler assembly in communication with the
engine to receive exhaust gases from the engine, the muffler
assembly being positioned substantially along the central axis. The
muffler assembly includes a downstream attenuation portion, an
upstream portion, an intermediate attenuation portion positioned
substantially under the engine, and a recess at least partially
defined by the downstream attenuation portion and the intermediate
attenuation portion. The recess has a depth greater than a height
of the intermediate attenuation portion, and the engine is
positioned substantially within the recess.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a side view of a motorcycle having an exhaust
system embodying the present invention;
[0008] FIG. 2 is a partial cutaway perspective view of the exhaust
system of FIG. 1.
[0009] FIG. 3 is a partial cutaway top view of a muffler assembly
of the exhaust system shown in FIG. 1.
[0010] FIG. 4 is a partial cutaway side view of the muffler
assembly of FIG. 1.
[0011] FIG. 5 is a graph representative of exhaust pressure versus
crank angle illustrating the effect of the exhaust system of FIG.
1.
[0012] FIG. 6 is a graph representative of engine output versus
engine speed illustrating the effect of the exhaust system.
[0013] FIG. 7 is an enlarged side view of the muffler assembly, the
engine, and the transmission of FIG. 1.
[0014] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. Unless specified or limited otherwise,
the terms "mounted," "connected," "supported," and "coupled" and
variations thereof are used broadly and encompass both direct and
indirect mountings, connections, supports, and couplings. Further,
"connected" and "coupled" are not restricted to physical or
mechanical connections or couplings.
DETAILED DESCRIPTION
[0015] FIG. 1 illustrates 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 to receive
power from the engine. The rear wheel 16 is driven by the power of
the engine 14 through the transmission 17 (and a drive member such
as a belt). An air-fuel mixture is ignited in a combustion chamber
(not shown) for each cylinder of the engine 14. Following
combustion in a given combustion chamber, the exhaust gases
(containing mixed products of the combustion reaction and some
residual, un-reacted components) are expelled through an exhaust
port into an exhaust system 18 of the motorcycle.
[0016] The exhaust system 18, as shown in FIGS. 1-4 and 7, includes
brackets 20 for mounting to the motorcycle 10. The exhaust system
18 includes a pair of header pipes (i.e., "headers") 22, a
collector section 26, a catalytic converter 30, and a
sound-muffling section 34. The headers 22 are exhaust conduits
leading directly from the engine 14. The sound-muffling section 34
includes a first sound-muffling ("attenuation") portion 34A and a
second sound-muffling ("attenuation") portion 34B. The collector
section 26, the catalytic converter 30, the first sound-muffling
("attenuation") portion 34A, and the second sound-muffling
("attenuation") portion 34B collectively define a muffler assembly
35. In the illustrated embodiment, the muffler assembly 35 is
positioned substantially along a central axis of the motorcycle 10
(defined by the front wheel 15 and the rear wheel 16). Each of the
first attenuation portion 34A and the second attenuation portion
34B make up at least one fifth, or 20 percent, of the length of the
muffler assembly 35 as measured along a single axis (e.g., the
central axis) or individual axis segments following the general
contour of the muffler assembly 35. Preferably, each of the first
attenuation portion 34A and the second attenuation portion 34B make
up about a third of the length of the muffler assembly 35. The
portion of the muffler assembly 35 forward of the second
attenuation portion 34B also makes up at least 20 percent of the
length of the muffler assembly 35, and preferably, about a third of
the length of the muffler assembly 35.
[0017] An upstream end 36A of each header 22 is coupled to the
engine 14 to receive exhaust gases from a respective exhaust port
of the engine 14. The headers 22 define exhaust flow passages that
are separate from one another, each header 22 routing exhaust gases
directly from an exhaust port of the engine 14 to a downstream
exhaust component. A downstream end 36B of each of the headers 22
leads into an upstream end 35A of the muffler assembly 35,
specifically, the collector section 26. The upstream end 35A of the
muffler assembly 35 is positioned generally forward of the engine
14. The illustrated collector section 26 is an exhaust conduit
defining a 2-into-1 exhaust flow passage joining the two separate
exhaust flow passages of the headers 22 into a single, larger
exhaust flow passage adjacent the catalytic converter 30.
