U.S. patent application number 12/662884 was filed with the patent office on 2010-11-18 for heat insulator mounting structure.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Akio Sugimoto, Ichiro Yamagiwa, Yoshio Yano.
Application Number | 20100287919 12/662884 |
Document ID | / |
Family ID | 42993790 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100287919 |
Kind Code |
A1 |
Yamagiwa; Ichiro ; et
al. |
November 18, 2010 |
Heat Insulator mounting structure
Abstract
According to the present invention, a heat insulator mounting
structure able to reduce noise propagated around a vehicle is
provided. The heat insulator mounting structure includes an exhaust
pipe disposed so that an upper half surface thereof is positioned
higher than a horizontal lower surface of a vehicle body, a first
shield portion for covering an upper surface of the exhaust pipe
above the horizontal lower surface of the vehicle body, and a pair
of second shield portions extending downwards below the horizontal
lower surface of the vehicle body from both ends of the first
shield portion in the circumferential direction of the exhaust
pipe.
Inventors: |
Yamagiwa; Ichiro; (Kobe-shi,
JP) ; Yano; Yoshio; (Kobe-shi, JP) ; Sugimoto;
Akio; (Kobe-shi, JP) |
Correspondence
Address: |
Juan Carlos A. Marquez;c/o Stites & Harbison PLLC
1199 North Fairfax Street, Suite 900
Alexandria
VA
22314-1437
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
|
Family ID: |
42993790 |
Appl. No.: |
12/662884 |
Filed: |
May 10, 2010 |
Current U.S.
Class: |
60/320 |
Current CPC
Class: |
F01N 13/14 20130101;
F01N 1/24 20130101; B60K 13/04 20130101; F01N 2260/20 20130101 |
Class at
Publication: |
60/320 |
International
Class: |
F01N 13/14 20100101
F01N013/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2009 |
JP |
2009-118327 |
Claims
1. A heat insulator mounting structure comprising: an exhaust pipe
disposed so that at least a portion of said exhaust pipe is
positioned above a lower surface of a vehicle body; a first shield
portion for covering an upper surface of said exhaust pipe above
the lower surface of the vehicle body; and a pair of second shield
portions extending downwards below the lower surface of the vehicle
body from both ends of said first shield portion in the
circumferential direction of said exhaust pipe.
2. The heat insulator mounting structure according to claim 1,
wherein said first shield portion and/or second shield portions
include a perforated plate opposed to said exhaust pipe.
3. The heat insulator mounting structure according to claim 2,
wherein a space on an opposite side of said exhaust pipe with
respect to said perforated plate is closed, through holes of said
perforated plate opening to said space.
4. The heat insulator mounting structure according to claim 2,
wherein a space on an opposite side of said exhaust pipe with
respect to said perforated plate, through holes of said perforated
plate opening to said space, includes a plurality of closed spaces,
said plural closed spaces having mutually different widths in a
direction orthogonal to said perforated plate.
5. The heat insulator mounting structure according to claim 2,
wherein a space on an opposite side of said exhaust pipe with
respect to said perforated plate, through holes of said perforated
plate opening to said space, includes a plurality of closed spaces,
the number of said through holes opening to each of said plural
closed spaces and/or a diameter of said through holes being
different between said plural closed spaces.
6. The heat insulator mounting structure according to claim 1,
wherein said first shield portion and second shield portions
includes an inner plate-like member opposed to said exhaust pipe
and an outer plate-like member disposed on a opposite side of said
exhaust pipe with respect to said inner plate-like member so as to
be opposed to said inner plate-like member, a space between said
inner plate-like member and outer plate-like member is closed, said
pair of second shield portions extend from both the ends of said
first shield portion obliquely downwards so as to approach each
other, and in said first shield portion a plurality of through
holes are formed in said inner plate-like member, while in said
second shield portions a plurality of through holes are formed in
said outer plate-like portion.
7. The heat insulator mounting structure according to claim 1,
wherein the lower surface of the vehicle body includes a bent lower
surface swelling upwards to form a depressed portion, at least a
portion of said exhaust pipe is disposed within said depressed
portion, said first shield portion is disposed between said bent
lower surface and exhaust pipe, said second shield portions extend
from both of the ends of said first shield portion in the
circumferential direction of said exhaust pipe downwards below said
depressed portion, said first shield portion and second shield
portions are constituted by a single perforated plate, and a space
between said bent lower surface and perforated plate is closed.
8. The heat insulator mounting structure according to claim 1,
wherein lower ends of said second shield portions are positioned at
the same height as or higher than a lower end of said exhaust
pipe.
9. The heat insulator mounting structure according to claim 1,
wherein spacing between said pair of second shield portions is
equal to or larger than the outside diameter of said exhaust
pipe.
10. The heat insulator mounting structure according to claim 1,
wherein lower ends of said second shield portions are positioned at
the same height as or higher than a lower end of said exhaust pipe,
and spacing between said pair of second shield portions is equal to
or larger than the outside diameter of said exhaust pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a structure for mounting a
heat insulator which is for cutting off the transfer of heat from
an exhaust pipe to a vehicle body.
[0003] 2. Description of the Related Art
[0004] Heretofore, as heat insulator mounting structures, those
described in Japanese Patent Application Laid-Open No. Hei 9
(1997)-32545 (Patent Document 1) and No. 2000-190744 (Patent
Document 2) have been known.
