EXHAUST MUFFLER FIELD OF THE INVENTION

This invention relates to improvements in devices for reducing the noise level of exhaust gases, particularly for reducing engine exhaust noise of an internal combustion engine.

BACKGROUND TO THE INVENTION

Vehicles with gasoline or diesel powered engines produce exhaust gases as a by-product of internal combustion. These exhaust gases are expelled from the engine when the exhaust valves open. These exhaust gases then pass through a network of sealed exhaust pipes. Due to the high energy created during the combustion process in the engine, exhaust gases when they first enter the exhaust pipes will contain a variety of sound frequencies most of which are not very acoustically pleasing to the ear.

Mufflers are used on vehicles as a way to 'muffle' or reduce the sound level of the exhaust gases leaving the engine. They can also be used to tune the exhaust note (like a musical- instrument) by cancelling out undesirable sounds leaving behind only those which are deemed pleasant to some people. The muffler is usually located at a point at the rear of the vehicle immediately before the location where exhaust gases are vented to the atmosphere. The three most common types of mufflers used today absorption mufflers, diffusion mufflers and Hemholtz chambers.

An absorption muffler is most commonly used by performance muffler manufacturers as it gives the least resistance to the exhaust gases that pass through. Absorption mufflers work by using a straight perforated tube that is en- cased or wrapped in sound deadening material. In this design, the exhaust gases are able to pass through with almost no resistance while the various frequencies of sounds contained in the gases are absorbed by the material around the perforated tube. Typical materials used for sound deadening are fibreglass, stainless steel mesh and ceramics, A diffusion muffler splits the flow of the exhaust gases up into a series of different paths using a series of plates and tubes called baffles. These baffles cause the exhaust to follow a longer path when passing through the muffler. As the exhaust twists its way through these series of tubes and plates, it loses

velocity (energy) and in so doing, several sound frequencies are lost due to sound wave reflection and superpostion. This in turn tunes the exhaust note that exits the muffler.

The Hemholtz Chamber is also known as a Cancellation Muffler or Resonator. The Hemholtz: chamber is designed very carefully to be a specific volume and length. As the sounds in the exhaust gases enter on one end, a resonant frequency is established in the chamber that causes all other sounds at that specific frequency to be cancelled out. As this type of muffler only cancels out one frequency in the exhaust, they are rarely used by themselves, but in conjunction with a Diffusion or Absorption Muffler.

In summary, conventional exhaust mufflers either use restrictive passages to reduce the noise level of the exhaust, which has the effect of reducing the efficiency of the engine, or they use free flowing passages which improve the efficiency of the engine but only insufficiently decrease the noise level of the exhaust. Conventionai mufflers also use a bulky housing that requires a large area to fit under the vehicles chassis. SUMMARY OF THE INVENTION

In one aspect, the present invention provides a gas exhaust muffler for reducing the noise level of exhaust gas, the muffler having an intake pipe, an exhaust pipe, and a transition pipe extending between the intake and exhaust pipes, the transition pipe defining a sound reduction chamber of the muffler, wherein the transition pipe has a cross-sectional area equal to or greater than that of the intake pipe but relative to the intake pipe is wider in a first cross- sectional dimension and narrower in a second cross-sectional dimension transverse to the first dimension.

One object of the current invention is to provide a modified absorption-type muffler which seeks to have lower noise emissions as compared to conventional cylindrical pipe core mufflers. It is currently believed that by changing the cross- sectional shape of the transition (or core) pipe to be flattened compared to the that of the intake pipe, whereby the cross-sectional area of the two pipes is essentially the same (or that of the core pipe is larger), sound wave propagation through the transition pipe is adversely affected; a non-symmetrical sound wave propagation and relfectioπ pattern within the transition pipe is obtained, resulting

in increased sound wave attenuation at the exhaust pipe inlet. That is _r by changing the cross-sectional shape of the transition (or core) pipe component of the muffler from the conventionally used circular or square shape into a non-point symmetrical shape, eg an oval, a more effective muffling of sound conveyed or associated with the exhaust gases from, for example an internal combustion engine of a vehicle, can be achieved.

