Muffler

A muffler includes a first chamber, a second chamber, an extender tube, a reverse flow tube, and a separation chamber. The first chamber is coupled to an exhaust inlet of the muffler. The extender tube is coupled to the first chamber and the second chamber. The exhaust gas flows from the first chamber to the second chamber through the extender tube in a first direction. The reverse flow tube coupled to the second chamber. The exhaust gas flows through the second chamber from the extender tube to the reverse flow tube in a second direction different than the first direction. The separation chamber that provides spatial separation between the first and second chamber.

FIELD

This disclosure relates in general to a combustion noise suppression process or system for an internal combustion engine.

BACKGROUND

An internal combustion engine, as well as other devices, produce unwanted acoustic waves or noise. The combustion of air and fuel creates noise. The operation of pistons, crankshafts, gears, belts and pulleys creates noise. A muffler, which may also be referred to as a silencer, provides structure for reducing the noise or magnitude of the acoustic waves. The muffler may include materials that partially absorb the acoustic waves. The muffler may include structure that introduces destructive interference to reduce the magnitude of the acoustic waves. Challenges remain in maximizing the reduction in noise or magnitude of acoustic waves produced by the internal combustion engine.

DETAILED DESCRIPTION

FIG. 1illustrates an engine10including a muffler11or silencer. An input pipe or tube15of the muffler11delivers exhaust gas from the engine to the muffler11. As a valve connecting the engine10and the input tube opens, an acoustic pressure wave generated from combustion is propagated through the inlet pipe. The muffler11helps to reduce the combustion generated sound waves through geometry that causes acoustic pressure cancelation through impedance mismatch from muffler geometry features. The exhaust gas continues out from the muffler11through the output pipe or tube13. The partial cancellation of one sound wave upon another may be referred to as destructive interference and result in transmission loss. The transmission loss is a parameter that describes the acoustic attenuation capacity of the muffler. The transmission loss parameter may not take into account the source strength, source impedance, or termination impedance. As a result, the transmission loss parameter may not be equivalent to the sound reduction (e.g., sound reduction in dB) of the engine noise, but the transmission loss parameter may be a close indicator of the sound reduction in the engine noise. In one example, insertion loss, may describe the sound reduction on a frequency basis. The transmission loss or the insertion loss may be a metric to measure the effect of the muffler11in reducing the noise of the engine10.

The engine10may be a small internal combustion engine defined according to a displacement of the engine10or a volume of the muffler11. The volume of the muffler may be 50-400 cubic inches or another size. The volume of the engine10may be 10 to 65 cubic inches or another size. Example lengths for the muffler11may be 4 to 14 inches (e.g., 12 inches) or another value, and example diameters for the muffler11may be 3 to 6 inches or another value. The small internal combustion engine may be applicable to chainsaws, lawn mowers, wood chippers, stump grinders, concrete trowels, mini excavators, concrete saws, portable saw mills, weed trimmers, all-terrain vehicles, wood splitters, pressure washers, garden tillers, tractors, plows, snow blowers, welding equipment, generators, and other devices.

The engine10may include one cylinder, two cylinders or another number of cylinders. The one or more cylinders may generate noise or sound waves as a result of the oscillations of one or more pistons through the one or more cylinders, which are shaped to receive the one or more pistons. The one or more pistons may be guided through the one or more cylinders by a connecting rod that is connected to a crankshaft by a crankpin. A combustion chamber includes a combustion chamber adjacent to a head of the piston. The combustion chamber is formed in a cylinder head. The combustion chamber is connected to the muffler11through an exhaust port. In one phase of a combustion cycle for the piston, the exhaust port is blocked from the combustion chamber by an exhaust valve, and in a subsequent phase, the exhaust port is in gaseous connection with the combustion chamber to release exhaust gas through the exhaust port to the muffler11.

The combustion cycle may also generate noise or sound waves that travel to the muffler through the cylinder head or housing or through the exhaust port. The connecting road and crankpin may generate noise or sounds waves that travel to the muffler11. The engine10may include other sources of noise or sounds waves including a gearing system, a valve-train system (including valves hitting seats), an intake system including a manifold, a fuel supply, a speed governor, a cooling system, an exhaust system, a lubrication system, and a starter system.

