Note: Descriptions are shown in the official language in which they were submitted.
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MUFFLER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This international application claims the benefit of Japanese
Patent
Application No. 2013-003714 filed January 11, 2013 in the Japan Patent
Office, and the entire disclosure of Japanese Patent Application No.
2013-003714 is incorporated herein.
TECHNICAL FIELD
[0002] The present invention relates to a muffler that reduces exhaust
noise.
BACKGROUND ART
[0003] In an exhaust system for an automobile, exhaust noise is reduced by
a
muffler provided in an exhaust flow path. For example, low-frequency air
column resonance generated in a tubular portion having a long actual length
is a factor that increases muffled exhaust noise. Thus, measures are taken,
such as reducing the air column resonance by providing a sub-muffler in
series with a main muffler. Moreover, Patent Document 1 includes a
structure in which a muffler of a side branch type resonant system is
provided between the main muffler and the sub-muffler.
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0004] Patent Document 1: Japanese Unexamined Patent Application
Publication
No. 2005-105918
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] As a muffler of a resonant system, a muffler of a Helmholtz type
resonant
system is known in addition to the above-described muffler of the side branch
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type resonant system. However, the Helmholtz type muffler is formed with a
structure in which the exhaust flow path leads to a resonance chamber having a
large volume via a long and narrow communication path, and thus, a problem
has been found in which the structure is inevitably complicated.
[0006] In one aspect of the present invention, it is preferable to form a
muffler
of a Helmholtz type resonant system with a simple structure.
MEANS FOR SOLVING THE PROBLEMS
[0007] An aspect of the present invention is a muffler that comprises a
first
tubular member that forms an exhaust flow path of an internal combustion
engine, and a second tubular member that is connected to the first tubular
member and forms the exhaust flow path together with the first tubular member.
A double pipe portion is formed in which an end portion of the first tubular
member is inserted into the second tubular member from an end portion thereof.
A leading end portion of the second tubular member is joined to an outer
periphery of the first tubular member. A portion that forms the double pipe
portion of the second tubular member comprises a first portion located closer
to an end of the first tubular member, and a second portion that is located
closer to an end of the second tubular member and that has an enlarged
diameter compared with the first portion. A resonance chamber is formed
between the first tubular member and the second portion. A communication
path that allows communication between the exhaust flow path and the
resonance chamber is formed between the first tubular member and the first
portion. A Helmholtz type resonant system is formed by the resonance
chamber and the communication path.
[0008] According to such a configuration, exhaust noise can be reduced in
a
connection between the first tubular member and the second tubular member.
Furthermore, the Helmholtz type resonant system can be formed with a simple
structure because the resonance chamber and the communication path of the
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Helmholtz type resonant system are formed using the double pipe portion
formed by the two tubular members that form the exhaust flow path.
[0009] In the above-described configuration, a spacer that inhibits
contact
between the first tubular member and the second tubular member may be
provided in the communication path, and the spacer may be arranged so as to
secure an air passage on an outer circumference of the first tubular member so
that the communication path is not blocked.
According to such a
configuration, the communication path is less likely to be blocked, and an
effect of reducing exhaust noise can thereby be enhanced.
[0010] Furthermore, in the above-described configuration, each of the
first
tubular member and the second tubular member may be formed as a single part.
According to such a configuration, it is not necessary to separately use
dedicated components to form the Helmholtz type resonant system, and thus,
space saving, cost reduction, and the like can be sought.
[0011] It is to be noted that one aspect of the present invention can
be achieved
in various forms, such as an exhaust system including a muffler, and a method
for muffling exhaust noise, besides the above-described muffler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a plan view of an exhaust system of an embodiment.
FIG 2 is a sectional view taken along a line II-II in FIG. 1.
FIG. 3A is an exploded perspective view of a muffler, and FIG. 3B is a
transparent perspective view of the muffler.
FIG. 4 is a sectional view taken along a line IV-IV in FIG. 2.
EXPLANATION OF REFERENCE NUMERALS
[0013] 1 ...exhaust system, 2 ... flow path member, 3 ...
catalytic converter,
4... sub-muffler, 5 ... main muffler, 10 first tubular member, 11 ... reduced
diameter portion, 12.. .body portion, 20...
second tubular member,
21. enlarged
diameter portion, 22... body portion, 23... leading end portion,
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30... muffler, 31 ... resonance chamber, 32 ... communication path, 40... wire
mesh
MODE FOR CARRYING OUT THE INVENTION
[0014] An embodiment in which the present invention is applied will be
described below with reference to drawings.
