MUFFLER

Abstract

Provided is a muffler having a double pipe portion formed therein in which an end portion of a first tubular member is inserted into a second tubular member from an end portion thereof. A leading end portion of the second tubular member is joined to an outer periphery of the first tubular member. A portion that forms the double pipe portion of the second tubular member comprises a first portion located closer to an end of the first tubular member, and a second portion that is located closer to an end of the second tubular member and that has an enlarged diameter compared with the first portion. A resonance chamber is formed between the first tubular member and the second portion. A communication path that allows communication between an exhaust flow path and the resonance chamber is formed between the first tubular member and the first portion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application claims the benefit of Japanese Patent Application No. 2013-003714 filed Jan. 11, 2013 in the Japan Patent Office, and the entire disclosure of Japanese Patent Application No. 2013-003714 is incorporated herein.

TECHNICAL FIELD

The present invention relates to a muffler that reduces exhaust noise.

BACKGROUND ART

In an exhaust system for an automobile, exhaust noise is reduced by a muffler provided in an exhaust flow path. For example, low-frequency air column resonance generated in a tubular portion having a long actual length is a factor that increases muffled exhaust noise. Thus, measures are taken, such as reducing the air column resonance by providing a sub-muffler in series with a main muffler. Moreover, Patent Document 1 includes a structure in which a muffler of a side branch type resonant system is provided between the main muffler and the sub-muffler.

PRIOR ART DOCUMENTS

Patent Documents

• Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-105918

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

As a muffler of a resonant system, a muffler of a Helmholtz type resonant system is known in addition to the above-described muffler of the side branch type resonant system. However, the Helmholtz type muffler is formed with a structure in which the exhaust flow path leads to a resonance chamber having a large volume via a long and narrow communication path, and thus, a problem has been found in which the structure is inevitably complicated.

In one aspect of the present invention, it is preferable to form a muffler of a Helmholtz type resonant system with a simple structure.

Means for Solving the Problems

An aspect of the present invention is a muffler that comprises a first tubular member that forms an exhaust flow path of an internal combustion engine, and a second tubular member that is connected to the first tubular member and forms the exhaust flow path together with the first tubular member. A double pipe portion is formed in which an end portion of the first tubular member is inserted into the second tubular member from an end portion thereof. A leading end portion of the second tubular member is joined to an outer periphery of the first tubular member. A portion that forms the double pipe portion of the second tubular member comprises a first portion located closer to an end of the first tubular member, and a second portion that is located closer to an end of the second tubular member and that has an enlarged diameter compared with the first portion. A resonance chamber is formed between the first tubular member and the second portion. A communication path that allows communication between the exhaust flow path and the resonance chamber is formed between the first tubular member and the first portion. A Helmholtz type resonant system is formed by the resonance chamber and the communication path.

According to such a configuration, exhaust noise can be reduced in a connection between the first tubular member and the second tubular member. Furthermore, the Helmholtz type resonant system can be formed with a simple structure because the resonance chamber and the communication path of the Helmholtz type resonant system are formed using the double pipe portion formed by the two tubular members that form the exhaust flow path.

In the above-described configuration, a spacer that inhibits contact between the first tubular member and the second tubular member may be provided in the communication path, and the spacer may be arranged so as to secure an air passage on an outer circumference of the first tubular member so that the communication path is not blocked. According to such a configuration, the communication path is less likely to be blocked, and an effect of reducing exhaust noise can thereby be enhanced.

Furthermore, in the above-described configuration, each of the first tubular member and the second tubular member may be formed as a single part. According to such a configuration, it is not necessary to separately use dedicated components to form the Helmholtz type resonant system, and thus, space saving, cost reduction, and the like can be sought.

It is to be noted that one aspect of the present invention can be achieved in various forms, such as an exhaust system including a muffler, and a method for muffling exhaust noise, besides the above-described muffler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an exhaust system of an embodiment.

FIG. 2 is a sectional view taken along a line II-II in FIG. 1.

FIG. 3A is an exploded perspective view of a muffler, and FIG. 3B is a transparent perspective view of the muffler.

FIG. 4 is a sectional view taken along a line IV-IV in FIG. 2.

