Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
2000-09-29
2003-02-18
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
C181S272000
Reexamination Certificate
active
06520286
ABSTRACT:
The present invention relates to devices for silencing a flow of gas such as exhaust gasses originating from a combustion device, a method for silencing such a flow, a vehicle comprising one or more such devices and a stationary power generating installation comprising one or more such devices. The invention also relates to a system comprising an engine and a silencer, as well as a method for operating such a system, in which method the combination of an efficient sound attenuation and a low back pressure is used to achieve hitherto unattainable advantages with respect to engine performance and economy.
While a number of silencer designs are known, most of these are not particularly beneficial with respect to flow dynamic properties. As a result of intensive studies of the flow dynamic behaviour and requirements of silencer systems, the invention provides both basic physical principles to be complied with by silencer designs in order to obtain hitherto unattainable combinations of effective noise damping, low back pressure (pressure drop across the silencer device) and small size—and specific novel mechanical design features, such as physical conformations of the passages or bodies involved in the flow path—which co-operate with a suitable overall design to provide superior combinations of performance results.
It is well known within the art to silence a flow of gas by directing the flow into an inlet passage to a container, through one or more chambers in said container intercommunicating by means of passages, through a diffuser associated with one of said passages and into an outlet passage from said container.
In the case of tailor-made solutions for one-off installations or very small production series, application of the traditional method has not been able to provide optimal solutions except in exceptional cases where the element of luck has been a factor. This is due to the fact that the economical and practical possibilities for carrying out experiments and consequent design and/or dimensioning modifications and changes are not at hand.
Furthermore, the large number of parameters and considerations having implications for the sound attenuation in a silencing device have in the past prevented those skilled in the art from designing and dimensioning such a device simply and reliably in such a manner that a desired sound attenuation with an acceptable loss of pressure through the device and acceptable overall dimension were consistently achieved.
One aspect of the present invention, to be discussed in greater detail in the following, relates to a device having a curved passage for interconnecting an acoustic chamber with another acoustic chamber or with an exterior volume. A number of devices having curved passages are known. Thus, U.S. Pat. No. 4,317,502, U.S. Pat. No. 4,635,753, DE 463 156, DE 467 515, DE 570 630, DE 614 930, U.S. Pat. No. 4,579,195, U.S. Pat. No. 3,692,142, DE 26 12 421, DE 27 15 053, U.S. Pat. No. 4,126,205, CH 313 645, U.S. Pat. No. 4,046,219, DE 736 635, SU 165 634, DE 557 140 and DE 469 259 disclose various types of devices having one or more curved passages.
It is characteristic of the devices according to the present invention that they are based on design principles which are aimed at obtaining desired sound attenuation characteristics and at the same time low or very low back pressures. The design principles involve observing certain general physical/mathematical principles in connection with the particular given parameters relating to at least space constraints and the design, the design including of one or more passages leading the flow into and/or out of one or more chambers of the device, as well as one or more diffusers diffusing at least a part of the gas flow through one or more of the passages. Important parameters in this regard are the number and extent of changes of geometric configuration and arrangement and the relative dimensions of one ore more chambers and the passage or passages connecting the chambers or connecting chambers with an exterior volume. as well as the number of changes of cross-sectional are of the gas flow and the values of the individual changes in cross-sectional area. Hereby, very interesting silencer designs have been obtained which combine small size with effective sound attenuation and low back pressure.
One aspect of the invention relates to a device for silencing a gas flow directed therethrough and being adapted for installation in a flow system, said device comprising:
a casing,
at least one acoustic chamber and contained in the casing, said chamber being through-flowed by gas,
at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
said device showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area a
i
and a relatively higher cross-sectional area A
i
,
the device fulfilling the following criteria:
(i) the average sound attenuation {overscore (&Dgr;dB)} conferred by each transition of cross-sectional area, approximated by the following expression:
Δ
dB
_
=
1
n
k
∑
i
=
1
n
log
10
A
i
a
i
,
(
1
)
n being the total number of transitions of cross-sectional area of the device, A
i
being the relatively higher cross-sectional area at the i′th transition of cross-sectional area of the gas flow, a
i
being the relatively lower cross-sectional area at the i′th change of cross-sectional area of the gas flow, k being a constant of the value 6.25 dB,
is at least
8.0 dB when the device comprises no more than two acoustic chambers,
6.0 dB when the device comprises three acoustic chambers,
5.0 dB when the device comprises 4 or more acoustic chambers,
(ii) the pressure loss across each acoustic chamber expressed as the dimensionless parameter &zgr;
j
′, defined as the ratio between the static pressure loss over the chamber and the dynamic pressure at a location in said passage:
ζ
j
′
=
Δ
p
j
1
2
ρ
u
2
,
(
2
)
&Dgr;p
j
being the static pressure loss over the j′th chamber, exclusive of the static pressure loss over a monolith optionally comprised in the j′th chamber, &rgr; being the density of the gas at said location, u being a velocity of the gas at said location, preferably the mean gas velocity,
is at the most 1.0.
Another aspect of the invention is the above-mentioned aspect comprising a curved passage connecting two acoustic chambers or connecting an acoustic chamber with an exterior environment. This aspect can be defined as a device for silencing a gas flow directed therethrough and being adapted for installation in a flow system, said device comprising:
a casing,
at least one acoustic chamber contained in the casing, said chamber being through-flowed by gas,
at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
said device showing at least two transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area a
i
and a relatively higher cross-sectional area A
i
,
at least one passage selected from said at least one passage being curved,
wherein the following applies to at least one selected chamber selected from said at least one acoustic chamber:
the mean cross-secti
Frederiksen Eyvind
Frederiksen Lars
Frederiksen Svend
Sorenson Spencer C.
Birch & Stewart Kolasch & Birch, LLP
Dang Khanh
Silentor Holding A/S
LandOfFree
Silencer and a method of operating a vehicle does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silencer and a method of operating a vehicle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silencer and a method of operating a vehicle will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3170635