Muffler device

A small-sized muffler having porous partition walls includes a first expansion chamber, a second expansion chamber, a third expansion chamber and a fourth expansion chamber. A first porous partition wall is longitudinally arranged within the third expansion chamber so as to define a fifth expansion chamber. Similarly, a second porous partition wall is longitudinally arranged within the first expansion chamber so as to define the sixth expansion chamber. The first porous partition wall and the second porous partition wall are provided with small holes over their entire surface. The first porous partition wall and the second porous partition wall are each formed as a convexly curved surface curved toward the center of the muffler around the first feeding pipe and the second feeding pipe, respectively.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a muffler device for an internal combustion 
engine, and more particularly, to a muffler having a porous partition wall 
arranged therein. 2. Description of the Background Art 
Japanese Utility-Model Laid-Open No. Sho 56-83622 discloses a muffler 
device in which an inner side of the muffler is partitioned by a plurality 
of partition walls to form a plurality of expansion chambers in a 
lengthwise direction. Each of the expansion chambers communicates with a 
communicating pipe. At the same time, a porous partition wall is arranged 
near an outlet port of a feeding pipe communicating with the exhaust pipe. 
In the above embodiment, when a certain distance is not maintained between 
an outlet of the feeding pipe and the porous partition wall, an 
undesirable influence may occur hindering the efficient flow of exhaust. 
Although the porous partition wall is arranged at a right angle with 
respect to an axial line of the feeding pipe, the outlet port of the 
feeding pipe cannot be arranged near the porous partition wall by an 
amount more than a specified distance. Therefore, the size of the muffler 
must be increased. 
When the feeding pipe and the communicating pipe are overlapped with one 
another, the porous partition wall must be bent in order to be arranged 
between the feeding pipe and the communicating pipe. The result is that a 
shape of the porous partition wall may become complicated. 
When a plurality of feeding pipes or communicating pipes are present near 
or passing through the porous partition wall, an extending position of 
each of the pipes on the porous partition wall must avoid formation of 
some small holes. Thus, as the number of feeding pipes or communicating 
pipes is increased, a range of small holes which can be formed at the 
porous partition wall is limited, and an opening area of the small holes 
is reduced. 
However, if each of the aforesaid problems is to be resolved concurrently, 
the structure inside of the muffler may become complicated. A degree of 
freedom in layout about the porous partition wall, feeding pipe, 
communicating pipe and partition wall is remarkably restricted. 
SUMMARY OF THE INVENTION 
In order to solve the aforesaid problems, the muffler device of the present 
invention includes a muffler communicating with an exhaust pipe of an 
internal combustion engine. An inner side of the muffler is partitioned by 
partition walls to make a plurality of expansion chambers. The expansion 
chambers are interconnected with communicating pipes. A porous partition 
wall is arranged near an outlet port of a feeding pipe continuous with the 
exhaust pipe. The porous wall is arranged within the expansion chambers 
substantially in parallel with the feeding pipe. 
In the present invention, it is possible to arrange the porous partition 
wall so as to enclose the outer circumference of the feeding pipe. 
Further, in this case, it is also possible to curve the porous partition 
wall toward the center of the muffler. 
A plurality of feeding pipes and partition walls may be arranged inside of 
the muffler. Since the porous partition walls are arranged within the 
expansion chambers in parallel with the feeding pipes, the inner sides of 
the expansion chambers are partitioned by the porous partition walls into 
a plurality of sub-chambers. In this specification, this dividing form is 
defined as a longitudinal division, and an arranging form of the porous 
partition wall is defined as a longitudinal setting. 
Because of this arrangement, it is not necessary to arrange the porous 
partition walls a predetermined distance away from the outlets of the 
feeding pipes. The result is that the entire muffler can be made short in 
length and its size can be made small. 
Additionally, since the porous partition walls are arranged in parallel 
with the feeding pipes, the shape of the porous partition walls can be 
simplified. Even in an arrangement where the feeding pipes and the 
communicating pipes are overlapped with one another, it is not necessary 
to form the porous partition wall into a complex shape. 
Also, since the feeding pipes or communicating pipes do not pass through 
the porous partition walls, and the porous partition walls are not 
positioned on extended lines of these pipes, it is possible to form some 
small holes on substantially the entire porous partition wall to insure 
sufficient opening area over the entire porous partition wall. 
Accordingly, irrespective of the fact that each of the aforesaid problems 
can be solved concurrently, the structure within the muffler can be 
simplified and a restriction of layout in regard to the porous partition 
wall, feeding pipes, communicating pipes and partition wall is reduced, 
resulting in that a degree of freedom in regard to the layout of the 
component elements in the internal structure of the muffler is also 
increased. 
Further, if the porous partition walls are arranged to enclose the feeding 
pipes, the porous partition walls can be made relatively small in size. In 
addition, even in the case where a plurality of feeding pipes or 
communicating pipes are present to cause a certain restriction in 
arranging space, they may be arranged in a relative easy manner. 