Therefore, exhaust gases from both combustion chambers are treated
by the catalytic converter 30.
[0018] The second attenuation portion 34B defines an intermediate
portion 35C of the muffler assembly 35 between the upstream end 35A
and a downstream end 35B of the muffler assembly 35, along the
underside of the engine 14. The first attenuation portion 34A,
positioned generally at the downstream end 35B, is positioned
generally rearward of the engine 14. A muffler shell or casing 35D
(made up of one or more pieces) extends from the upstream end 35A
to the downstream end 35B, defining an outer surface of the muffler
assembly 35. Although, the casing 35D can be assembled from
multiple pieces in some embodiments, it defines a generally
continuous outer surface without abrupt transitions from one
portion of the muffler assembly 35 to the next.
[0019] Downstream of the catalytic converter 30, exhaust gases flow
through the intermediate portion 35C to the first attenuation
portion 34A at the downstream end 35B. As described above, the
intermediate portion 35C extends longitudinally underneath the
engine 14, but alternate shaping and positioning of the exhaust
components on the motorcycle 10 are optional. As described in
further detail below, exhaust gases from the catalytic converter 30
are directed substantially straight through the intermediate
portion 35C to the first attenuation portion 34A, and at least a
portion of the exhaust gases flow back from the first attenuation
portion 34A into the second attenuation portion 34B before exiting
the muffler assembly 35 at a pair of outlets 35E.
[0020] Returning now to the treatment of the exhaust gases at the
upstream end 35A, the catalytic converter 30 improves the emissions
quality of the exhaust gases expelled from the engine 14 with the
use of one or more known catalyst materials (referred to
hereinafter simply as catalyst 38), which are contained within the
catalytic converter 30. The catalyst 38 reacts with undesirable
exhaust gas components to produce more desirable products before
being exhausted to the atmosphere via outlets 35E. Specifically,
nitrogen oxides (NO.sub.x) can be converted to nitrogen (N.sub.2)
and oxygen (O.sub.2), while carbon monoxide (CO) can be converted
to carbon dioxide (CO.sub.2).
[0021] The temperature of the catalyst 38 affects its performance.
It is necessary to warm-up, or "light off", the catalyst 38 above a
minimum threshold temperature to obtain a desired level of
performance from the catalytic converter 30 to effectively alter
the undesirable exhaust gas components as described above. 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 up the catalyst as quickly as possible to obtain sufficient or
optimal performance. One way to get quicker light off of the
catalyst 38 is to place the catalytic converter 30 close to the
engine 14, which is a source of heat via the hot exhaust gases
flowing through the headers 22 to the catalytic converter 30.
[0022] However, placing the catalytic converter 30 at the
downstream ends 36 of the headers 22 can have an undesirable effect
on the exhaust gas pressure dynamics as compared to a placement
further downstream. This undesirable effect can be somewhat reduced
by using multiple catalytic converters 30 in parallel. However, the
use of multiple catalytic converters 30 causes an undesirable
increase in catalyst light off time (in addition to increasing
cost, size, and weight). Regardless of its position in the exhaust
system 18, the catalyst 38 is a substantial obstruction in the flow
passage and, therefore, causes a sudden increase in flow resistance
at its upstream end. This causes a positive pressure exhaust wave
or pulse to be reflected back towards the engine 14 through the
headers 22. The dynamics of the exhaust gases coming from the
engine 14 and the reflected waves moving towards the engine impacts
the engine performance (i.e., horsepower and torque output).
[0023] Under certain operating conditions, a reflected exhaust
pulse hinders the exhaust scavenging process as well as the ability
for the cylinder to become charged with fresh intake air (which can
also affect the input of fuel into the cylinder). If the exhaust
wave that is reflected off the catalyst 38 arrives at either
combustion chamber during valve overlap (the time that both the
intake and exhaust valves are open), there is a significant
performance loss due to decreased volumetric efficiency. With high
exhaust gas pressure downstream of the combustion chamber, the net
pressure differential that draws fresh air into the cylinder is
reduced. Hence, less air and fuel fills the cylinder, and
volumetric efficiency is spoiled, resulting in a "hole" in
horsepower and torque output. The reduced output occurs over the
range of engine speeds where the positive exhaust wave returns
during valve overlap. Generally, a longer distance between the
cylinders and the catalyst 38 results in power loss at lower engine
speeds, and a shorter distance between the cylinders and the
catalyst 38 results in power loss at higher engine speeds.
