Heat Insulator mounting structure

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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.

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.

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

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.

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.

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.

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.

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.

Thus, the noise propagated around the vehicle can be effectively reduced with a simple structure.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

According to the present invention, the noise propagated around a vehicle can be reduced effectively with a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

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;

FIG. 2 is a diagram showing a modification (1) of the first embodiment;

FIG. 3 is a diagram showing a modification (2) of the first embodiment;

FIG. 4 is a sectional view showing a heat insulator mounting structure according to a second embodiment of the present invention;

FIG. 5 is a diagram showing a modification (1) of the second embodiment;

FIG. 6 is a diagram showing a modification (2) of the second embodiment;

FIG. 7 is a diagram showing a modification (3) of the second embodiment;

FIG. 8 is a diagram showing a modification (4) of the second embodiment;

FIG. 9 is a diagram showing a modification (5) of the second embodiment;

FIG. 10 is a diagram showing a modification (6) of the second embodiment;

FIG. 11 is a diagram showing a modification (7) of the second embodiment;

FIG. 12 is a diagram showing a modification (8) of the second embodiment;

FIG. 13 is a diagram showing analytic models; FIG. 13A is a comparative model and FIG. 13B is a working model 1;

FIG. 14 is a diagram showing an analysis result obtained with using the analytic models of FIG. 13;

FIG. 15 is a diagram showing an analytic model (a working model 2) for verifying a sound absorbing effect;

FIG. 16 is a diagram showing an analysis result obtained with using the analytic model of FIG. 15;

FIG. 17 is a diagram showing an analytic model (a working model 3) for verifying a sound absorbing effect; and

FIG. 18 is a diagram showing an analysis result obtained with using the analytic model of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment

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.

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).

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.

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 α which is formed in a bent manner so as to swell upwards.

The depressed portion α 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 α 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 α.

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.

The first shield portion 131 is disposed within the depressed portion α, while the second shield portions 132 are positioned outside the depressed portion α. 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.

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.

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

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).

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.

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.

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.

In this embodiment, the vehicle body is provided on the body lower surface 11 with the depressed portion α formed so as to swell upwards, and an upper half surface of the exhaust pipe 12 is disposed within the depressed portion α. The first shield portion 131 is disposed between the bent lower surface 11b as the surface forming the depressed portion α and the exhaust pipe 12, and the second shield portions 132 extend downwards under the depressed portion α from both ends of the first shield portion 131 in the circumferential direction of the exhaust pipe 12.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

A space S1 between the perforated plate 141 and the back plate 142 is closed.

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.

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.

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

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.

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.

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.

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.

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

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.

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.

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.

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.

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 α, and an upper half surface of the exhaust pipe 12 is disposed within the depressed portion α (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 α 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.

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.

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.

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.

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.

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.

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.

In this modification the closed spaces S5 and S6 are different also in volume.

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.

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.

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.

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.

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.

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.

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.

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° 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.

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.

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.

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).

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.

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.

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.

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)

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

Analytic models are shown in FIG. 13.

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.

A sound source 24 corresponding to the exhaust pipe is disposed at a circular arc center of the shield portion 23.

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.

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.

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.

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.

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

FIG. 15 shows an analytic model.

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.

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.

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.

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.

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

FIG. 17 shows an analytic model.

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.

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.

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.

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.

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.

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.

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.

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

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.

Heat Insulator mounting structure

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CPC

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Priority Claims (1)