An exhaust system 1 shown in FIG. 1 forms an exhaust flow path, which
is a flow path of exhaust gas discharged from an internal combustion engine of
an automobile. The exhaust system 1 is mainly configured with a flow path
member 2 of a tubular shape forming the exhaust flow path having a long
actual length. The exhaust system 1 has a catalytic converter 3, a sub-muffler
4, and a main muffler 5 arranged in series with each other in order from the
upstream of the exhaust flow path (from the left in FIG. 1) along the flow
path
member 2 (the exhaust flow path).
[0015] The flow path member 2 comprises a first tubular member 10 that
forms
the exhaust flow path in the downstream of the sub-muffler 4, and a second
tubular member 20 that is connected to a downstream-side end portion of the
first tubular member 10 and forms the exhaust flow path in the upstream of the
main muffler 5. In the flow path member 2, the sub-muffler 4 and the main
muffler 5 are connected to each other via the first tubular member 10 and the
second tubular member 20.
[0016] As shown in FIG. 2, FIG. 3A, and FIG. 3B, the first tubular member
10 is
a member formed by processing a circular pipe part having an outside diameter
R1 (60.5 mm, for example), and is configured as a single part. Specifically,
the first tubular member 10 is a member formed by reducing in diameter an end
portion located in the downstream side (the right side in FIG. 2) of the
circular
pipe part having the outside diameter R1, specifically a portion having a
length
LI from an end, to an outside diameter R2 (54.7 mm, for example) that is
smaller than the outside diameter Rl. In an explanation below, the portion
having the length Li from the end of the first tubular member 10 is referred
to
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as a "reduced diameter portion 11", and the remaining portion is referred to
as
a "body portion 12".
[0017] The second tubular member 20 is a member formed by processing the
circular pipe part having the outside diameter R1 similarly to the first
tubular
member 10, and is configured as a single part similarly to the first tubular
member 10. Specifically, the second tubular member 20 is a member formed
by enlarging in diameter an end portion located in the upstream side (the left
side in FIG. 2) of the circular pipe part having the outside diameter R1,
specifically a portion having a length L2 from an end, to an outside diameter
larger than the outside diameter Rl. Specifically, the second tubular member
20 is gradually increased in outside diameter from a position the length L2
apart from the end toward the end, and becomes largest in outside diameter
(120 mm, for example) at a position a length L3 apart from the end (L3<L2).
Then, the second tubular member 20 is gradually decreased in outside diameter
from a position a length L4 apart from the end (L4<L3) toward the end. Such
a shape is formed by performing a diameter enlarging process on the portion
having the length L2 from the end and then performing a diameter reducing
process on a portion having the length L4 from the end, for example. In an
explanation below, the portion having the length L2 from the end in the second
tubular member 20 is referred to as an "enlarged diameter portion 21", and the
remaining portion is referred to as a "body portion 22".
[0018] The downstream-side end portion of the first tubular member 10,
specifically the entirety of the reduced diameter portion 11 and part of the
body
portion 12, is inserted into the second tubular member 20 from an
upstream-side end portion (a leading end portion 23 of the enlarged diameter
portion 21) of the second tubular member 20 in such a manner that central axes
thereof are coincident with each other. In this way, a double pipe portion
including the first tubular member 10 as an inner pipe and the second tubular
member 20 as an outer pipe (a portion in which the first tubular member 10 and
the second tubular member 20 overlap with each other) is formed in a
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connection (a joint to be described later and a portion adjacent thereto)
between the first tubular member 10 and the second tubular member 20. The
connection between the first tubular member 10 and the second tubular member
20 functions as a muffler 30 of a Helmholtz type resonant system, as will be
described below.
[0019] That is, the second tubular member 20, specifically the leading end
portion 23 of the enlarged diameter portion 21, is joined (welded all around
in
the present embodiment) to the first tubular member 10, specifically on an
outer periphery of the body portion 12. In this way, in the double pipe
portion,
a dead-end space is formed that communicates with the exhaust flow path,
between the first tubular member 10 and the second tubular member 20.
Specifically, a resonance chamber 31 having a large volume is formed between
the body portion 12 of the first tubular member 10 and the enlarged diameter
portion 21 of the second tubular member 20. In other words, a volume
required as the resonance chamber 31 is secured by the enlarged diameter
portion 21 of the second tubular member 20. Besides, a communication path
32 is formed between the reduced diameter portion 11 of the first tubular
member 10 and the body portion 22 of the second tubular member 20. The
communication path 32 is a space a cross-sectional area of which orthogonal to
an axial direction is smaller than that of the resonance chamber 31, and
allows
communication between the exhaust flow path and the resonance chamber 31.
The resonance chamber 31 and the communication path 32 are designed to
configure the Helmholtz type resonant system.
[0020] Provided in the communication path 32 is a wire mesh 40, which is a
metal buffer member. The wire mesh 40 functions as a spacer to inhibit
contact between the first tubular member 10 and the second tubular member 20.