[0024] In the illustrated exhaust system 18, the catalytic
converter 30 is positioned within the first half of the total
exhaust gas flow length between the engine 14 and the outlets 35E.
Furthermore, as shown in FIGS. 2-4, at least a portion of the
collector section 26 is positioned within a resonator chamber 42,
which substantially surrounds or encloses the catalytic converter
30. In the illustrated embodiment, the catalytic converter 30 is
entirely circumferentially enclosed within the resonator chamber 42
along the full length of the catalytic converter 30. In some
embodiments, the resonator chamber 42 does not fully surround or
enclose the catalytic converter 30, but rather is adjacent to or
partially surrounding the catalytic converter 30. One or more
apertures or openings 46 define a perforated section 50 fluidly
coupling the exhaust flow passage of the collector section 26 with
the resonator chamber 42, thus providing an expansion in the flow
passage at the perforated section 50. As shown in FIGS. 2-4, the
openings 46 are circular in shape and are equally-spaced around the
circumference of the collector section 26. The openings 46 may have
other shapes and/or other orientations in other embodiments.
[0025] The resonator chamber 42 serves as a "dead end" expansion
volume in that the only passageways into and out of the resonator
chamber 42 are the openings 46. Thus, all the exhaust gases that
enter the resonator chamber 42 through the openings 46 eventually
flow out of the resonator chamber 42 through the openings 46 and
subsequently pass through the catalytic converter 30. On the other
hand, the exhaust gases that do not enter the resonator chamber 42
can pass directly into and through the catalytic converter 30. Flow
into the catalytic converter 30 is unobstructed in that there are
no physical obstructions to prevent exhaust flow straight from the
headers 22 and through the catalytic converter 30, only the
flow-restrictive nature of the catalytic converter 30, itself.
[0026] 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, which
typically runs from the front or alongside the engine to a location
rearward of the engine. Rather, the collector section 26 of the
illustrated exhaust system 18 serves to consolidate the exhaust gas
flow passages of the headers 22 over a short length such that the
perforated section 50 and the catalytic converter 30 are positioned
at or substantially adjacent the downstream ends 36 of each of the
headers 22 and within about the first 40% of the total flow length
between the engine exhaust ports and the outlets 35E. For example,
the length from the rear cylinder exhaust port to the perforated
section 50 is about 612 millimeters, and the length from the
perforated section 50 to the outlets 35E is about 950
millimeters.
[0027] The above description highlights some of the difficulties
with simply taking a catalytic converter from a downstream location
and moving it to a far upstream location for quicker light off. The
resonator chamber 42 and the perforated section 50 of the present
invention enable both quick light off and satisfactory power output
of the engine 14.
[0028] When the exhaust valve (not shown) of one cylinder opens, a
high pressure wave propagates down the associated header pipe 22.
When this wave arrives at the perforated section 50, its pressure
is dissipated by the expansion of the resonator chamber 42. A
secondary wave (the remaining component of the original high
pressure wave) is incident on the catalyst 38. A portion of the
secondary wave of exhaust gases passes through the catalytic
converter 30 and on toward the first attenuation portion 34A. The
portion of the secondary wave that does not go through the
catalytic converter 30 is reflected off the catalyst 38 and back
toward the engine 14. Before propagating to the upstream ends 36A
of the headers 22, the pressure of the reflected wave is further
diminished by expansion that occurs as the reflected wave
encounters the perforated section 50. Therefore, the reflected wave
that eventually makes it back toward the engine 14 is dissipated
through expansions at the perforated section 50 (in addition to the
portion which is passed through the catalytic converter 30). In
addition to dissipation, a wave cancellation effect occurs under
certain operating conditions and is tuned at least in part by the
number of openings 46 and the size of the volume within the
resonator chamber 42. In the occurrence of wave cancellation, two
waves traveling in opposite directions are incident upon one
another and at least one of the waves is cancelled out. For
example, a wave of fresh exhaust gases from the engine 14 can
cancel the effect of a reflected wave traveling from the collector
section 26 toward the engine 14.
