U.S. patent number 3,672,464 [Application Number 05/072,678] was granted by the patent office on 1972-06-27 for muffler for internal combustion engine.
This patent grant is currently assigned to Donaldson Company, Inc.. Invention is credited to John A. Campbell, Douglas W. Rowley.
United States Patent |
3,672,464 |
Rowley , et al. |
June 27, 1972 |
MUFFLER FOR INTERNAL COMBUSTION ENGINE
Abstract
A muffler for internal combustion engines which employs a
converging-diverging nozzle and a length of perforated tubing to
effect sound attenuation with minimum back pressure. The perforated
tube is axially disposed in a cylindrical casing, projecting
forwardly from the muffler outlet and defining alternate flow
passages. The nozzle member is disposed in the perforated tube, its
mouth positioned at the tube inlet and spaced downstream from the
muffler inlet. An imperforate baffle disposed in the annular
passage between the perforated tube and cylindrical casing
intermediate the ends of the nozzle member lengthens the passage
with respect to the alternate, causing the divided gas flows to
travel different distances prior to recombination and exhaust.
Inventors: |
Rowley; Douglas W. (St. Paul,
MN), Campbell; John A. (Minneapolis, MN) |
Assignee: |
Donaldson Company, Inc.
(Minneapolis, MN)
|
Family
ID: |
22109125 |
Appl.
No.: |
05/072,678 |
Filed: |
September 16, 1970 |
Current U.S.
Class: |
181/253 |
Current CPC
Class: |
F01N
1/06 (20130101); F01N 1/003 (20130101) |
Current International
Class: |
F01N
1/06 (20060101); F01N 1/00 (20060101); F01n
001/00 () |
Field of
Search: |
;181/44,47R,48,63,46,57,59,41,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Gonzales; John F.
Claims
What is claimed is:
1. A muffler comprising:
a housing defining a longitudinal chamber having an inlet and an
outlet;
a perforated tube disposed in substantial axial alignment with the
chamber inlet, the perforated tube having an inlet end spaced a
predetermined distance from the chamber inlet and an outlet end
communicating directly with the chamber outlet;
an imperforate nozzle member disposed in the perforated tube, the
nozzle member having a mouth generally conforming to and disposed
at the inlet end of the tube, and a portion converging to a throat
and a portion diverging from the throat to an outlet conforming to
the perforate tube;
and an imperforate baffle disposed in the passage between the
perforated tube and the housing intermediate the ends of the nozzle
member, the baffle constructed and arranged to divert the flow of
exhaust gases between the outer surface of the nozzle means and the
perforated tube.
2. The muffler as defined by claim 1, wherein the housing, the
perforated tube, the nozzle member and the imperforate baffle are
circular in shape and concentrically disposed.
3. The muffler as defined by claim 1, wherein the constituent parts
of the muffler are constructed and arranged to divide flow through
the passage between the perforated tube and the housing and the
passage through the nozzle member essentially equally.
4. The muffler as defined by claim 1, and further comprising a
second perforated tube having an inlet end and an outlet end, the
second perforated tube being of the same size as the first claimed
perforated tube and disposed in spaced axial alignment therewith,
the inlet end of the second perforated tube communicating directly
with the chamber inlet and the outlet end being supported within
the housing by an imperforate member.
5. The muffler as defined by claim 1, wherein the divergent portion
of the nozzle member tapers more gradually than the converging
portion.
6. The muffler as defined by claim 1, wherein the imperforate
baffle supports the perforated tube within the housing.
Description
The invention is directed to mufflers for internal combustion
engines in which sound attenuation is effected with a minimum of
back pressure.
The preferred embodiment of the invention consists of a cylindrical
casing defining a longitudinal chamber and having an inlet and
outlet. A perforated tube of lesser length than the cylindrical
casing is axially and concentrically disposed therein, projecting
forwardly from the casing outlet and supported by one or more
baffles. As described, the casing and perforated tube define a pair
of alternating flow passages (which communicate by virtue of the
perforations), one through the tube and one in the annular area
defined between the tube and casing.
Disposed in the perforated tube at its inlet is an imperforate
convergent-divergent nozzle member the mouth of which is spaced
from the muffler inlet. The divergence of the nozzle member
downstream of its throat is gradual to decrease boundary layer
separation as flow decelerates.
An imperforate tube-supporting baffle disposed intermediate the
ends of the nozzle member fully blocks the annular passage, thus
causing the exhaust gases entering that region to pass inside the
perforated tube upstream of the baffle, along the outer surface of
the nozzle member and out from the tube into the annular passage
beyond the baffle. The nozzle member is shorter than the perforate
tube so that the exhaust gases passing through the alternate flow
paths can recombine prior to exhaust through the muffler
outlet.
We have found that the structure described above is extremely
effective in attenuating sound generated by an internal combustion
engine while keeping back pressure, which hampers efficiency of the
engine, to a minimum. We believe the reasons for this performance
to be at least twofold:
(1) The acoustical impedance of the nozzle throat is greater than
that at the nozzle mouth. Consequently, a portion of the sound
waves attempting to enter the nozzle member are reflected back,
thereby reducing the sound level. (2) By reason of the imperforate
baffle, the annular flow passage is longer than the nozzle-tube
flow passage. Consequently, upon recombination of gases at a point
downstream of the nozzle the sound waves carried in the medium of
the respective exhaust gas flows are out of phase with respect to
each other, and cancellation further reduces the sound level.