The sound waves that travel through the muffler11and are attenuated by the muffler11may be classified as low frequency sound waves and mid to high frequency sound waves. In other examples three classifications may be used such as low frequency, middle frequency, and high frequency. The low frequency sound waves may be in a first range and the high frequency sound waves may be in a second range. Examples for the low frequency range may be less than 500 hertz or 40 to 400 hertz. Examples for the high frequency range may be 500 to 5000 hertz or 1 kHz to 10 kHz. The sounds in the low frequency range may be produced by the mechanical components of the engine10. The low frequency range may be dominated by combustion noise produced in the engine10. The low frequency range may be dependent on the number of cylinders of the engine10. The sounds in the high frequency range may be exhaust noise produced by the gas flows through the muffler11. The exhaust noise may be caused by turbulent flow in the gas flows or interaction of the gas flows interacting with surfaces within the engine10. The turbulent flows include changes in pressure and velocity within the gas flows. Aerodynamic forces create noise from the gas flow when the gas flows change direction or velocity in response to fluid mechanics of the gas flows flowing over or against external structure such as edges or surfaces. The sounds in the high frequency range may also include sound waves produced by an exhaust related device such as a turbocharger, a super charger, or an after cooler. In many examples, combustion noise dominates the low frequency range and exhaust noise dominates the mid to high frequency range, but other examples are possible.

Sensors may be located at various locations in the engine10including the cylinders, manifold, a cooling system, and exhaust. Data collected by the sensors may be analyzed by a controller to generate a command to adjust one or more passages (e.g., actuate a valve) in the muffler11. Data collected by the sensors may be analyzed by the controller to determine noise levels or a frequency range for the noise levels.

The phrases “coupled with” or “coupled to” include directly connected to or indirectly connected through one or more intermediate components. Additional, different, or fewer components may be provided. Additional, different, or fewer components may be included.

The housing of the muffler11may be formed from a metal such as steel and may include any combination of a sound absorbing material, a ferrous material, or an anti-corrosion material. Example materials include ferrous alloys, aluminum, aluminized steel, titanium alloys, and ceramics. Ferrous materials may be particularly resistance to the heat expelled by the engine10. Anti-corrosion materials may prevent rust or other corrosion, which may be caused by any combination of water, salt, or other environmental conditions placed on the engine10and muffler11.

FIG. 2illustrates an example muffler11a,which includes an input pipe15, an output pipe13, and a housing17or canister. The muffler is illustrated as cylindrical but may also be oval, octagonal, rectangular, or another shape in cross section. The housing17includes at least three chambers, a first chamber21, a second chamber25, and a third chamber23. The third chamber23is a spatial separation between the first chamber21and the second chamber25. Additional chambers may be included.

As described in more detail in other embodiments, exhaust gases may be present in the third chamber23or the third chamber23may be blocked off entirely and used specifically for spatial separation between the first chamber21and the second chamber25.

A first baffle16divides the first chamber21and the third chamber23, and a second baffle18divides the third chamber23and the second chamber25. A first tube27(e.g., canister length tube) traverses the first chamber21, the third chamber23, and the second chamber25. A second tube29(e.g., partial length tube) traverses the second chamber25and the third chamber23. The first tube27includes a first group of perforations31on the input side in the first chamber21and a second group of perforations33on the output side in the second chamber25. The second tube29includes a first group of perforations35in the third chamber23and a third group of perforations37on the adjacent side in the second chamber25. The perforations are holes in the tubing. The first group of perforations35may be omitted. In some examples, exhaust gases may flow from the second chamber25to the third chamber23. Additional, different or fewer components may be included.FIG. 3illustrates another view of the muffler11aincluding arrows A1-A3indicative of the flow of exhaust gases.

In operation, exhaust gas flows into the first chamber21from the input pipe15and then through the first tube27into the second chamber25, as shown by arrows A1and A2. The first tube27may not be connected to the input pipe15, which has several advantages. Some of the advantages relates to the cost and ease of manufacturing the first tube27. A tube that does not bend to connect to the input pipe15does not require the step of bending. In addition, the tube requires less material than a longer tube that bends to connect to the input pipe15.

