Patent Description:
Engines may be employed to propel or power various devices. For example, a gas turbine engine may be employed to propel a vehicle, such as an aircraft. In the example of the vehicle as an aircraft, the aircraft may also have an additional power unit, such as an auxiliary power unit, to supply power to other components associated with the aircraft and to supply power while the aircraft is on the ground, for example. In addition, in the example of the vehicle as a small size aircraft, such as business jets, these aircraft may employ a micro power unit to supply power to other components of the aircraft and to supply power while the aircraft is on the ground. Micro power units may also be employed by ground based vehicles, to supply power to additional components associated with the ground based vehicles. The operation of the auxiliary power unit and the micro power unit to supply power on the ground, however, may result in noise, which is undesirable for passengers and crew onboard the vehicle, and for service personnel outside. Mufflers for such power units are for example known from <CIT> and <CIT>.

Accordingly, it is desirable to provide a muffler for use with an engine, such as an engine associated with an auxiliary power unit or micro power unit, for reducing the noise experienced by passengers, crew, and service personnel, for example, during the operation of the auxiliary power unit or micro power unit. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

According to various embodiments, provided is a muffler. The muffler includes a housing defining a first chamber, a second chamber and a third chamber. The first chamber is positioned opposite the third chamber within the housing, and the housing is fluidly coupled to a source of exhaust gases via an inlet. The muffler includes at least a pair of nested protrusions in communication with the inlet and configured to receive the exhaust gases. The pair of nested protrusions is coupled to a respective surface of a pair of plates disposed in the housing such that one of the pair of nested protrusions is spaced apart from and opposite another of the pair of nested protrusions to define a tortuous path for the exhaust gases that terminates at an outlet defined along an outer circumference of one of the pair of plates. The first chamber is downstream from the pair of plates and in fluid communication with the outlet. The muffler includes a first tube fluidly coupled between the first chamber and the second chamber that is configured to direct the exhaust gases from the first chamber to the second chamber. The muffler includes a second tube fluidly coupled between the second chamber and the third chamber that is configured to direct the exhaust gases from the second chamber to the third chamber.

The first chamber includes a perforated tube disposed axially within the first chamber. The perforated tube is fluidly coupled to the first tube and configured to direct the exhaust gases from the first chamber to the first tube. The muffler has a longitudinal axis, the pair of plates extend along the longitudinal axis, the first tube extends along an axis substantially parallel to the longitudinal axis and the perforated tube extends along a centerline substantially perpendicular to the longitudinal axis. The second chamber is disposed about the pair of plates proximate the outlet and fluidly isolated from the outlet. The muffler includes a third tube disposed in the third chamber and configured to direct the exhaust gases from the third chamber to exit the muffler. The pair of nested protrusions have a polygonal shape. The source of exhaust gases is a header pipe associated with an engine of a power unit. The pair of plates includes a first plate opposite and spaced apart from a second plate, the first plate including a first surface opposite a second surface, the second plate including a third surface opposite a fourth surface, and the pair of nested protrusions include a first pair of nested protrusions defined on the first surface of the first plate and a second pair of nested protrusions defined on the third surface of the second plate, the first pair of nested protrusions facing the second pair of nested protrusions to define the tortuous path. The first pair of nested protrusions is offset from the second pair of nested protrusions to define the tortuous path. The muffler includes a deswirl assembly coupled about a perimeter of the housing. The housing further comprises a first housing wall, a second housing wall coupled to the first housing wall and a third housing wall, the deswirl assembly coupled to the second housing wall, and the second chamber is defined between the first housing wall, the second housing wall and the first chamber. The third chamber is defined between one of the pair of plates and the third housing wall. The pair of nested protrusions include concentric circular protrusions. The second tube is defined in a sub-housing, and the sub-housing is coupled to one of the pair of plates.

Also provided is a muffler for an engine. The muffler includes a housing defining a first chamber, a second chamber and a third chamber. The first chamber is positioned opposite the third chamber within the housing, the second chamber is radially outboard of the first chamber, and the housing is configured to be fluidly coupled to the engine and is configured to receive exhaust gases from the engine via an inlet. The muffler includes a pressure attenuator including a first plate and a second plate in communication with the inlet and configured to receive the exhaust gases. The first plate and the second plate cooperate to define a tortuous path that extends radially from the inlet. The first plate includes a first pair of nested protrusions offset from a second pair of nested protrusions of the second plate. The pressure attenuator is upstream from the first chamber and the first chamber is fluidly coupled to the pressure attenuator via an outlet defined at an outer perimeter of the first plate. The muffler includes a first tube fluidly coupled between the first chamber and the second chamber configured to direct the exhaust gases from the first chamber to the second chamber. The muffler includes a second tube fluidly coupled between the second chamber and the third chamber configured to direct the exhaust gases from the second chamber to the third chamber.

The first chamber includes a perforated tube disposed axially within the first chamber and the perforated tube is fluidly coupled to the first tube and configured to direct the exhaust gases from the first chamber to the first tube. The muffler has a longitudinal axis, the first plate and the second plate extend along the longitudinal axis, the first tube extends along an axis substantially parallel to the longitudinal axis and the perforated tube extends along a centerline substantially perpendicular to the longitudinal axis. The muffler includes a deswirl assembly coupled about a perimeter of the housing and the housing further comprises a first housing wall, a second housing wall coupled to the first housing wall and a third housing wall, the deswirl assembly coupled to the second housing wall, and the second chamber is defined between the first housing wall, the second housing wall and the first chamber. The muffler includes a third tube disposed in the third chamber and configured to direct the exhaust gases from the third chamber to exit the muffler.

In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with any type of device that would benefit from sound attenuation and the use of the muffler with an auxiliary power unit or a micro power unit described herein is merely one exemplary embodiment according to the present disclosure. In addition, while the muffler is described herein as being used with an auxiliary power unit or a micro power unit onboard a vehicle, such as a bus, motorcycle, train, motor vehicle, marine vessel, aircraft, rotorcraft and the like, the various teachings of the present disclosure can be used with an engine on a stationary platform. Further, it should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure. In addition, while the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that the drawings are merely illustrative and may not be drawn to scale.

