U.S. patent application number 17/542062 was filed with the patent office on 2022-06-16 for exhaust pipe.
The applicant listed for this patent is FUTABA INDUSTRIAL CO., LTD.. Invention is credited to Kosuke Onoda, Shunsuke Sameshima, Masayuki Sudo.
Application Number | 20220186642 17/542062 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-16 |
United States Patent
Application |
20220186642 |
Kind Code |
A1 |
Sameshima; Shunsuke ; et
al. |
June 16, 2022 |
EXHAUST PIPE
Abstract
An exhaust pipe includes a tubular portion and a space forming
portion. The tubular portion forms an exhaust flow path in an
exhaust system of an internal combustion engine. The tubular
portion has a tubular shape. The space forming portion is provided
along at least one of an inner surface and an outer surface of the
tubular portion and forms at least one branch space between the
space forming portion and the tubular portion. The at least one
branch space communicates with the exhaust flow path and has a
function as a side-branch muffler. The at least one branch space
includes a space with a length that is one third or more of an
entire length of the exhaust system.
Inventors: |
Sameshima; Shunsuke;
(Okazaki-shi, JP) ; Onoda; Kosuke; (Okazaki-shi,
JP) ; Sudo; Masayuki; (Okazaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUTABA INDUSTRIAL CO., LTD. |
Okazaki-shi |
|
JP |
|
|
Appl. No.: |
17/542062 |
Filed: |
December 3, 2021 |
International
Class: |
F01N 1/08 20060101
F01N001/08; F01N 1/16 20060101 F01N001/16; F01N 13/02 20060101
F01N013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2020 |
JP |
2020-208805 |
Claims
1. An exhaust pipe comprising: a tubular portion forming an exhaust
flow path in an exhaust system of an internal combustion engine;
and a space forming portion provided along at least one of an inner
surface and an outer surface of the tubular portion and forming at
least one branch space between the space forming portion and the
tubular portion, the at least one branch space communicating with
the exhaust flow path and having a function as a side-branch
muffler, wherein the at least one branch space comprises a space
with a length that is one fifth or more of an entire length of the
exhaust system.
2. The exhaust pipe according to claim 1, wherein the tubular
portion is a longest tubular portion of a tubular body forming the
exhaust flow path in the exhaust system.
3. The exhaust pipe according to claim 1, wherein the at least one
branch space comprises a space with a length that is one third or
more of the entire length of the exhaust system.
4. The exhaust pipe according to claim 1, wherein the at least one
branch space comprises two branch spaces with lengths different
from each other.
5. The exhaust pipe according to claim 1, wherein the at least one
branch space comprises two branch spaces each having a length that
is one fifth or more of the entire length of the exhaust
system.
6. The exhaust pipe according to claim 1, wherein the space forming
portion is provided along the inner surface of the tubular
portion.
7. The exhaust pipe according to claim 1, wherein the space forming
portion comprises a tubular inner pipe member disposed inside the
tubular portion and forming a double-wall pipe together with the
tubular portion, wherein the inner pipe member comprises: an
attached portion attached to the inner surface of the tubular
portion; and a separated portion spaced apart from the inner
surface of the tubular portion, and wherein the at least one branch
space comprises a space formed between the separated portion and
the tubular portion.
8. The exhaust pipe according to claim 7, wherein an area defined
by an outer edge of the separated portion in a cross-section
perpendicular to an axial direction of the double-wall pipe is
encompassed by an area defined by an outer edge of the attached
portion in the cross-section.
9. The exhaust pipe according to claim 1, wherein the tubular
portion comprises a curved portion forming a curve in the exhaust
flow path.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of Japanese
Patent Application No. 2020-208805 filed on Dec. 16, 2020 with the
Japan Patent Office, the entire disclosure of which is incorporated
herein by reference.
BACKGROUND
[0002] The present disclosure relates to an exhaust pipe.
[0003] In exhaust systems of internal combustion engines, noise is
reduced by mufflers provided in exhaust flow paths. For example,
Japanese Unexamined Utility Model Application Publication No.
S61-138813 discloses an exhaust system in which a branch pipe,
which is divided from an exhaust pipe forming part of an exhaust
flow path, functions as a side-branch muffler.
SUMMARY
[0004] In such an exhaust system, low-frequency resonance that is
dependent on the entire length of the exhaust system may be
generated as a type of noise. Unfortunately, in the exhaust system
disclosed in S61-138813, the branch pipe, which functions as a
side-branch muffler, is short, thereby hindering noise reduction in
the low frequency region.
[0005] It is desirable that one aspect of the present disclosure
provides a technique to facilitate noise reduction in the low
frequency region.
