US2805730A

US2805730A - Muffler tubes

Info

Publication number: US2805730A
Application number: US350975A
Authority: US
Inventors: Lindsay M Applegate
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-24
Filing date: 1953-04-24
Publication date: 1957-09-10
Anticipated expiration: 1974-09-10

Description

Sept. 10, 1957 L. M. AF'PLEGATE MUFFLER TUBES Filed April 24. 1953 United States Patent MUFFLER TUBE Lindsay M. Applegate, Salem, Greg.

Application April 24, 1953, Serial No. 350,975

Claims. (Ci. ISL-42) This invention is an improvement in flexible muffling tubes used for internal combustion engines.

Flexible muflling tubes are already known in this art, some having been patented in the United States as early as 1925. These earlier types, however, have achieved only very limited adoption although the acoustic principles exemplified therein are unquestioned. There are known also in this art various types of mufflers with rigid walls in which the exhaust gasses pass through the mufiler unimpeded by baffles or other obstructions. The muffling of sound therein is accomplished by the use of sound absorbing materials such as steel or mineral wools to which the exhaust gases have access through a perforated pipe passing through the muflier or by other equivalent means. The acoustic principles employed by these types of muffling appliances are used also in my present invention.

The principal object of my invention is to produce a mufliing tube which will serve efiiciently and economically as a straight-through type of muffler and combine therewith the recognized advantages of flexible exhaust tubing.

A second object is to produce a muffling tube that can be readily manufactured with conventional machines and which can readily be handled by conventional methods in repair shops.

A third object is to obtain more effective muffling and longer effective life of muffling tubes by appropriate spatial relationship of components bringing about optimum utilization of sound absorbing properties of component materials.

Another object is to provide a flexible tubular muffler which can be readily adapted to a wide variety of engines and vehicles, even though manufactured in only a few sizes, by virtue of favorable dimensional relationships permitted by this invention.

Other objects may be inferred from the following specification describing my present invention and from the claims by which it is succinctly defined.

My invention is illustrated in Figures 1 and 2 which are respectively a longitudinal partly sectional view of my invention and a partly sectional end view.

Figures 1 and 2 show my invention in a preferred form favorable to efliciency and desirable mechanical characteristics. A conventional flexible tube 1 encloses two other components. The inner surface of the assemblage is a channelled spiral 2 wound with space between turns. A winding 3 of combustion-resistant fibrous material such as asbestos or glass cord is Wound around the spiral 2 and is retained thereon by the channel edges 4 on the outside of strip 2.

The operation of the tube as shown in Figure 1 depends on the absorption of sound in the space between the outer tube 1 and the inner tube 2. The fibrous material 3 provides a large surface and has a yielding structure that promotes dissipation of sound energy. The exhaust gas inside tube 2 has access to the fibrous material 3 through the spaces 5 between successive turns of the inner tube 2. The internal roughness of tube 2 causes some turbulence in the movement of gas through the tube and this contributes also to suppression of noise but this is in addition to the absorption of sound by the fibrous material 3 and the space in which it is placed.

2,805,730 Patented Sept. 10, 1957 The fibrous material 3 shown in Figures 1 and 2 is preferably of combustion-resistant material such as asbestos or similar fibrous material. Permeability, looseness, and large effective surface are important for attaining optimum conditions of sound absorbtion.

In determining the dimensions in my invention it will be observed that the ordinary mufl ler is usually only about two feet long, but that the total length of muffler pipe and mui'fler is usually ten feet or more. The muffling effect of two feet of tube as made in this invention can be about one-fourth or less than that of a conventional muffler and still, by virtue of the greater length employed, be as effective as the conventional mutfler. This permits the cross sectional area of the tube in my invention to be of the same order as that of the conventional exhaust pipe. An internal diameter of one and one-half inches in tube 2 for example, a radial thickness of the order of one-eighth inch in the fibrous layer 3, and an ordinary flexible tube 1 with an internal diameter of about one and three-fourths or two inches allows a structure that is economical, reasonably compact, and effective. The muffling effect of layer 3 increases with thickness and is dependent on the characteristics of the absorbent material used between the inside and outside tubes.