[0005] A vehicle having any of such conventional heat insulator
mounting structures is provided with a depressed portion which is
formed so as to swell upwards at a lower surface of a vehicle body
and is also provided with an exhaust pipe disposed under the
depressed portion. A heat shied plate is attached to the vehicle,
the plate having a curved portion curved arcuately and including
plural holes and also having flat plate portions extending radially
outwards from both circumferential ends of the curved portion. More
specifically, the curved portion is disposed between the curved
lower surface which forms the depressed portion and the exhaust
pipe and extends along the outer periphery of the exhaust pipe. And
the pair of flat plate portions extending from both the ends of the
curved portion are fixed to the lower surface of the vehicle body
with bolts.
[0006] According to this structure, a Helmholtz structure is formed
by forming an air layer between the vehicle body and the heat
shielding plate, so that not only a heat insulating function but
also a sound absorbing function can be exhibited.
SUMMARY OF THE INVENTION
[0007] According to the heat insulator mounting structures
described in Patent Documents 1 and 2, a noise component released
from the exhaust pipe toward the curved lower surface of the
vehicle can be reduced by the Helmholtz structure, but a noise
reducing effect against the noise propagated around the vehicle is
not satisfactory and a further noise reduction is requested.
[0008] In view of the above-mentioned circumstances, it is an
object of the present invention to provide a heat insulator
mounting structure which can reduce noise propagated around a
vehicle.
[0009] The heat insulator mounting structure according to the first
aspect of the present invention includes: an exhaust pipe disposed
so that at least a portion of the exhaust pipe is positioned above
a lower surface of a vehicle body; a first shield portion for
covering an upper surface of the exhaust pipe above the lower
surface of the vehicle body; and a pair of second shield portions
extending downwards below the lower surface of the vehicle body
from both ends of the first shield portion in the circumferential
direction of the exhaust pipe.
[0010] According to this structure, the transfer of heat from the
exhaust pipe to the vehicle body side can be suppressed by the
first shield portion.
[0011] Further, the second shield portions extending downwards
below the lower surface of the vehicle body suppress the noise
generated from the exhaust pipe from passing through the space
between the lower surface of the vehicle body and the ground and
going out in the width direction of the vehicle body directly or
while reflected less times.
[0012] Thus, the noise propagated around the vehicle can be
effectively reduced with a simple structure.
[0013] According to the heat insulator mounting structure of the
second aspect of the present invention, the first shield portion
and/or second shield portions include a perforated plate opposed to
the exhaust pipe.
[0014] According to this structure, since the perforated plate is
opposed to the exhaust pipe, it is possible to enhance the noise
absorbing effect against the noise generated from the exhaust
pipe.
[0015] According to the heat insulator mounting structure of the
third aspect of the present invention, a space on an opposite side
of the exhaust pipe with respect to the perforated plate is closed,
through holes of the perforated plate opening to the space.
[0016] According to this structure, it is possible to obtain a
sound absorbing effect of a sound absorbing structure of Helmholtz
constituted of the perforated plate and a closed air layer present
behind the perforated plate. That is, by adjusting the porosity of
the perforated plate and the thickness of the back air layer, it
becomes possible to enhance the sound absorbing effect at a desired
frequency. Consequently, the sound absorbing effect can be
exhibited more effectively while taking into account the frequency
characteristic of the noise generated from the exhaust pipe.
[0017] According to the heat insulator mounting structure of the
fourth aspect of the present invention, a space on an opposite side
of the exhaust pipe with respect to the perforated plate, through
holes of the perforated plate opening to the space, includes a
plurality of closed spaces, the plural closed spaces having
mutually different widths in a direction orthogonal to the
perforated plate.
[0018] According to this structure, since specially high sound
absorbing effect can be exhibited against noises of plural specific
frequencies, high sound absorbing effect can be obtained within
further wider frequency range.
[0019] According to the heat insulator mounting structure of the
fifth aspect of the present invention, a space on an opposite side
of the exhaust pipe with respect to the perforated plate, through
holes of the perforated plate opening to the space, includes a
plurality of closed spaces, the number of the through holes opening
to each of the plural closed spaces and/or a diameter of the
through holes being different between the plural closed spaces.
[0020] According to this structure, since specially high sound
absorbing effect can be exhibited against noises of plural specific
frequencies, high sound absorbing effect can be obtained within
further wider frequency range.
[0021] According to the heat insulator mounting structure of the
sixth aspect of the present invention, the first shield portion and
second shield portions includes an inner plate-like member opposed
to the exhaust pipe and an outer plate-like member disposed on a
opposite side of the exhaust pipe with respect to the inner
plate-like member so as to be opposed to the inner plate-like
member, a space between the inner plate-like member and outer
plate-like member is closed, the pair of second shield portions
extend from both end portions of the first shield portion obliquely
downwards so as to approach each other, and in the first shield
portion a plurality of through holes are formed in the inner
plate-like member, while in the second shield portions a plurality
of through holes are formed in the outer plate-like portion.
[0022] According to this structure, since the sound released from
the exhaust pipe and reflected by the ground can be received with
the outer plate-like member of the second shield portions including
the plural through holes, the noise from the exhaust pipe can be
absorbed more effectively.
[0023] According to the heat insulator mounting structure of the
seventh aspect of the present invention, the lower surface of the
vehicle body includes a bent lower surface swelling upwards to form
a depressed portion, at least a portion of the exhaust pipe is
disposed within the depressed portion, the first shield portion is
disposed between the bent lower surface and exhaust pipe, the
second shield portions extend from both of the ends of the first
shield portion in the circumferential direction of the exhaust pipe
downwards below the depressed portion, the first shield portion and
second shield portions are constituted by a single perforated
plate, and a space between the bent lower surface and perforated
plate is closed.