Further, if the porous partition wall is bent in a convex shape to project 
toward a center of the muffler, the porous partition wall can be made 
smaller, resulting in that a space enclosed by the porous partition wall 
can be made as small as possible. In addition, the curved arrangement of 
the wall allows it to be arranged in a narrow space more easily. Its 
rigidity is also increased, resulting in that its anti-vibrating 
characteristic is also improved. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The muffler includes a cylindrical case 1, a front cap 2 arranged at a 
front end of the case 1, and an end cap 3 arranged at a rear end of the 
case 1. An inner side of the case 1 is constructed such that a first 
expansion chamber 7, a second expansion chamber 8, a third expansion 
chamber 9 and a fourth expansion chamber 10 are formed in this order by 
partition walls 4, 5 and 6 from an upstream side to a downstream side, 
respectively. 
A first feeding pipe 11 connected to an exhaust pipe (not illustrated) 
passes through the front cap 2, the partition wall 4 and the partition 
wall 5. An end part 12 of the first feeding pipe 11 which is downstream 
from the partition wall 5 enters the third expansion chamber 9, and its 
outlet port 13 is opens into the third expansion chamber 9. 
The end part 12 of the first feeding pipe 11 is formed, at its 
circumferential wall part, with many small holes 14. A first porous 
partition wall 15 is arranged substantially in parallel with the end part 
12, thereby defining a fifth expansion chamber 17 within the third 
expansion chamber 9 and enclosing the first feeding pipe 11. 
The first porous partition wall 15 is arranged to be connected between the 
forward partition wall 5 and the rearward partition wall 6. Many small 
holes 16 are formed on the entire surface of the first porous partition 
wall 15. Opposing ends of the first porous partition wall 15 are connected 
to the, partition wall 5 and the partition wall 6 in an axial direction of 
the first feeding pipe 11. 
In addition, a second feeding pipe 20 connected to another exhaust pipe 
(not shown) passes through the front cap 2 and is arranged within the 
first expansion chamber 7. An outlet port 21 of the second feeding pipe 20 
is positioned at an upstream side of the partition wall 4. Many small 
holes 22 are formed in the circumferential wall of the second feeding pipe 
20. 
A second porous partition wall 23 is arranged within the first expansion 
chamber 7 substantially in parallel with the second feeding pipe 20. A 
plurality of small holes 24 are formed in an entire surface of the second 
porous partition wall 24. Opposing ends of the second porous partition 
wall 24 are connected to the front cap 2 and the partition wall 4, thereby 
defining a sixth expansion chamber 25 within the first expansion chamber 7 
and enclosing the second feeding pipe 20. 
The first expansion chamber 7 and the second expansion chamber 8 
communicate with each other by a first communicating pipe 30 passing 
through the partition wall 4. The third expansion chamber 9 and the fourth 
expansion chamber 10 communicate with each other by a second communicating 
pipe 31 passing through the partition wall 6. 
The fourth expansion chamber 10 and the surrounding atmosphere communicate 
with each other by the first tail pipe 32 passing through the end cap 3. 
Similarly, the second expansion chamber 8 and the surrounding atmosphere 
communicate with each other by the second tail pipe 33 passing through the 
partition wall 5, the partition wall 6 and the end cap 3. 
Muffler members 34, 35 are arranged in the fourth expansion chamber 10, and 
are fixed to the first tail pipe 32 and the second tail pipe 33, 
respectively. 
As shown in FIG. 2, an upstream end of the first tail pipe 32 is closed by 
a cap 36, and its circumferential wall near the cap 36 is formed with many 
small holes 37. A portion of the first tail pipe 32 which is covered by 
the muffler member 34 is also formed with many small holes 38. 
Further, the upstream end of the second tail pipe 33 is also closed by a 
cap 40, and its circumferential wall near the cap 40 is formed with many 
small holes 41. A portion of the second tail pipe 33 which is covered by 
the muffler member 35 is also formed with many small holes 42. 
Referring now to FIG. 3, the second porous partition wall 23 encloses the 
second feeding pipe 20 to form a substantially U-shaped convex curved 
member facing toward the central side of the case 1. The second porous 
partition wall 23 is welded to the front cap 2 and the partition wall 4. 
As shown in FIG. 4, the first communicating pipe 30 is connected to the 
first feeding pipe 11 by a bracket 45. 
Referring now to FIG. 5, the first porous partition wall 15 has the same 
shape as that of the second porous partition wall 23, and both ends of the 
first porous partition wall 15 are welded to the partition wall 6 and the 
partition wall 5. 
