U.S. patent number 3,744,589 [Application Number 05/261,373] was granted by the patent office on 1973-07-10 for swirling flow muffler.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Robert C. Mellin.
United States Patent |
3,744,589 |
Mellin |
July 10, 1973 |
SWIRLING FLOW MUFFLER
Abstract
In preferred form, a sound attenuating device receiving internal
combustion engine exhaust gases including a closed cylindrical body
having tangentially attached inlet and outlet ports providing
unbaffled helical flow of the gases through the cylindrical body. A
first layer of acoustical material is positioned within said closed
cylindrical member in conformance to the interior surface thereof
and can be spaced therefrom depending upon the particular material
used. A second layer of acoustical material is concentrically
disposed about a cylindrical resonator attached to one end of the
closed cylindrical body. The second layer of acoustical material
substantially conforms to the exterior surface of the resonator and
can also be spaced therefrom depending upon the materials used. A
perforated cylindrical member having a closed end is attached to
the other end of the cylindrical body. The closed end of the
perforated cylindrical member extends toward but is spaced from the
end of the resonator which extends approximately half the axial
length of the closed cylindrical body. Upon entrance into the inlet
port, a substantial portion of the sound waves impinge against both
layers of acoustical material so that both high frequency and
medium frequency sound waves are absorbed by the material as the
gases progress through the unbaffled helical flow path to the
outlet port. The annulus itself is effective to cancel wavelengths
associated with the circumferential distance. In addition, the
muffler chamber exhibits lined expansion chamber noise reduction
characteristics. This arrangement provides desirable sound
attenuating results without creating a substantial pressure drop
across the device.
Inventors: |
Mellin; Robert C. (Brighton,
MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
22993017 |
Appl.
No.: |
05/261,373 |
Filed: |
June 9, 1972 |
Current U.S.
Class: |
181/256 |
Current CPC
Class: |
F01N
1/04 (20130101); F01N 1/10 (20130101); F01N
2490/15 (20130101) |
Current International
Class: |
F01N
1/10 (20060101); F01N 1/04 (20060101); F01N
1/02 (20060101); F01N 1/08 (20060101); F01n
001/10 () |
Field of
Search: |
;181/40,42,50,55,57-59 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Gonzales; John F.
Claims
I claim:
1. A sound attenuating device for an internal combustion engine
characterized by low pressure drop thereacross comprising: means
defining a generally cylindrical silencing chamber having end walls
and a longitudinal axis; inlet and outlet conduits communicating
with axially spaced points on said means and tangentially disposed
with respect thereto adjacent the outer periphery thereof and
extending into the interior of said body to direct exhaust gases
from said engine in an unbaffled helical flow path through said
chamber; a first cylindrical body of acoustical absorbing material
coaxially disposed within said chamber and adjacent to the outer
periphery of said chamber so that its inner periphery is exposed to
sound waves in the flow path for absorbing the latter; and a second
cylindrical body of acoustical absorbing material coaxial with said
chamber and within said first mentioned body of acoustical
absorbing material interiorly peripherally bounding the exhaust gas
helical flow path on its outer surface to helically direct the gas
flow against the interior surface of said first cylindrical body of
acoustical material, the annular circumference being effective to
attenuate related wavelength sound waves and said bodies of
acoustical material being effective to absorb ranges of sound
wavelengths in the high and medium portion of the frequency
spectrum, whereby said device cancels a substantial portion of
sound energy in the fluid pass therethrough.
2. A sound attenuating device for an internal combustion engine
characterized by low pressure drop thereacross comprising: means
defining a generally cylindrical silencing chamber having end walls
and a longitudinal axis; inlet and outlet conduits communicating
with axially spaced points on said means and tangentially disposed
with respect thereto adjacent the outer periphery thereof; a first
cylindrical body of acoustical absorbing metal foam coaxial with
said chamber and inside the same adjacent to and spaced from the
outer periphery of said chamber so that its inner periphery is
exposed to sound waves in the flow path for absorbing the latter; a
second cylindrical body of acoustical absorbing metal foam
interiorly peripherally bounding the exhaust gas helical flow path
on its outer surface to direct the sound waves against the interior
surface of said first cylindrical body of metal foam; said bodies
consequently defining a flow path space therebetween and said inlet
and outlet conduits extending into the interior of said first body
directing exhaust gases from said engine in an unbaffled helical
flow path through the space in said chamber; and a resonator member
centrally disposed within said second cylindrical body and
acoustically coupled to said cylindrical chamber, the annular
circumferential path being effective to attenuate sound waves of
related wavelength and said bodies of acoustical metal foam being
effective to absorb high and medium frequency ranges of sound
wavelengths; said resonator member further attenuating low
frequency sound waves in the exhaust gases, whereby said device
cancels a substantial portion of sound energy in the fluid passing
therethrough.