As used herein, the term "axial" refers to a direction that is generally parallel to or coincident with an axis of rotation, axis of symmetry, or centerline of a component or components. For example, in a cylinder or disc with a centerline and generally circular ends or opposing faces, the "axial" direction may refer to the direction that generally extends in parallel to the centerline between the opposite ends or faces. In certain instances, the term "axial" may be utilized with respect to components that are not cylindrical (or otherwise radially symmetric). For example, the "axial" direction for a rectangular housing containing a rotating shaft may be viewed as a direction that is generally parallel to or coincident with the rotational axis of the shaft. Furthermore, the term "radially" as used herein may refer to a direction or a relationship of components with respect to a line extending outward from a shared centerline, axis, or similar reference, for example in a plane of a cylinder or disc that is perpendicular to the centerline or axis. In certain instances, components may be viewed as "radially" aligned even though one or both of the components may not be cylindrical (or otherwise radially symmetric). Furthermore, the terms "axial" and "radial" (and any derivatives) may encompass directional relationships that are other than precisely aligned with (e.g., oblique to) the true axial and radial dimensions, provided the relationship is predominantly in the respective nominal axial or radial direction. As used herein, the term "substantially" denotes within <NUM>% to account for manufacturing tolerances.

With reference to <FIG>, a functional block diagram illustrates a muffler <NUM> employed with an exemplary engine <NUM>. In this example, the engine <NUM> is associated with a power unit <NUM>, which is onboard a vehicle <NUM>. For example, the power unit <NUM> may be employed with various applications including aerospace (small jets and turboprops; charter companies; fractional companies; corporate fleets; and special mission aircraft). Other applications include military vehicles (e.g., M1 Tank, Joint Light Tactical Vehicle, Paladin, etc.); mobile command posts; mobile medical facilities; and emergency response. Ground based vehicle applications include tracked vehicles and artillery pieces. Military ground power equipment applications include command posts, remote power supplies, medical units, and integrated aircraft systems. Portable power systems applications include remote power generation systems and rapid deployment power systems. Thus, in other examples, the power unit <NUM> (including the engine <NUM> and the muffler <NUM>) may be employed on a stationary platform. As will be discussed, the muffler <NUM> receives exhaust gases <NUM> from the engine <NUM>, and attenuates the sound generated by the engine <NUM> to reduce the noise experienced by passengers, crew, and service personnel. In certain instances, the muffler <NUM> may also receive cooling fluid, such as cooling air <NUM>, from the engine <NUM> or a cooling fan <NUM> associated with the engine <NUM>, which may be used to cool the muffler <NUM>. After passing through the muffler <NUM>, the exhaust gases <NUM> may exit the power unit <NUM> and the vehicle <NUM>, or may be directed to another secondary muffler downstream.

The engine <NUM> comprises any suitable engine, including, but not limited to, a gas turbine engine, an internal combustion engine, a Wankel engine, etc. As the muffler <NUM> may be employed with any type of engine <NUM> that generates the exhaust gases <NUM> and optionally cooling air <NUM>, the engine <NUM> will not be discussed in detail herein. Briefly, in the example of the engine <NUM> as a Wankel engine, the engine <NUM> employs an eccentric rotary design to convert pressure into rotating motion. The engine <NUM> is configured to combust a fuel and air mixture to generate the rotary movement, which is used to generate electrical power. The fuel is any suitable combustible fuel, including, but not limited to jet fuel (unleaded kerosene or a naphtha-kerosene blend), aviation gasoline, biofuels, diesel, gasoline, and the like. In one example, the engine <NUM> includes one or more spark coils to generate an electric spark to ignite the fuel, and the resulting combustion drives a rotor of the engine <NUM>. The rotor, in turn, drives an output shaft <NUM>. One end of the output shaft <NUM> is coupled to a starter-generator <NUM> to drive the starter-generator <NUM> to generate electric power for the vehicle <NUM>, and the other end of the output shaft <NUM> is coupled to the cooling fan <NUM>. The cooling fan <NUM> provides the cooling air <NUM> to cool the engine <NUM> and the muffler <NUM>. The electric power generated by the starter-generator <NUM> is provided to a consumer <NUM> associated with the vehicle <NUM>, including, but not limited to a heating, ventilation and cooling system, a lighting system, a starter system, a flight instrument system, etc..

The power unit <NUM> comprises an auxiliary power unit or a micro power unit, which is coupled to the vehicle <NUM> to supply electrical power when the vehicle <NUM> is on the ground, for example. As the muffler <NUM> and the engine <NUM> may be associated with any type of power unit <NUM>, the power unit <NUM> will not be discussed in detail herein. Briefly, in one example, the power unit <NUM> is a micro power unit, such as that described in commonly assigned <CIT> et. , and published as <CIT>, the relevant portion of which is hereby incorporated by reference herein. The engine <NUM>, the starter-generator <NUM>, the cooling fan <NUM> and the muffler <NUM> may be contained within a housing <NUM> to enable the power unit <NUM> to be removable from the vehicle <NUM>. Generally, as discussed, the power unit <NUM> includes the engine <NUM>, which generates power to drive the starter-generator <NUM> to supply electric power to the consumer <NUM> of the vehicle <NUM>.

As discussed, the muffler <NUM> is in fluid communication with the engine <NUM> to receive the exhaust gases <NUM>, and optionally, is in fluid communication with the cooling fan <NUM> to receive the cooling air <NUM>. With reference to <FIG>, and additional reference to <FIG>, the muffler <NUM> is shown in greater detail. In on example, the muffler <NUM> includes a housing <NUM>, a header pipe <NUM> (<FIG>), a pressure attenuator <NUM> (<FIG>), a first, forward chamber <NUM>, a first tube or first transfer tube <NUM> (<FIG>), a second, outer chamber <NUM> (<FIG>), a second tube or second transfer tube <NUM> (<FIG>), a third, aft chamber <NUM>, a third tube or exhaust pipe <NUM> and a deswirl assembly <NUM>.

With reference to <FIG>, the housing <NUM> surrounds and encloses the pressure attenuator <NUM>, the forward chamber <NUM>, the first transfer tube <NUM>, the outer chamber <NUM>, the second transfer tube <NUM>, and the aft chamber <NUM>. The housing <NUM> also encloses and surrounds a portion of the header pipe <NUM> and the exhaust pipe <NUM>. The housing <NUM> is composed of a metal or metal alloy, and may be cast, stamped, forged, or additively manufactured. In this example, the housing <NUM> includes a first housing wall <NUM>, a second housing wall <NUM> and a third housing wall <NUM>. The first housing wall <NUM> is upstream from the third housing wall <NUM> in a direction of fluid flow through the muffler <NUM>. The first housing wall <NUM> is substantially frustoconical, however, the first housing wall <NUM> may have any desired shape. The second housing wall <NUM> is coupled to the first housing wall <NUM> and the third housing wall <NUM>. The second housing wall <NUM> is substantially cylindrical. The second housing wall <NUM> also defines an intake bore <NUM> (<FIG>). The intake bore <NUM> enables a portion of the header pipe <NUM> to pass into the interior of the housing <NUM>. The third housing wall <NUM> is substantially conical, and defines an exhaust bore <NUM>. The exhaust bore <NUM> enables a portion of the exhaust pipe <NUM> to pass out of the housing <NUM>.