EXPLANATION OF REFERENCE NUMERALS

1 . . . exhaust system, 2 . . . flow path member, 3 . . . catalytic converter, 4 . . . sub-muffler, 5 . . . main muffler, 10 . . . first tubular member, 11 . . . reduced diameter portion, 12 . . . body portion, 20 . . . second tubular member, 21 . . . enlarged diameter portion, 22 . . . body portion, 23 . . . leading end portion, 30 . . . muffler, 31 . . . resonance chamber, 32 . . . communication path, 40 . . . wire mesh

MODE FOR CARRYING OUT THE INVENTION

An embodiment in which the present invention is applied will be described below with reference to drawings.

An exhaust system 1 shown in FIG. 1 forms an exhaust flow path, which is a flow path of exhaust gas discharged from an internal combustion engine of an automobile. The exhaust system 1 is mainly configured with a flow path member 2 of a tubular shape forming the exhaust flow path having a long actual length. The exhaust system 1 has a catalytic converter 3, a sub-muffler 4, and a main muffler 5 arranged in series with each other in order from the upstream of the exhaust flow path (from the left in FIG. 1) along the flow path member 2 (the exhaust flow path).

The flow path member 2 comprises a first tubular member 10 that forms the exhaust flow path in the downstream of the sub-muffler 4, and a second tubular member 20 that is connected to a downstream-side end portion of the first tubular member 10 and forms the exhaust flow path in the upstream of the main muffler 5. In the flow path member 2, the sub-muffler 4 and the main muffler 5 are connected to each other via the first tubular member 10 and the second tubular member 20.

As shown in FIG. 2, FIG. 3A, and FIG. 3B, the first tubular member 10 is a member formed by processing a circular pipe part having an outside diameter R1 (60.5 mm, for example), and is configured as a single part. Specifically, the first tubular member 10 is a member formed by reducing in diameter an end portion located in the downstream side (the right side in FIG. 2) of the circular pipe part having the outside diameter R1, specifically a portion having a length L1 from an end, to an outside diameter R2 (54.7 mm, for example) that is smaller than the outside diameter R1. In an explanation below, the portion having the length L1 from the end of the first tubular member 10 is referred to as a “reduced diameter portion 11”, and the remaining portion is referred to as a “body portion 12”.

The second tubular member 20 is a member formed by processing the circular pipe part having the outside diameter R1 similarly to the first tubular member 10, and is configured as a single part similarly to the first tubular member 10. Specifically, the second tubular member 20 is a member formed by enlarging in diameter an end portion located in the upstream side (the left side in FIG. 2) of the circular pipe part having the outside diameter R1, specifically a portion having a length L2 from an end, to an outside diameter larger than the outside diameter R1. Specifically, the second tubular member 20 is gradually increased in outside diameter from a position the length L2 apart from the end toward the end, and becomes largest in outside diameter (120 mm, for example) at a position a length L3 apart from the end (L3<L2). Then, the second tubular member 20 is gradually decreased in outside diameter from a position a length L4 apart from the end (L4<L3) toward the end. Such a shape is formed by performing a diameter enlarging process on the portion having the length L2 from the end and then performing a diameter reducing process on a portion having the length L4 from the end, for example. In an explanation below, the portion having the length L2 from the end in the second tubular member 20 is referred to as an “enlarged diameter portion 21”, and the remaining portion is referred to as a “body portion 22”.

The downstream-side end portion of the first tubular member 10, specifically the entirety of the reduced diameter portion 11 and part of the body portion 12, is inserted into the second tubular member 20 from an upstream-side end portion (a leading end portion 23 of the enlarged diameter portion 21) of the second tubular member 20 in such a manner that central axes thereof are coincident with each other. In this way, a double pipe portion including the first tubular member 10 as an inner pipe and the second tubular member 20 as an outer pipe (a portion in which the first tubular member 10 and the second tubular member 20 overlap with each other) is formed in a connection (a joint to be described later and a portion adjacent thereto) between the first tubular member 10 and the second tubular member 20. The connection between the first tubular member 10 and the second tubular member 20 functions as a muffler 30 of a Helmholtz type resonant system, as will be described below.

