US 3692142 A
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United States Patent Stemp A 1 Sept. 19, 1972  SPIRAL MUFFLER  Inventor: Leslie William Stemp, Ashford, En-
gland  Assignee: Cowl Industries Limited, Ontario,
Canada  Filed: June 14, 1971  Appl.No.: 152,959
 Foreign Application Priority Data June 19, 1970 Great Britain ..29,825/7O . US. Cl. ..181/50, 181/66, 181/69  lnt. Cl. ..F0ln l/10, F01n1/12  Field of Search ..181/50, 42, 58, 66, 67-70, 181/61-63  References Cited UNITED STATES PATENTS 1,015,698 l/l912 Maximw, ..181/50 1,289,856 12/1918 Maxim ..181/66 2,841,235 7/1958 Curoni ..181/67 3,018,841 1/1962 Gerlich ..l8l/66 3,563,340 2/1971 Duthion ..181/66 FOREIGN PATENTS OR APPLICATIONS 426,769 4/1935 Great Britain ..181/50 495,576 11/1938 Great Britain ..181/66 829,012 2/1960 Great Britain ..181/67 634,222 8/1936 Germany 18 1/66 Primary ExaminerR0bert S. Ward, Jr. Attorney-Rogers, Bereskin & Parr 57 ABSTRACT A mufi'ler or silencer having a spiral duct centrally disposed within a housing, with sound absorbent material between the ends of the housing and the ends of the spiral duct to reduce noise.
11 Claims, 7 Drawing Figures Pmmmswwwn 3.692.142
SHEET 1 0F 2 INVENTOR. LESLIE WILLIAM STEMP PATENTEDSEP 9 m2 SHEET 2 0F 2 4 INVENTOR. LESLIE WILLIAM STEMP SPIRAL MUFFLER This invention relates toan improved muffler or silencer for reducing the exhaust noise of internal combustion engines, intake noise of compressors and the like.
There is a multitude of muffler designs in current use, and many conventional mufflers are reasonably efficient. However, there is room for improvement in sound attenuation and reduction of back pressure, and these qualities are not easy to achieve in a muffler of relatively'small size.
-Objects of the present inventionare to provide a muffler that has excellent sound attenuation characteristics, low back pressure, and relatively small size.
In a preferred form, the invention consists of a generallycylindrical housing having generally conical caps at each end, each cap containing sound absorbing material. A spiral duct is positioned in the housing and it has an inner end which communicates with an inlet pipe extending into the housing through one of said conical caps, and an outer end which terminates near the wall of the housing. The axis of the spiral duct is colinear with the axis of the housing. At least one wall of the spiral duct is lined with sound absorbing material. The spiral duct is separated from each conical cap by means of perforated'plates respectively positioned at each side of the spiral duct, so that the sound absorbing material in the conical caps is exposed, through the perforations in said plates, to the gas flowing through the spiral duct. The gas is discharged from the mufiler in either of two ways: (a) in one embodiment, axially, by means of deflectors which direct the gas from the outer end of the spiral duct through the other of. said conical caps to an outlet pipe extending axially into said second. conical cap, or (b) in another embodiment, tangentially, by means of an opening formed in the wall of the housing, such opening beingin direct communication with the outer end of the spiral duct. I
A preferred embodiment of the invention'is illustrated in'the accompanying drawing, wherein:
FIG. 1 is a plan view of an improved muffler according to the invention, showing in broken lines some of the internal parts of the muffler; I
FIG. 2 is a sectional view, taken along'the line 8-8 of FIG. 1, showing the configuration of a spiral duct contained within the housing;
FIG. 3 is a sectional view taken along the line C-C of FIG. 1;
FIG. 4 is a plan view of a bulkhead contained within the housing of FIG. 1; 2
FIGS. 5a and 5b are plan views of the perforated plates respectively employed at the upstream and downstream sides of the spiral duct; and
FIG. 6 is a plan view showing the shape of a metal piece used for making a conical cap.
- Referring to the drawings, and particularly to FIGS. 1 and 2, an improved muffler according to the invention is generally indicated by reference numeral 10, and it includes a housing ll having a cylindrical central portion 12 and two end caps 13 and 1.4 of generally conical shape. A spiral duct '15 is disposed within the central portion 12 of the housing 11, and it will be described in greater detail below.