The header pipe <NUM> is fluidly coupled to the engine <NUM> to receive the exhaust gases <NUM>. The header pipe <NUM> is received through the intake bore <NUM>, and terminates at the pressure attenuator <NUM> at an end 204a. In this example, with reference to <FIG>, the header pipe <NUM> bends or curves between the intake bore <NUM> and the end 204a to direct the exhaust gases <NUM> into a center of the pressure attenuator <NUM>. In one example, the header pipe <NUM> extends through a sub-housing <NUM> associated with the second transfer tube <NUM>. The end 204a of the pressure attenuator <NUM> is received and coupled to an annular flange <NUM>, which extends axially outward from a portion of the pressure attenuator <NUM>.

The pressure attenuator <NUM> extends radially within the housing <NUM>. In one example, the pressure attenuator <NUM> includes two spaced apart plates, a first plate <NUM> and an opposed second plate <NUM>. In this example, each of the first plate <NUM> and the second plate <NUM> are circular to comport with the shape of the second housing wall <NUM>, however, the first plate <NUM> and the second plate <NUM> may have any desired shape, including, but not limited to, rectangular, oval, square, etc. With brief reference to <FIG>, the first plate <NUM> includes at least a pair of nested protrusions, and in this example, the first plate <NUM> includes five first protrusions 246a-246e. With reference back to <FIG>, in this example, the first protrusions 246a-246e are concentric to a central axis C of the first plate <NUM> and the second plate <NUM>, and are substantially evenly spaced radially along a longitudinal axis L of the muffler <NUM>. It should be noted that the first protrusions 246a-246e may be arranged in other patterns on the first plate <NUM> and may not be evenly spaced. Each of the first protrusions 246a-246e extend axially from a first surface 240a of the first plate <NUM>. The first surface 240a is opposite a second surface 240b. In this example, each of the first protrusions 246a-246e are planar or extend from the first surface 240a along an axis substantially parallel to the central axis C. In other examples, the first protrusions 246a-246e may extend from the first surface 240a at an angle so as to extend along an axis oblique to the central axis C. Each of the first protrusions 246a-246e have an end coupled to the first surface 240a, and an opposite end or terminal end <NUM>. The terminal end <NUM> of each of the first protrusions 246a-246e is spaced apart from a third surface 242a of the second plate <NUM>.

With brief reference to <FIG>, the second plate <NUM> includes at least a pair of nested protrusions, and in this example, the second plate <NUM> includes five second protrusions 250a-250e. With reference back to <FIG>, in this example, the second protrusions 250a-250e are concentric to the central axis C of the first plate <NUM> and the second plate <NUM>, and are substantially evenly spaced radially along the longitudinal axis L of the muffler <NUM>. It should be noted that the second protrusions 250a-250e may be arranged in other patterns on the second plate <NUM> and may not be evenly spaced. Each of the second protrusions 250a-250e extend axially from the third surface 242a of the second plate <NUM>. The third surface 242a is opposite a fourth surface 242b. In this example, each of the second protrusions 250a-250e are planar or extend from the third surface 242a along an axis substantially parallel to the central axis C. In other examples, the second protrusions 250a-250e may extend from the third surface 242a at an angle so as to extend along an axis oblique to the central axis C. Each of the second protrusions 250a-250e have an end coupled to the third surface 242a, and an opposite end or terminal end <NUM>. The terminal end <NUM> of each of the second protrusions 250a-250e is spaced apart from the first surface 240a of the first plate <NUM>. In this example, the second plate <NUM> defines a bore <NUM> that forms an inlet of the pressure attenuator <NUM>. The bore <NUM> is fluidly coupled to the header pipe <NUM>. The annular flange <NUM> is defined about the bore <NUM> and extends outwardly from the fourth surface 242b of the second plate <NUM>. In this example, the first protrusions 246a-246e and the second protrusions 250a-250e are circular, however, it should be noted that the first protrusions 246a-246e and the second protrusions 250a-250e may have any desired shape.

In one example, with reference back to <FIG>, the second plate <NUM> is coupled to and integrally formed with the second housing wall <NUM>. In this example, a plurality of struts <NUM> interconnect the second plate <NUM> with the second housing wall <NUM>. The struts <NUM> are spaced apart about the circumference of the second plate <NUM> and the second housing wall <NUM> to define a plurality of apertures <NUM>. Each of the apertures <NUM> has a generally race-track shape. The apertures <NUM> enable the fluid to flow along the exterior of the second housing wall <NUM> in the outer chamber <NUM>. The third housing wall <NUM> is coupled to the second housing wall <NUM> and is in fluid communication with the apertures <NUM>. As will be discussed, the sub-housing <NUM> fluidly isolates the aft chamber <NUM> from the outer chamber <NUM>.

With reference back to <FIG>, in this example, the first protrusions 246a-246e face the second protrusions 250a-250e and are offset or misaligned from the second protrusions 250a-250e along the longitudinal axis L. By spacing the terminal end <NUM>, <NUM> of the first protrusions 246a-246e and the second protrusions 250a-250e, respectively, from the corresponding one of the first surface 240a and the third surface 242a and misaligning the first protrusions 246a-246e from the second protrusions 250a-250e, an undulating tortuous path <NUM> for the exhaust gases <NUM> is defined between the first protrusions 246a-246e and the second protrusions 250a-250e along the longitudinal axis L. The tortuous path <NUM> extends radially from the inlet defined by the bore <NUM> to an outer perimeter or circumference <NUM> of the first plate <NUM>. The outer circumference <NUM> of the first plate <NUM> is spaced apart from a chamber wall <NUM> of the forward chamber <NUM> and defines an outlet <NUM> about the outer circumference <NUM> for the exhaust gases <NUM> to enter into the forward chamber <NUM>. The tortuous path <NUM> results in pressure loss for the exhaust gases <NUM>, which has to make sharp turns to pass between gaps <NUM> defined between the respective terminal end <NUM>, <NUM> and the respective first surface 240a and third surface 242a. The tortuous path <NUM> reduces pressure, and thus, velocity of incoming flow. The velocity reduction limits flow noise generation, while incoming acoustic pulses are also attenuated via viscous dissipation along the long path length out of the first plate <NUM> and the second plate <NUM>.