Some of the advantages relate to the attenuation of sound. The high frequency exhaust flow noise may be caused by pulses of air from the combustion cycle of the engine10. Because the gas collects in first chamber21before flowing into the first tube27, the first chamber21acts as a damper to smooth out the amplitude of the pulses of the exhaust flow noise. That is, the impact of each pulse is spread out over time as the first chamber21fills with gas and flows into the first tube27.

The exhaust gas does not flow into the third chamber23from the first tube27, which increases the distance of the path of the exhaust gas flows. Exhaust gases may flow from the second group of perforations33to fill, at least in part, the second chamber25and provide exhaust gases through the third group of perforations37to the second tube29, in a direction shown by arrow A3.

The third chamber23may be sealed from the first chamber21, the second chamber25, or both. The third chamber23may be sealed from the rest of the muffler. The third chamber23may be sealed from the exhaust system and the exterior of the muffler. In some example, insubstantial amounts of the exhaust gas may flow into the third chamber23due to gaps in the construction of the muffler11a.

A dimension of the third chamber23is selected according to the frequency spectrum of the engine10. That is, the engine10may produce sounds of different frequency depending on the size and shape of the engine10, the application of the engine10, the running revolutions per minute (RPM) that the engine10is likely operated at, the loading on the engine, or the RPM when the engine10is idling. The frequency spectrum may be dependent on the number of cylinders in the engine10. One or more dimensions of the housing17may be calculated as a fraction of a wavelength of a frequency selected from the frequency spectrum. The selected frequency may be a harmonic of the frequency spectrum. In one example, the dimensions of the housing17may be selected according to the frequency spectrum of the engine10.

The dimension of the third chamber23may be a length of the third chamber23in the longitudinal direction of the muffler11a.Example widths may include ½ inch, 1 inch, 2 inches, or another value. The width of the third chamber23may be selected according to the overall length of the muffler11a.The length of third chamber23may be a fraction of the length of the muffler11a.The length of the third chamber23may be less than ⅓ (one third) of the overall length of the muffler11a.The length of the third chamber23may be less than ⅙ (one sixth) of the overall length of the muffler11a.Examples of fractions or ratios between the length of the third chamber23and the overall length of the muffler11amay include ⅛, 1/12, or 1/20.

The length of the third chamber23may be open space filled with air. The length of the third chamber23may include a fill material such as foam, rubber or plastic. The length of third chamber may include a conductive material such as metal (e.g., steel). The conductive material may be multiple plates of material coupled together. The dimension of the third chamber23may be a thickness of the baffles16and18. In one alternative, the third chamber23is selected by volume. Example volumes include 5-20 cubic inches.

The first tube27extended through the first chamber21and second chamber25improves the low frequency performance effect from the first chamber23in attenuated sound waves in the low frequency range. Third chamber23provides an impedance mismatch between the first chamber21and the second chamber25. The third chamber23causes some of the sound waves to reflect back to chamber21and some of the sound wave to be transmitted to the second chamber25. By having a spatial separation of the first chamber21to the second chamber25, given by the length of the third chamber23, the acoustic transmission loss performance can be greatly improved in the lower frequency range.FIG. 6, described in more detail below, illustrates how the length of this third chamber23shifts the transmission loss curve to a lower frequency while greatly improving the attenuation capacity.

FIGS. 4 and 5illustrate another embodiment. Muffler11bincludes first chamber121, second chamber125, and third chamber123. Muffler11bincludes a single tube51that traverses the three chambers and facilitates the flow of exhaust gases as shown by arrow A4. One or more dimensions of the third chamber123may be selected according to the sound spectrum of the engine10. The single tube51may be a quarter wave resonator with a length (L) that is tuned to ¼thof the frequency (f) of the pipe wavelength (e.g., f=c/4L where c represents the speed of sound). Additional, different or fewer components may be included.