3. A sound attenuating device as described in claim 2 further
comprising the resonator member being attached to one end of said
means and extending substantially to the mid-portion of said
silencing chamber; and a perforated second resonator member
attached to the opposite end of said means and extending toward
said resonator but terminating so as to provide a space
therebetween; said resonators being acoustically coupled to said
silencing chamber whereby said bodies of acoustical metal foam, the
annular circumferential path and said resonators cooperate to
substantially cancel the sound energy in exhaust gases flowing
through said device.
Description
The present invention relates to a swirling flow muffler and more
particularly to a swirling flow muffler including cylindrical
bodies of acoustical material bounding a helical flow path
therethrough and absorbing both high frequency and medium frequency
sound energy in the exhaust gases received from an internal
combustion engine.
Heretofore, it has been proposed to absorb acoustic energy by
passing a fluid medium through a sound attenuating container
containing flow obstructing baffles or other flow interfering
structures utilized to create helical flow path therethrough. In an
arrangement using baffles or other fixed members to produce a
circuitous flow through the unit, sound energy is effectively
dampened by virtue of the viscous dissipation in the circuitous
flow path and cancellation in resonator components. Use of these
dissipation members, however, necessarily obstructs flow through
the muffling container consequently developing an undesirable
exhaust gas back pressure. Therefore, it is a purpose of this
invention to provide a sound attenuating device developing a
swirling flow through a cylindrical muffler container without
creating a significant pressure drop thereacross eliminating
undesirable engine back pressure.
A further purpose of this invention is to provide a sound
attenuating device incorporating cylindrical bodies of acoustical
material to dampen both high and medium frequency sound energies as
the gases transverse a helical flow path. These features are
accomplished by providing a closed cylindrical muffler container
having spaced outlet and inlet ports tangentially attached to the
container requiring the gases to impinge against surfaces of the
cylindrical bodies creating a helical flow path. A first
cylindrical body of acoustical material is placed adjacent the
inside surface of the cylindrical muffler container while a second
cylindrical body of acoustical material having a reduced diameter
is positioned coaxially within the first body so that the flow path
is defined between the inner surface of the first body and the
outer surface of the second body. In this manner a portion of the
sound waves are required to be exposed to the inside surface of the
first body which dampens both high frequency and medium frequency
sound energy while a substantial portion of the sound waves are
also exposed to the outer surface of the second acoustical body
which likewise dampens both high and medium frequency sound energy.
In addition, the device is effective to also attenuate a portion of
the sound energy by virtue of the wavelengths associated therewith
cancelling through wave interference on the annular circumference
of the acoustical bodies. Further reduction in sound energy is
obtained by the entire unit acting as a lined expansion chamber.
The two cylindrical bodies of sound absorbing material and the
helical flow path combine to substantially eliminate high and
medium frequency sound energy normally existing in vehicle exhaust
gases.
A general object of the present invention is to provide an improved
acoustical absorbing swirling flow muffler providing an unbaffled
helical flow path therethrough without generating a substantial
back pressure.
Another object of the subject invention is to provide an improved
muffler having a swirling helical flow path that is created by
attaching inlet and outlet conduits to the muffler at tangential
positions and including spaced cylindrical bodies of acoustical
material with the muffler defining the flow path substantially
dampening both high and medium frequency sound energies of the
gases flowing therethrough.