[0006] One aspect of the present disclosure provides an exhaust
pipe that comprises a tubular portion and a space forming portion.
The tubular portion forms an exhaust flow path in an exhaust system
of an internal combustion engine. The tubular portion has a tubular
shape. The space forming portion is provided along at least one of
an inner surface and an outer surface of the tubular portion and
forms at least one branch space between the space forming portion
and the tubular portion. The at least one branch space communicates
with the exhaust flow path and has a function as a side-branch
muffler. The at least one branch space includes a space with a
length that is one third or more of an entire length of the exhaust
system.
[0007] Such a configuration provides the branch space that
functions as a side-branch muffler with a relatively long length,
thereby reducing noise in the low frequency region.
[0008] In one aspect of the present disclosure, the tubular portion
may be a longest tubular portion of a tubular body forming the
exhaust flow path in the exhaust system.
[0009] In one aspect of the present disclosure, the at least one
branch space may comprise a space with a length that is one third
or more of the entire length of the exhaust system. Such a
configuration provides an even longer branch space that functions
as a side-branch muffler, thereby further facilitating noise
reduction in the low frequency region.
[0010] In one aspect of the present disclosure, the at least one
branch space may comprise two branch spaces with lengths different
from each other. Such a configuration has a muffling effect on
sound waves with a wider range of frequencies.
[0011] In one aspect of the present disclosure, the at least one
branch space may comprise two branch spaces each having a length
that is one fifth or more of the entire length of the exhaust
system. Such a configuration has the muffling effect on sound waves
with a wider range of frequencies in the low frequency region.
[0012] In one aspect of the present disclosure, the space forming
portion may be provided along the inner surface of the tubular
portion. Such a configuration allows the branch spaces to be formed
with the outer shape of the tubular portion maintained.
[0013] In one aspect of the present disclosure, the space forming
portion may comprise a tubular inner pipe member disposed inside
the tubular portion and forming a double-wall pipe together with
the tubular portion. The inner pipe member comprises an attached
portion and a separated portion. The attached portion is attached
to the inner surface of the tubular portion. The separated portion
is spaced apart from the inner surface of the tubular portion. The
at least one branch space may comprise a space formed between the
separated portion and the tubular portion. With such a
configuration, the branch space is formed by providing a
double-wall pipe structure and, thus, can be relatively easily
formed.
[0014] In one aspect of the present disclosure, an area defined by
an outer edge of the separated portion in a cross-section
perpendicular to an axial direction of the double-wall pipe may be
encompassed by an area defined by an outer edge of the attached
portion in the cross-section. Such a configuration allows the
branch space to be formed with the outer shape of the tubular
portion maintained.
[0015] In one aspect of the present disclosure, the tubular portion
may comprise a curved portion. The curved portion forms a curve in
the exhaust flow path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Example embodiments of the present disclosure will be
described hereinafter with reference to the accompanying drawings,
in which:
[0017] FIG. 1 is a plan view showing an exhaust system of an
internal combustion engine;
[0018] FIG. 2A is an enlarged view showing a connection between a
second tubular member and a second catalytic converter;
[0019] FIG. 2B is an enlarged view showing a connection between a
second tubular member and a muffler;
[0020] FIG. 3A is a cross-sectional view taken along a line
IIIA-IIIA in FIG. 2A;
[0021] FIG. 3B is a cross-sectional view taken along a line
IIIB-IIIB in FIG. 2A;
[0022] FIG. 3C is a diagram showing the cross-section of the
attached portion in FIG. 3A and the cross-section of the separated
portion in FIG. 3B in an overlapping manner;
[0023] FIG. 4 is a schematic view showing the exhaust system of the
internal combustion engine of FIG. 1 in a simplified manner;
[0024] FIG. 5 is a graph showing a muffling effect of the exhaust
system; and
[0025] FIG. 6 is a schematic diagram showing communication holes
according to a modified example.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
1. Configuration
[0026] Referring to FIG. 1, an exhaust system 1 is disposed under
the floor of a vehicle. The exhaust system 1 forms an exhaust flow
path that is a flow passage for exhaust gas discharged from an
internal combustion engine 100 of the vehicle.
[0027] The exhaust system 1 comprises at least one exhaust part. As
the at least one exhaust part, the exhaust system 1 comprises, in
the order from the upstream side of the exhaust flow path (from the
left side in FIG. 1), an exhaust manifold 2, a first catalytic
converter 3A, a second catalytic converter 3B, and a muffler 4. The
exhaust gas discharged from the internal combustion engine 100
flows through the exhaust manifold 2 and into the first catalytic
converter 3A. Each of the first catalytic converter 3A and second
catalytic converter 3B comprise a catalyst. The first and second
catalytic converters 3A, 3B reform or collect environmental
pollutants in the exhaust gas. The muffler 4 reduces noise in the
exhaust system 1.