It should be noted that while the terminal end <NUM>, <NUM> is illustrated herein as being smooth, the terminal end <NUM>, <NUM> of one or more of the first protrusions 246a-246e and the second protrusions 250a-250e may be serrated, scalloped, or have a different shape. In addition, while the first plate <NUM> and the second plate <NUM> are illustrated herein as extending along the longitudinal axis L over substantially an entirety of the forward chamber <NUM>, in other embodiments, the first plate <NUM> and the second plate <NUM> may have a reduced height or length along the longitudinal axis L such that the first plate <NUM> and the second plate <NUM> extend along the longitudinal axis L for only a portion of the forward chamber <NUM>. The first plate <NUM> and the second plate <NUM> are each composed of metal or metal alloy, and may be stamped, cast, machined, additively manufactured, etc. In one example, the first plate <NUM> and the second plate <NUM> may be stamped with grooves for the first protrusions 246a-246e and the second protrusions 250a-250e, respectively, and the first protrusions 246a-246e and the second protrusions 250a-250e may be separately formed, via stamping, for example, and fixedly coupled to the grooves of the respective first plate <NUM> and the second plate <NUM> via welding or brazing, for example. Optionally, one or more pins may be employed to couple the first plate <NUM> to the second plate <NUM> to maintain the gap <NUM> between the first plate <NUM> and the second plate <NUM>.

It should be noted that in other embodiments, the pressure attenuator <NUM> for the muffler <NUM> may be configured differently to define the tortuous path <NUM> to reduce pressure and velocity of incoming airflow. For example, with reference to <FIG>, a side view of a pressure attenuator <NUM> is shown. As the pressure attenuator <NUM> includes components that are the same or similar to components of the pressure attenuator <NUM> discussed with regard to <FIG>, the same reference numerals will be used to denote the same or similar components. The pressure attenuator <NUM> extends radially within the housing <NUM>. It should be noted that the housing <NUM> may be modified, if desired, to accommodate the shape of the pressure attenuator <NUM>.

In one example, the pressure attenuator <NUM> includes two spaced apart plates, a first plate <NUM> and an opposed second plate <NUM>. In this example, with reference to <FIG>, each of the first plate <NUM> and the second plate <NUM> are substantially D-shaped. With reference to <FIG>, the first plate <NUM> includes at least a pair of nested protrusions, and in this example, the first plate <NUM> includes four first protrusions 312a-312d. The first protrusions 312a-312d are nested relative to each other about an axis A300 of the first plate <NUM> and the second plate <NUM> (<FIG>), and are substantially evenly spaced along a first surface 302a of the first plate <NUM>. It should be noted that the first protrusions 312a-312d may be arranged in other patterns on the first plate <NUM> and may not be evenly spaced. Each of the first protrusions 312a-312d extend axially from the first surface 302a of the first plate <NUM>. The first surface 302a is opposite a second surface 302b. In this example, each of the first protrusions 312a-312d are planar or extend from the first surface 302a along an axis substantially parallel to the axis A300. In other examples, the first protrusions 312a-312d may extend from the first surface 302a at an angle so as to extend along an axis oblique to the axis A300. Each of the first protrusions 312a-312d have an end coupled to the first surface 302a, and an opposite end or terminal end <NUM>. The terminal end <NUM> of each of the first protrusions 312a-312d is spaced apart from a third surface 304a of the second plate <NUM>.

With reference back to <FIG>, the second plate <NUM> includes at least a pair of nested protrusions, and in this example, the second plate <NUM> includes four second protrusions 316a-316d. The second protrusions 316a-316d are nested relative to each other about an axis A300 of the first plate <NUM> and the second plate <NUM>, and are substantially evenly spaced along the third surface 304a of the second plate <NUM>. It should be noted that the second protrusions 316a-316d may be arranged in other patterns on the second plate <NUM> and may not be evenly spaced. Each of the second protrusions 316a-316d extend axially from the third surface 304a of the second plate <NUM>. The third surface 304a is opposite a fourth surface 304b. In this example, each of the second protrusions 316a-316d are planar or extend from the third surface 304a along an axis substantially parallel to the axis A300 (<FIG>). In other examples, the second protrusions 316a-316d may extend from the third surface 304a at an angle so as to extend along an axis oblique to the axis A300. Each of the second protrusions 316a-316d have an end coupled to the third surface 304a, and an opposite end or terminal end <NUM>. The terminal end <NUM> of each of the second protrusions 316a-316d is spaced apart from the first surface 302a of the first plate <NUM>. In this example, the second plate <NUM> defines the bore <NUM> that forms an inlet of the pressure attenuator <NUM>. With brief reference to <FIG>, as discussed, the bore <NUM> is fluidly coupled to the header pipe <NUM>. The annular flange <NUM> is defined about the bore <NUM> and extends outwardly from the fourth surface 304b of the second plate <NUM>.

In this example, the first protrusions 312a-312d and the second protrusions 316a-316d have an arbitrary shape or a polygonal shape. With reference to <FIG> and <FIG>, each of the first protrusions 312a-312d and the second protrusions 316a-316d have a substantially D-shape or include a planar segment <NUM> and an arcuate segment <NUM> that cooperate to enclose a volume. The planar segment <NUM> extends substantially perpendicular to the longitudinal axis L. The volume enclosed by the planar segment <NUM> and the arcuate segment <NUM> is different or increases from the innermost first protrusion 312a and the innermost second protrusion 316a to the outermost first protrusion 312d and the outermost second protrusion 316d. It should be noted that the D-shape illustrated and described herein is merely just one example of a polygonal shape that may be employed to form one or more of the first protrusions 312a-312d and the second protrusions 316a-316d. Other examples include, but are not limited to stars, pentagons, lobed-shapes, daisy shapes, etc. In addition, it should be noted that a pressure attenuator may be formed in which protrusions having the shape of the first protrusions 312a-312d and/or the second protrusions 316a-316d alternate with the circular shape of the first protrusions 246a-246e and the second protrusions 250a-250e. Moreover, it should be noted that a plate of a pressure attenuator may be formed in which a protrusion having the shape of the first protrusions 246a-246e and/or the first protrusions 312a-312d is mixed with protrusions having a polygonal shape. For example, a plate of a pressure attenuator may be formed such that each protrusion of the plate has a unique polygonal shape.