The sound attenuation is not done at the expense of an extensive
pressure build-up within the muffler. "Straight through"
construction, which arises from axial and concentric disposition of
the nozzle member and perforated tube with respect to the muffler
inlet and outlet, presents a minimum resistance to exhaust gas
flow. Further, the diverging portion of the nozzle member tapers
gradually to decrease flow separation, thus preserving the
continuous and steady flow characteristic necessary for minimum
pressure build-up.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of a muffler embodying the
inventive principle;
FIG. 2 is an end view of a muffler as viewed from the muffler
intake; and
FIG. 3 is an end view of a muffler as viewed from the muffler
exhaust.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the figures, a muffler intended for use with internal
combustion engines and embodying the inventive principle as
represented generally by the numeral 11. Muffler 11 consists of a
cylindrical casing 12 of predetermined length having annular end
caps 13 and 14 which respectively define the muffler inlet and
outlet.
A tube 15 is axially and concentrically disposed in casing 12, its
outlet end being sealably affixed to end cap 14, as by welding, and
its inlet end spaced from the muffler inlet a predetermined
distance. Tube 15 has a plurality of perforations 16 extending over
the major portion of its length, all of which lie within casing 12.
The outlet end of tube 15 may be slit, as at 17, for connection to
a tailpipe.
Tube 15 is supported internally by a first annular baffle 18 which
includes a plurality of perforations 19, and a second annular
baffle 21 which is imperforate. Baffle 21 is constructed and
arranged to block the annular passage defined by tube 15 and casing
12.
Disposed within tube 15, commencing at its inlet end and projecting
rearwardly therefrom, is a nozzle member 22 having an abruptly
tapering converging portion 23, a throat 24 and a diverging portion
25 which tapers gradually into engagement with the inner surface of
tube 15. Nozzle member 22 is imperforate, and as best shown in FIG.
1, baffle 21 is disposed at a point intermediate its ends. Thus,
the flow of exhaust gases entering the annular passage are forced
inside tube 15 upstream of baffle 21 (as represented by the
arrows), and back out of tube 15 downstream of baffle 21. Thus, it
is apparent that exhaust gases entering the annular passage must
necessarily take a longer journey than those passing directly
through nozzle member 22 and tube 15 prior to recombination
downstream of the nozzle outlet.
Disposed in the muffler inlet is a tube 26 which is of the same
size as tube 15 and is disposed in axial alignment therewith. Tube
26 is also formed with a plurality of perforations 27, all of which
lie within cylindrical casing 12, and is given support by end cap
13 and another annular support member 28. The inlet end of tube 26
may include one or more slits 29 to facilitate connection of
muffler 11 to an exhaust pipe.
The size, shape and arrangement of the constituent parts of muffler
11 are chosen so that the flow of exhaust gases entering tube 26 is
divided as evenly as possible between the longer annular passage
and the passage through nozzle 22 and tube 15. Thus, the flow of
exhaust gases through perforations 27 of tube 26 into the dead end
chamber defined by end cap 13 and support member 28, which assists
in the attenuation of sound to a limited degree. That portion of
the flow proceeding directly to nozzle member 22 is caused by
portion 23 to converge upon throat 24, at which point it attains
its maximum velocity and lowest static pressure. The flow then
proceeds in a smooth pattern by virtue of the gradual divergence of
portion 25 and continues on through tube 15. A portion of the sound
waves existing in the gaseous medium, however, are prevented from
passing through throat 24 by virtue of the increased acoustical
impedance encountered at that point. A portion of the waves are
reflected back, which serves to significantly attenuate the sound
level.
The remaining portion of exhaust gas flow passes through the longer
annular passage, and, at a point downstream of the outlet of
imperforate nozzle member 22 begins to recombine with the flow that
has moved through nozzle 22 and into tube 15. The sound waves
carried through the alternate flow passage, in seeking their paths
of least resistance, must also journey further before the
recombination. As a result, the sound waves moving through the
alternate passages are out of phase by the time they reach a point
of recombination, thus effecting a significant wave cancellation
and further attenuation of sound. The result is a substantial
decrease in the sound level emanating from the internal combustion
engine.
By virtue of the "straight through" construction and the gradual
taper of diverging portion 25, the flow of exhaust gases, whether
through the central or annular passage, encounters minimum fluid
resistance. Thus, the back pressure which hampers operating
efficiency of the internal combustion engine is kept to a minimum
while sound attenuation takes place.
As can be readily observed, the structure which permits this
desirable operation is extremely simple and comprises a minimum
number of parts. This is due in large part to the unique
disposition of nozzle member 22, which not only attenuates sound
and preserves laminar flow, but also defines with baffle 21 a
portion of the longer annular passage which effects the downstream
cancellation of out of phase sound waves.
* * * * *