Moreover, the wire mesh 40 also has a function of reducing stress of thermal
contraction difference between the first tubular member 10 and the second
tubular member 20. It is to be noted that an outside diameter of the wire mesh
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40 is equal to or smaller than the outside diameter R1 of the body portion 12
of
the first tubular member 10.
[0021] However,
if the communication path 32 is blocked by the wire mesh 40,
excitation force of sound pressure that generates a resonance phenomenon
becomes less likely to be transmitted to the resonance chamber 31. Thus, the
wire mesh 40 is arranged so that an air passage is secured in an outer
circumference of the first tubular member 10. Specifically, in the present
embodiment, a plurality of (three in this example) the wire meshes 40 having a
circular arc shape along the outer periphery of the first tubular member 10
are
arranged on some parts of the entire outer circumference (range of 360
degrees) of the first tubular member 10, as shown in FIG. 4. The three wire
meshes 40 are not as long as the entire outer circumference of the first
tubular
member 10 even when all of them are pieced together. Besides, the three wire
meshes 40 are arranged shifted from each other in an axial direction of the
first
tubular member 10 (on different positions in the axial direction) (see FIG.
2).
Consequently, the air passage is secured successfully on the outer
circumference of the first tubular member 10.
[0022] The muffler 30 is designed such that a resonance frequency
thereof is
coincident with an Nth-order mode (N is a natural number, and 1 in the present
embodiment) of air column resonance frequency of a pipe, and the end of the
first tubular member 10 is arranged so as to be at a position of the maximum
sound pressure of the Nth mode.
[0023] According to the embodiment described above in detail, the
following
effects are obtained.
[Al] The muffler 30 comprises the first tubular member 10 that forms the
exhaust flow path of the internal combustion engine, and the second tubular
member 20 that is connected to the first tubular member 10 and forms the
exhaust flow path together with the first tubular member 10. In the
connection between the first tubular member 10 and the second tubular member
20, the double pipe portion is formed in which the end of the first tubular
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member 10 is inserted into the second tubular member 20 from the leading end
portion 23 thereof, and the leading end portion 23 of the second tubular
member 20 is joined to the outer periphery of the first tubular member 10.
The portion that forms the double pipe portion of the second tubular member
20 comprises the body portion 22 located closer to the end of the first
tubular
member 10, and the enlarged diameter portion 21 that is located closer to the
end of the second tubular member 20 and that has the enlarged diameter
compared with the body portion 22. The resonance chamber 31 is formed
between the first tubular member 10 and the enlarged diameter portion 21.
The communication path 32 that allows communication between the exhaust
flow path and the resonance chamber 31 is formed between the first tubular
member 10 and the body portion 22. The Helmholtz type resonant system is
formed by the resonance chamber 31 and the communication path 32.
[0024] Thus, according to the present embodiment, air column resonance
can be
inhibited at the connection between the first tubular member 10 and the second
tubular member 20, and as a result, exhaust noise can be reduced. Moreover,
the Helmholtz type resonant system can be configured with a simple structure
because the resonance chamber 31 and the communication path 32 of the
Helmholtz type resonant system are formed using the double pipe portion
formed by the first tubular member 10 and the second tubular member 20 that
form the exhaust flow path. Especially, since the Helmholtz type resonant
system is adopted, a muffling effect can be enhanced by increasing the volume
of the resonance chamber 31. Although it may be possible to create a
through-hole in the first tubular member 10 and to cause the through-hole to
function as the communication path of the Helmholtz type resonant system,
sufficient effect is less likely to be obtained by such a structure because
the
length of the communication path is no more than the through-thickness of the
first tubular member 10. In this regard, the structure having the long
communication path is achieved in the present embodiment, and noise
reduction effect can thereby be enhanced.
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[0025] [A2] The wire mesh 40 that inhibits contact between the first
tubular
member 10 and the second tubular member 20 is provided in the
communication path 32. The wire mesh 40 is arranged so as to secure the air
passage on the outer circumference of the first tubular member 10 so that the
communication path 32 is not blocked. Thus, according to the present
embodiment, the communication path 32 is less likely to be blocked, and an
effect of reducing exhaust noise can thereby be enhanced.
[0026] [A3] Each of the first tubular member 10 and the second tubular
member
20 is formed as a single part. Thus, according to the present embodiment, it
is
not necessary to separately use dedicated components to form the Helmholtz
type resonant system, and thus, space saving, cost reduction, and the like can
be sought. Specifically, in a configuration in which dedicated components to
form a muffler (a resonance chamber and a communication path) are added to
the components forming the exhaust flow path, the structure is likely to be
complicated and larger, and the number of the components is increased as well
as the number of portions to be joined (welded), which is likely to result in
increase in cost. In contrast, the muffler 30 of the present embodiment is
configured with the first tubular member 10 and the second tubular member 20
forming the exhaust flow path and, furthermore, the number of the portions to
be joined (welded) is one. Thus, the muffler 30 of the present embodiment
has an advantage that space saving, cost reduction, and the like can be easily
sought. In addition, since the muffler 30 of the present embodiment is
configured with the tubular members, there is another advantage that the
muffler 30 has a bending workability and can be easily applied to a layout of
the exhaust system 1.