The position of the tube51may be varied vertically or radially in any direction in the muffler11b.In one example, the tube51is at or near the vertical center of the muffler11b.In another example, the tube51may be slanted to an angle with the longitudinal axis of the muffler11b.That is the input pipe15may be positioned at a different vertical height than the output tube13. The tube51may extend to the housing of the muffler11b.The tube51may be in contact with the end caps of the muffler11b.In one example, the tube51includes one or more end caps that contact the housing. In another example, the tube51may be shorted at one end or both and not contact the housing.

The perforations131and133are illustrated in uniform arrangement. The perforations131and133may be evenly distributed over a portion of the tube51. The axial length of the perforations may be minimized. A quantity of the perforations may be minimized to have the fewest perforations but still provide adequate flow for the exhaust gas.

The perforations reduce acoustic flow generated noise. The perforations apply an acoustic impedance boundary condition (e.g., according to Mechel's formula). This acoustic impedance increases the transmission loss slightly, particularly at higher frequencies. As the perforations are smaller, the acoustic impedance is higher accordingly, transmission loss increases.

FIGS. 6, 7 and 8illustrate another embodiment for a muffler11c.FIG. 6illustrates an exploded view of the muffler11cincluding an input pipe15, a seal283, a flow bracket285, a muffler bracket281, and an output pipe13. A housing277of the muffler11cincludes an input side baffle243including at least one opening (e.g., exactly one opening) and an output side baffle241including at least one opening (e.g., exactly one opening).

The sides of the housing277are closed by an upstream side end cap263and a downstream side end cap265. The upstream side end cap263and the downstream side end cap265may include ridge members264that provide increased stiffness of the end caps and reduce ringing sounds from propagating through the upstream side end cap263and the downstream side end cap265. The ridge members265may have an oblong shape or another shape. In addition, a ring289may provide additional sound buffering.

The seal283prevents exhaust, air or other gas from escapes the connection point between the input pipe15and the housing277of the muffler11c.The seal283may also serve as additional material (e.g., steel) to weld the inlet pipe15to the housing277. The muffler bracket281may include an opening for the input pipe15. The muffler bracket281may receive screws or another fastener for securing the input pipe15and the housing277of the muffler11cto the engine10. The muffler bracket281may provide another coupling point between the engine10and the muffler11c.Fasteners couple the muffler bracket281to the housing277and from the muffler bracket281to the engine10.

FIG. 7illustrates the internal components of the muffler11cand housing277. The muffler11cincludes at least three chambers or compartments including an upstream chamber221coupled to the exhaust inlet of the muffler11c,a downstream chamber225coupled to the exhaust outlet of the muffler11c,and a third chamber or a central chamber223between the downstream chamber225and the upstream chamber221.

The dimensions of the central chamber223may be selected according to one or more frequencies of sounds produced by the engine10. Alternatively, the dimensional of the central chamber223may be selected according to experimental testing (e.g., trial and error) of the attenuation performed by the muffler11cat different sizes of the central chamber223.

In the longitudinal direction of the muffler, a dimension of the central chamber223may be about 10 to 60 millimeters (e.g., 19.6 millimeters). When the central chamber223is cylindrically shaped, the dimension of the central chamber223in the longitudinal direction of the muffler is a height of the cylinder. The length of the central chamber223may be selected according to the overall length of the muffler11c.The length of central chamber223may be a fraction of the length of the muffler11a.The length of the central chamber223may be less than ⅙ (one sixth) of the overall length of the muffler11c.Examples of fractions or ratios between the length of the central chamber223and the overall length of the muffler11amay include ⅛, 1/12, or 1/20.

A first tube or extender tube251extends from the upstream chamber221through the central chamber223to the downstream chamber225. The first tube251include a first set of openings231in communication with the upstream chamber221and a second set of openings233in communication with the downstream chamber225.

The spacer ring289is in contact with the extender tube251and the downstream side end cap265. The spacer ring289reduces sound waves or vibrations that travel between the extender tube251and the downstream side end cap265. The spacer ring289may be sized too small to vibrate at the frequency range of the sound waves carried by the exhaust gas.