[0028] The exhaust system 1 also comprises tubular members. Each
tubular member constitutes a tubular body forming the exhaust flow
path. Each tubular member is connected to the at least one exhaust
part at least at one end the tubular member. Each tubular member
forms the exhaust flow path in the upstream or downstream of the at
least one exhaust part of the exhaust system 1. As the tubular
members, the exhaust system 1 comprises a first tubular member 5A,
a second tubular member 5B, and a third tubular member 5C. The
first, second, and third tubular members 5A, 5B, 5C are, for
example, circular pipes each having a perfectly circular
cross-section with an almost consistent outer diameter. The term
"perfectly circular" as used herein does not mean to describe the
shape of a perfect circle in a strict sense, but means to
distinguish a circular shape from an oval shape. The same applies
hereinafter.
[0029] The first tubular member 5A is connected to the first and
second catalytic converters 3A, 3B and forms the exhaust flow path
therebetween. The second tubular member 5B is connected to the
second catalytic converter 3B and the muffler 4 and forms the
exhaust flow path therebetween. The third tubular member 5C is
connected to the muffler 4 and forms the exhaust flow path in the
downstream of the muffler 4. The exhaust gas that flows through the
muffler 4 is discharged from the third tubular member 5C to the
outside of the exhaust system 1. In FIGS. 1 to 2B, the direction in
which the exhaust gas flows through the exhaust flow path is from
left to right, that is, the direction indicated by an arrow Y.
[0030] At least one of the tubular members comprises a curved
portion. The curved portion forms a curve in the exhaust flow path
in the exhaust system 1. The exhaust system 1 is disposed under the
floor of a vehicle as mentioned above. Under the floor of a
vehicle, there are many other components, such as a propeller
shaft, cross members, side members, and a fuel tank of the vehicle,
in addition to the exhaust system 1. Thus, in order to avoid
interference with these components, the exhaust flow path of the
exhaust system 1 comprises the curved portion and, thereby, the
exhaust flow path is at least partly curved as in exhaust systems
of common vehicles.
[0031] Specifically in the exhaust system 1, the first and second
tubular members 5A, 5B are provided with the curved portion as
shown in FIG. 1. Particularly, the second tubular member 5B is
provided with curved portions 51A to 51D at the positions where a
double-wall pipe, which will be described below, is formed.
[0032] Out of the tubular members, the longest member is provided
with a space forming portion, which will be described below. In the
example shown in FIG. 1, the second tubular member 5B is the
longest among the first, second, and third tubular members 5A, 5B,
5C. The second tubular member 5B is, thus, provided with the space
forming portion. Hereinafter, the configuration where the second
tubular member 5B is provided with the space forming portion is
referred to also as an exhaust pipe 10 with muffler function. The
exhaust pipe 10 with muffler function corresponds to one example of
the exhaust pipe. Moreover, the tubular member provided with the
space forming portion, namely the second tubular member 5B,
corresponds to one example of the tubular portion.
[0033] The space forming portion is provided along at least one of
the inner surface and the outer surface of the tubular portion,
forming at least one branch space. The at least one branch space
refers to a space that communicates with the exhaust flow path and
functions as a side-branch muffler.
[0034] As an example of the space forming portion that is formed
along the inner surface of the tubular portion, the second tubular
member 5B is provided with a first inner pipe member 6A and a
second inner pipe member 6B. Both the first and second inner pipe
members 6A, 6B have a tubular shape. Specifically, the first and
second inner pipe members 6A, 6B are circular pipes each having a
perfectly circular cross-section.
[0035] Each of the first and second inner pipe members 6A, 6B is
disposed inside the second tubular member 5B and forms the
double-wall pipe together with the second tubular member 5B. In
other words, in the portion of the second tubular member 5B where
the first inner pipe member 6A or the second inner pipe member 6B
is disposed, the double-wall pipe is formed in which the second
tubular member 5B serves as the outer pipe and the first inner pipe
member 6A or the second inner pipe member 6B serves as the inner
pipe. The first and second inner pipe members 6A, 6B are not
visible from the outside of the exhaust system 1, but shown with
solid lines in the drawings to facilitate understanding.