In this example, the first protrusions 312a-312d face the second protrusions 316a-316d and are offset or misaligned from the second protrusions 316a-316d along the longitudinal axis L. With reference to <FIG>, by spacing the terminal end <NUM>, <NUM> of the first protrusions 312a-312d and the second protrusions 316a-316d, respectively, from the corresponding one of the first surface 302a and the third surface 304a and misaligning the first protrusions 312a-312d from the second protrusions 316a-316d, the undulating tortuous path <NUM> for the exhaust gases <NUM> (<FIG>) is defined between the first protrusions 312a-312d and the second protrusions 316a-316d along the longitudinal axis L. The tortuous path <NUM> extends radially from the inlet defined by the bore <NUM> to an outer perimeter or circumference <NUM> of the first plate <NUM>. The outer circumference <NUM> of the first plate <NUM> defines an outlet <NUM> about the outer circumference <NUM> for the exhaust gases <NUM> to enter into the forward chamber <NUM> (<FIG>). The tortuous path <NUM> results in pressure loss for the exhaust gases <NUM> (<FIG>), which has to make sharp turns to pass between gaps <NUM> defined between the respective terminal end <NUM>, <NUM> and the respective first surface 302a and third surface 304a.

It should be noted that while the terminal end <NUM>, <NUM> is illustrated herein as being smooth, the terminal end <NUM>, <NUM> of one or more of the first protrusions 312a-312d and the second protrusions 316a-316d may be serrated, scalloped, or have a different shape. The first plate <NUM> and the second plate <NUM> are each composed of metal or metal alloy, and may be stamped, cast, machined, additively manufactured, etc. The first plate <NUM> and the second plate <NUM> may be stamped with grooves for the first protrusions 312a-312d and the second protrusions 316a-316d, respectively, and the first protrusions 312a-312d and the second protrusions 316a-316d may be separately formed, via stamping, for example, and fixedly coupled to the grooves of the respective first plate <NUM> and the second plate <NUM> via welding or brazing, for example. Optionally, one or more pins may be employed to couple the first plate <NUM> to the second plate <NUM> to maintain the gap <NUM> between the first plate <NUM> and the second plate <NUM>.

It should be noted that in other embodiments, the first plate <NUM> and the second plate <NUM> of the pressure attenuator <NUM> for the muffler <NUM> may be configured differently to define the tortuous path <NUM> to reduce pressure and velocity of incoming airflow. For example, with reference to <FIG>, a front view of a first plate <NUM> is shown and in <FIG>, a front view of a second plate <NUM> is shown. As the first plate <NUM> and the second plate <NUM> include components that are the same or similar to components of the first plate <NUM> and the second plate <NUM> of the pressure attenuator <NUM> discussed with regard to <FIG>, the same reference numerals will be used to denote the same or similar components. The first plate <NUM> and the second plate <NUM> extend radially within the housing <NUM>. It should be noted that the housing <NUM> may be modified, if desired, to accommodate the shape of the first plate <NUM> and the second plate <NUM>.

In one example, the first plate <NUM> is opposite the second plate <NUM> to define a pressure attenuator. In this example, each of the first plate <NUM> and the second plate <NUM> are substantially kidney-shaped, and extend along a plate longitudinal axis PL. With reference to <FIG>, the first plate <NUM> includes at least a pair of nested protrusions, and in this example, the first plate <NUM> includes four first protrusions 410a-410d. The first protrusions 410a-410d are nested relative to each other about an axis A400 of the first plate <NUM> and the second plate <NUM> (<FIG>), and are substantially evenly spaced along a first surface 400a of the first plate <NUM>. It should be noted that the first protrusions 410a-410d may be arranged in other patterns on the first plate <NUM> and may not be evenly spaced. Each of the first protrusions 410a-410d extend axially from the first surface 400a of the first plate <NUM>. The first surface 400a is opposite a second surface 400b. In this example, each of the first protrusions 410a-410d are planar or extend from the first surface 400a along an axis substantially parallel to the axis A400. In other examples, the first protrusions 410a-410d may extend from the first surface 400a at an angle so as to extend along an axis oblique to the axis A400. Each of the first protrusions 410a-410d have an end coupled to the first surface 400a, and an opposite end or terminal end <NUM>. When assembled opposite the second plate <NUM>, the terminal end <NUM> of each of the first protrusions 410a-410d is spaced apart from a third surface 402a of the second plate <NUM> (<FIG>).

With reference to <FIG>, the second plate <NUM> includes at least a pair of nested protrusions, and in this example, the second plate <NUM> includes four second protrusions 414a-414d. The second protrusions 414a-414d are nested relative to each other about an axis A400 of the first plate <NUM> and the second plate <NUM>, and are substantially evenly spaced along the third surface 402a of the second plate <NUM>. It should be noted that the second protrusions 414a-414d may be arranged in other patterns on the second plate <NUM> and may not be evenly spaced. Each of the second protrusions 414a-414d extend axially from the third surface 402a of the second plate <NUM>. The third surface 402a is opposite a fourth surface 402b. In this example, each of the second protrusions 414a-414d are planar or extend from the third surface 402a along an axis substantially parallel to the axis A400. In other examples, the second protrusions 414a-414d may extend from the third surface 402a at an angle so as to extend along an axis oblique to the axis A400. Each of the second protrusions 414a-414d have an end coupled to the third surface 402a, and an opposite end or terminal end <NUM>. When assembled opposite the first plate <NUM>, the terminal end <NUM> of each of the second protrusions 414a-414d is spaced apart from the first surface 400a of the first plate <NUM> (<FIG>). In this example, the second plate <NUM> defines the bore <NUM> that forms an inlet of the pressure attenuator. The second plate <NUM> may also include the annular flange <NUM> defined about the bore <NUM> and extending outwardly from the fourth surface 402b of the second plate <NUM>.

In this example, the first protrusions 410a-410d and the second protrusions 414a-414d have an arbitrary shape or a polygonal shape. With reference to <FIG> and <FIG>, each of the first protrusions 410a-410d and the second protrusions 414a-414d have a substantially kidney shape that encloses the volume. The volume enclosed by each of the first protrusions 410a-410d and the second protrusions 414a-414d is different or increases from the innermost first protrusion 410a and the innermost second protrusion 414a to the outermost first protrusion 410d and the outermost second protrusion 414d. It should be noted that the kidney shape illustrated and described herein is merely just one example of a polygonal shape that may be employed to form one or more of the first protrusions 410a-410d and the second protrusions 414a-414d. Other examples include, but are not limited to stars, pentagons, lobed-shapes, daisy shapes, etc. In addition, the first protrusions 410a-410d and the second protrusions 414a-414d may comprise circles or ovals.