That is, the second tubular member 20, specifically the leading end portion 23 of the enlarged diameter portion 21, is joined (welded all around in the present embodiment) to the first tubular member 10, specifically on an outer periphery of the body portion 12. In this way, in the double pipe portion, a dead-end space is formed that communicates with the exhaust flow path, between the first tubular member 10 and the second tubular member 20. Specifically, a resonance chamber 31 having a large volume is formed between the body portion 12 of the first tubular member 10 and the enlarged diameter portion 21 of the second tubular member 20. In other words, a volume required as the resonance chamber 31 is secured by the enlarged diameter portion 21 of the second tubular member 20. Besides, a communication path 32 is formed between the reduced diameter portion 11 of the first tubular member 10 and the body portion 22 of the second tubular member 20. The communication path 32 is a space a cross-sectional area of which orthogonal to an axial direction is smaller than that of the resonance chamber 31, and allows communication between the exhaust flow path and the resonance chamber 31. The resonance chamber 31 and the communication path 32 are designed to configure the Helmholtz type resonant system.

Provided in the communication path 32 is a wire mesh 40, which is a metal buffer member. The wire mesh 40 functions as a spacer to inhibit contact between the first tubular member 10 and the second tubular member 20. Moreover, the wire mesh 40 also has a function of reducing stress of thermal contraction difference between the first tubular member 10 and the second tubular member 20. It is to be noted that an outside diameter of the wire mesh 40 is equal to or smaller than the outside diameter R1 of the body portion 12 of the first tubular member 10.

However, if the communication path 32 is blocked by the wire mesh 40, excitation force of sound pressure that generates a resonance phenomenon becomes less likely to be transmitted to the resonance chamber 31. Thus, the wire mesh 40 is arranged so that an air passage is secured in an outer circumference of the first tubular member 10. Specifically, in the present embodiment, a plurality of (three in this example) the wire meshes 40 having a circular arc shape along the outer periphery of the first tubular member 10 are arranged on some parts of the entire outer circumference (range of 360 degrees) of the first tubular member 10, as shown in FIG. 4. The three wire meshes 40 are not as long as the entire outer circumference of the first tubular member 10 even when all of them are pieced together. Besides, the three wire meshes 40 are arranged shifted from each other in an axial direction of the first tubular member 10 (on different positions in the axial direction) (see FIG. 2). Consequently, the air passage is secured successfully on the outer circumference of the first tubular member 10.

The muffler 30 is designed such that a resonance frequency thereof is coincident with an Nth-order mode (N is a natural number, and 1 in the present embodiment) of air column resonance frequency of a pipe, and the end of the first tubular member 10 is arranged so as to be at a position of the maximum sound pressure of the Nth mode.

According to the embodiment described above in detail, the following effects are obtained.

[A1] The muffler 30 comprises the first tubular member 10 that forms the exhaust flow path of the internal combustion engine, and the second tubular member 20 that is connected to the first tubular member 10 and forms the exhaust flow path together with the first tubular member 10. In the connection between the first tubular member 10 and the second tubular member 20, the double pipe portion is formed in which the end of the first tubular member 10 is inserted into the second tubular member 20 from the leading end portion 23 thereof, and the leading end portion 23 of the second tubular member 20 is joined to the outer periphery of the first tubular member 10. The portion that forms the double pipe portion of the second tubular member 20 comprises the body portion 22 located closer to the end of the first tubular member 10, and the enlarged diameter portion 21 that is located closer to the end of the second tubular member 20 and that has the enlarged diameter compared with the body portion 22. The resonance chamber 31 is formed between the first tubular member 10 and the enlarged diameter portion 21. The communication path 32 that allows communication between the exhaust flow path and the resonance chamber 31 is formed between the first tubular member 10 and the body portion 22. The Helmholtz type resonant system is formed by the resonance chamber 31 and the communication path 32.

Thus, according to the present embodiment, air column resonance can be inhibited at the connection between the first tubular member 10 and the second tubular member 20, and as a result, exhaust noise can be reduced. Moreover, the Helmholtz type resonant system can be configured with a simple structure because the resonance chamber 31 and the communication path 32 of the Helmholtz type resonant system are formed using the double pipe portion formed by the first tubular member 10 and the second tubular member 20 that form the exhaust flow path. Especially, since the Helmholtz type resonant system is adopted, a muffling effect can be enhanced by increasing the volume of the resonance chamber 31. Although it may be possible to create a through-hole in the first tubular member 10 and to cause the through-hole to function as the communication path of the Helmholtz type resonant system, sufficient effect is less likely to be obtained by such a structure because the length of the communication path is no more than the through-thickness of the first tubular member 10. In this regard, the structure having the long communication path is achieved in the present embodiment, and noise reduction effect can thereby be enhanced.