The relative dimensions of parts and spacings shown in Figures 1 and 2 are subject to design for good performance and convenience in manufacture. The spaces 5 between the rearward edges of the turns and the forward edges of the preceding turns in the direction of advance of the turns, as shown in Figure l, are required to give the gasses in the tube access to the sound-absorbent material 3. The composite tube can be rolled continuously forming in succession the inner spiral 2, the spiral of soundabsorbent material 3 wound on the exterior of the turns of 2, and the enclosing flexible tube 1. The technique of tube manufacture is such that it will ordinarily be expected that the sound-absorbent material 3 will fit closely to the inside of outer tube 1. This has the advantage of holding the three parts of the composite tube firmly together for handling, cutting, and attachment of fittings.

The spaces shown between the successive turns of the sound-absorbent material 3 are provided to permit unimpeded access of the exhaust gases to the sides, and, consequently, the maximum convenient area, of material 3. These spaces need not be large when the material 3 is characterized by an open mesh-like structure as long as the material is clean. In service, however, carbon and rust may tend to decrease the sizes of the openings and therefore they should be large enough when first manufactured to provide for this.

The individual mechanical components of the composite tube shown in Figures 1 and 2 could be described in various ways but for convenience in description, es-

' pecially in the claims, certain conventionalities applicable to this art should be understood. The outer tube 1, preferably metallic, may well be described as a spirally wound strip formed with interlocking edges, and this will ordinarily be understood from the usual expression flexible tube. The inner tube or winding 2 can be a simple spiral of flat strip with the edges bent outward to form a channel as shown in the drawing. The strip, wound with space between adjacent edges, is referred to conveniently as a spaced wound strip.

This spirally wound inner strip, when referred to as spaced, is limited to construction in which there is ample clearance between turns for unimpeded access of gases in the tube to the sound absorbent material wound on and parallel to the spaced turns of the inner strip. This distinguishes my invention from those in which the inner tube is composed of over-lapping turns of strips or of other construction in which perforations or equivalent means are used to provide radial passageway to the sound absorbent material for the gases in the tube. This arrangement is described in the claims as non-overlapping to distinguish the fully spaced turns from arrangements in which the strip is wound in overlapping or in inter.- locking turns as in the outer tube of Figure l.

i The expressions concave section or channel-shaped section are used to describe the cross-section of the strip of which the inner tube 2 is wound and to distinguish this simple cross-section of strip from the more complicated strips of S-shaped or other configurations with interlocking edges. There is no way for the channel-shaped strip to be interlocked. The sound absorb nt material 3 may be, for example, steel wool formed into a rape or cord-like strand. Glass or asbestos fibers formed into a rope or cord may similarly be used. This material is porous or fibrous in the sense that many interstiees and a large area of surface are provided to facilitate the absorption of sound. The degree of compactness of the fibrous structure is limited to that which will permit mechanical displacement and friction between the fibers to promote the dissipation of the sound energy. This material is conveniently described as sound absorbent. The wound material 3 is referred to as a strip of sound absorbent material which, of course, as an expression, may include the cross-sectign of a round cord as well as any other convenient cross-section.

I claim:

1. A muffling tube comprising a non-overlapping channel-shaped strip spirally wound with separation between adjacent turns of the strip, the rearwardedge of each turn of the spirally wound channel-shaped strip being spaced from the forward edge of the preceding tm'n in the direction of advance of the turns, a spirally wound strip of porous material of approximately the width of the channel of said channel-shaped strip wound parallel and out side said channel-shaped strip and retained thereon by the externally disposed channel edges thereof, and a substantially gas-tight flexible interlocking-wound-strip tube concentrically enclosing said channel-shaped strip and said porous strip.

2. A flexible tube comprising a spaced-turn spiral of non-overlapping channel-shaped strip with the channel edges outward, the rearward edge of each turn of the spiral ofc'hannel-shaped strip being spaced from the forward edge of the preceding turn in the direction of ad- Vance of the turns, a spaced-turn spiral of fibrous strip wound on and parallel to the said spiral of channel-shaped strip, and occupying substantially the full width thereof,

and a flexible tube "concentrically enclosing said, spaced wound strips.