In this example, the first protrusions 410a-410d face the second protrusions 414a-414d and are offset or misaligned from the second protrusions 414a-414d so as to define the undulating tortuous path <NUM> between the first plate <NUM> and the second plate <NUM> when assembled. The tortuous path <NUM> extends radially from the inlet defined by the bore <NUM> (<FIG>) to an outer perimeter or circumference <NUM> of the first plate <NUM> (<FIG>). The outer circumference <NUM> of the first plate <NUM> defines an outlet <NUM> about the outer circumference <NUM> for the exhaust gases <NUM> to enter into the forward chamber <NUM> (<FIG>). The tortuous path <NUM> results in pressure loss for the exhaust gases <NUM> (<FIG>), which has to make sharp turns to pass between gaps <NUM> defined between the respective terminal end <NUM>, <NUM> and the respective first surface 400a and third surface 402a when the first plate <NUM> is coupled to the second plate <NUM>.

It should be noted that while the terminal end <NUM>, <NUM> is illustrated herein as being smooth, the terminal end <NUM>, <NUM> of one or more of the first protrusions 410a-410d and the second protrusions 414a-414d may be serrated, scalloped, or have a different shape. The first plate <NUM> and the second plate <NUM> are each composed of metal or metal alloy, and may be stamped, cast, machined, additively manufactured, etc. The first plate <NUM> and the second plate <NUM> may be stamped with grooves for the first protrusions 410a-410d and the second protrusions 414a-414d, respectively, and the first protrusions 410a-410d and the second protrusions 414a-414d may be separately formed, via stamping, for example, and fixedly coupled to the grooves of the respective first plate <NUM> and the second plate <NUM> via welding or brazing, for example. Optionally, one or more pins may be employed to couple the first plate <NUM> to the second plate <NUM> to maintain the gap <NUM> between the first plate <NUM> and the second plate <NUM>.

With reference back to <FIG>, the forward chamber <NUM> is substantially frustoconical, however, the forward chamber <NUM> may have any polygonal shape, including, but not limited to cylindrical, hemispherical, etc. The forward chamber <NUM> is downstream from the pressure attenuator <NUM> and is fluidly coupled to the outlet <NUM>. The forward chamber <NUM> includes the chamber wall <NUM>, which extends from the outlet <NUM> to proximate the first housing wall <NUM>. In this example, the chamber wall <NUM> is spaced apart from the first housing wall <NUM> to define the outer chamber <NUM> between the chamber wall <NUM> and the first housing wall <NUM>. The chamber wall <NUM> is substantially hemispherical, but the chamber wall <NUM> may have any polygonal shape, including, but not limited to cylindrical, frustoconical, etc. (<FIG> and <FIG>). The chamber wall <NUM> may be one-piece, and may be composed of metal or metal alloy and stamped, cast, machined etc. to define the forward chamber <NUM>. The chamber wall <NUM> also defines a chamber bore 260a. The chamber bore 260a receives the first transfer tube <NUM> to enable the first transfer tube <NUM> to direct the exhaust gases <NUM> out of the forward chamber <NUM>.

The forward chamber <NUM> also includes and is fluidly coupled to a perforated tube <NUM>. The perforated tube <NUM> is composed of a metal or metal alloy, and is stamped, cast, machined, additively manufactured, etc. The perforated tube <NUM> is cylindrical and coaxial with the central axis C. Thus, the perforated tube <NUM> extends along an axis, which is coaxial with the central axis C and substantially perpendicular to the longitudinal axis L. The perforated tube <NUM> is coupled to the second surface 240b of the first plate <NUM> at a first tube end 270a and extends from the first plate <NUM> to the chamber wall <NUM> where a second tube end 270b is coupled to the chamber wall <NUM>. The perforated tube <NUM> defines a plurality of holes or perforations <NUM>, which are spaced apart about a perimeter or circumference of the perforated tube <NUM> from the first tube end 270a to proximate the second tube end 270b. The perforations <NUM> enable the exhaust gases <NUM> from the forward chamber <NUM> to flow into the perforated tube <NUM>. The perforated tube <NUM> is fluidly and physically coupled to the first transfer tube <NUM>.

The first transfer tube <NUM> is fluidly coupled between the forward chamber <NUM> and the outer chamber <NUM>. The first transfer tube <NUM> is composed of metal or metal alloy, and is stamped, cast, machined, additively manufactured, etc. The first transfer tube <NUM> is cylindrical, and has a solid outer wall. The first transfer tube <NUM> is fixedly coupled to the perforated tube <NUM> via welding, for example, and is coupled to the chamber wall <NUM>. The first transfer tube <NUM> has a first transfer inlet 210a defined at the perforated tube <NUM>, and a first transfer outlet 210b defined at the chamber wall <NUM> (<FIG>). The first transfer tube <NUM> extends radially, along an axis substantially parallel to the longitudinal axis L, and substantially perpendicular to the central axis C. The first transfer tube <NUM> directs the exhaust gases <NUM> from the forward chamber <NUM> to the outer chamber <NUM>.

The outer chamber <NUM> is defined between the chamber wall <NUM> and the first housing wall <NUM>, and between the outer circumference <NUM> of the pressure attenuator <NUM> and the second housing wall <NUM>. Thus, the outer chamber <NUM> is defined by a portion of the housing <NUM> exterior to the pressure attenuator <NUM> and the forward chamber <NUM>. Stated another way, the outer chamber <NUM> is radially and axially outboard of the forward chamber <NUM> and the pressure attenuator <NUM>. The outer chamber <NUM> is defined to extend about or circumscribe the first plate <NUM> and the second plate <NUM>, but is fluidly isolated from the pressure attenuator <NUM>. In one example, a volume of the outer chamber <NUM> is different, and less than, a volume of the forward chamber <NUM>. It should be noted that the outer chamber <NUM>, however, may have any desired volume that may be greater or less than the volume of the forward chamber <NUM> to target predetermined frequencies. The forward chamber <NUM> and the outer chamber <NUM> are each generally an expansion chamber. The dimensions of the outer chamber <NUM> may be tuned to frequencies that are not treated by the forward chamber <NUM> or the aft chamber <NUM>. The outer chamber <NUM> is fluidly coupled to the first transfer tube <NUM> and the second transfer tube <NUM>. The first transfer tube <NUM> directs the exhaust gases <NUM> into the outer chamber <NUM>, while the second transfer tube <NUM> directs the exhaust gases <NUM> into the aft chamber <NUM>.