A further object of the subject invention is the provision of an
improved sound attenuating swirling flow internal combustion engine
exhaust gas muffler including a closed cylindrical container having
tangentially connected inlet and outlet conduits creating a helical
flow path for the gases received in the container, a first
cylindrical body of sound absorbing material coaxial with the
container with its outer surface spaced therefrom, a second
cylindrical body of sound absorbing material coaxial with the first
body and spaced therefrom the space between the inner surface of
the first body and the outer surface of the second body defining
the flow path so that a substantial portion of the sound waves
contact these surfaces, and a resonator tube coaxially within the
second body so that a substantial portion of the sound energy in
the exhaust gases is cancelled or absorbed by the absorbing
material, the annular dimensions of the bodies and the
resonator.
A further object of the subject invention is to provide an improved
sound attenuating swirling flow muffler for use with internal
combustion engines providing an unbaffled flow path therethrough
and incorporating sound absorbing material resulting in sound
absorption quality achieved by presently used mufflers in a more
economical fashion without creating a substantial pressure drop
thereacross.
The novel features which I believe to be characteristic of my
invention are set forth with particularity in the appended claims.
My invention itself, however, both as to its organization and
method of operation may be best understood by reference to the
following description taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a perspective view with portions broken away of a
specific embodiment of the subject invention.
FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 1.
FIG. 3 is a cross-sectional view taken on line 3--3 of FIG. 2.
FIG. 4 is a cross-sectional view of a modified form of the subject
invention.
For purposes of illustration reference is made to FIG. 1 wherein a
swirling flow muffler assembly 10, constructed in accordance with
this invention, is illustrated as including a cylindrical container
12 having a longitudinal axis 13 and including closed ends 14 and
16. Inlet conduits 18 and 20 are tangentially connected to the
closed cylinder 12 adjacent the closed ends 14 and 16,
respectively. An outlet conduit 22 is tangentially connected to the
cylindrical container 12 near its mid-portion as shown. A first
cylindrical body 24 of sound absorbing or acoustical material is
positioned within the closed cylinder 12 but spaced therefrom as
indicated at 25. The body 24 can be positioned in engagement with
the inner surface of the cylinder 12 if desired. A second
cylindrical body 26 of sound absorbing or acoustical material
coaxially extends approximately half the axial length of the closed
cylinder 12 and is connected to end 14 at an attached stiffening
plate 15. It also is concentrically disposed about a first
cylindrical sleeve 28 of a resonator assembly 30 while being spaced
therefrom as indicated at 27. The body 26 can also be placed in
engagement with the outer surface of sleeve 28 if desired. The
sleeve 28 is also connected to the plate 15 on end 14 of the closed
cylinder 12 and has a cylindrical plate 32 containing an aperture
34 secured to its free end 36. The plate 32 receives a relatively
smaller tubular sleeve 38 which is retained in the aperture 34 of
plate 32. The smaller sleeve 38 extends approximately half the
axial length of sleeve 28 and has a portion 39 protruding from the
sleeve 28 as shown in FIG. 1. The muffler assembly 10 also includes
perforated cylindrical member 40 attached to a stiffening plate 17
secured to end 16 of cylinder 12 and extends inwardly toward end 36
of the sleeve 28. The perforated cylinder 40 includes a closed end
42 so that gases entering inlet 20 will encounter the perforations
in the sleeve but cannot pass through the end thereof.
The inlet conduits 18 and 20, as previously mentioned, are
tangentially connected to the cylindrical container 12 and extend
into space 43, of the embodiment of the invention shown in FIGS.
1-3, so that a helical flow path is created causing the gases to
follow a spiral path until they exit outlet 22. When the inlet
conduits are connected to respective manifolds of an internal
combustion engine, such as those present in a V-type engine, the
gases are received within the space 43 and traverse the unit to
outlet 22. It is apparent that a major portion of the gases will
come into direct contact with inner surface 44 of the first body 24
so that a substantial portion of the sound waves in the gases will
be dampened by the absorption qualities of the material forming the
body 24 as they pursue the helical swirling flow path through
muffler 10. Also, as the gases flow through the muffler 10, a
portion of the sound energy will also be dampened by virtue of the
wave interference around the annular circumference and the lined
expansion chamber characteristic of the entire unit. The second
body 26 of acoustical material is positioned so that a portion of
the sound waves will necessarily engage its outer surface 46 so
that it will be effective to likewise dampen a portion of the sound
energy present in the fluid as it flows through its helical path in
the unit. In order to assure dampening of low frequency acoustical
energy in some installations it would be necessary to incorporate
the resonator assembly 30 as illustrated in FIG. 1. Likewise, the
cylindrical member 40 is effective as a resonator to dampen low
frequency energy existing in the fluid when received by the
swirling muffler 10. More specifically, the perforated cylindrical
resonator 40 attenuates sound frequencies in the range of 85 Hz.