[0036] As shown in FIGS. 2A, 3A, and 3B, the first inner pipe
member 6A comprises an attached portion 61A and a separated portion
62A. FIG. 3A is a cross-sectional view showing a portion of the
above-described double-wall pipe composed of the second tubular
member 5B and the attached portion 61A in which the portion is cut
along a plane perpendicular to the axial direction of the
double-wall pipe. The cross-section in FIG. 3A (the cross-section
taken along the line IIIA-IIIA in FIG. 2A) is hereinafter referred
to as a first cross-section. FIG. 3B is a cross-sectional view
showing a portion of the above-described double-wall pipe composed
of the second tubular member 5B and the separated portion 62A in
which the portion is cut along a plane perpendicular to the axial
direction of the double-wall pipe. The cross-section in FIG. 3B
(the cross-section taken along the line IIIB-IIIB in FIG. 2A) is
hereinafter referred to as a second cross-section.
[0037] As shown in FIGS. 2A and 3A, the outer surface of the
attached portion 61A is almost identical in shape to the inner
surface of the second tubular member 5B. The outer surface of the
attached portion 61A is in contact with the inner surface of the
second tubular member 5B along the entire circumference in the
direction around the axis of the second tubular member 5B. The
outer surface of the attached portion 61A is attached to the inner
surface of the second tubular member 5B by welding. Both the first
inner pipe member 6A and the second tubular member 5B are, for
example, circular pipes each having a perfectly circular
cross-section. Thus, the outer diameter of the attached portion 61A
is, for example, almost the same as the inner diameter of the
second tubular member 5B.
[0038] As shown in FIG. 3A, the area defined by an outer edge S1 of
the attached portion 61A in the first cross-section nearly
corresponds to the area defined by an inner edge T of the second
tubular member 5B in the first cross-section. The expression of two
areas nearly corresponding to each other as used herein means that
the two areas have almost the same size, that is, the shapes and
surface areas of the two areas are almost the same.
[0039] As shown in FIGS. 2A and 3A, the outer surface of the
separated portion 62A is situated inside of the inner surface of
the second tubular member 5B in the exhaust flow path. The
separated portion 62A and the second tubular member 5B are spaced
apart from each other. Both the first inner pipe member 6A and the
second tubular member 5B are, for example, circular pipes each
having a perfectly circular cross-section. Thus, the outer diameter
of the separated portion 62A is smaller than, for example, the
inner diameter of the second tubular member 5B. The outer diameter
of the separated portion 62A is, for example, almost consistent
except the portion of the separated portion 62A situated on the
upstream side of the exhaust flow path. The portion on the upstream
side extends to the attached portion 61A as will be described
below, and gradually expands in diameter toward the attached
portion 61A.
[0040] In the first inner pipe member 6A, the separated portion 62A
is narrower than the attached portion 61A. The first inner pipe
member 6A is, for example, a circular pipe having a perfectly
circular cross-section. Thus, the inner diameter of the separated
portion 62B is smaller than, for example, the inner diameter of the
attached portion 61A.
[0041] FIG. 3C is a diagram showing the cross-section of the
attached portion 61A in FIG. 3A and the cross-section of the
separated portion 62A in FIG. 3B in an overlapping manner with the
centers of these portions aligned. As shown in FIG. 3C, the area
defined by an outer edge S2 of the separated portion 62A in the
second cross-section is encompassed by the area defined by the
outer edge S1 of the attached portion 61A in the first
cross-section. A certain area is "encompassed" by another area as
described herein means that the size of the certain area is smaller
than that of the other area. In other words, it means that the
certain area completely fits into the other area when these areas
are overlapped.
[0042] For example as shown in FIGS. 1 and 2A, the attached portion
61A forms the upstream end of the double-wall pipe composed of the
second tubular member 5B and the first inner pipe member 6A. The
separated portion 62A forms the portion of the double-wall pipe
situated downstream of the attached portion 61A. That is, a space
7A formed between the second tubular member 5B and the separated
portion 62A is closed in the axial direction of the double-wall
pipe at the upstream end of the double-wall pipe by the attached
portion 61A. The space 7A formed between the second tubular member
5B and the separated portion 62A communicates with the exhaust flow
path at the downstream end of the double-wall pipe. In other words,
the space 7A formed between the second tubular member 5B and the
separated portion 62A is included in the at least one branch space
described above. Hereinafter, the space 7A formed between the
second tubular member 5B and the separated portion 62A is referred
to as a first branch space 7A.
[0043] As shown in FIG. 2B, the second inner pipe member 6B
comprises an attached portion 61B and a separated portion 62B. The
attached portion 61B and the separated portion 62B are configured
similarly to the above-described attached portion 61A and separated
portion 62A respectively. However, the portion of the separated
portion 62B situated on the downstream side of the exhaust flow
path, instead of the portion on the upstream side of the exhaust
flow path, extends to the attached portion 61B, as will be
described below. The outer diameter of the separated portion 62B is
almost consistent except the portion on the downstream side. The
portion on the downstream side gradually expands in diameter toward
the attached portion 61B.
