Silencer for internal combustion engine

Details Silencer for internal combustion engine Silencer for internal combustion engine

2000-02-09

2001-07-17

Nappi, Robert E. (Department: 2837)

Acoustics

Sound-modifying means

Muffler, fluid conducting type

C181S227000, C181S228000, C181S282000

Reexamination Certificate

active

06260659

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silencer for an internal combustion engine suitable for application to a motorcycle or a four-wheeled motor vehicle or the like.
2. Description of Background Art
In an internal combustion engine used in a motorcycle or the like, if an exhaust noise is released as it is into the atmosphere, there occurs an explosive noise. To suppress the generation of such an explosive noise, a silencer is attached to the vehicle for allowing the exhaust gas to pass therethrough and absorbing sound waves to turn down the exhaust noise.
FIG. 6
schematically illustrates a longitudinal sectional configuration of a multi-stage expansion chamber type silencer
1
. The silencer
1
has a generally cylindrical silencer body
2
. The silencer body
2
comprises a circumferential wall
3
, front and rear walls (front and rear partition walls)
4
a
,
4
d
which close the circumferential wall
3
, and partition walls
4
b
and
4
c
as intermediate walls. With these walls there are formed first, second and third expansion chambers (first to third chambers)
5
a
,
5
b
,
5
c.
An exhaust pipe
6
for introducing a gas (also called exhaust gas) G into the silencer body
2
is installed through the front partition wall
4
a
of the silencer body
2
, while a tail pipe
9
for discharging the gas G from the interior of the silencer body
2
is installed through the rear partition wall
4
d
of the silencer body. Further, inner pipes
7
and
8
are installed through the intermediate partition walls
4
b
and
4
c
. In
FIG. 6
, arrows indicate flowing directions of the gas G.
In the silencer
1
shown in
FIG. 6
, the first to third expansion chambers
5
a
to
5
c
are contiguous to one another in three stages, but the silencer
1
can be expressed by way of a single chamber (single expansion chamber) silencer
12
as a model as illustrated in FIG
7
.
As illustrated in FIG
7
, the silencer
12
has a generally cylindrical expansion chamber
14
as a silencer body. The expansion chamber
14
is made up of a circumferential wall
16
having an overall length of L and front and rear partition walls
18
,
20
which close the circumferential wall
16
and which has a diameter of ∅C.
An exhaust pipe
22
with a diameter ∅A for introducing the gas G into the expansion chamber
14
is installed through the front partition wall
18
of the expansion chamber
14
, while a tail pipe
24
with a diameter of ∅B for discharging the gas G from the interior of the expansion chamber
14
is installed through the rear partition wall
20
of the expansion chamber. Also in
FIG. 7
, arrows indicate a flowing direction of the gas G.
A comparison will now be made between the first expansion chamber
5
a
in the silencer
1
illustrated in FIG.
6
and the silencer
12
as a single chamber model illustrated in FIG.
7
. It is seen that the front partition wall
4
a
in the silencer
1
and the front partition wall
18
in the silencer
12
correspond to each other, that the partition wall
4
b
in the silencer
1
and the rear partition wall
20
in the silencer
12
correspond to each other, that the exhaust pipe
6
in the silencer
1
and the exhaust pipe
22
in the silencer
12
correspond to each other, and that the inner pipe
7
in the silencer
1
and the tail pipe
24
in the silencer
12
correspond to each other. Also as to the remaining second and third expansion chambers
5
b
,
5
c
in the silencer
1
, they can be expressed likewise by the silencer
12
as a single chamber model illustrated in FIG.
7
.
In the silencer
12
of
FIG. 7
, a noise deadening characteristic, an engine output characteristic (exhaust blow-through characteristic), and compactness are considered to be important points. It is known that the noise deadening characteristic is improved by enlarging the diameter ∅A of the exhaust pipe
22
and by shortening the distance, a, from a gas outlet end of the pipe
22
to an inner wall
26
of the rear partition wall
20
and the distance, b, from a gas inlet side of the tail pipe
24
to an inner wall
28
of the front partition wall
18
to increase the flow resistance of the exhaust gas G.
However, in the case where the flow resistance of the exhaust gas G is increased by shortening the distance, from the gas outlet end of the exhaust pipe
22
to the inner wall
26
of the rear partition wall
20
or the distance, b, from the gas inlet end of the tail pipe
24
to the inner wall
28
of the front partition wall
18
, there arises the problem that the engine output becomes lower. In other words, there exists a reciprocal relation, so-called trade-off relation, for the noise deadening characteristic such that the exhaust blow-through characteristic of the engine is deteriorated.
In view of the above point and for making a desired noise deadening characteristic and a desired engine output characteristic compatible with each other, the applicant in the present case has experientially designed a silencer so that the ratio of the distance, a, to the diameter ∅A of the exhaust pipe
22
and the ratio of the distance, b, to the diameter B of the tail pipe
24
are (a/∅A)≧1.2 and (b/∅B)≧1.2, respectively.
The length of the exhaust pipe for communication of the expansion chamber (the expansion chamber
5
a
in
FIG. 6
) located on the most upstream side with an exhaust port of the internal combustion engine (not shown) is related to a torque characteristic relative to the rotational speed of the engine, while the diameter of the tail pipe which is open to the atmosphere from the expansion chamber (the expansion chamber
5
c
in
FIG. 6
) located on the most downstream side is related to the displacement of the internal combustion engine and the size of a normal rotational speed range.
Therefore, for attaining optimization while taking balance among the three characteristics of noise deadening characteristic, engine output characteristic and compactness, it has so far been required to adjust the distances a and b in each expansion chamber, adjust the overall length L and adjust the diameter of each inner pipe for connection between adjacent expansion chambers.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention has been accomplished taking the above-mentioned problems into account and it is an object of the invention to provide a silencer for an internal combustion engine which permits a further optimization of both engine output characteristic and compactness while ensuring a desired noise deadening characteristic.
According to the present invention there is provided a silencer for an internal combustion engine having a generally hollow, cylindrical expansion chamber constituted of a circumferential wall and front and rear partition walls disposed in front and rear positions with respect to the circumferential wall. An exhaust pipe is disposed through the front partition wall to introduce a gas into the expansion chamber. A tail pipe disposed through the rear partition wall to discharge the gas from the interior of the expansion chamber. An inside diameter of the exhaust pipe is assumed to be ∅A and the distance from a gas outlet end of the exhaust pipe to an inner wall of the rear partition wall is assumed to be a, the inside diameter ∅A and the distance, a, are in a relation of 0.6≦(a/∅A)<1.2.
According to the invention just described above, by setting the relation between the exhaust pipe inside diameter ∅A and the distance, a, from the exhaust pipe gas outlet end to the inner wall of the rear partition wall at 0.6≦(a/∅A)<1.2, there can be obtained a silencer having an optimum combination of engine output characteristic and compactness while ensuring a desired noise deadening characteristic.
Further, by setting relation between the tail pipe inside diameter ∅B and the distance, b, from the tail pipe gas inlet end to the inner wall of the front partition wall at 0.25≦(b/∅B)<1.2, there can be obtain

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