The second transfer tube <NUM> is fluidly coupled between the outer chamber <NUM> and the aft chamber <NUM>. The second transfer tube <NUM> is substantially cylindrical, and has a racetrack or oval cross-section. The second transfer tube <NUM> has a solid outer wall. In one example, with reference to <FIG>, the second transfer tube <NUM> is defined in the sub-housing <NUM>. The sub-housing <NUM> is composed of metal or metal alloy, and is stamped, cast, machined, additively manufactured, etc. The sub-housing <NUM> is generally annular, and includes a first end 215a opposite a second end 215b. The first end 215a is circumferentially open, and is enclosed by the fourth surface 242b of the second plate <NUM> (<FIG>). The sub-housing <NUM> cooperates with the second plate <NUM> to fluidly isolate the aft chamber <NUM> from the outer chamber <NUM>. The second transfer tube <NUM> is defined radially inward toward a center of the sub-housing <NUM>, but is spaced apart from the header pipe <NUM>. The second end 215b of the sub-housing <NUM> may be conical such that the sub-housing <NUM> tapers from the second transfer tube <NUM> along the second end 215b (<FIG>). The second end 215b is substantially circumferentially enclosed, and defines a bore <NUM>. With reference to <FIG>, the bore <NUM> receives the exhaust pipe <NUM> to couple the exhaust pipe <NUM> to the muffler <NUM>. The sub-housing <NUM> is fixedly coupled to the third housing wall <NUM> via brazing or welding, for example, and the sub-housing <NUM> is coupled to the fourth surface 242b of the second plate <NUM> via brazing or welding, for example. The second transfer tube <NUM> extends radially, along an axis substantially parallel to the longitudinal axis L, and substantially perpendicular to the central axis C. The second transfer tube <NUM> directs the exhaust gases <NUM> from the outer chamber <NUM> to the aft chamber <NUM> defined within the sub-housing <NUM>.

The aft chamber <NUM> is defined within the sub-housing <NUM> between the second transfer tube <NUM> and the exhaust pipe <NUM>. With continued reference to <FIG>, the sub-housing <NUM> includes an aft chamber wall <NUM>, which is coupled to the fourth surface 242b of the second plate <NUM> and the third housing wall <NUM>. Thus, the aft chamber <NUM> is defined between the second plate <NUM> and the third housing wall <NUM>, and is fluidly isolated from the pressure attenuator <NUM>. The aft chamber <NUM> is fluidly coupled to the second transfer tube <NUM> to receive the exhaust gases <NUM> from the outer chamber <NUM>, and is fluidly coupled to the exhaust pipe <NUM>.

The exhaust pipe <NUM> is fluidly coupled to the aft chamber <NUM> and extends beyond the housing <NUM> of the muffler <NUM> to direct the exhaust gases <NUM> from the muffler <NUM>. The exhaust pipe <NUM> is composed of metal or metal alloy, and is stamped, cast, machined, additively manufactured, etc. The exhaust pipe <NUM> is cylindrical, and is solid. The exhaust pipe <NUM> is fixedly coupled to the bore <NUM> of the sub-housing <NUM> via brazing or welding, for example, and is coupled to the exhaust bore <NUM> of the third housing wall <NUM> via brazing or welding, for example. The exhaust pipe <NUM> extends axially, along an axis substantially perpendicular to the longitudinal axis L, and substantially parallel to the central axis C. The exhaust pipe <NUM> directs the exhaust gases <NUM> from the muffler <NUM>, and in one example, directs the exhaust gases <NUM> to an ambient environment surrounding the engine <NUM> (<FIG>). Alternatively, the exhaust pipe <NUM> may be fluidly coupled to a downstream secondary muffler.

With reference back to <FIG>, in one example, the deswirl assembly <NUM> is defined about the second housing wall <NUM>. It should be noted that in certain embodiments, the muffler <NUM> need not include the deswirl assembly <NUM> and the deswirl assembly <NUM> may be optional. The deswirl assembly <NUM> includes an outer assembly wall <NUM> and at least one or a plurality of vanes <NUM>. The deswirl assembly <NUM> is composed of metal or metal alloy, and is cast, machined, forged, additively manufactured, etc. The outer assembly wall <NUM> is annular, and is concentric with the second housing wall <NUM>. The outer assembly wall <NUM> extends about the perimeter of the second housing wall <NUM>, and is spaced apart from the second housing wall <NUM> to define an airflow path <NUM>. The outer assembly wall <NUM> has a first wall end 290a and a second wall end 290b. The first wall end 290a is upstream from the second wall end 290b, and receives the cooling air <NUM> (<FIG>) from the cooling fan <NUM>. The outer assembly wall <NUM> is substantially planar from the first wall end 290a to proximate the second wall end 290b. The second wall end 290b is coupled to a guide flange <NUM>. The guide flange <NUM> is annular (<FIG>), and curves radially inward from a first flange end 291a to a second flange end 291b. The curvature of the guide flange <NUM> directs the cooling air <NUM> along an exterior surface of the third housing wall <NUM>. The guide flange <NUM> is composed of metal or metal alloy, and is cast, stamped, machined, additively manufactured, etc. The guide flange <NUM> is coupled to the second wall end 290b via welding or brazing, for example, however, other techniques may be employed. For example, the guide flange <NUM> may be integrally formed with the outer assembly wall <NUM>.

The vanes <NUM> are spaced apart about the perimeter of the second housing wall <NUM> and coupled between the second housing wall <NUM> and the outer assembly wall <NUM>. The vanes <NUM> are coupled to the second housing wall <NUM>, via brazing or welding, for example, and are coupled to the outer assembly wall <NUM> via brazing or welding, for example, or may be integrally formed with the outer assembly wall <NUM>. The vanes <NUM> extend along an axis substantially parallel to the centerline C and substantially perpendicular to the longitudinal axis L, however, in other embodiments, the vanes <NUM> may be orientated differently. With reference to <FIG>, each of the vanes <NUM> has a leading end 294a and an opposite trailing end 294b along the airflow path <NUM>. The leading end 294a is proximate the first wall end 290a, and the trailing end 294b is proximate the second wall end 290b. The vanes <NUM> remove tangential velocity from the cooling air <NUM> as it flows through the deswirl assembly <NUM> along the airflow path <NUM>.