FIG. 8illustrates the muffler11cincluding arrows A5and A6for the direction of exhaust flow through the muffler11c.The direction of the flow of air (first direction as shown by arrow A5) through the extender tube251is downstream from the exhaust inlet to the exhaust outlet. The first direction is a geometric direction substantially in the direction of a line drawn in the three dimensional space of the muffler11cfrom the exhaust inlet to the exhaust outlet.

A second tube or a reverse flow tube253coupled to the downstream chamber225. The reverse flow tube253includes a set of openings235and is coupled to the exhaust outlet for escaping the muffler11c.The exhaust gas flows through the downstream chamber225from the extender tube251to the reverse flow tube253. The direction of air flow (second direction as shown by arrow A6) from the extender tube251to the reverse flow tube is different than the direction of air from the exhaust inlet to the exhaust outlet. The second direction may be opposite to the first direction. The second direction may be substantially parallel to the first direction such as an internal angle is within 20 degrees. The second direction may include a substantial component that is parallel to the first direction. The second direction is a geometric direction substantially in the direction of a line drawn in the three dimensional space of the muffler11cfrom the exhaust outlet to the exhaust inlet. The flow of air in the reverse flow tube253extends the distance of the flow of air from the exhaust inlet to the exhaust outlet. The flow of exhaust changes direction approximately 180 degrees in the flow of air from the exhaust to the exhaust outlet. Thus, the first direction is substantially parallel to and in an opposite direction to the second direction.

The exhaust inlet, from inlet pipe15may be spaced from the extender tube251. The exhaust from the inlet pipe15may substantially fill the upstream chamber221before the gas enters the extender tube251through the first set of openings231. The arrangement of the inlet pipe15and extender tube251may specify a predetermined pressure in the upstream chamber221before gas flows through the extender tube251. Similarly, the set of openings233of the extender tube251is spaced from the set of openings235in the reverse flow tube253. Thus, the exhaust from the extender tube251may substantially fill the downstream chamber225before the gas enters the reverse flow tube251. The arrangement of the set of openings233and the set of openings235may specify a predetermined pressure in the downstream chamber225before gas flows into the reverse flow tube251. Because the exhaust flow from the extender tube251fills the downstream chamber225, pulses in the exhaust flow are further smoothed out over time.

The output side baffle241and the input side baffle243each include an opening269to receive the extender tube251and each opening268may include a collar for receiving and guiding the extender tube251. In addition, the output side baffle241includes a flange267for receiving an end of the reverse flow tube253. The flange267may include a collar or raised lip that extends above the output side baffle241. The reverse flow tube253is supported by the flange267such that the reverse flow tube253contacts the output side baffle241, and the reverse flow tube253does not pass through the second baffle.

The extender tube251may be spaced from end cap263by spacing261. The spacing261may be in the range of 1 to 100 millimeters. Examples include 5, 10, and 13 millimeters. In other examples, the spacing261is omitted (e.g., spacing of 0 millimeters).

A length of the extender tube251may be in the range of 100 to 400 millimeters, or preferably 225 to 275 millimeters (e.g., 254 millimeters). The length of the extender251may impact the low frequency attenuation effect of the central chamber223. Additional length may provide additional attenuation. A length of the reverse flow tube253may be in the range of the 50 to 200 millimeters, or preferably 125 to 175 millimeters (e.g., 134 millimeters). The length of the reverse flow tube253may be approximately half of the length of the extender tube251.

The length of the central chamber223may be less than a quarter wavelength of sound waves from the engine10coupled to the muffler11c.That is, the central chamber223may be sized too small to act as a quarter wave resonator, Helmholtz resonator or Helmholtz oscillator. Thus, each substantial frequency of the sound waves produced by the engine10through mechanical movements (low frequency range) is less than the resonant frequency of a Helmholtz resonator having the dimensions of the central chamber. Substantial frequency components are frequency components making up a threshold power (e.g., power level in dB or percentage of the total power) in the frequency spectrum of the sound of the engine10. Dominant frequency components are above the threshold power level in the frequency spectrum. The substantial frequency components may be a set of predetermined frequencies of the sound of the engine10.

In one example, the dimensions for the central chamber223may be determined according to a size factor (sf) defined from the substantial frequency as described in Equation 1:

sf=AV*L,Eq.⁢1
such that A is opening area of the central chamber223connected to the extender tube251, V is a volume of the central chamber223, and L is a length of the extender tube251.

