Motor vehicles – Power – Hoods
Reexamination Certificate
2001-12-05
2004-04-13
Johnson, Brian L. (Department: 3618)
Motor vehicles
Power
Hoods
C180S069230, C181S224000, C181S226000, C293S117000, C454S900000
Reexamination Certificate
active
06719078
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a ventilable silencer unit and a ventilable silencer device, which have both a ventilating function to ventilate cooling air to the engine of an automobile, for example, and a silencing function to silence the noises to be radiated from the inside of the engine room or the like.
BACKGROUND ART
The noises of the automobile such as a car, a motor truck or an auto bus are coarsely divided into internal ones, to be felt by a driver or passenger, and external ones, to be felt by outside persons. Individual noise controls have been made from the viewpoints of improving the marketability and preventing the noise pollution.
The external noises are coarsely classified according to their sources into engine noises, drive line noises, exhaust line noises and tire noises. On the other hand, these engine noises contain not only the mechanical noises made by the engine body but also intake line noises or cooling fan noises.
Especially in recent years, the problem of external noises has risen, stressing the idle noises of a Diesel engine. Against the sound, as radiated from the engine, of a higher contribution in the external noises, there has been made a control for reducing the external noises by arranging a shielding cover
74
having sound absorbing and shielding characteristics sideways or below an engine
70
, as shown in
FIG. 14
, to absorb or shield the noises to be radiated from the engine block or oil pan.
Where cooling air is taken into a radiator
72
from a ventilating passage
75
of a front grille
73
by a fan
71
, however, the noises which are radiated forward of the vehicle from the ventilating passage
75
of the front grille
73
are loud even if the engine room
72
is surrounded by the shielding cover
74
. Thus, there arises a problem that the external noises cannot be effectively reduced. Additionally, the noises raising the problem in the external noises of the engine
70
have a relatively low frequency, around 1 KHz, and a large wavelength. These noises are hard to silence by the shielding cover
74
or a sound absorbing member attached to the cover
74
. As a result, they are not absorbed by the shielding cover
74
, but rather are reflected. Since these reflected noises additionally leak from the ventilating passage
75
, there arises a problem that the external noises are more difficult to reduce.
On the other hand, the space around the engine room of the automobile is restricted, and it is desired to make the weight as small as possible. Therefore, the ventilable silencer device for the front grille of the automobile is required to be relatively light and thin in the ventilating direction and to have a wall shape sparing the space.
In Japanese patent application Kokai publication No. 8-177456, for example, there has been proposed a silencer which has an air resistance reduced at the ventilating time by arranging the Helmholtz type silencer in the partition portion around a partitioned air passage.
However, this silencer is troubled by a problem that the Helmholtz type silencer employed is a resonator for a single frequency, and therefore it is not suited for a wide band range. Against the noises, such as the engine noises, containing frequency components of the wide band range and having a substantially homogeneous acoustic pressure distribution around the radiator or in front of the vehicle, it is necessary to provide a silencer covering a plurality of frequencies.
Therefore, the independent air passages have to be individually provided with Helmholtz type resonators of different resonance frequencies or different shapes. As a result, the entire structure is complicated, raising a problem in that the manufacturing cost is raised.
In addition, the Helmholtz type resonance frequencies are determined depending upon many factors, including the sound velocity, the diameter of an introduction hole, the number of introduction holes, the thickness of the introduction hole portion, and the volume, thereby raising the problem that the design is complicated.
Here, if the Helmholtz type resonance frequency f is expressed for the sound velocity c, the diameter d of the introduction holes, the number k of introduction holes, the volume V, and the thickness tc of the introduction hole portions:
f=
(
c/
2&pgr;)×
SQRT
(
C
0
/V
),
wherein:
&bgr;=&pgr;/2; and
C
0
=k
&pgr;(2
d
)
2
/(
tc+&bgr;×d/
2).
In the case of the Helmholtz type resonance silencer, the structure is complicated and uses a large space so that it is hard to mount in a silencer device required to be thin for the front grille or the like. Moreover, the silencing frequency is single, so it is difficult to enhance the noise reducing effect over a wide band and against the engine noises.
Where the resonance silencer is employed in the front grille or like of the automobile, moreover, it cannot be monolithically molded by a molding method, such as an injection molding method using a synthetic resin or a metal. This requires a step of fixing the silencer, manufactured at a different step and suited for the frequency of noises to be silenced, on a passage wall, thereby raising the manufacturing cost.
In Japanese Patent Application No. 10-305306, on the other hand, we have proposed a silencer device
80
in which a branch passage
82
having a fixed sectional shape is arranged in parallel with a main passage
81
and in which an entrance opening
83
and an exit opening
84
of the branch passage
82
are opened in front of and at the back of the main passage
81
, as shown in FIG.
15
.
This silencer device is effective for the case in which the depth in the ventilating direction can be sufficient. Against the noises containing a low-frequency band, however, there arises a problem that the silencer device is hard to apply where the depth is restricted, as in the front grille of the automobile.
On the other hand, this silencer is characterized to silence both the sound waves of a fundamental frequency determined by the length of the silencing passage and the sound waves of a frequency which is the fundamental frequency multiplied by an integer. However, this silencer is troubled by a problem that its noise reducing effect is insufficient by any means against noises such as the engine noises covering a wide frequency band from a low frequency.
The present invention has been conceived to solve the above and/or other problems, and has an object to provide a silencer unit and a silencer device which can be applied to a portion such as the front grille or bumper of an automobile, and to not take up a large area in a ventilation front, or a large depth in a ventilating direction.
Another object of the present invention is to provide a ventilable silencer unit and a ventilable silencer device, which can not only reduce noises, such as the external noises of an engine over a relatively wide frequency band, but also retain the draft, such as cooling air into the engine room, sufficiently.
DISCLOSURE OF THE INVENTION
A ventilable silencer unit and a ventilable silencer device for achieving the objects described above are constructed in the following manners.
1) According to the present invention, there is provided a ventilable silencer unit comprising a box body including, a ventilation portion, a silencer portion adjacent to said ventilation portion and a dividing partition located between said ventilation portion and said silencer portion,
said ventilation portion is formed of a ventilating passage opened through front end and back end of said box body.
said silencer portion being formed by closing front end and back end of said box body and including at least one partition plate to make a plurality of silencing passages of different length,
each of said silencing passages communicating with said ventilation passage through at least one opening formed in said dividing partition, and,
at least one of said silencing passages being provided with at least one passage extending partition to extend the length of said silencing passage.
These plur
Isuzu Motors Limited
Johnson Brian L.
Phan Hau
Staas & Halsey , LLP
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