In one example, with reference to <FIG>, with the first protrusions 246a-246e coupled to the first plate <NUM>, the second protrusions 250a-250e coupled to the second plate <NUM> and the second housing wall <NUM> formed, the first plate <NUM> is spaced apart from the second plate <NUM> coupled to the second housing wall <NUM> to define the gap <NUM> (<FIG>). Alternatively, with the first protrusions 312a-312d coupled to the first plate <NUM>, the second protrusions 316a-316d coupled to the second plate <NUM> and the second housing wall <NUM> formed, the first plate <NUM> is spaced apart from the second plate <NUM> coupled to the second housing wall <NUM> to define the gap <NUM> (<FIG>). As a further alternative, with the first protrusions 410a-410d coupled to the first plate <NUM>, the second protrusions 414a-414d coupled to the second plate <NUM> and the second housing wall <NUM> formed, the first plate <NUM> is spaced apart from the second plate <NUM> coupled to the second housing wall <NUM> to define the gap <NUM> (<FIG> and <FIG>). The header pipe <NUM> is positioned through the sub-housing <NUM> and coupled to the second plate <NUM>. With the chamber wall <NUM>, the perforated tube <NUM> and the first transfer tube <NUM> formed, the perforated tube <NUM> is coupled to the first transfer tube <NUM>, via welding, brazing, etc. The chamber wall <NUM> is positioned about the perforated tube <NUM> and the first transfer tube <NUM> is inserted through the chamber bore 260a of the chamber wall <NUM>. The chamber wall <NUM> is coupled to the second plate <NUM> via welding, brazing, etc. The first housing wall <NUM> is coupled to the second housing wall <NUM> via welding, brazing, etc. to form a seal. With the second transfer tube <NUM> defined in the sub-housing <NUM>, the sub-housing <NUM> is coupled to the second plate <NUM> via welding, brazing, etc. to form a seal. The third housing wall <NUM> is coupled to the sub-housing <NUM> via welding, brazing, etc. to form a seal. The vanes <NUM> of the deswirl assembly <NUM> are coupled to the second housing wall <NUM>, and the outer assembly wall <NUM> is coupled to the vanes <NUM>. The guide flange <NUM> is coupled to the outer assembly wall <NUM> via welding, brazing, etc..

With the muffler <NUM> assembled, the muffler <NUM> is fluidly coupled to the engine <NUM> (<FIG>). In one example, the header pipe <NUM> is fluidly coupled to an exhaust manifold associated with the engine <NUM> (<FIG>) to receive the exhaust gases <NUM>. The deswirl assembly <NUM> is placed in fluid communication with the cooling fan <NUM> to receive the cooling air <NUM> (<FIG>). During operation of the engine <NUM>, such as the Wankel engine, the exhaust gases <NUM> have high energy. The exhaust gases <NUM> flow from the engine <NUM> through the header pipe <NUM> into the pressure attenuator <NUM>. The exhaust gases <NUM> flow radially through the tortuous path <NUM> and exit the pressure attenuator <NUM> at the outer circumference <NUM> of the first plate <NUM> into the forward chamber <NUM>. It should be noted that the gap <NUM> may be adjusted (increased or decreased) by moving the first plate <NUM> and/or the second plate <NUM> if desired based on the operating characteristics of the engine <NUM> (<FIG>). The exhaust gases <NUM> expand in the forward chamber <NUM>, and flow into the perforated tube <NUM>. The exhaust gases <NUM> flow from the perforated tube <NUM> into the first transfer tube <NUM>. The first transfer tube <NUM> directs the exhaust gases <NUM> into the outer chamber <NUM>. From the outer chamber <NUM>, the exhaust gases <NUM> flow through the second transfer tube <NUM> to the aft chamber <NUM>. From the aft chamber <NUM>, the exhaust gases <NUM> flow into the exhaust pipe <NUM> where the exhaust gases <NUM> are directed external to the muffler <NUM>. The cooling air <NUM> received by the deswirl assembly <NUM> provides cooling to the muffler <NUM> during the operation of the engine <NUM> (<FIG>).

Thus, the muffler <NUM> receives the high-energy exhaust gases <NUM> from the engine <NUM> (<FIG>) and reduces the pressure of the exhaust gases without generating excessive velocity with the pressure attenuator <NUM>, which limits noise generation. The forward chamber <NUM> and the outer chamber <NUM> cooperate as expansion chambers to attenuate the sound generated by the exhaust gases. The compact size of the muffler <NUM> enables the muffler <NUM> to be used within the power unit <NUM> and the muffler <NUM> may be positioned within the housing <NUM> of the power unit <NUM>. In addition, the integration of the deswirl assembly <NUM> with the muffler <NUM> reduces components associated with the power unit <NUM>. It should be noted that while the pressure attenuator <NUM> is described herein as circular having the first plate <NUM> and second plate <NUM> with a circular shape, the pressure attenuator <NUM> is described herein as D-shaped having the first plate <NUM> and second plate <NUM> with the D-shape; the pressure attenuator having the first plate <NUM> and the second plate <NUM> having the kidney shape, a pressure attenuator and the associated plates for use with the muffler <NUM> may have any desired shape, including, but not limited to, kidney shaped, D-shaped, circular, oval, polygonal, etc. Thus, the shapes of the plates <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is merely an example. Moreover, as discussed, the shapes of the first protrusions 246a-246e, the second protrusions 250a-250e, the first protrusions 312a-312d, the second protrusions 316a-316d, the first protrusions 410a-410d and the second protrusions 414a-414d are merely an example, as the first protrusions 246a-246e, the second protrusions 250a-250e, the first protrusions 312a-312d, the second protrusions 316a-316d, the first protrusions 410a-410d and the second protrusions 414a-414d may have any polygonal shape. Moreover, each of the plates <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may have any number of the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM> and the second protrusions <NUM> and the shape of the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM> and the second protrusions <NUM> may vary along the respective plate <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> such that the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM>, the second protrusions <NUM>, the first protrusions <NUM> and the second protrusions 414a associated with the particular plate <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> need not have the same shape.

Claim 1:
A muffler, comprising:
a housing (<NUM>) defining a first chamber (<NUM>), a second chamber (<NUM>) and a third chamber (<NUM>), the first chamber positioned opposite the third chamber within the housing, the housing fluidly coupled to a source of exhaust gases via an inlet;
at least a pair of nested protrusions (246a-e, 250a-e, 312a-d, 316a-d, 410a-d, 414a-d) in communication with the inlet and configured to receive the exhaust gases, the pair of nested protrusions coupled to a respective surface of a pair of plates (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) disposed in the housing such that one of the pair of nested protrusions is spaced apart from and opposite another of the pair of nested protrusions to define a tortuous path (<NUM>) for the exhaust gases that terminates at an outlet defined along an outer circumference of one of the pair of plates, the first chamber downstream from the pair of plates and in fluid communication with the outlet, wherein the second chamber is disposed about the pair of plates proximate the outlet and is fluidly isolated from the outlet;
a first tube (<NUM>) fluidly coupled between the first chamber and the second chamber configured to direct the exhaust gases from the first chamber to the second chamber; and
a second tube (<NUM>) fluidly coupled between the second chamber and the third chamber configured to direct the exhaust gases from the second chamber to the third chamber.