[A2] The wire mesh 40 that inhibits contact between the first tubular member 10 and the second tubular member 20 is provided in the communication path 32. The wire mesh 40 is arranged so as to secure the air passage on the outer circumference of the first tubular member 10 so that the communication path 32 is not blocked. Thus, according to the present embodiment, the communication path 32 is less likely to be blocked, and an effect of reducing exhaust noise can thereby be enhanced.

[A3] Each of the first tubular member 10 and the second tubular member 20 is formed as a single part. Thus, according to the present embodiment, it is not necessary to separately use dedicated components to form the Helmholtz type resonant system, and thus, space saving, cost reduction, and the like can be sought. Specifically, in a configuration in which dedicated components to form a muffler (a resonance chamber and a communication path) are added to the components forming the exhaust flow path, the structure is likely to be complicated and larger, and the number of the components is increased as well as the number of portions to be joined (welded), which is likely to result in increase in cost. In contrast, the muffler 30 of the present embodiment is configured with the first tubular member 10 and the second tubular member 20 forming the exhaust flow path and, furthermore, the number of the portions to be joined (welded) is one. Thus, the muffler 30 of the present embodiment has an advantage that space saving, cost reduction, and the like can be easily sought. In addition, since the muffler 30 of the present embodiment is configured with the tubular members, there is another advantage that the muffler 30 has a bending workability and can be easily applied to a layout of the exhaust system 1.

[A4] The muffler 30 is designed such that the resonance frequency thereof is coincident with the Nth-order mode of the air column resonance frequency of the pipe, and the end of the first tubular member 10 is arranged so as to be at the position of the maximum sound pressure of the Nth mode. Thus, according to the present embodiment, the maximum reduction can be obtained with the mode coincident with the resonance frequency. Furthermore, the air column resonance can be inhibited by reducing the sound pressure by a certain volume even in the other mode.

[A5] The first tubular member 10 has the reduced diameter portion 11 formed therein, and the wire mesh 40 having the outside diameter equal to or smaller than the outside diameter R1 of the body portion 12 is used. Thus, the first tubular member 10 having the wire mesh 40 attached thereon can be easily inserted into the second tubular member 20. Consequently, according to the present embodiment, the first tubular member 10 and the second tubular member 20 can be assembled to each other more easily.

Although the embodiment of the present invention has been described above, it is needless to say that the present invention is not limited to the above embodiment and can take various forms.

[B1] The wire mesh 40 shown in the above embodiment is an example, and the configuration is not limited to this. For example, the wire mesh 40 may be one in number or may be two or more in number. The position in which the wire mesh 40 is arranged is also not limited in particular. Specifically, two C-shaped wire meshes having a shape of a halved ring, for example, may be arranged shifted in the axial direction of the first tubular member 10. Moreover, a member other than the wire mesh 40 may be used as the spacer. Furthermore, the spacer may be formed by processing (for example, by forming projecting portions on) at least one of the first tubular member 10 and the second tubular member 20. Alternatively, a configuration without the spacer may be possible.

[B2] The first tubular member 10 may be formed of a plurality of parts. For example, when a circular pipe part having the outside diameter R2 and a circular pipe part having the outside diameter R1 are used, an area to be reduced in diameter can be decreased, or the diameter reducing process itself can be eliminated. Similarly, the second tubular member 20 may also be formed of a plurality of parts.

[B3] The first tubular member 10 may comprise no reduced diameter portion 11. For example, it may be possible to insert the first tubular member 10 on which the wire mesh 40 is attached into the second tubular member 20, and then, to reduce the diameter of the leading end portion 23 of the second tubular member 20.

[B4] In the above embodiment, the first tubular member 10 and the second tubular member 20 are formed using the circular pipe parts having the same outside diameter. However, the configuration is not limited to this. For example, a circular pipe part having an outside diameter larger than that of the first tubular member 10 may be used as the second tubular member 20. Moreover, the first tubular member 10 and the second tubular member 20 may be formed using parts other than the circular pipe part (a tubular member having a section of oval or polygonal shape, for example).