[0024] According to this structure, the entire space between the
bent lower surface of the vehicle body and the perforated plate can
be utilized effectively and the heat insulator mounting structure
can be formed more compactly.
[0025] According to the heat insulator mounting structure of the
eighth aspect of the present invention, lower ends of the second
shield portions are positioned at the same height as or higher than
a lower end of the exhaust pipe.
[0026] According to this structure, it is possible to prevent the
vehicle height (height from the ground up to the lowest portion of
the vehicle body) from becoming excessively low.
[0027] According to the heat insulator mounting structure of the
ninth aspect of the present invention, spacing between the pair of
second shield portions is equal to or larger than the outside
diameter of the exhaust pipe.
[0028] According to this structure, since the spacing between the
pair of second shield portions is larger than the outside diameter
of the exhaust pipe, the exhaust pipe can be installed easily even
in such cases as after fixing the second shield portions to the
vehicle body.
Effect of the Invention
[0029] According to the present invention, the noise propagated
around a vehicle can be reduced effectively with a simple
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1A is a perspective view and FIG. 1B is a sectional
view, both showing a heat insulator mounting structure according to
a first embodiment of the present invention;
[0031] FIG. 2 is a diagram showing a modification (1) of the first
embodiment;
[0032] FIG. 3 is a diagram showing a modification (2) of the first
embodiment;
[0033] FIG. 4 is a sectional view showing a heat insulator mounting
structure according to a second embodiment of the present
invention;
[0034] FIG. 5 is a diagram showing a modification (1) of the second
embodiment;
[0035] FIG. 6 is a diagram showing a modification (2) of the second
embodiment;
[0036] FIG. 7 is a diagram showing a modification (3) of the second
embodiment;
[0037] FIG. 8 is a diagram showing a modification (4) of the second
embodiment;
[0038] FIG. 9 is a diagram showing a modification (5) of the second
embodiment;
[0039] FIG. 10 is a diagram showing a modification (6) of the
second embodiment;
[0040] FIG. 11 is a diagram showing a modification (7) of the
second embodiment;
[0041] FIG. 12 is a diagram showing a modification (8) of the
second embodiment;
[0042] FIG. 13 is a diagram showing analytic models; FIG. 13A is a
comparative model and FIG. 13B is a working model 1;
[0043] FIG. 14 is a diagram showing an analysis result obtained
with using the analytic models of FIG. 13;
[0044] FIG. 15 is a diagram showing an analytic model (a working
model 2) for verifying a sound absorbing effect;
[0045] FIG. 16 is a diagram showing an analysis result obtained
with using the analytic model of FIG. 15;
[0046] FIG. 17 is a diagram showing an analytic model (a working
model 3) for verifying a sound absorbing effect; and
[0047] FIG. 18 is a diagram showing an analysis result obtained
with using the analytic model of FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Embodiments of the present invention will be described below
with reference to the drawings.
First Embodiment
[0049] FIG. 1A shows a heat insulator mounting structure 1
according to a first embodiment of the present invention. FIG. 1B
is a sectional view (A1-A1 section) perpendicular to an axial
direction of an exhaust pipe 12 shown in FIG. 1A.
[0050] In the mounting structure 1, a shield plate 13 as a heat
insulator is attached to the exhaust pipe 12 of an automobile. This
automobile is provided at a lower portion thereof with a body
bottom plate 10, the body bottom plate 10 being disposed nearly
horizontally and partitioning between a vehicle compartment and the
exterior (in FIG. 1A there is shown only an end face by a
dash-double dot line).
[0051] The exhaust pipe 12, which conducts exhaust gas discharged
from an engine to the exterior, is attached to a lower surface 11
(hereinafter referred to as the "body lower surface 11") of the
body bottom plate 10. The exhaust pipe 12 is formed in a
cylindrical shape and is disposed so that the axis thereof extends
rectilinearly in the longitudinal direction of the vehicle body.
The exhaust pipe 12 is supported for example by a stay (not shown)
fixed to the body lower surface 11 and extending downwards.
[0052] As shown in FIG. 1B, the body lower surface 11 is bent so as
to swell upward (to the vehicle compartment side) as seen from the
axial direction of the exhaust pipe 12. The exhaust pipe 12 is
disposed in a depressed portion .alpha. which is formed in a bent
manner so as to swell upwards.
[0053] The depressed portion .alpha. means a space which is
positioned higher than the height of a nearly horizontally
extending surface (referred to as "horizontal lower surface 11a",
hereinafter) of the body lower surface 11, and which is surrounded
by a surface (referred to as "bent lower surface 11b", hereinafter)
bent from the horizontal lower surface 11a. In this embodiment, the
horizontal lower surface 11a is positioned lowest in the body lower
surface 11. The exhaust pipe 12 is fixed to the body lower surface
11 so that an upper half surface of the exhaust pipe 12 is
positioned within the depressed portion .alpha. as seen from the
axial direction of the exhaust pipe 12. The exhaust pipe 12 may be
disposed in such a manner that the whole circumference thereof is
positioned within the depressed portion .alpha..