[0029] In the twin-cylinder engine 14 of the illustrated
embodiment, in which both cylinders feed the single catalytic
converter 30, the reflected wave off of the catalyst 38 is split at
the collector section 26 and continues up both header pipes 22. In
any exhaust configuration with multiple header pipes feeding a
single catalytic converter, the reflected wave off of the catalyst
is split at the collector among the header pipes. Therefore, the
combination of the perforated section 50 and the resonator chamber
42 can deliver particularly good performance in twin-cylinder,
shared exhaust setups, such as on the motorcycle 10 of FIG. 1.
Although the exhaust system 18 is shown and primarily described for
operation with a 2-into-1 setup, it is also useful for
single-cylinder engines, and multi-cylinder engines with separated
or shared exhaust systems.
[0030] FIGS. 5 and 6 illustrate the enhanced performance afforded
by features of the exhaust system 18. FIG. 5 is a
computer-simulated graph representative of exhaust pressure (at the
port) versus crankshaft angle of the engine 14 while operating at a
relatively high engine speed, such as 8000 RPM. One pressure plot
in FIG. 5 is for a baseline configuration with a catalytic
converter positioned similarly to the catalytic converter 30 in the
muffler assembly 35 of the illustrated exhaust system 18. The
baseline configuration, which is represented by a solid line, does
not include the perforated section 50 or the resonator chamber 42,
but is otherwise identical to the illustrated exhaust system 18. A
second pressure plot in FIG. 5, indicated by the dashed line, is
for the engine 14 with the exhaust system 18, including the
perforated section 50 and the resonator chamber 42. The plots on
the graph of FIG. 5 illustrate the effect of a reflected exhaust
wave arriving at the exhaust port during valve overlap, generally
around top dead center (TDC, 360 degrees as indicated in FIG. 5).
The exhaust system 18 having the perforated section 50 and the
resonator chamber 42 experiences a much lower exhaust pressure
during valve overlap. The comparatively high exhaust pressure
during valve overlap for the baseline configuration leads to
decreased volumetric efficiency and decreased engine output as
described above. Due to the location of the catalytic converter 30
adjacent the downstream ends 36 of the headers 22 (i.e., short
exhaust length between the engine 14 and the catalyst 38), the
reflected exhaust wave is present at the exhaust port during valve
overlap at these relatively high engine speeds.
[0031] FIG. 6 is a computer-simulated graph illustrating the
resulting power loss for an engine operating at speeds at which a
reflected exhaust wave arrives at the exhaust port during valve
overlap. The solid line on the graph of FIG. 6 represents the
engine 14 with the theoretical baseline configuration described
above, which 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 between 2 and 4 more horsepower. This represents up to
about a 5 percent increase in power (measured at about 6000
rpm).
[0032] Turning now to the structure and exhaust flow downstream of
the catalytic converter 30, a first passage 60 (e.g., pipe) shown
in FIGS. 2-4 receives the exhaust gases from the catalytic
converter 30. The first passage 60 is positioned within a chamber
62 of the second attenuation portion 34B. However, exhaust gases
inside the first passage 60 are not allowed to communicate with the
chamber 62 of the second attenuation portion 34B directly. The
first passage 60 extends through first and second chambers 64, 68
of the first attenuation portion 34A and opens into a third chamber
72 of the first attenuation portion 34A. First, second, and third
bulkheads 74A, 74B, 74C combine with the outer casing 35D to define
the first, second, and third separate chambers 64, 68, 72 of the
first attenuation portion 34A. The first passage 60 is perforated
at the locations passing through the first and second chambers 64,
68 of the first attenuation portion 34A to allow communication of
the exhaust gases from the first passage 60 into the first and
second chambers 64, 68 and vice versa.
[0033] The flow of exhaust gases changes direction in the third
chamber 72 of the first attenuation portion 34A and enters a second
passage 76 (e.g., pipe). The second passage 76 passes through the
first and second chambers 64, 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 the locations passing
through the first and second chambers 64, 68 of the first
attenuation portion 34A to allow communication of the exhaust gases
from the first passage 60 into the first and second chambers 64, 68
and vice versa. The second passage 76 has a cross-sectional size
approximately the same as that of the first passage 60.