The dimensions of the central chamber223may be selected such that the resonant frequency of the quarter wave resonator is out of the range of the substantial frequency components of the engine10. Equation 2 defines the resonate frequency (f) of the chamber according to the speed of sound as a function of temperature (c) and the wavelength chamber length (λ). Using equation 2, consider an example with c=500 m/s and λ=19.6 mm. Then the quarter wavelength resonance frequency of this chamber is 6.4 kHz. This frequency is too high to be useful for noise attenuation in this muffler. Thus, the quarter wave resonant frequency is this example chamber is out of the range of substantial frequency components of the engine10and a length of the central chamber223is less than a quarter wavelength of sound waves of a set of predetermined frequencies from an engine coupled to the muffler.

FIG. 9illustrates another example for the muffler11c.Like reference numerals inFIG. 9describe the same components perform in substantially the same manner as the examples ofFIGS. 7 and 8.FIG. 9includes a cap300for the reverse flow tube253. The cap300blocks the flow of gas from entering the central chamber223. The cap300may be fixed on the end of reverse flow tube253. The cap253may screw into the flange267.

In one example, the cap253may include a valve biased into a closed position by a spring. The valve moves in response to the pressure of the gas in the reverse flow tube253. As the pressure of the gas increases the valve moves to an increasingly open position. The bias force in the spring of the valve may be selected according to a load on the engine10. When the load is above a threshold, the valve is opened to allow gas into the central chamber223. When the load is below the threshold, the valve remains closed.

FIG. 10illustrates the sound attenuation performance of a muffler including the third chamber described herein. The combustion noise of an engine may include low frequencies such as below 200 Hz or 100 Hz. The solid line inFIG. 6illustrates the performance of a muffler without a third chamber, the dotted line illustrates the performance of the same muffler with a third chamber having a first thickness (small thickness), and the dashed line illustrates the performance of the same muffler with a third chamber having a second thickness (large thickness).

The solid line includes a trough70corresponding to a local low amount of attenuation, and mound80corresponding to a local high amount of attenuation. The dotted line illustrates that the trough70is moved to trough71and the mound80is moved to mound81with lower frequencies when the third chamber is added. The lower frequencies better match the combustion noises of the engine. The difference between the troughs70and80and the difference between mounds71and81may be calculated as a function of the thickness of the third chamber. Accordingly, the dash line illustrates that the trough70is moved to trough72and the mound80is moved to mound82with lower frequencies when a larger third chamber is added.

In addition, increased attenuation performance is attained in a higher frequency range. The higher frequency range may be 500 to 1000 Hz.FIG. 6illustrates that the dotted line for the first thickness of the third chamber corresponds to higher attenuation at mound91compared to mound90when no third chamber is used. Similarly, the dashed line for the second thickness of the third chamber corresponds to even higher attenuation at mound92.

FIG. 11illustrates the attenuation of the muffler using a single thickness and an extender tube (e.g., tube51) traverses two or more of the chambers in the muffler. In this example, the solid line corresponds to a third chamber having a one inch thickness, which is similar to the dotted line inFIG. 6. The dotted line corresponds to the same third chamber with the extender tube added.FIG. 7illustrates that the addition of the extender tube causes the mound for the lowest frequency to shift to lower frequencies (e.g., below 100 Hz) and increase the attenuation at higher frequencies (e.g., between 500 and 1000 Hz). Without the spatial separation between the first chamber21and second chamber25, the extender tubes (e.g., tube51) would have little to no effect on low frequency transmission loss.

FIG. 12illustrates the lateral placement of the third chamber in the canister of the muffler. Positioning the baffle near the center of the chamber will most likely yield the highest transmission Loss, particularly in the mid-frequency range (e.g., 200-1000 Hz). A dual-chamber muffler has a small mound shape in the low frequency range, followed by a larger mound shape. The second mound shape is what is most effected by baffle placement for a dual-chamber muffler.