[0044] As shown in FIGS. 1 and 2B, the attached portion 61B forms
the downstream end of the double-wall pipe composed of the second
tubular member 5B and the second inner pipe member 6B. The
separated portion 62B forms the portion of the double-wall pipe
situated upstream of the attached portion 61B. That is, a space 7B
formed between the second tubular member 5B and the separated
portion 62B is closed in the axial direction of the double-wall
pipe at the downstream end of the double-wall pipe by the attached
portion 61B. The space 7B formed between the second tubular member
5B and the separated portion 62B communicates with the exhaust flow
path at the upstream end of the double-wall pipe. In other words,
the space 7B formed between the second tubular member 5B and the
separated portion 62B is also included in the at least one branch
space described above. Hereinafter, the space 7B formed between the
second tubular member 5B and the separated portion 62B is referred
to as a second branch space 7B.
[0045] FIG. 4 is a schematic view showing the exhaust system 1 of
FIG. 1 in a simplified manner. For easier understanding of the
length of the branch space, the exhaust system 1 in FIG. 4 is
simplified in a manner such that both the first and second tubular
members 5A, 5B have no curved portions and the exhaust parts are
linearly arranged. The length of each branch space refers to the
length from the portion where the branch space is closed to the
portion where the branch space communicates with the exhaust flow
path.
[0046] In FIG. 4, the sound pressures of resonance that can be
generated in the exhaust system 1 are also shown. Such resonance is
a type of noise in the exhaust system 1. The wavelength of
resonance is dependent on a length La of the exhaust system 1. The
term "length La of the exhaust system 1" as used herein means the
entire length of the exhaust system 1. In other words, the term
"length La of the exhaust system 1" as used herein means the entire
length of the exhaust flow path in the exhaust system 1. In FIG. 4,
the exhaust flow path in the exhaust system 1 is schematically
shown in a linear manner. Thus, the length from an end Pa1 to an
end Pa2 corresponds to the length La of the exhaust system 1. The
end Pa1 is the end of the exhaust manifold 2 that is connected to
the internal combustion engine 100. The end Pa2 is the end of the
third tubular member 5C that is open to the outside of the exhaust
system 1. In the actual exhaust system 1, the exhaust flow path is
not completely linear as shown in FIG. 1. In such a case, the
length along the shape of the exhaust flow path is the length of
the exhaust system 1. Moreover, in the case where the exhaust flow
path is, for example, curved inside the exhaust part(s), the length
of the exhaust system 1 is larger than the length of the appearance
of the exhaust system 1 due to the length(s) of the curve(s) and
the like.
[0047] As the sound pressures of resonance that can be generated in
the exhaust system 1, FIG. 4 shows specifically the sound pressures
of a standing wave D1 in the first mode, a standing wave D2 in the
second mode, and a standing wave D3 in the third mode. The standing
wave D1 has an antinode at the end Pa1, a node at the end Pa2, and
no further nodes therebetween. One quarter of a wavelength
.lamda.d1 of the standing wave D1 is equal to the length La of the
exhaust system 1 ((1/4).lamda.d1=La). The standing wave D2 has an
antinode at the end Pa1, a node at the end Pa2, and one more node
therebetween. One quarter of a wavelength .lamda.d2 of the standing
wave D2 is equal to one third of the length La of the exhaust
system 1 ((1/4).lamda.d2=(1/3)La). The standing wave D3 has an
antinode at the end Pa1, a node at the end Pa2, and two more nodes
therebetween. One quarter of a wavelength .lamda.d3 of the standing
wave D3 is equal to one fifth of the length La of the exhaust
system 1 ((1/4).lamda.d3=(1/5)La).
[0048] Side-branch mufflers having a side-branch space with a
length Lbn that is one quarter of the wavelength .lamda. of noise
(Lbn=(1/4).lamda.) have the muffling effect particularly on such
noise. Noise in the exhaust system 1 at a lower frequency has a
longer wavelength. In other words, noise in the low frequency
region has a longer wavelength. From the perspective of reducing
noise in the low frequency region, the exhaust system 1, thus, is
provided with the branch space with a length that is one fifth or
more of the length La of the exhaust system 1. From the perspective
of further reducing noise in a lower frequency region, the exhaust
system 1 may be provided with the branch space with a length that
is one third or more of the length La of the exhaust system 1.