[0034] Exhaust gases enter the chamber 62 of the second attenuation
portion 34B, which is provided with an aperture plate 80 (FIGS. 2
and 4) dividing the chamber 62 into sub-chambers that are in
communication with each other through the aperture plate 80. The
chamber 62 of the second attenuation portion 34B and the aperture
plate 80 function as a quarter wave tuner to cancel a particular
range of sound waves generated at the engine 14. A portion of the
flow of exhaust gases from the second passage 76 travels through
the aperture plate 80 to an end plate 84 separating the chamber 62
of the second attenuation portion 34B from the resonator chamber
42. That portion of the flow of exhaust gases is then reflected off
the end plate 84 and can act against a pulse of exhaust gases
flowing in the opposite direction to cancel out all or a portion of
the sound energy.
[0035] From the chamber 62 of the second attenuation portion 34B,
exhaust gases exit the muffler assembly 35 through a pair of outlet
passages 88 (e.g., pipes) shown in FIGS. 2-4, each of which passes
through the first and second chambers 64, 68 of the first
attenuation portion 34A. The outlet passages 88 are perforated at
the locations passing through the first and second chambers 64, 68
of the first attenuation portion 34A to allow communication of the
exhaust gases from the outlet passages 88 into the first and second
chambers 64, 68 and vice versa.
[0036] The muffler assembly 35 is configured to substantially
surround the engine 14 along a central axis in the longitudinal
direction of the motorcycle 10 defined by the front wheel 15 and
the rear wheel 16. The catalytic converter 30 and the resonator
chamber 42 extend substantially upright in front of the engine 14
and the first sound attenuation portion 34A fits up between the
engine 14 and the rear wheel 16 of the motorcycle 10 (FIG. 1). The
muffler assembly 35 has a substantially flat lower surface 96
defined by the outer casing 35D. The first attenuation portion 34A
has a height H.sub.1 measured up from the lower surface 96 to its
highest point. The resonator chamber 42 has a height H.sub.2
measured up from the lower surface 96 to its highest point. The
second attenuation portion 34B has a minimum height H.sub.3 less
than one half the respective heights H.sub.1, H.sub.2 of the first
attenuation portion 34A and the resonator chamber 42. In some
embodiments, the height H.sub.3 of the second attenuation portion
is about one third (or about 33% of) the height H.sub.1 of the
first attenuation portion 34A and about 40% of the height H.sub.2
of the resonator chamber 42.
[0037] Even with a small space with which to work (below the engine
14), the muffler assembly 35 is configured to take advantage of the
space by utilizing the intermediate portion 35C as the second
attenuation portion 34B. Likewise, where there is more ample space
on the motorcycle 10 (immediately in front of and behind the engine
14), the muffler assembly 35 is also configured to take advantage
of that space via the catalytic converter 30, the resonator chamber
42, and the first attenuation portion 34A. The first attenuation
portion 34A extends not only behind the engine 14, but also upwards
above a lower edge 17A of the transmission 17 (FIG. 7), such that
the first attenuation portion 34A is positioned substantially
between the transmission 17 and the rear wheel 16. In some
embodiments, the engine 14 and the transmission 17 are partially or
wholly contained within a shared housing (e.g., a common casting
including at least an engine crankcase portion and a transmission
case portion).
[0038] The muffler assembly 35 defines an indentation or recess
100, which is contoured to receive the lower part of the engine 14,
substantially matching a contour of the lower edge 14A of the
engine 14. The depth of the recess 100 is equal to the height
H.sub.1 of the first attenuation portion 34A minus the height
H.sub.3 of the second attenuation portion 34B. Thus, the engine 14
is received into the recess 100 to a depth about two times the
height H.sub.3 of the second attenuation portion 34B.
[0039] Thus, the invention provides, among other things, a compact
muffler assembly 35 having an attenuation portion 34B below the
engine 14, and a recess 100 configured to receive a significant
portion of the engine 14. Various features and advantages of the
invention are set forth in the following claims.
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