[0054] The shield plate 13 is disposed between the bent lower
surface 11b of the vehicle body and the exhaust pipe 12. The shield
plate 13 is fixed to the horizontal lower surface 11a of the
vehicle body so as to partition between the bent lower surface 11b
and the exhaust pipe 12. More specifically, the shield plate 13 is
formed by bending a single metallic plate for example by roll
forming. The shield plate 13 includes a first shield portion 131
which is in the shape of a semi-cylinder, a pair of second shield
portions 132 which is each in the shape of a flat plate and which
extends from both circumferential ends of the first shield portion
131 tangentially with respect to the two ends, and fixing portions
133 continuous with the second shield portions 12 and extending
obliquely upwards and in the opposite direction of the exhaust pipe
12, the fixing portions 133 bent at the vicinity of the extending
ends, then extending nearly horizontally away from the second
shield portions 132 and fixed to the horizontal lower surface 11a
of the vehicle body.
[0055] The first shield portion 131 is disposed within the
depressed portion .alpha., while the second shield portions 132 are
positioned outside the depressed portion .alpha.. That is, in the
shield plate 13, the second shield portions 132 are extending
portions which extend downwards below the horizontal lower surface
11a of the vehicle body. The shield plate 13 is mounted so that
lower ends of the second shield portions 132 are level with a lower
end of the exhaust pipe 12.
[0056] The fixing portions 133 are provided continuously in the
axial direction of the shield plate 13 (in the cylinder axis
direction of the first shield portion 131), and vertical mounting
through holes 133a are formed close to both axial ends of each
fixing portion 133. Using the mounting holes 133a, the shield plate
13 is fixed to the horizontal lower surface 11a of the vehicle body
with bolts or the like.
[0057] In this embodiment the shield plate 13 is attached to the
body lower surface 11 so that the cylinder center axis of the first
shield portion 131 is aligned with that of the exhaust pipe 12.
Effect of the First Embodiment
[0058] The heat insulator mounting structure 1 of the first
embodiment includes the exhaust pipe 12 which is disposed in such a
manner that its upper half surface is positioned higher than the
horizontal lower surface 11a of the vehicle body, the first shield
portion 131 which covers the upper surface of the exhaust pipe 12
above the horizontal lower surface 11a of the vehicle body, and a
pair of second shied portions 132 extending downwards below the
horizontal lower surface 11a of the vehicle body from both ends of
the first shield portion 131 in the circumferential direction of
the exhaust pipe 12 (in the circumferential direction of a circle
centered on the center axis of the exhaust pipe 12 in FIG. 1B).
[0059] According to this structure, the transfer of heat from the
exhaust pipe 12 to the vehicle body side can be suppressed by the
first shield portion 131.
[0060] Further, the second shield portions 132 extending downwards
below the body lower surface 11 suppress the noise generated from
the exhaust pipe 12 from passing through the space under the body
lower surface 11 (the space between the body lower surface 11 and
the ground) and going out in the width direction of the vehicle
body directly or while reflected less times.
[0061] Thus, the noise propagated around the vehicle can be reduced
effectively with a simple structure. It is also possible to reduce
noise propagated from side door glass surfaces of the vehicle into
the vehicle compartment.
[0062] In this embodiment, the vehicle body is provided on the body
lower surface 11 with the depressed portion .alpha. formed so as to
swell upwards, and an upper half surface of the exhaust pipe 12 is
disposed within the depressed portion .alpha.. The first shield
portion 131 is disposed between the bent lower surface 11b as the
surface forming the depressed portion .alpha. and the exhaust pipe
12, and the second shield portions 132 extend downwards under the
depressed portion .alpha. from both ends of the first shield
portion 131 in the circumferential direction of the exhaust pipe
12.
[0063] According to this structure, the transfer of heat from the
exhaust pipe 12 to the body bottom plate 10 through the bent lower
surface 11b is suppressed.
[0064] Further, the shield plate 13 is mounted so that the lower
ends of the second shield portions 132 are positioned at the same
height as the lower end of the exhaust pipe 12.
[0065] According to this structure, the second shield portions 132
is suppressed from being excessively near to the ground and it is
possible to ensure a sufficient space below the vehicle body. That
is, by provision of the second shield portions 132, it is possible
to prevent the vehicle height from becoming excessively low.
Modifications of the First Embodiment
1
[0066] The fixing portions 133 of the shield plate 13 are not only
continuous with the lower ends of the second shield portions 132,
but may be also horizontally extended from the boundaries between
the first shield portion 131 and the second shield portions 132, as
indicated by fixing portions 133' in FIG. 2A.
[0067] The fixing portions 133' are provided not only continuously
in parallel with the cylinder center axis of the first shield
portion 131 as shown in FIG. 2A, also at intervals in the axial
direction. More specifically, fixing portions 133'' may be
provided, for example, at only both ends in the direction parallel
to the cylinder center axis of the first shield portion 131, as
shown in FIG. 2B. The fixing portions 133 shown in FIG. 1 can be
similarly provided.
2
[0068] The pair of second shield portions 132 is not only extended
vertically downwards in parallel with each other, but may be
extended also obliquely downwards so as to narrow the mutually
opposed spacing downwards, as shown by a pair of second shield
portions 132' in FIG. 3A.
[0069] According to this structure, it is possible to suppress
noise, which is generated from the exhaust pipe 12 and reflected by
the second shield portions 132', from being leaked from the space
surrounded by the first shield portion 131 and the second shield
portions 132'. That is, with the second shield portions 132', it is
possible to increase the number of times the noise from the exhaust
pipe 12 is reflected by the inner surface of the shield plate 13
and hence the sound absorbing effect becomes more outstanding.