[0049] The first and second branch spaces 7A, 7B are designed, for
example, to have lengths different from each other. Specifically, a
length Lb1 of the first branch space 7A is designed to be one fifth
of the length La of the exhaust system 1 (Lb1=(1/5)La). As
described above, the first branch space 7A is closed on the
upstream side of the exhaust flow path by the attached portion 61A
and communicates with the exhaust flow path on the downstream side
of the exhaust flow path. Thus, the length Lb1 of the first branch
space 7A refers specifically to the length of the separated portion
62A. In other words, the length Lb1 of the first branch space 7A
refers to the length from an end Pb1 of the separated portion 62A
situated on the upstream side of the exhaust flow path to an end
Pb2 of the separated portion 62A on the downstream side.
[0050] Moreover, a length Lb2 of the second branch space 7B is
designed to be one third of the length La of the exhaust system 1
(Lb2=(1/3)La). As described above, the second branch space 7B is
closed on the downstream side of the exhaust flow path by the
attached portion 61B and communicates with the exhaust flow path on
the upstream side of the exhaust flow path. Thus, the length Lb2 of
the second branch space 7B refers specifically to the length of the
separated portion 62B. In other words, the length Lb2 of the second
branch space 7B refers to the length from an end Pb3 of the
separated portion 62B situated on the upstream side of the exhaust
flow path to an end Pb4 of the separated portion 62B on the
downstream side.
2. Effects
[0051] According to the embodiment described in detail above, the
following effects can be achieved.
[0052] (2a) In the exhaust system 1, the first and second branch
spaces 7A, 7B are formed. The first branch space 7A has a length
that is one fifth or more of the length La of the exhaust system 1.
The second branch space 7B also has a length that is one fifth or
more of the length La of the exhaust system 1. Such a configuration
provides the branch spaces, which function as side-branch mufflers,
with relatively long lengths, thereby reducing noise in the low
frequency region. Such a configuration has the muffling effect
particularly on the standing wave D3 in the third mode or sound
waves with frequencies lower than that of the standing wave D3.
[0053] (2b) In the exhaust system 1, the second branch space 7B is
formed. The second branch space 7B has a length that is one third
or more of the length La of the exhaust system 1. Such a
configuration provides the branch space, which functions as a
side-branch muffler, with an even longer length, thereby further
reducing noise in the low frequency region. Such a configuration
has the muffling effect particularly on the standing wave D2 in the
second mode or sound waves with frequencies lower than that of the
standing wave D2.
[0054] (2c) In the exhaust system 1, the first and second branch
spaces 7A, 7B are formed. The first and second branch spaces 7A, 7B
have lengths different from each other. Such a configuration has
the muffling effect on sound waves with a wider range of
frequencies.
[0055] (2d) In the exhaust system 1, the first and second branch
spaces 7A, 7B are formed. Each of the first and second branch
spaces 7A, 7B has a length that is one fifth or more of the length
La of the exhaust system 1. Such a configuration has the muffling
effect on sound waves with a wider range of frequencies within a
frequency region that includes the frequency of the standing wave
D3 in the third mode and lower frequencies.
[0056] Referring now to FIG. 5 which is a graph showing the
muffling effect in the exhaust system. In this graph, the
horizontal axis represents the frequency of a sound wave while the
vertical axis represents the amount of noise reduction. The solid
line shows the muffling effect of the exhaust system 1. The broken
line shows the muffling effect of an exhaust system with no branch
space. The three dash-dotted lines show, in order from low to high,
the frequency of the standing wave D1 in the first mode, the
frequency of the standing wave D2 in the second mode, and the
frequency of the standing wave D3 in the third mode that can be
generated in the exhaust system 1. In the example shown in FIG. 5,
the frequency of the standing wave D1 in the first mode is about 42
Hz, the frequency of the standing wave D2 in the second mode is
about 125 Hz, and the frequency of the standing wave D3 in the
third mode is about 208 Hz.
[0057] As shown in FIG. 5, noise in the low frequency region is
reduced more in the exhaust system 1 than in the exhaust system
with no branch space. The exhaust system 1 has a high muffling
effect particularly on the standing wave D3 in the third mode and
the standing wave D2 in the second mode. The exhaust system 1 has
the muffling effect also on a sound wave with a frequency that is
about three times higher than that of the standing wave D2 in the
second mode.
[0058] (2e) The first and second inner pipe members 6A, 6B are
disposed along the inner surface of the second tubular member 5B.