The resonator assembly 30, including sleeves 28 and 38, is designed
to provide maximum attenuation sound frequencies in the vicinity of
200 Hz. Since the bodies 24 and 26 of acoustical material are
effective to dampen sound energy having frequencies above 500 Hz
with excellent dampening characteristics above 1,000 Hz, the
assembly 10 is effective to substantially dampen vehicle engine
sounds at all frequency levels.
While the embodiment shown, for purposes of illustration only,
includes the resonator assembly 30 and the perforated cylindrical
sleeve 40, it is not essential that these units be provided in
every installation. Desirable results can be obtained by
positioning the second body 26 of acoustical material relative to
the first body 24 so that the sound waves will be required to
substantially engage both of these layers as the gases enter the
inlet conduits 18 or 20 and traverse the unit to outlet 22 through
the helical path which must necessarily result because of the
tangential connection of the inlet 18 and the outlet port 22.
Further, the acoustical characteristics of the swirling flow
muffler 10 can be enhanced by extending the axial length of the
second body 26 of acoustical material for the full length of the
unit so that it engages end 16. Of course, this would eliminate use
of the resonators 30 and 40.
While two inlets 18 and 20 are shown, the unit would be equally
operative if one inlet only were used and the outlet was positioned
at the end remote from the inlet, for example at end 16 away from
inlet 18, so that the gases would be required to travel the full
length of the muffler unit 10.
The bodies 24 and 26 of acoustical material can be composed of any
material which is capable of resisting the heat applied by internal
combustion engine exhaust gases. Examples of acceptable materials
include metal foams, perforated metal or various fiberglass
compositions, any of which are well known in the art. In a specific
embodiment, a metal foam was used which was pressed to 25 percent
density from an initial thickness of one-half inch, finally
resulting in a layer of 1/10 inch thickness. A 3/4 inch space 48
was provided between layer 24 and the inner surface of the closed
cylinder 12 while a 3/8 inch space 50 was provided between layer 26
and the first sleeve 28 of the resonator assembly 30. The metal
foam can be a nickel alloy or any other metal composition but an
iron or iron-chromium composition would be preferable because they
provide better durability characteristics. As shown in FIG. 4, the
bodies 24 and 26 of acoustical material can be of a fiberglass
composition and can be of a thickness to engage the inner surface
of the container 12 and the outer surface of the sleeve 28. It is
necessary that the fiberglass be heat resistant while providing
sound dampening qualities. Use of any desirable material for the
bodies 24 and 26 is, of course, within the purview of this
invention.
In operation, engine exhaust gases enter inlet conduits 18 and 20
and follow a helical flow path until they exit outlet conduit 22.
While following the helical path, a major portion of the sound
waves contact surfaces 44 and 46 of the bodies 24 and 26 allowing
the acoustical material to absorb a significant portion of the
sound energy at high and medium frequencies. A portion of the sound
energy is canceled because the wavelengths are related to the
annular circumferential distance. The entire unit also acts as a
lined expansion chamber for sound reduction. The resonator assembly
30 can be tuned or acoustically coupled to the container to meet a
particular requirement and cancel a substantial portion of the
remaining low frequency sound energy.
The swirling flow muffler 10 of the subject invention is capable of
providing desirable sound attenuation results while creating a
significantly low pressure drop across the unit. This is primarily
due to the fact that the gases flow through an unbaffled path and
are not required to pass through a sound absorbing material in
traversing the muffler 10.
While a preferred embodiment of the subject invention has been
described for purposes of illustration, it is not intended to limit
the scope of my invention except as required by the following
appended claims:
* * * * *