[0070] In the modification shown in FIG. 3A, the spacing between
lower ends of the pair of second shield portions 132' is equal to
the outside diameter of the exhaust pipe 12 as seen from the axial
direction of the exhaust pipe 12.
[0071] According to this structure, even after mounting the shield
plate 13 to the body lower surface 11, the exhaust pipe 12 can be
passed through between the lower ends of the pair of second shield
portions 132' and can be disposed in the space surrounded by the
first shield portion 131 and the second shield portions 132'. Thus,
the fixing work for the exhaust pipe 12 becomes easier.
[0072] The second shield portions 132' do not overlap the exhaust
pipe 12 as seen from vertically below. Therefore, it is possible to
move the exhaust pipe 12 vertically to mount and remove it.
[0073] Further, since the environment of the exhaust pipe 12 is
covered with the shield plate 13 except its vertically lower
portion, leakage of noise generated from the exhaust pipe 12 can be
kept to a minimum.
[0074] The fixing portions 133 to be fixed to the horizontal lower
surface 11a may be extended from the lower ends of the second
shield portions 132' as indicated by fixing portions 133'' in FIG.
3A or may be extended from the boundaries between the first shield
portion 131 and the second shield portions 132', respectively, as
indicated by fixing portions 133''' in FIG. 3B.
Second Embodiment
[0075] FIG. 4 is a sectional view showing a heat insulator mounting
structure 2 according to a second embodiment of the present
invention. FIG. 4 corresponds to the sectional view of the mounting
structure 1 shown in FIG. 1B.
[0076] The mounting structure 2 of this second embodiment is a
structure wherein the shield plate 13 in the mounting structure 1
of the first embodiment is replaced by a shield structure 14. Other
structural points are the same as in the mounting structure 1 of
the first embodiment. Therefore, the same components as in the
first embodiment are identified by the same reference numerals as
in the first embodiment and explanations thereof will here be
omitted.
[0077] The shield structure 14 includes a perforated plate 141
opposed to the exhaust pipe 12 and a back plate 142 disposed so as
to confront the perforated plate 141 on the opposite side of the
perforated plate 141 with respect to the exhaust pipe 12.
[0078] The perforated plate 141 includes a cylindrical portion
formed in a semi-cylindrical shape and a pair of extending portions
extending from both circumferential ends of the cylindrical portion
obliquely downwards so as to be narrowed each other, with a
plurality of through holes 141a formed therein. The plural through
holes 141a are formed so as to be dispersed nearly uniformly
throughout the entire surface of the perforated plate 141.
[0079] From the standpoint of improving the sound absorbing effect
it is preferable that the through holes 141a be fine holes. For
example, it is preferable that the diameter of each through hole
141a be at least smaller than the thickness of the perforated plate
141.
[0080] The back plate 142 includes a cylindrical portion formed in
a semi-cylindrical shape and a pair of extending portions extending
from both circumferential ends of the cylindrical portion obliquely
downwards so as to narrow each other, as substantially similarly as
the perforated plate 141.
[0081] A space S1 between the perforated plate 141 and the back
plate 142 is closed.
[0082] By the term "closed" it is meant that the space between the
perforated plate 141 and the back plate 142 is closed so that the
through holes 141a of the perforated plate 141 are the only
passages providing communication between the space between the
perforated plate 141 and the back plate 142 and the exterior.
[0083] More specifically, end edges of extending portions of the
perforated plate 141 and those of extending portions of the back
plate 142 are connected together through side plates 143 disposed
nearly horizontally, whereby the space formed between the
perforated plate 141 and the back plate 142 is closed in the
circumferential direction of the exhaust pipe 12. Both ends of the
space in the axial direction of the exhaust pipe 12 are also closed
with partition members such as side plates or the like.
[0084] The shield structure 14 is fixed to the horizontal lower
surface 11a through fixing portions 144 which extend nearly
horizontally. The shield structure 14 is disposed so that its lower
ends are level with the lower end of the exhaust pipe 12 and so as
not to obstruct the space vertically below the exhaust pipe 12.
Effect of the Second Embodiment
[0085] In the heat insulator mounting structure 2 of the second
embodiment, as described above, the shield structure 14 includes
the perforated plate 141 opposed to the exhaust pipe 12. In the
perforated plate 141, the through holes 141a are formed in each of
the semi-cylindrical portion and extending portions of the
perforated plate 141.
[0086] According to this structure, since the perforated plate 141
confronts the exhaust pipe 12, it is possible to enhance the
absorbing effect against the noise generated from the exhaust pipe
12.
[0087] The through holes 141a may be formed in both of the
semi-cylindrical portion and extending portions of the perforated
plate 141, also may be formed in only one of them.
[0088] Moreover, the space S1 positioned on the opposite side of
the perforated plate 141 with respect to the exhaust pipe 12 and to
which the through holes 141a of the perforated plate 141 open is
closed.
[0089] According to this structure the shield structure 14
constitutes a Helmholtz structure comprising the perforated plate
141 and the closed air layer (closed space S1) formed behind the
perforated plate. Therefore, by adjusting the porosity of the
perforated plate 141 and the thickness of the back air layer, it
becomes possible to enhance the sound absorbing effect at a desired
frequency. As a result, the sound absorbing effect can be exhibited
more effectively while taking into account the frequency
characteristic of the noise generated from the exhaust pipe 12.
Modifications of the Second Embodiment
1
[0090] The through holes are not formed only in the plates disposed
at the positions confronting the exhaust pipe 12, but may be formed
also in plates disposed at the positions confronting the ground.
