US 3927731 A
A muffler silencer having two coaxial, opposed inlets leading to a spiral duct centrally disposed within a housing, the outlet of the spiral duct being connected to an outlet extending from the body of the housing.
Description (OCR text may contain errors)
[ Dec. 23, 1975 United States Patent 1191 Lancaster MUFFLER WITH SPIRAL DUCT AND 2,468,384 4/1949 Tyskewicz............................. 3,018,841 3,066,755
1/1962 Gerlich............ 12/1962 DOUBLE INLETS  Inventor:
Diehl 3,400,784 9/1968 Thrasher.......... 3,692,142 3,744,589
Stemp.......... 7/1973 Canada I Primary Examiner-Ge0rge H. Miller, Jr.  Flled' 1974 Assistant ExaminerVit W. Miska 2 11 Appl. No.1 459,840
Attorney, Agent, or Firm-Rogers, Bereskin & Parr Sa H e mma 1 1mm d ewm S W e D- 0.1 e l b .md X C ayn T w a C m A m R wen. T tcs S t M .mmm v 01 MM t wn t mw h e Om e umm mmu 0 U Akh 8 7 6 N6 1 7 Nw l 5 F5 m0 m5 4 l "00 1 mm. aw L C d UIF 1]] 2 00 555 [1:1
0 .m S u 0 h e m s f m o u y g d .1 F b g e.m r D m f 4 00 .mm d m n .l mC a3 t e 1 u o m m 6 6 1 00 M M A" .lD m Sm mm 1 mAm 0 am REM I9 NH U3 8 B O 61 2 U.S. Patent Dec. 23, 1975 MUFFLER WITH SPIRAL DUCT AND DOUBLE INLETS This invention relates to an improved muffler or silencer for reducing the exhaust noise of internal combustion engines and the like. I
A number of prior mufflers have utilized spiral ducts for conveying exhaust gases through the muffler. An advantage of such mufflers is that it is possible to obtain a relatively long effective duct length (and hence good noise attenuation characteristics) in a muffler of comparatively small size. However, even with spiral ducts it is not easy to. achieve-satisfactory noise attenuation in a muffler of small size, without sacrificing efficiency.
Objects of the present invention are to provide a muffler that'has excellent sound characteristics, low back pressure, and relatively small size.
In a preferred form, the invention consists of a generally cylindrical housing having an inlet at each end of the housing, a spiral duct centrally disposed within the housing and which has an inner end that is in communication witheach of the housing inlets, and an outlet which is connected to an opening in the circumferential wall of the housing. The spiral duct is positioned with its axis parallel to'the axis of the housing, and its outer ends are preferably spaced from the end walls of the housing to provide spaces in which sound absorbent material may be installed By providing two inlets, the radius of the spiral duct atits inner end can be much smaller than otherwise, and thus the diameter of the housing will be kept to a minimum. Also, by providing opposed inlet pipes, there tends to be some cancellation of noise from cylinders which are not firing in step.
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;
FIG. 2 is a sectional view, taken along the line 2-2 of FIG. 1;
FIG. 3 is a perspective view showing the muffler of FIG. 1 with a tailpipe which extends at right angles to the axis of the muffler; and
FIG. 4 is a perspective view showing the muffler of FIG. 1 with a tailpipe which is parallel to the axis of the muffler.
Referring to the drawings, and particularly to FIGS. 1 and 2, an improved muffler according to the present invention is generally indicated by reference numeral 10, and it includes a housing 11 having a cylindrical central portion 12 and two relatively narrow end caps 13 and 14 of generally cylindrical shape. The end caps 13 and 14 preferably contain conventional sound absorbing material such as rock-wool (indicated by reference numerals l and 16 respectively), which is held in place by perforated plates or screens 17 and 18 respectively. A spiral duct 19 is positioned within the central portion 12 of the housing 11.
An inlet pipe 20 extends coaxially through the housing 11 and it has outer ends 21 and 22 which protrude beyond the respective end caps 13 and 14. The outer ends 21 and 22 of the pipe 20 constitute inlets through which exhaust gases from an engine may enter the muffler 10. A portion of the inlet pipe 20 is cut out to form a longitudinal opening 23 which extends between the plates 17, 18. The inlet pipe 20 is securely fastened to the end caps 13 and 14 by any conventional means capable of providing a gas tight seal.
The axis of the spiral duct 19 is co-axial with the axis of the housing 11, and its width is equal to the width of central portion 12: ofsthe housing 11. The inner end of the spiral duct 19 is open and is located at the centre of the housing 11 and it is in communication with the longitudinal opening 23 of the inlet pipe 20. The radius of the spiral duct 19 initially is equal to the radius of the inlet pipe 20, and it increases evenly from its inner end to its outer end. The spiral duct 19 may be constructed from a plurality of semicylindrical plates joined together by any suitable means, or from a single piece of sheet metal,-and the outer surface of the outer-most turn of the spiral duct 19 constitutes the outer wall of the central portion 12 of the housing 11. The inner end of the spiral duct 19 terminates in a short bent portion 24 which providesa smooth surface against which the gases may flow when leaving the longitudinal opening 23 of inlet pipe 20. The bent portion 24 also serves as a conveninet junction for one end of a lining 25 which covers one wall of spiral duct 19, and for one end of a thin perforated screen or piece of expanded sheet metal 26, which covers and secures the lining. 25 against the wall of the spiral duct 19. Both the lining 25 and the screen 26 preferably extend the full width and the entire length of the spiral duct.l9, and both are secured to the inner wall of housing 11 at the outer end of spiral duct 19. The lining25 may be of any suitable sound absorbing material capable of withstanding the heat and forces to which it is subjected, such as rockwool.