Such a configuration allows the branch spaces to be formed with the
outer shape of the second tubular member 5B maintained. It is,
thus, possible to form the exhaust pipe 10 with muffler function
that can be arranged in the same space as in the configuration
where the second tubular member 5B merely functions as an exhaust
flow path. The configuration where the second tubular member 5B
merely functions as an exhaust flow path as mentioned herein refers
to a configuration where the second tubular member 5B is not
provided with the first and second inner pipe members 6A, 6B and
the first and second branch spaces 7A, 7B are not formed.
[0059] (2f) Each of the first and second inner pipe members 6A, 6B
forms the double-wall pipe together with the second tubular member
5B. The first branch space 7A is formed between the second tubular
member 5B and the separated portion 62A of the first inner pipe
member 6A. The second branch space 7B is formed between the second
tubular member 5B and the separated portion 62B of the second inner
pipe member 6B.
[0060] With such a configuration, the branch spaces are formed by
providing a double-wall pipe structure and, thus, can be relatively
easily formed.
[0061] (2g) The area defined by the outer edge S2 of the separated
portion 62A in the second cross-section is encompassed by the area
defined by the outer edge S1 of the attached portion 61A in the
first cross-section. Such a configuration allows the branch space
to be formed with the outer shape of the second tubular member 5B
maintained. Thus, the external dimension of the exhaust pipe 10
with muffler function is reduced as compared with a configuration
where a branch space is formed by expanding the tubular portion in
the circumferential direction of the double-wall pipe.
[0062] (2h) The second tubular member 5B is provided with curved
portions 51A to 51D at the positions where the double-wall pipe is
formed, that is, where the first inner pipe member 6A or the second
inner pipe member 6B is disposed. Such a configuration allows the
branch spaces to be formed irrespective of with or without the
curved portions in the tubular portion, thereby providing longer
branch spaces.
3. Other Embodiments
[0063] An embodiment of the present disclosure has been described
hereinabove. The present disclosure, however, should not be limited
to the above-described embodiment and may be carried out in
variously modified manners.
[0064] (3a) In the above-described embodiment, two branch spaces,
namely the first and second branch space 7A, 7B, are formed in the
second tubular member 5B. However, there may be one branch space,
or three or more branch spaces formed in the tubular portion.
[0065] (3b) In the above-described embodiment, the first and second
branch spaces 7A, 7B are formed in the second tubular member 5B.
The first and second branch spaces 7A, 7B have lengths different
from each other. In the case where two or more branch spaces are
formed in the tubular portion, each branch space may have the same
length as the other branch space(s) or may have a length different
from the other branch space(s). That is, each of the branch spaces
may reduce noise at the same frequency as the frequency reduced in
other branch spaces, or may reduce noise at a frequency different
from the frequencies reduced in other branch spaces.
[0066] (3c) In the above-described embodiment, the first branch
space 7A reduces noise at the frequency of the standing wave D3 in
the third mode. The second branch space 7B reduces noise at the
frequency of the standing wave D2 in the second mode. In this
manner, the aforementioned at least one branch space may comprise a
branch space that reduces noise at the frequency of at least one
standing wave out of the standing waves in the first to third
modes.
[0067] (3d) In the above-described embodiment, the first and second
branch spaces 7A, 7B have lengths that are one fifth or more of the
length La of the exhaust system 1. However, the lengths of the
branch spaces formed in the tubular portion are not limited to one
fifth or more of the length of the tubular portion. For example,
the lengths of the branch spaces formed in the tubular portion may
be, for example, one third or more, one half or more, two thirds or
more, three quarters or more, or four fifths or more of the length
of the tubular portion. Moreover, the lengths of the branch spaces
formed in the tubular portion may be, for example, the same as the
length of the tubular portion.
[0068] (3e) In the above-described embodiment, each space formed
between the second tubular member 5B and the first inner pipe
member 6A and between the second tubular member 5B and the second
inner pipe member 6B is closed at one end of the double-wall pipe
and communicates with the exhaust flow path at the other end,
thereby forming the first and second branch spaces 7A, 7B. However,
the branch spaces may be formed in a different way.
[0069] For example, the branch space may be formed as in an exhaust
pipe 11 with muffler function shown in FIG. 6. In the exhaust pipe
11 with muffler function, the space formed between the second
tubular member 5B and an inner pipe member 6C is closed at both
ends of the double-wall pipe and communicates with the exhaust flow
path through communication holes 8 formed in the middle portion of
the double-wall pipe. Thus, two branch spaces 7C, 7D are
formed.
[0070] In FIG. 6, a group of perfectly circular holes is shown as
the communication holes 8. However, the number of holes
constituting the communication holes is not particularly limited.