. the outer wall of the outermost turn of the spiral duct An inlet pipe 16 extends from the apex of the cap 13 I metal, for example perforated mild steel sheet having about forty percent (40) open area. The ends of the inlet pipe 16 are welded or otherwise securely fastened to the cap 13 and to the bulkhead 17, respectively. The bulkhead 17 is formed with a central opening 18 (FIG. 5a which is of the same diameter as the diameter of the inlet pipe 16 and which is aligned therewith. The interior of the cap 13 is filled with sound absorbing material 19 such as rock wool.
' The axis of the spiral duct 15 is coaxial with the axis of the housing 11, and its width is equal to the'width of the central portion 12 of the housing 1 l. The inner end of the spiral duct 15 is open and is disposed at thecenter of the housing 11; it is in communication with the inner end of the inlet pipe 16..The radius of the spiral duct initially is equal to the radius of the inlet pipe 16, but the radius increases smoothly from the inner end of the spiral ductlS to the outer end thereof. The outer end of'the metal sheet from which the spiral duct 15 is formed is curved inwardly and is secured to 15, as shown at 20, thus forming a cylindrical surface which constitutes the central portion 12 of the housing 11. The spiral duct may be constructed from a plurality of semicylindrical plates fastened together by any suitable means, or from a single piece of sheet metal. T he inner end of the duct 15 terminates in a short bent portion 21, the bight portion of which provides a smooth surface against which the incoming gases flow as they enter the spiral duct 15. The bent portion 21 also pro.- vides a convenient anchor point for one end of a lining 22 which covers one wall of the spiral duct 15, and for one end of a perforated or expanded metal sheet 23, represented in FIG. 2 by broken lines, which keeps the lining 22 in place against the wall of the spiral duct 15. The width of the metal sheet 23 is the same as that of the spiral duct 15. The lining 22 may be of any suitable sound absorbing material capable of withstanding the temperature and forces to which it is subjected, such as rock wool.
Although the lining 22 is shown as attached to only one wall of the spiral duct 15, it will be understood that both walls of the spiral duct 15 could be lined, if desired. However, it has been found that good results may be obtained if the lining is applied to the wall shown, which is on the low pressure side of the gas stream flowing through the spiral duct 15. Similarly, although a perforated sheet 23 is shown for keeping the lining 22 in place, it will be understood that if the lining 22 is of woven material or is otherwise of unitary construction, the lining 22 may be attached to the spiral duct 15 by means of clips, rivets, etc., or it may be formed into a long sheath into which the metal sheet forming the spiral duct 15 may be inserted. Alternatively, the lining may be formed in tubular shape so that it takes the form of the spiral duct 15 itself.
In the embodiment of the invention shown in the drawings, the gases emerge from the muffler axially, and this is accomplished as follows. The gases approaching the outer wall of the central portion 12 of the housing 11 are directed in an axial direction by means of several deflectors 24 towards a bulkhead 25. The bulkhead 25 is similar to the bulkhead 17, except that insteadof having a central opening 18, the bulk- .head 25 has a wide peripheral notch 26 through which the gases enter the end cap 14. A smaller bulkhead 27 is fixed inside the end cap 14 downstream from the bulkhead 25, and it has a similar notch 28 aligned with the notch 26. A channel-shaped plate '29 bridges the notches 26 and 28 of the bulkheads 25 and 27 and provides a passage way for the gases betweenthe spiral duct 15 and an expansion chamber 30 located downstream from the bulkhead 27. An outlet pipe 31 is secured to the end cap 14 at the apex thereof, and communicates at its inner end with the expansion chamber 30, so that gases leave the muffler axially through the outlet pipe 31.
The spiral duct may be spot welded to the bulkheads 17 and 25, or alternatively spiral grooves may be formed in the bulkheads l7 and for receiving the edges of the spiral duct 15. The shape of the spiral duct 15 is also largely a matter of choice; for example, the cross-section of the spiral duct 15 may be rectangular (when viewed at right angles to the axis of the 'mufiler 10), square or circular. The length of the central portion 12 of the housing 11 can also be varied, and may either be less or greater than its diameter. However, for best results the spiral duct 15 should have at least about two and one-half turns; more turns would provide greater sound attenuation at the possible expense of somewhat greater back pressure. The distance between the walls of the duct (hereinafter called duct width) is shown in FIG. 2 as being substantially constant, but this is also a matter of choice and could be modified if desired. For example, the duct width could increase from the inner end of the spiral duct 15 to the outer end; this would give a shorter duct length for a given diameter, and lower back pressure atthejpossible expense of noise attenuation. Conversely if the duct width decreased outwardly, the duct would be longer for a given diameter, and the noise attenuation would likely be somewhat improved, at the possible expense of back pressure.