[B5] The resonance chamber 31 shown in the above embodiment is an example, and the configuration is not limited to this. For example, although the resonance chamber 31 is formed by the enlarged diameter portion 21 that is expanded into an approximately trapezoidal shape when viewed from the side (viewed from a direction orthogonal to the axial direction) in the above embodiment, the resonance chamber, instead of this, may be formed by an enlarged diameter portion expanded into, for example, an approximately triangular shape or an approximately rectangular shape.

[B6] In the above embodiment, the configuration has been exemplified in which the muffler 30 is arranged in the exhaust flow path connecting the sub-muffler 4 and the main muffler 5 to each other. However, the configuration is not limited to this. Moreover, the configuration of the exhaust system on which the present invention is premised is also not limited to the above embodiment, and a configuration without a sub-muffler may be adopted, for example. Furthermore, a positional relationship between the first tubular member (an inner pipe of the double pipe portion) and the second tubular member (an outer pipe of the double pipe portion), i.e., whether they are located upstream or downstream, may be opposite to that in the above embodiment. That is, the second tubular member may be arranged in the upstream of the exhaust flow path, and the first tubular member may be arranged in the downstream of the exhaust flow path.

[B7] Each of the elements of the present invention is a conceptual one, and is not limited to the above embodiment. For example, the function of one element may be dispersed over a plurality of elements, or the functions of a plurality of elements may be integrated to one element. Moreover, at least part of the configuration of the above embodiment may be replaced by a known configuration having a similar function.

Claims

1. A muffler comprising: a first tubular member that forms an exhaust flow path of an internal combustion engine; anda second tubular member that is connected to the first tubular member and forms the exhaust flow path together with the first tubular member,wherein a double pipe portion is formed in which an end portion of the first tubular member is inserted into the second tubular member from an end portion thereof,wherein a leading end portion of the second tubular member is joined to an outer periphery of the first tubular member,wherein a portion that forms the double pipe portion of the second tubular member comprises a first portion located closer to an end of the first tubular member, and a second portion that is located closer to an end of the second tubular member and that has an enlarged diameter compared with the first portion,wherein a resonance chamber is formed between the first tubular member and the second portion,wherein a communication path that allows communication between the exhaust flow path and the resonance chamber is formed between the first tubular member and the first portion, andwherein a Helmholtz type resonant system is formed by the resonance chamber and the communication path.

2. The muffler according to claim 1, wherein a spacer that inhibits contact between the first tubular member and the second tubular member is provided in the communication path, andwherein the spacer is arranged so as to secure an air passage on an outer circumference of the first tubular member so that the communication path is not blocked.

3. The muffler according to claim 1, wherein each of the first tubular member and the second tubular member is formed as a single part.

4. The muffler according to claim 1, wherein the second tubular member is connected to an end portion in the downstream side of the first tubular member.

5. The muffler according to claim 4, wherein the first tubular member is a member comprising a reduced diameter portion, which is a portion formed by reducing in diameter a portion having a specified length from a downstream-side end of a circular pipe part, and a body portion, which is a non-reduced-diameter portion,wherein the second tubular member is a member comprising an enlarged diameter portion, which is a portion formed by enlarging in diameter a portion having a specified length from an upstream-side end of a circular pipe part, and a body portion, which is a non-enlarged-diameter portion,wherein a downstream-side end portion including an entirety of the reduced diameter portion and part of the body portion of the first tubular member is inserted into the second tubular member,wherein the resonance chamber, which is a dead-end space that communicates with the exhaust flow path, is formed between the body portion of the first tubular member and the enlarged diameter portion of the second tubular member, andwherein the communication path is formed between the reduced diameter portion of the first tubular member and the body portion of the second tubular member, the communication path being a space, a cross-sectional area of which orthogonal to an axial direction is smaller than that of the resonance chamber and which allows communication between the exhaust flow path and the resonance chamber.

6. The muffler according to claim 1, wherein the second portion is shaped such that the second portion is gradually increased in outside diameter from a position a length L2 apart from the end toward the end, becomes largest in outside diameter at a position a length L3 apart from the end (L3<L2), and is gradually decreased in outside diameter from a position a length L4 apart from the end (L4<L3) toward the end.