Although the lining 25 is shown as attached to only one side of spiral duct 19, it will be understood that both sides of thespiral duct 19 could be lined, if desired. However, it has been found that good results may be obtained if the lining 25 is secured to the wall as shown in FIG. 2, which wall is on the low pressure side of the gas stream flowing through the spiral duct 19. Similarly, although a perforated screen 26 is shown for securing the lining 25 against the spiral duct 19, it will be understood that any woven material or any other material of unitary construction can be used, providing that such material can withstand the temperatue and forces to which it is subjected. In fact, the lining 25 may simply be fastened to the spiral duct 19 by conventional means, for example, by rivets, clips and the like, or it may be formed into a long sheath into which the metal sheet forming the spiral duct 19 may be inserted.
Gases which have entered the inlet pipe 20 through the outer ends 21 and 22 thereof pass through the opening 23 and travel through the spiral duct 19 until they reach a slot 27 formed in the outer wall of the housing 11. Attached to the outer surface of housing 11 and enclosing the slot 27 is a manifold 28 through which the gases are discharged from the housing 11. The manifold 28 may be formed in any desired shape to suit the particular engine to which the muffler is to be attached. In FIG. 3 the manifold 28 is shown as being perpendicular to the axis of the housing 1 l, and in FIG. 4 it is shown with its axis parallel to the axis of housing '1 1. Alternatively, in some cases it may not be necessary to have a manifold at all, and instead the exhaust gases would emerge directly into the atmosphere through the slot 27.
The shape of the spiral duct 19 is shown in FIGS. 1 and 2 as being spiral in coss-section; however, it may be rectangular, square, or circular in cross-section. Also, the length of the central portion 12 of the housing 11 can be varied, and may be either less or greater than its diameter. However, for best results, the spiralduct 19 should have at least two and one-half turns; more turns would provide greater sound attenuation at the possible expense of greater back pressure. Although the dis tance between the walls of the spiral duct 19 or the duct pitch, is shown in FIG. 2 as being relatively constant, this can be varied as wel].'For example, the duct pitch could increase from the inner end to the outer end of the spiral duct; this would result in less back pressure, at the possible expense of less noise attenuation. Conversely, the duct pitch could decrease from the inner end to the outer end; in this case noise attenuation would be improved at the possible expense of back pressure.
The housing 11 is shown in FIGS. 1, 3 and 4 as being separate from the end caps 13 and 14. However, it will be understood that the housing 11 may be of unitary construction with the perforated screens or plates 17 and 18 being fitted internally within the housing 11', thus obviating the need for separate end caps 13 and 14.
What I claim is:
'1. Apparatus for silencing an engine and the like, the apparatus comprising:
a generally cylindrical housing disposed about a longitudinal axis and having two opposed end walls and a circumferential side wall;
two opposed inlets for conveying exhaust gases into said housing, said inlets being positioned at respectively opposite ends of said housing on a common axis substantially coincident with said longitudinal axis of the housing;
a spiral duct in said housing, said spiral duct having an inlet at the centre of the said duct and an outlet at the outer periphery of said duct, said spiral duct having an axis positioned substantially coincident with the longitudinal axis of the housing, and said spiral duct inlet being in communication with the said housing inlets through said end wall; and,
an outlet for conveying exhaust gases from said housing, said outlet being disposed at said circumferential side wall of the housing and communicating with said spiral duct outlet.
2. Apparatus as claimed in claim 1, wherein the said housing inlets are formed by opposite end portions of an elongate pipe which extends longitudinally through said housing and which has a central slot located in communication with the inlet of the spiral duct.
3. In an apparatus for silencing an engine and the like comprising: a cylindrical housing disposed about a longitudinal axis and having two opposed end walls and a circumferential side wall; and a spiral duct in said housing, said spiral duct having an inlet at the centre of said duct and an outlet at the outer periphery of said duct, and said spiral duct having an axis positioned substantially coincident with the longitudinal axis of the housing;
the improvement comprising: two opposed inlets for conveying exhaust gases into said housing, said inlets being positioned at respectively opposite ends of said housing and being formed by opposite end portions of an elongate pipe which extends through said housing end walls and longitudinally through said housing on an axis substantially coincident with the longitudinal axis of the housing; said pipe having a central slot located in communication with the inlet of said spiral duct; and an outlet for conveying exhaust gases from said housing, said outlet being disposed at said circumferential side wall of the housing and communicating with said spiral duct outlet.