[0027] [A4] The muffler 30 is designed such that the resonance frequency
thereof is coincident with the Nth-order mode of the air column resonance
frequency of the pipe, and the end of the first tubular member 10 is arranged
so
as to be at the position of the maximum sound pressure of the Nth mode.
Thus, according to the present embodiment, the maximum reduction can be
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obtained with the mode coincident with the resonance frequency. Furthermore,
the air column resonance can be inhibited by reducing the sound pressure by a
certain volume even in the other mode.
[0028] [A5] The first tubular member 10 has the reduced diameter portion
11
formed therein, and the wire mesh 40 having the outside diameter equal to or
smaller than the outside diameter R1 of the body portion 12 is used. Thus, the
first tubular member 10 having the wire mesh 40 attached thereon can be easily
inserted into the second tubular member 20. Consequently, according to the
present embodiment, the first tubular member 10 and the second tubular
member 20 can be assembled to each other more easily.
[0029] Although the embodiment of the present invention has been described
above, it is needless to say that the present invention is not limited to the
above
embodiment and can take various forms.
[B1] The wire mesh 40 shown in the above embodiment is an example,
and the configuration is not limited to this. For example, the wire mesh 40
may be one in number or may be two or more in number. The position in
which the wire mesh 40 is arranged is also not limited in particular.
Specifically, two C-shaped wire meshes having a shape of a halved ring, for
example, may be arranged shifted in the axial direction of the first tubular
member 10. Moreover, a member other than the wire mesh 40 may be used as
the spacer. Furthermore, the spacer may be formed by processing (for
example, by forming projecting portions on) at least one of the first tubular
member 10 and the second tubular member 20. Alternatively, a configuration
without the spacer may be possible.
[0030] [B2] The first tubular member 10 may be formed of a plurality of
parts.
For example, when a circular pipe part having the outside diameter R2 and a
circular pipe part having the outside diameter R1 are used, an area to be
reduced in diameter can be decreased, or the diameter reducing process itself
can be eliminated. Similarly, the second tubular member 20 may also be
formed of a plurality of parts.
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[0031] [B3] The
first tubular member 10 may comprise no reduced diameter
portion 11. For example, it may be possible to insert the first tubular member
on which the wire mesh 40 is attached into the second tubular member 20,
and then, to reduce the diameter of the leading end portion 23 of the second
tubular member 20.
[0032] [B4] In the above embodiment, the first tubular member 10 and
the
second tubular member 20 are formed using the circular pipe parts having the
same outside diameter. However, the configuration is not limited to this.
For example, a circular pipe part having an outside diameter larger than that
of
the first tubular member 10 may be used as the second tubular member 20.
Moreover, the first tubular member 10 and the second tubular member 20 may
be formed using parts other than the circular pipe part (a tubular member
having a section of oval or polygonal shape, for example).
[0033] [B5] The resonance chamber 31 shown in the above embodiment is
an
example, and the configuration is not limited to this. For example, although
the resonance chamber 31 is formed by the enlarged diameter portion 21 that is
expanded into an approximately trapezoidal shape when viewed from the side
(viewed from a direction orthogonal to the axial direction) in the above
embodiment, the resonance chamber, instead of this, may be formed by an
enlarged diameter portion expanded into, for example, an approximately
triangular shape or an approximately rectangular shape.
[0034] [B6] In the above embodiment, the configuration has been
exemplified in
which the muffler 30 is arranged in the exhaust flow path connecting the
sub-muffler 4 and the main muffler 5 to each other. However,
the
configuration is not limited to this. Moreover, the configuration of the
exhaust system on which the present invention is premised is also not limited
to the above embodiment, and a configuration without a sub-muffler may be
adopted, for example. Furthermore, a positional relationship between the first
tubular member (an inner pipe of the double pipe portion) and the second
tubular member (an outer pipe of the double pipe portion), i.e., whether they
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are located upstream or downstream, may be opposite to that in the above
embodiment. That is, the second tubular member may be arranged in the
upstream of the exhaust flow path, and the first tubular member may be
arranged in the downstream of the exhaust flow path.
[0035] [B7] Each of the elements of the present invention is a conceptual
one,
and is not limited to the above embodiment. For example, the function of
one element may be dispersed over a plurality of elements, or the functions
of a plurality of elements may be integrated to one element. Moreover, at
least part of the configuration of the above embodiment may be replaced by
a known configuration having a similar function.