The cross-sectional areas of the intake and exhaust pipes may be substantially the same, for example, they could both be cylindrical tubes. Exhaust back pressure, which otherwise leads to diminished engine performance can then be optimised.

The transition pipe may be a plurality of individual pipe sections arranged in parallel as regards the exhaust gas flow. The surne of the cross-sectional areas of the plurality of pipes would then advantageously be the same or larger than the intake pipe. Preferably, the ratio of the first cross-sectional dimension to the second cross-sectional dimension is between 4: 1 and 16:1. In the case of the plurality of individual pipe sections, the width of the transition pipe is taken to be the sum of the widths of the individual pipe sections.

The cross sectional shape of the transition pipe may be rectangular, substantially rectangular with- radiused comers, rectangular with bύll-nosed shorter sides, curved, elliptical, or oval. The transition pipe is preferably rectilinear or undulated in longitudinal (that is, gas flow) direction of the pipe. ^' The walls of the transition pipe may be at least partially corrugated walls, thereby to provide additional interference patterns for reflected sound waves. Preferably, the transition pipe has perforations in an external wall. The arrangement of perforations could be such they are uniform in size and distribution, random in size and distribution, or uniform in size and random in distribution. Such perforations provide a further avenue for sound waves to pass through and reflect from, assisting in the sound reduction in the transition pipe. Preferably, the exhaust muffler includes tapered pipe sections extending between the transition pipe and each of the intake pipe and exhaust pipes. These tapered pipe sections may transition into the transition pipe with a predetermined radii of curvature. This measure will contribute to a more even gas

flow through the muffler. These tapered pipe sections may also preferably have perforations in their external walls.

The transition pipe would be enclosed within an external muffler housing as is known in the art. Advantageously, the void formed between the muffler housing and transition pipe is filled with a sound absorbing packing material, as known in the art.

The present invention is preferably embodied in a glasspack or cherry bomb absorption muffler.

The exhaust muffler of the present invention was particularly conceived for use with an interna! combustion engine, either in land vehicles but also boat or aircraft engines.

In a second aspect, the present invention provides a gas exhaust muffler for reducing the noise level of exhaust gas, the muffler having an intake pipe, an exhaust pipe, a sound muffling box connected to the intake pipe and exhaust pipe, and a plurality of internal pipes connected to and extending substantially along the length of and within the sound muffling box, the internal pipes being arranged in a stacked or nested manner.

The cross-sectional shape of the internal pipes may be rectangular, substantially rectangular with radiused corners, rectangular with bull-nosed shorter sides, curved, elliptical, or oval.

Preferably, there is at least one point at which the distance between adjacent pipe walls is greater than or equal to two millimetres.

The muffling box is preferably enclosed within a muffler housing. Preferably, a void is formed between the muffler housing and the muffling box that is filled with a sound absorbing packing material. Such packing material assists in further reducing the noise emitted from the exhaust.

The muffler housing may have a cross-sectional area that is 10-20% larger than the intake pipe and exhaust pipe. This has the benefit of providing a slimline exhaust muffler that easily fits under a vehicle without any height adjustment of the vehicle being necessary. Further, such a compact nature allows the muffler to be positioned near the engine where it is more effective in reducing the noise level of the exhaust.

In a third aspect, the present invention provides a method of reducing noise emitted by an exhaust muffler of an internal combustion engine including the following steps: a) providing an intake pipe of a predetermined cross-sectional area, b) providing at least one internal pipe connected to the intake pipe and an exhaust pipe, the internal pipe having a cross-sectiona! area equal to or greater than that of the internal pipe and, relative to the internal pipe, is wider in a first lateral dimension and narrower in the transverse dimension, where the width of the internal pipe when there is more than one pipe adjacent each other is the sum of the individual pipe widths. BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will be described with reference to the accompanying figures, in which:

Figure 1 shows a schematic a top plan vϊew of a gas exhaust muffler enclosed within a muffler housing according to an embodiment of this invention; ^' Figures 1a) to c) show the same exhaust muffler as in Figure 1, showing examples of the arrangements of perforations in an external wall of the transition or core pipe of the muffler;