For example, as shown in FIG. 5, the through holes may not be
formed in the extending portion of the perforated plate 141
(portions below the horizontal lower surface 11a), but through
holes 142a and 143a may be formed in extending portions of the back
plate 142 and also in side plates 143.
[0091] More specifically, a heat insulator mounting structure
according to this modification includes an inner plate-like member
(perforated plate 141) opposed to the exhaust pipe 12 and an outer
plate-like member (back plate 142) which is disposed on the
opposite side of the inner plate-like member with respect to the
exhaust pipe 12 so as to confront the inner plate-like member. A
space S1 between the inner and outer plate-like members is closed.
Extending portions of the perforated plate 141 and of the back
plate 142, which portions are positioned lower than the horizontal
lower surface 11a of the vehicle body, extend obliquely downwards
from ends of cylindrical portions so as to approach the exhaust
pipe 12. Plural through holes 141a are formed in the cylindrical
portion of the perforated plate 141 and plural through holes 142a
and 143a are formed in the extending portions of the back plate 142
and also in side plates 143.
[0092] According to this structure, the through holes 142a and 143a
opening to the closed space S1 are formed in plates opposed to the
ground (extending portions of the back plate 142 and side plates
143) of the shield structure 14 which forms the closed space S1 in
the interior thereof. Therefore, the sound released from the
exhaust pipe 12 and reflected by the ground can be received by the
extending portions of the back plate 142 and the side plates 143
which include the plural through holes 142a and 143a. Consequently,
it is possible to absorb noise from the exhaust pipe 12 in a more
effective manner. The sound absorbing effect can be exhibited also
against noises amplified under the floor such as road noise.
2
[0093] Not only the air layer between the perforated plate 141 and
the back plate 142, but also an air layer S2 between a perforated
plate 141' disposed around the exhaust pipe 12 and a bent lower
surface 11b of the vehicle body is utilized to absorb sound as
shown in FIG. 6A.
[0094] The structure shown in FIG. 6A is equivalent to the
structure wherein plural through holes are formed in the first and
second shield portions 131 and 132 of the shield plate 13 shown in
FIG. 1 and both ends of the air layer S2 in the axial direction of
the exhaust pipe 12 are closed. That is, the body lower surface 11
includes a bent lower surface 11b which swells upwards to form a
depressed portion .alpha., and an upper half surface of the exhaust
pipe 12 is disposed within the depressed portion .alpha. (see FIG.
1). The perforated plate 141' includes an arcuate portion (first
shield portion) disposed between the bent lower surface 11b and the
exhaust pipe 12 and extending portions (second shield portions)
extending downwards below the depressed portion .alpha. from the
both ends of the arcuate portion (see FIG. 1). The space S2 between
the bent lower surface 11b and the perforated plate 141' is
closed.
[0095] As shown in FIG. 6B, a pair of extending portions of the
perforated plate 141' extending downwards below the horizontal
lower surface 11a may be formed to come closer to each other toward
below. The perforated plate 141' is constructed so that the lower
ends thereof are level with the lower end of the exhaust pipe 12
and so as not to obstruct the space vertically below the exhaust
pipe 12.
[0096] According to the structures shown in FIGS. 6A and 6B, the
entire space between the perforated plate 141' and the bent lower
surface 11b can be utilized effectively and hence the heat
insulator mounting structure can be formed more compactly. Besides,
since the back plate 142 is not needed, the manufacturing cost can
be reduced in comparison with the structure shown in FIG. 4.
3
[0097] There may be adopted such a structure as shown in FIG. 7
wherein a plurality of through holes 142a are formed in the back
plate 142 of he shield structure 14 and a space S4 between the back
plate 142 and the bent lower surface 11b is closed.
[0098] According to this structure, the space between the
perforated plate 141 and the bent lower surface 11b is divided into
plural (two) air layers (S3, S4) by the back plate 142 as the
perforated plate. Consequently, sound can be absorbed by utilizing
the through holes 141a of the perforated plate 141 and the through
holes 142a of the back plate 142, whereby a high sound absorbing
effect can be exhibited in a wider frequency band.
4
[0099] FIG. 8 is a vertical sectional view taken through the center
axis of the exhaust pipe 12 in a heat insulator mounting structure
according to a still further modification of the second embodiment.
As shown in the same figure, a back plate 142 may be bent for
example by press working so as to divide an air layer on the back
side of the perforated plate 141 into plural closed spaces S5 and
S6 in the axial direction of the exhaust pipe 12.
[0100] In the structure of FIG. 8, closed spaces S5 and S6 are
arranged alternately in the axial direction of the exhaust pipe 12.
The closed spaces S5 and S6 are different in the spacing (the
spacing in the radial direction of the exhaust pipe 12) from the
perforated plate 141 to the back plate 142 (a bent bottom surface).
That is, the closed spaces S5 and S6 are different from each other
in width (thickness of the air layer in each closed space) in the
direction orthogonal to the perforated plate 141.
[0101] In this modification the closed spaces S5 and S6 are
different also in volume.
[0102] According to this structure, a particularly high sound
absorbing effect can be exhibited against noises of two different
frequencies and hence it is possible to exhibit a high sound
absorbing effect in a wider frequency band.
5
[0103] As shown in FIG. 9, a back plate 142 may be bent for example
by press working so as to divide an air layer on the back side of
the perforated plate 141 into plural closed spaces S7 in the axial
direction of the exhaust pipe 12.
