Exhaust silencer and communicating pipe thereof

Details Exhaust silencer and communicating pipe thereof Exhaust silencer and communicating pipe thereof

2000-02-04

2001-06-05

Nappi, Robert E. (Department: 2837)

Acoustics

Sound-modifying means

Muffler, fluid conducting type

C181S281000, C181S282000, C181S269000, C181S268000, C181S227000, C181S228000, C181S251000, C181S255000

Reexamination Certificate

active

06241044

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust silencer of an internal combustion engine used for construction equipment and the like and a communicating pipe thereof.
2. Description of Related Art
An exhaust silencer called a “muffler” is connected to an exhaust pipe of an internal combustion engine used for a construction equipment etc. for reducing exhaust noise from a combustion chamber.
Conventionally, various arrangements are known for the exhaust silencer. In an internal combustion engine of construction equipment, a multistage-expansion type in which sound is damped by repeating contraction and expansion of exhaust gas and a resonant type in which the exhaust gas is resonated for damping sound are known as conventional examples of the exhaust silencer.
A conventional example of the multistage-expansion type exhaust silencer is shown in FIG.
15
.
In
FIG. 15
, the conventional exhaust silencer
100
has three partitions
52
A to
52
C aligned in an axial direction for partitioning an inside of a drum-shaped body
51
into four chambers
51
A to
51
D, a communicating pipe
53
supported by the partitions
52
A to
52
C coaxially with the body
51
, an inlet pipe
54
with an end and intermediate portion thereof being secured to the body
51
to face the uppermost-stream chamber
51
A, and an outlet pipe
55
with an end and intermediate portion thereof being secured to the body
51
to face the lowermost-stream chamber
51
D.
Among the partitions
52
A to
52
C, a large opening
52
D to intercommunicate adjacent chambers is formed on the partitions
52
A and
52
C supporting both end sides of the communicating pipe
53
. Both ends
53
A of the communicating pipe
53
respectively facing the first chamber
51
A and the fourth chamber
51
D is closed, and a large number of communicating hole
53
B is formed on a circumference of the communicating pipe
53
.
An end
54
A of the inlet pipe
54
is closed and a plurality of communicating hole
54
B is formed on a circumference of the communicating pipe
54
. The outlet pipe
55
has a plurality of communicating hole
55
B and an end being open to the air.
Flow of the exhaust gas sent from the outlet pipe is straightened in radial direction by the communicating holes
54
B of the inlet pipe
54
and is sent to the first chamber
51
A, and the exhaust gas is damped by being sent from the first chamber
51
A to the second chamber
51
B through the opening
52
D. Subsequently, the exhaust gas flows to inside of the communicating pipe
53
through the communicating holes
53
B, circulates with angle thereof being changed into an axial direction, and is sent to the third chamber
51
C through the communicating holes
53
B. Further, the exhaust gas is sent from the third chamber
51
C to the fourth chamber
51
D through the opening
52
D to flow into the outlet pipe
55
through the communicating holes
55
B, which is discharged into the air.
Accordingly, the circulating exhaust gas repeatedly experiences total of four contractions and expansions by the two openings
52
D and the two communicating holes
53
B, thereby conducting so-called multistage-expansion type damping. Especially, the exhaust gas passes a predetermined length (a predetermined time) in the communicating pipe
53
while being contracted without full expansion, thus experiencing effective damping effect.
However, following disadvantage occurs in the multistage-expansion type exhaust silencer.
Though the opening
52
D for contracting the exhaust gas is formed on the partitions
52
A and
52
C for dividing adjacent chambers, sufficient damping effect cannot be obtained when the opening area of the opening
52
D is large.
More specifically, the opening
52
D is an opening formed on the partitions
52
A and
52
C and there is only small length in the gas flow direction. Accordingly, rectification effect is deteriorated when the opening are is enlarged in accordance with increase in flow velocity of the exhaust gas.
Accordingly, when the rectification effect is lowered by enlarging the opening
52
D of the respective partitions
52
A and
52
C in the conventional example, though there are apparently four damping chambers (the first chamber
51
A to the fourth chamber
51
D), only two practically effective damping chambers, i.e. upstream chamber and lower-stream chamber provided on both sides of the central partition
52
B, can be established, which deteriorates noise reduction effect.
A conventional example of resonant type exhaust silencer will be described below.
Generally, the resonant type exhaust silencer has a plurality of chamber inside drum-shaped body divided by partitions, a part of the plurality of chambers being a resonant chamber for damping the exhaust noise.
For example, the resonant chamber is formed on a position between two damping chambers. A communicating pipe stretches over the two damping chambers sandwiching the resonant chamber and passes through the resonant chamber. An intermediate portion of the communicating pipe is exposed to the resonant chamber, and a large number of communicating holes are formed on a circumference of the intermediate portion to intercommunicate an inside of the communicating pipe and an inside of the resonant chamber.
A substantial part of the exhaust gas sent from the upstream damping chamber is sent to the lower-stream chamber through the communicating pipe and the rest is sent to the resonant chamber through the communicating holes. The exhaust gas (pressure wave thereof) reflects in the resonant chamber to reduce energy thereof especially on a resonant range thereof. The exhaust gas returned from the resonant chamber to the communicating pipe by pulsation etc. joins the exhaust gas flowing toward the lower-stream dumping chamber.
However, following problems occur in the resonant type exhaust silencer.
First, only specific frequency of the exhaust noise is damped in the resonant chamber and noise reduction for the entire range of the exhaust noise cannot be expected.
Since the resonant chamber has to be tuned for each type of the internal combustion engine, which complicates design and deteriorates at none-tuned frequency.
Further, since a large space is required for the exhaust silencer to have the resonant chamber, the size of the exhaust silencer itself has to be made large.
A combination of the above multistage-expansion type and the resonant type has been developed.
Since the ordinary multistage-expansion type exhaust silencer alternately circulates the exhaust gas between the inside of the pipe and the damping chamber through a pipe hole to damp the exhaust noise, resistance is caused to raise backpressure by repeating contraction and expansion of the exhaust gas passing the pipe hole.
To solve the above disadvantage, a control valve has been used for controlling the backpressure (Japanese Patent Laid-Open Publication No. Hei 11-22444).
Though the above arrangement is basically a multistage-expansion type having a plurality of damping chamber inside a cylindrical shell, a communicating pipe passing through, for instance, three damping chambers are provided, and a controllably openable control valve is provided inside the communicating pipe to a position corresponding to an intermediate chamber.
At low engine speed, the control valve is closed to shut the communicating pipe. Accordingly, the exhaust gas passing the communicating pipe enters into the intermediate damping chamber from upstream side relative to the control valve and is discharged to lower-stream side of the communicating pipe relative to the control valve. In other words, the intermediate damping chamber functions as a multistage-expansion type exhaust silencer, so that damping effect can be improved.
On the other hand, the control valve is opened at high engine speed to release shutting of the communicating pipe. Accordingly, a part of the exhaust gas passing the communicating pipe directly flows into the lower-stream damping chamber and another part enters into and go out of the intermediate da

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