Figure 2 shows a schematic end view of the exhaust muffler of Figure 1;

Figure 2A shows a schematic end view of a transition pipe having an elliptical cross-section, with the intake tube, according to another embodiment of the present invention;

Figure 3 shows a longitudinal section of the gas exhaust muffler of Figure

1 ;

Figures 4 and 5 show schematic top and end views, respectively, in which the transition pipe and tapered pipe sections have a corrugated external wall;

Figures 6 and 7 show schematic top and end views, respectively, of an exhaust muffler according to an embodiment of the invention in which the transition pipe includes a plurality of individual pipe sections;

Figures 8 and 9 show schematic side and end views, respectively, of an exhaust muffler (without external housing) according to an embodiment of the invention in which the transition pipe is undulating in shape;

Figures 10 and 11 show a schematic top and cross-sectional view respectively of an exhaust muffler according to an embodiment of the invention in

which there are stacked internal pipes of rectangular with bull-nosed shorter sides cross-section; and

Figure 12 shows a schematic top view respectively of an exhaust muffler according to an embodiment of the invention in which there are nested internal pipes of an elliptical cross-section.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention may be implemented in a variety of ways and the embodiments illustrated are to be considered only as illustrative constructions.

Figures 1 to 3 schematically shows an exhaust gas muffler for sue with vehicles having an internal combustion engine. The muffler 8 has an intake pipe 4, an exhaust pipe 5 and a transition pip© 1 extending between the intake pipe 4 and exhaust pipe 5, through which exhaust gas from the engine can flow. The transition pipe 1 is connected to the intake pipe 4 and exhaust pipe 5 by tapered pipe sections 2,3. The transition pipe 1 and tapered pipe sections 2,3 are enclosed by a muffler housing 6 in a known manner.

The intake and exhaust pipes 4,5 are of the same cross-sectional configuration and are cylindrical in shape. Transition pipe 1 (also referred to in the art as a core pipe) extends between intake and exhaust pipes 4,5 and is wider in one direction W and narrower in the other H compared to the intake and exhaust pipes 4,5.

Connecting the intake and exhaust pipes 4,5 to the transition pipe 1 are tapered pipe sections 2,3. Those tapered sections are connected to the intake and exhaust pipes 4,5 and narrow and widen respectively to join the narrower and wider parts of the transition pipe 1. The tapered pipe sections 2,3 have a predetermined radii of curvature 9,10 when joining the transition pipe 1 to the intake and exhaust pipes 4,5 respectively. The radii of curvature 9,10 allows a smooth transition between the different pipes 4,1,5. A longitudinal cross-section of the muffler device 100 is shown in Figure 3 and shows the radii of curvature 9,10 of the tapered pipe sections 2,3 in greater detail- The transition pipe 1 as shown has a ratio between the first cross-sectional dimension W and the second cross-sectional direction H of 6.45:1 , .and has approximately the same cross-sectional area as that of the intake pipe 4. The optimum ratio of W:H is between 4:1 and 16:1.

In use, gas flows into the intake pipe 4, through a tapered pipe section 2, and into the flattened transition pipe 1. The flow is is not restricted from entering the transition pipe 1 due to the cross-sectional areas of the transition pipe 1 being the same or greater than the intake pipe 4, ^" However, the reduction in second cross-sectional dimension H does result in 1. the exhaust gas in the transition pipe 1 having a lower pressure and 2. an increase in the number of times the sound waves entering the transition pipe 1 hit the wails and are reflected, causing a reduction in the intensity of the sound, thereby emitting a gas of reduced noise level at the exhaust pipe 5. The muffler 8 is enclosed within a muffler housing 6 that has a slightly larger height than pipes 4 and 5 respectively and may have a steel plate 7 positioned centrally within the muffler housing 6. This steel plate 7 provides additional support for the transition pipe 1 and makes the entire muffler 8 more rigid. Figure 1 shows the transition pipe 1 and tapered pipe sections 2,3 being non-perforated. Both the transition pipe 1 and the tapered pipe sections 2,3 can be perforated 35, Figures 1a) to c) show the same exhaust muffler 8 as in Figure 1 , showing examples of the arrangements of perforations in an external wall of a transition pipe. In Figure 1a), the perforations 35 are uniform in size and distribution. In Figure 1 b), the perforations 35 are random in size and distribution. In Figure 1c), the perforations 35 are uniform in size and random in distribution. The tapered pipe sections 2,3 are not shown as being perforated in ^' the figures, but may be perforated in the same manner as shown in the transition pipe 1 in Figures 1 a)-c). The perforations 35 provide noise dampening by allowing the sound waves entering the transition pipe to pass through to the sound dampening packing in the void 30 between the transition pipe 1 and the muffler housing 6. The sound waves are then not only dampened by the packing material, which is typically fibreglass or steel wool, but reflect back into the sound reduction chamber defined by the transition pipe 1 with reduced intensity and capable of further such interactions with other perforations 35.