3. The combination of an inner tube formed of spaced non-overlappingstrip, spirally wound with the rearward edge of each turn being spaced from the forward edge of the preceding turn in the direction of advance of the turns, a strip of fibrous material around said inner tube, and a substantially gas-tight flexible tube. concentrically enclosing said inner. tube and fibrous material, said spaced non-overlapping strip being channel-shaped with the channel outward to hold said fibrous strip in place in said channel, said fibrous strip being wound on and parallel to the turns of said inner tube strip.

'4, A composite tube comprising an outer tube of spirally wound resilient flexible strip formed withinterlocking edges, an inner concentric spiral of non-overlapping resilient flexible strip, channel-shaped on the exterior of the spiral, wound, with space between adjacent turns, the rearward edge of, each turn of the inner spiral being spaced from the forward edge of the preceding turn in the direction of advance of the turns, and a spirally Wound strip of sound;absorbent material between the outer tube and inner. wound spiral, wound to lay in the channel on said inner spiral strip, and retained in contact with theedges of said channel.

5.. A composite, tube comprising an outer tube of spirally wound strip formed with interlocking edges, an inner concentric spiral of non-overlapping strip, formed with out-turned edges, wound with space between the adjacent edges of successive spiral turns, the rearward edge of each turn of the inner spiral being spaced from the forward edge of the preceding turn in the direction of advance of the turns, and a spirally wound strip of sound-absorbent material between the outer tube and the inner spiral strip, on said strip, and in contact with the out-turned edges thereof.

6. A composite tube comprising an outer tube of spirally wound strip formed With interlocking edges, an inner concentric spirally wound non-overlapping strip whose edges are turned outward to form a channel with space between the edges of adjacent spiral turns, the rearward edge of each turn of the inner strip being spaced from the forward edge of the preceding turn in the direction of advance of the tu ns, and a strip of porous material spirally wound in said channel on the outer side of said inner spirally wound strip, said porous strip being substantially the full width' of said inner spiral strip and retained thereon by out-turned sides of said channel.

7. A composite tube comprising an outer spirally wound strip formed with interlocking edges, an inner concentric non-overlapping channel-shapedstrip spirally wound with space between the edges of adjacent spiralturns, the rearward edge of each turn of the inner strip being spaced from the' forward edge of the preceding turn in the direction of advance of the turns, and a strip of porous material wound therewith and secured in place by being wound in the channel presented on the exterior of said inner spiral.

SfAcomposite tube comprising an outer spirally wound strip formed with interlocking edges, an inner concentric s irally wound non-overlapping strip of channel-shaped cross-section, the rearward edge of each turn of the inner spirally wound strip being spaced from the forward edge of the preceding turn in the direction of advance of the turns, and a combustion-resistant, sound-absorbent strip Wound between the inner and outer strips retained by the channel on the exterior of said inner strip.

9. A composite flexible tube comprising an outer flexible tube formed of a spirally wound flexible metallic strip with interlocking edges, an inner concentric tube formed of a spirally wound flexible metallic strip with space between the adjacent edges of successive turns, the rearward edge of each turn of the tube being spaced from the forwardedge of the preceding turn in the direction of advance of the turns, said inner tube strip having outturned edges forming a channel thereon, and a soundabsorbent, combustion-resistant coil of material of ap proximately the width of said channel wound between the outer and inner tubes around and parallel to the turns of said inner tube strip.

10, A composite tube. comprising an outer tube of spirally wound strip formed with interlocking edges, an inner concentric spiral of non-overlapping strip, formed with at least one out-turned edge, wound with the rearward edge of each turn of the inner spiral strip being spaced from the forward edgeof the preceding turn in the direction of advance of the turn, and a spirally wound strip of sound-absorbent material between the outer tube and the inner spiral strip, on said strip and in contact with said gut-turned edge thereof.

References Cited in. the file of this patent UNITED STATES PATENTS 1,530,324 Pribil Mar. 17, 19.25

2,014,368 Blundell Sept. 17, '1935 2,073,951 Servais Mar. 16, 1937 2,718,273 Dehaus Sept. 20, 1955 FOREIGN PATENTS 703,130v Germany Mar. 1 1941 $3 ,110 Great Britain" July 31, 1944