[0104] In the structure of FIG. 9, plural closed spaces S7 are
arranged at equal intervals in the axial direction of the exhaust
pipe 12. The closed spaces S7 are the same in width in the
direction orthogonal to the perforated plate 141 (thickness of an
air layer in each closed space) and also in volume. In the
perforated plate 141, the number of through holes 141a which open
to each closed space S7 differs in the axial direction of the
exhaust pipe 12. That is, plural through holes 141a are not
uniformly dispersed throughout the whole of the perforated plate
141, but are formed in the perforated plate 141 so as to be
different in porosity in each of plural regions (T1 and T2)
arranged in the axial direction of the exhaust pipe 12. The
porosity within a predetermined region of the perforated plate is a
value which an integrated area of all openings present in the
predetermined region of the perforated plate is divided by the area
of the predetermined region.
[0105] According to this structure, since the porosity of the
perforated plate 141 is not constant in the axial direction of the
exhaust pipe 12, a specially high sound absorbing effect can be
exhibited against noise of a specific frequency corresponding to
each porosity in the axial direction and hence it is possible to
exhibit a high sound absorbing effect in a wider frequency
band.
[0106] There may be adopted a structure wherein the through holes
141a passing through the perforated plate 141 are different in
diameter in each of plural regions (T1 and T2) arranged in the
axial direction of the exhaust pipe 12.
6
[0107] As shown in FIG. 10, the back plate 142 and the perforated
plate 141 may be bent for example by press working to form a
plurality of closed spaces S8 and S9 in the axial direction of the
exhaust pipe 12.
[0108] In the structure shown in FIG. 10, closed spaces S8 and S9
different in both volume and shape are arranged alternately in the
axial direction of the exhaust pipe 12.
[0109] In case of forming a recess by press working, the depth of
the recess may not be a predetermined depth or deeper. An example
is that the formation intervals of plural recesses are
predetermined and the recesses are formed by press working with use
of a tapered punch. That is, when a plate is press-worked to form
recesses each having a slant face of 45.degree. relative to a
reference plane of the plate, for example, the depth of each recess
(depth from the reference plane) is a half of the recess width
(width in the direction parallel to the reference plane) even at
maximum.
[0110] However, since the recesses are formed in both perforated
plate 141 and back plate 142 by press working respectively, the air
layer thickness is doubled in comparison with the case where only
one is subjected to press working.
[0111] That is, by projecting the perforated plate 141 toward the
exhaust pipe 12, the depths (depths in the radial direction of the
exhaust pipe 12) of the closed spaces S8 and S9 can be made larger
and it is possible to increase the volumes of those closed spaces
and their widths in the direction orthogonal to the perforated
plate 141.
7
[0112] In the structure (the structure of FIG. 6) which utilizes
the space between the perforated plate 141' and the bent lower
surface 11b without using the back plate 142, the perforated plate
141' may be bent in the axial direction of the exhaust pipe 12 to
form a plurality of closed spaces S10 and S11 in the axial
direction of the exhaust pipe 12 and between the perforated plate
141' and the bent lower surface 11b of the vehicle body, as shown
in FIG. 11. The closed spaces S10 and S11 are formed so that the
closed spaces S10 and S11 adjacent each other in the axial
direction are mutually different in thickness (thickness in the
direction orthogonal to the surface of the perforated plate 141'
opposed to the exhaust pipe 12).
[0113] According to this structure, the entire space between the
perforated plate 141' and the bent lower surface 11b can be
utilized effectively and it is possible to form a heat insulator
mounting structure more compactly. Since the back plate 142 is not
needed, the manufacturing cost is reduced. Further, an especially
high sound absorbing effect can be exhibited against noises of
different frequencies and hence it is possible to exhibit a high
sound absorbing effect within a wider frequency band.
8
[0114] In the structure (the structure of FIG. 6) which utilizes
the space between the perforated plate 141' and the bent lower
surface 11b without using the back plate 142, the perforated plate
141' may be bent to form a plurality of closed spaces in the
circumferential direction of the exhaust pipe 12 and between the
perforated plate 141' and the bent lower surface 11b of the vehicle
body, as seen from the axial direction of the exhaust pipe 12 shown
in FIG. 12A. In the structure of FIG. 12A, adjacent closed spaces
are mutually different in thickness and volume. The perforated
plate 141' extends and maintains its sectional shape in the
direction parallel to the axis of the exhaust pipe 12. The
perforated plate 141' of such a shape can be formed by roll
forming, for example. In this case, the manufacturing cost is
low.
[0115] Both ends of the perforated plate 141' in the axial
direction of the exhaust pipe 12 are deformed by press working, for
example, so as to come into close contact with the bent lower
surface 11b, whereby both ends of the space between the perforated
plate and the bent lower surface 11b are closed.
[0116] As shown in FIG. 12B which is a sectional view taken along
line A2-A2 in FIG. 12A, partition walls 145 may be disposed at
predetermined intervals in the axial direction of the exhaust pipe
12 to partition the space between the perforated plate 141' and the
bent lower surface 11b. Like the structure shown in FIG. 11, the
partition walls may be formed by bending the perforated plate 141'
by press working. With such partition walls, it is possible to
improve the strength of the sound absorbing structure.
(Analysis of Sound Absorbing Effect)
[0117] The following are the verification results of the sound
absorbing effect of heat insulator mounting structures according to
an embodiment of the present invention with using computer
simulation.
Analysis 1
[0118] Analytic models are shown in FIG. 13.