The shape of the holes is likewise not particularly limited, and
may be, for example, an oval shape, a polygonal shape, a polygonal
shape with round corners, or a star shape. The inner pipe member 6C
is not visible from the outside of the exhaust pipe 11 with muffler
function, but shown with solid lines in FIG. 6 to facilitate
understanding.
[0071] (3f) In the above-described embodiment, the first inner pipe
member 6A or the second inner pipe member 6B forms the double-wall
pipe together with the second tubular member 5B. However, the
tubular portion and the space forming portion may form a
multiple-wall pipe with, for example, triple walls or more.
[0072] (3g) In the above-described embodiment, the first inner pipe
member 6A or the second inner pipe member 6B forms the double-wall
pipe together with the second tubular member 5B. However, the space
forming portion does not have to form a multiple-wall pipe, such as
a double-wall pipe, together with the tubular portion.
[0073] In other words, each of the first inner pipe member 6A and
the second inner pipe member 6B is arranged inside the second
tubular member 5B, covering the inner surface of the second tubular
member 5B along the entire circumference in the direction around
the axis of the second tubular member 5B. However, the space
forming portion may be provided inside the tubular portion,
covering the inner surface of the tubular portion along part of the
circumference in the direction around the axis of the tubular
portion.
[0074] (3h) In the above-described embodiment, each of the first
and second inner pipe members 6A, 6B is provided along the inner
surface of the second tubular member 5B. However, the space forming
portion may be provided along the outer surface of the tubular
portion. In this case, the space forming portion may be provided
outside the tubular portion, covering the outer surface of the
tubular portion along the entire circumference in the direction
around the axis of the tubular portion. Alternatively, the space
forming portion may be provided outside the tubular portion,
covering the outer surface of the tubular portion along part of the
circumference in the direction around the axis of the tubular
portion.
[0075] (3i) In the above-described embodiment, out of the first,
second, and third tubular members 5A, 5B, 5C, the longest member,
namely the second tubular member 5B, is provided with the space
forming portion. When the tubular member to be provided with the
space forming portion is determined based on the length in this
manner, the length of each tubular member is acquired as follows.
Specifically, if the tubular member forms the exhaust flow path
between the internal combustion engine and the exhaust part
disposed at the uppermost stream position, the length of the
tubular member is from the end of the tubular member connected to
the internal combustion engine to the end connected to the exhaust
part. If the tubular member forms the exhaust flow path between two
exhaust parts, the length of the tubular member is from the end of
the tubular member connected to one of the exhaust parts to the end
connected to the other exhaust part. If the tubular member forms
the exhaust flow path on the downstream side of the exhaust part
disposed at the lowermost stream position, the length of the
tubular member is from the end of the tubular member connected to
the exhaust part to the end open to the outside of the exhaust
system.
[0076] (3j) In the above-described embodiment, out of the first,
second, and third tubular members 5A, 5B, 5C, the longest member,
namely the second tubular member 5B, is provided with the space
forming portion. However, the tubular member provided with the
space forming portion is not limited to the longest tubular member
out of multiple tubular members. That is, the tubular portion does
not have to be the longest portion of the tubular body forming the
exhaust flow path in the exhaust system.
[0077] (3k) In the above-described embodiment, the second tubular
member 5B consists of a single component. However, the tubular
portion may be composed of two or more components. For example, the
tubular portion may be a member comprising two or more tubular
components coupled to each other.
[0078] (3l) In the above-described embodiment, the first, second,
and third tubular members 5A, 5B, 5C and the first and second inner
pipe members 6A, 6B have perfectly circular cross-sections.
However, the cross-sectional shapes of the tubular members and an
inner pipe member are not particularly limited. The cross-sectional
shapes of these components may be, for example, oval shapes,
polygonal shapes, or polygonal shapes with round corners. Moreover,
these cross-sectional shapes and the cross-sectional areas thereof
may be variable.
[0079] (3m) In the above-described embodiment, the exhaust system 1
comprises the muffler 4; however, the muffler 4 may be
optional.
[0080] (3n) In the above-described embodiment, the exhaust system 1
is used in the internal combustion engine 100. However, the exhaust
system 1 may be used in internal combustion engines of, for
example, water vessels, aircrafts, and general-purpose
machines.
[0081] (3o) Functions of one component in the aforementioned
embodiments may be achieved by two or more components, and a
function of one component may be achieved by two or more
components. Moreover, functions of two or more components may be
achieved by one component, and a function achieved by two or more
components may be achieved by one component. Some of the components
of the above embodiments may be omitted. At least part of the
configurations of the aforementioned embodiments may be added to or
replaced with other configurations of the aforementioned
embodiments.
* * * * *