The shape of the transmission loss plot may be dependent on where the inlet (e.g., input pipe15) is located on the muffler. This effect may be particularly present at the higher frequencies. The muffler inlet length may operate as a quarter wave resonator. The shape of the transmission loss plot may be changed based on the shape of the muffler. The overall length of the muffler may impact the low frequency attenuation capacity. The transmission loss “mound” shape may be governed by this length. The muffler diameter may impact the attenuation capacity and/or height of these “mound” shapes. This is dependent on frequency, but generally true for the low-to-middle range frequencies (e.g., 100-1000 Hz). For a two chamber muffler (with or without the air gap separating the chambers), the ideal ratio may be at or near to 50/50.

FIG. 12illustrates simulations to illustrate that the third chamber or spatial separating chamber has an added benefit when using extended tubes. Extended tubes have little to no effect on the mid-to-low frequency range without the third chamber or separation. The mound, or corresponding trough, that represents the loss of the lowest frequency moves lower when the spatial separating chamber is included, as shown by the smaller dash line93, and even lower when the extender tube is included in combination with the spatial separating chamber, as shown by the dotted95.

FIG. 14illustrates an example flowchart for defining the third chamber according to the first, second, or third embodiments of the muffler described herein. Additional, different, or fewer acts may be provided. The acts are performed in the order shown or other orders. The acts may also be repeated.

At act S101, a thickness is selected for the baffle or third chamber of the muffler. The third chamber may be formed by two baffles having empty space or air between. On either side of the baffle or third chamber is an exhaust containing chamber that facilitates the flow of exhaust from the inlet of the muffler to the outlet.

At act S103, the attenuation of the muffler is measured or predicted at the first thickness. The attenuation may be measured using a microphone comparing the acoustic output of the engine without the muffler connected to the acoustic output of the engine with the muffler connected.

At act S105, the thickness of the baffle or third chamber is adjusted. The thickness of the baffle may be increased by adding plates that are sandwiched together. The thickness of a third chamber containing empty space or air may be increased by moving one of the baffles for the third chamber. Act S103and S105may be repeated until the attenuation of successive measurements increases in order to identify the optimal thickness. At act S107, an extender tube may be selected after the optimal thickness for the baffle or the third chamber is determined. The extender tube length can also be varied to yield optimal attenuation.

The acts ofFIG. 14may be performed by one or more controllers including a specialized processor, one or more memories and a communication interface. Instructions for the one or more controllers may be embodied on a non-transitory computer readable medium.

FIG. 15illustrates an example flowchart for manufacturing the mufflers according to the first, second or third embodiments of the muffler described herein. Additional, different, or fewer acts may be provided. The acts are performed in the order shown or other orders. The acts may also be repeated.

Act S201includes forming a cylindrical housing (e.g., housing277). The housing may be formed from a single piece of metal (e.g., steel or aluminum) that is formed into a cylinder and affixed to itself. One end of the piece of metal may be welded or otherwise secured to another end of the piece of metal. The piece of metal may be heated to facilitate changing the shape of the metal.

Act S203includes inserting a first baffle (e.g., input side baffle243) and a second baffle (e.g., output side baffle241) into the cylindrical housing. The baffles may include one or more openings. The baffles may include a flat face that is inserted to the interior of the housing such that the flat face of the first baffle faces the flat face of the second baffle. An open face of each baffle may face away from the cylinder of the housing.

Act S205includes sliding a first tube (e.g., extender tube251) through the first baffle and the second baffle. One or both of the first baffle and the second baffle may include a collar for guiding the first tube through the opening in the baffle. The first tube may have been formed from punching holes in an open ended pipe. The holes may be arranged in various patterns over a predetermined portion (e.g., ¼) of the tube. In some examples, acts S205is performed before S203and the first tube combined with the first baffle and/or the second baffle is inserted together into the cylindrical housing.

Act S207includes abutting a second tube (e.g., reverse flow tube253) against the second baffle. The second baffle may include an indentation or a collared flange for receiving the second tube. The second tube may be formed from punching holes in various patterns over a predetermined portion of the tube. Act S209includes securing at least one end cap (e.g., both against the housing and the reverse flow tube. Both upstream side end cap263and a downstream side end cap265.