Figures 4-θ show alternative configurations of the transition pipe 1 , such as that shown in Figure 2A which shows an end view of the pipe having an- elliptical

shape. Different shapes for the transition pipe 1 are possible; a corrugated shape is shown in Figures 4 and 5. Other 'suitable shapes include rectangular, rectangular with radiused comers, or oval. In such cases, the tapered, pipe sections 2,3 are configured to match the shape of the transition pipe 1. The transftion pipe can include a plurality of individual pipe sections 1B, and such an arrangement is shown in Figures 6 and 7. The internal pipe sections 1B are arranged adjacent each other and are parallel as regards the gas flow through the muffler. The internal pipe sections 1 B are shown as being of rectangular cross section - wfth bull-nosed sides, but could be curved, oval, elliptical, rectangular or rectangular with radiused edges. There may be 2 to 20 of these internal pipe sections 1B.

The transition pipe 1 can be rectilinear as shown in Figures 1-7 or can be undulating as shown in Figures 8 and 9. The transition pipe 1 could also be corrugated in this longitudinal direction. In another form of the invention, the gas exhaust muffler 8 has an intake pipe 4, an exhaust pipe 5 and a sound muffling box 14 connected to the intake and exhaust pipes 4,5. Within the sound muffling box 14, there is a plurality of internal pipes 13,19a-c arranged in a stacked or nested manner. Figures 10, 11 and 12 show such an arrangement. Figures 10 and 11 show an arrangement in which there are two non- perforated internal pipes 13 of rectangular with shorter bull-nosed sides cross- section. Each of these internal pipes are connected to the inner wall of the muffling box 14 and separated from each other. The distance between these parallel-spaced internal pipes 13, as well as internally between the walls, is greater than or equal to two millimetres. Tapered pipe sections 15,16 extend between the internal pipes 13 and each of the intake and exhaust pipes 4,5.

Figure 12 shows an arrangement in which the internal pipes 19, 19a-c are arranged in a nested manner. The four internal pipes 19, 19a-c are elliptical in shape and each pipe of smaller size is nested within a larger internal pipe, for example pipe with walls 19 is nested within pipe with walls 19a. That is, the four elliptical internal pipes 19, 19a, 19b and 19c comprised of non-perforated pipes have a larger size from the inner to outer elliptical shape pipes 19, 19a, 19b and 19c respectively.

Each smaller elliptical internal pipe 19,19a-c is attached to the inner wall of the larger elliptical internal pipe 19,19a-c, along the axial length at the outermost edges 20. White four elliptical internal pipes are shown, there may be from 2 to 20. The distance between adjacent pipe wall is greater than or equal to two millimetres at the point shown by Y on Figure 12, which is the point of maximum wall separation when the pipe walls are elliptical in shape.

The ends of the internal pipes 13,19,1Qa-C ₁ are radiused 17 to allow smooth gas flow around the walls of the internal pipes 13,19,19a-c.

The steel muffling box 14 has a 10-20% larger cross-sectional area than intake and exhaust pipes 4,5. The void formed between the muffler housing 6 and the muffling box 14 is filled with a sound absorbing packing material such as fibreglass or steel woof.

It will be realised by persons skilled in the art that numerous variations and/or modifications may be made to this exhaust muffler device as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.