[0119] As shown in FIG. 13A, an analytic model of a comparative
example, (referred to as "the comparative model" hereinafter),
includes a pair of side wall portions 21 of a vehicle, bottom
portions 22 extending in parallel with the ground G from lower ends
of the pair of side wall portion 21 toward the center of the
vehicular width respectively, and a semi-arcuate shield portion 23
continuous with the bottom portions 22 and swelling upwards at the
center of the vehicular width. The shield portion 23 of the
comparative example is disposed so that the ends of circular arc
thereof are level with lower surfaces of the bottom portions
22.
[0120] A sound source 24 corresponding to the exhaust pipe is
disposed at a circular arc center of the shield portion 23.
[0121] As shown in FIG. 13B, an analytic model embodying the
present invention, (referred to as "the working model 1"
hereinafter), is the same as the comparative model except a shield
portion 33. The shield portion 33 in the working model 1 is formed
by extending both ends of the circular arc of the shield portion 23
in the comparative model by a predetermined quantity toward the
ground G perpendicularly to the lower surfaces of the bottom
portions 22. That is, the working model 1 is constructed by adding
extending portions 33a to the comparative model. The shield portion
33 is formed so that a lower end of the sound source 24 is
positioned on a straight line connecting the pair of extending ends
of the shield portion 33.
[0122] For each of the comparative model and the working model 1,
predetermined noises were generated from the sound source 24 and at
that time the relative sound pressure levels were calculated for
sound waves acting on a region X (evaluation region X) located
under the side wall portions 21.
[0123] For the analysis of both comparative model and working model
1, FIG. 14 shows a relation between relative sound pressure levels
and frequencies (1000 Hz to 4000 Hz) of the sound waves acting on
the evaluation rations X.
[0124] FIG. 14 shows that the relative sound pressure level
decreases within the frequency band of 1000 Hz to 2000 Hz for the
working model 1 as compared with the comparative model.
[0125] Thus, it is seen that the sound absorbing effect is improved
by extending the shield portion 33 below the lower surface of the
vehicle toward the ground G.
Analysis 2
[0126] FIG. 15 shows an analytic model.
[0127] FIG. 15 shows an analytic model (referred to as "the working
model 2" hereinafter) embodying the present invention. A shield
portion 43 in the working model 2 includes extending portions 43a
continuous with the extending ends of the shield portion 33 in the
working model 1 used in the above analysis 1 and extending in
parallel with the lower surface of the vehicle along the center of
the vehicular width. The extending portions 43a are formed so that
their extending ends are at the same position as both ends of the
sound source 24 in terms of the vehicular width.
[0128] Also for the working model 2 as the above analysis 1,
predetermined noises were generated from the sound source 24 and
relative sound pressure levels were calculated for the sound waves
acting on the evaluation region X.
[0129] For the analysis using the working model 2, FIG. 16 shows a
relation between relative sound pressure levels acting on the
evaluation regions X and frequencies (1000 Hz to 4000 Hz). Analysis
results, of the above analysis 1 (the results of the comparative
model and the working model 1) are also shown in FIG. 16.
[0130] FIG. 16 shows that the relative sound pressure level
decreases in the frequency band of 1000 Hz to 1600 Hz for the
working model 2 as compared with the working model 1.
[0131] Thus, it is seen that when the shield portion 43 includes
the extending potions 43a bent from the ends extending downwards
below the vehicle lower surface and extending so as to approach the
sound source 24, the sound absorbing effect is further
improved.
Analysis 3
[0132] FIG. 17 shows an analytic model.
[0133] FIG. 17 shows an analytic model (referred to as "the working
model 3" hereinafter) embodying the present invention. A shield
portion 53 in the working model 3 is a sound absorbing structure
having a perforated plate 531 and a closed air layer S behind the
perforated plate. The working model 3 substantially corresponds to
the embodiment shown in FIG. 6.
[0134] The shield portion 53 is provided at both sides of the sound
source 24 in the vehicular width direction so as to extend
downwards below the lower surface of the vehicle. The lower end of
the sound source 24 is positioned on a straight line connecting the
pair of extending ends of the shield portion 53.
[0135] Also for the working model 3 as the above analysis 1,
predetermined noises were generated from the sound source 24 and
relative sound pressure levels were calculated for sound waves
acting on the evaluation region X.
[0136] For the analysis using the working model 3, FIG. 18 shows a
relation between the relative sound pressure levels acting on the
evaluation region X and frequencies (1000 Hz to 4000 Hz). Analysis
results of the above analysis 1 (results of the comparative model
and the working model 1) are also shown in FIG. 18.
[0137] FIG. 18 shows that the relative sound pressure level
decreases in the frequency band of 1000 Hz to 1250 Hz for the
working model 3 as compared with the working model 1.
[0138] Thus, it is seen that when the shield portion 53 is a sound
absorbing structure having the perforated plate 531 and the closed
air layer S behind the perforated plate, the sound absorbing effect
is improved.
[0139] Although embodiments of the present invention have been
described above, the present invention is not limited to the above
embodiments, but may be modified variously within the scope of
claims.
[0140] For example, the present invention is applicable to the case
where the body bottom plate 10 has the bent lower surface 11b, as
well as the case where the body bottom plate 10 is open at the
position corresponding to the bent lower. surface 11b.
INDUSTRIAL APPLICABILITY
[0141] The present invention is applicable to the case where a heat
insulator for suppressing the transfer of heat from an exhaust pipe
to a vehicle body is attached to the vehicle body.
* * * * *