Instead of discharging the gases into the expansion chamber 30, it is possible to extend the channel shaped plate 29 to the inner end of the outlet pipe 31. In this case, the plate 29 would be shaped so that it would provide a smooth enclosed duct for conveying the gases from the spiral duct 15 to'the outlet pipe 31, with no rapid expansion as provided by the expansion chamber 30. This arrangement may result in somewhat less back pressure.
The construction of the mufi'ler could be simplified considerably and the back pressure reduced still further by removing the gases tangentially from the outside of the central portion 12 of the housing 11, instead of through the outlet pipe 31. This is easily accomplished by merely forming an elongated opening in the periphery of the central portion 12 of the housing 11, for example in the region of the deflectors 24 of the embodiment shown in FIG. 1.
What I claim is:
1. Apparatus for silencing an engine and the like, comprising:
a. a housing having an inlet and an outlet, a side wall,
two end walls, and a longitudinal axis,
b. a spiral duct in said housing, said spiral duct having opposed ends, said spiral duct being positioned with its longitudinal axis parallel with the longitudinal axis of the housing, the ends of said spiral duct respectively being spaced inwardly from the end walls of the housing, said spiral duct having an inlet and an outlet,
c. first 'duct means for conveying gases from the inlet of the housing to the inlet of the spiral duct,
. second duct means for conveying gases from the outlet of the spiral duct to the outlet of the housing, and
e. sound absorbent material substantially filling the spaces between the ends of the spiral duct and the ends of the housing.
2. Apparatus as claimed in claim 1 wherein there are first and second spaced-apart, parallel bulkheads in said housing, said bulkheads being positioned to define a first compartment adjacent to one end wall of the housing, a second compartment adjacent to the first compartment, and a third compartment between the second compartment and the other of said end walls of the housing, said bulkheads having a plurality of openings through which gases may freely pass, said spiral duct being positioned in said second compartment and said sound absorbent material being placed in said first and third compartments.
3. Apparatus as claimed in claim 2 wherein the inlet of the spiral duct is adjacent to the longitudinal axis of the housing, wherein the housing inlet and outlet are respectively positioned in the end walls of the housing, and wherein the second bulkhead is formed with an opening through which gases passing through the spiral duct outlet may enter the third compartment.
4. Apparatus as claimed in claim 2 wherein the side wall of the housing is cylindrical and encloses the second compartment, and the end walls of the housing are conical and respectively enclose the first and third compartments.
5. Apparatus as claimed in claim 2 wherein the bulkheads are formed of perforated metal sheet.
6. Apparatus as claimed in claim 2 wherein at least one wall of the spiral duct is lined with sound absorbent material.
7. Apparatus as claimed in claim 3 wherein there is a third bulkhead in the third compartment, the third bulkhead being positioned between the second bulkhead and the outlet, the third bulkhead forming one wall of an expansion chamber that is in communication with and positioned between the outlet of the housing and the third compartment.
8. Apparatus as claimed in claim 7 wherein the first bulkhead has a central opening, and wherein the first duct means comprises a pipe that is connected between the inlet of the housing and said central opening.
9. Apparatus for silencing an engine and the like, comprising:
a. a housing having an inlet and an outlet, a side wall and two end walls,
b. a spiral duct in said housing, said spiral duct having an inlet and an outlet,
c. first duct means for conveying gases from the inlet of the housing to the inlet of the spiral duct,
d. second duct means for conveying gases from the outlet of the spiral duct to the outlet of the housing, and
e. sound absorbent material secured to at least one wall of said spiral duct and extending substantially the entire length of said spiral duct.
6 10. Apparatus as claimed in claim 9, wherein said length of said spiral duct. sound absorbent material is applied to a wall of said 11. Apparatus as claimed in claim 9, wherein all spiral duct which is on the low r r id f th inner surfaces of said spiral duct are lined with said gases flowing through the spiral duct, and said sound Sound absorbent mammalabsorbent material extends substantially the entire 5