Referring now to FIG. 6, the second porous partition wall 23 is formed as 
follows: a plurality of small holes 24 are punched into a flat plate of 
raw material to form a flat plate intermediate member 46, and subsequently 
it is press formed into a curved shape to become the second porous 
partition wall 23. Then, a recess is formed in the central part of the end 
portion of the side abutting against the front cap 2 so as to form a 
clearance between it and the front cap 2 during the welding operation. The 
first porous partition wall 15 is formed in a similar manner. 
Operation of the preferred embodiment of the present invention will now be 
described, with reference to FIG. 1. Exhaust gas fed out of the first 
feeding pipe 11 is expanded from the outlet port 13 and the small holes 14 
at the end part 12 into the fifth expansion chamber 17, and expanded 
through the small holes 16 of the first porous partition wall 15 into the 
third expansion chamber 9. The exhaust gas then flows from the third 
expansion chamber 9 into the second communicating pipe 31, and is expanded 
again within the fourth expansion chamber 10. The exhaust gas then passes 
through the first tail pipe 32 and is exhausted to the surrounding 
atmosphere. 
Similarly, the exhaust gas within the second feeding pipe 20 is expanded 
from the outlet port 21 and the small holes 22 into the sixth expansion 
chamber 25, and expanded through the small holes 24 of the second porous 
partition wall 23 into the first expansion chamber 7. The exhaust gas then 
flows from the first expansion chamber 7 into the first communicating pipe 
30, and the gas is expanded again within the second expansion chamber 8. 
The exhaust gas then passes through the second tail pipe 33 and is 
discharged to the surrounding atmosphere. 
As described above, when the first porous partition wall 15 and the second 
porous partition wall 23 are arranged in a longitudinal direction of the 
muffler, it does not become necessary to arrange the porous partition wall 
on each of the extended lines of the first feeding pipe 11 and the second 
feeding pipe 20 with a distance more than a predetermined amount from the 
outlet port of each of the feeding pipes. Accordingly, the entire muffler 
can be made short in length and small in size. 
Further, since the first porous partition wall 15 and the second porous 
partition wall 23 are merely arranged in parallel with the first feeding 
pipe 11 and the second feeding pipe 20, it is possible to simplify a shape 
of the porous partition wall. Even if the feeding pipe and the 
communicating pipe are overlapped with one another, it is not necessary to 
form the porous partition wall into a complex shape. 
Still further, since it is not necessary that the first feeding pipe 11 and 
the second feeding pipe 20 pass through the first porous partition wall 15 
and the second porous partition wall 23, and since it is not necessary 
that the first porous partition wall 15 and the second porous partition 
wall 23 be positioned on extended lines of them, it is possible to form 
the small holes 16, 24 on substantially the entire part of each of the 
porous partition walls, and an opening area of the small holes can be 
sufficiently assured. 
Accordingly, irrespective of the fact that each of the aforesaid problems 
can be solved, the structure in the muffler is simplified and restriction 
in layout about each of the porous partition walls 15, 23, the feeding 
pipes 11, 20, the communicating pipes 30, 31 and the partition walls 4, 5 
and 6 is reduced, resulting in that a degree of freedom in layout of the 
internal elements of the muffler is also increased. 
Further, since each of the feeding pipes 11, 20 is enclosed by the first 
porous partition wall 15 and the second porous partition wall 23, each of 
the first porous partition wall 15 and the second porous partition wall 23 
can be made relatively small in size. In addition, even in the case that a 
plurality of feeding pipes or communicating pipes or the like are present 
near it so as to have a certain restriction in arranging space, they may 
be installed in a relatively easy manner. 
Also, since each of the first porous partition wall 15 and the second 
porous partition wall 23 is bent to form a convex shape toward the center 
of the muffler, these porous partition walls 15, 23 can be made smaller 
than before, and the spaces (the fifth expansion chamber 17 and the sixth 
expansion chamber 25) enclosed by the porous partition walls 15, 23 can be 
made as small as possible. In addition, they are curved, such that their 
arrangement in a narrow space becomes easier, and at the same time, 
rigidity is also increased, resulting in an improved anti-vibration 
characteristic. 
FIG. 7 is a schematic diagram showing another form of the invention. A 
feeding pipe 50 projecting into the first expansion chamber 7, and the end 
51 of the first communicating pipe 30 upstream from the partition wall 4, 
are extended in a lengthwise direction to be overlapped with one another. 
Further, a porous partition wall 52 is arranged between the feeding pipe 
50 and the upstream end 51. The porous partition wall 52 has a structure 
similar to that of the aforesaid second porous partition wall 23, wherein 
many small holes 53 are arranged to enclose either the upstream end 51 of 
the first communicating pipe 30 or the feeding pipe 50. 
As described above, even where the constitution of the muffler is 
simplified and one feeding pipe 50 is installed, with the feeding pipe and 
the communicating pipe extending in a lengthwise direction to be 
overlapped, a complex shape of the porous partition wall 52 can be 
avoided. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.