Patent Publication Number: US-7905319-B2

Title: Venturi muffler

Description:
FIELD OF THE INVENTION 
     The present invention relates to mufflers for internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines create noise which is generated by the sudden expansion of internal combustion engine chamber exhaust gasses. As the combustion gasses are exhausted from each cylinder of the engine, a sound wave front travels at rapid sonic velocities through the exhaust system. Efforts have continued over many years to reduce or muffle the noise caused by combustion gasses. 
     U.S. Pat. No. 5,952,625 granted on Sep. 14, 1999 to Ronald G. Huff describes two major muffler classifications, namely, dissipative and reactive mufflers. Dissipative mufflers are typically composed of ducts or chambers filled with acoustic materials, such as fiberglass, steel wool or porous ceramics. Such materials absorb acoustic energy and transform it into thermal energy. Reactive mufflers are composed of a number of interconnected chambers of various sizes and shapes in which sound waves are reflected to dampen or attenuate waves of a set frequency, typically resonance frequency. Each type of muffler has its disadvantages and the patent seeks to improve reaction mufflers of the side branch type through the utilization of a plurality of concentric sound passages through which exhaust gasses flow from an inlet to an outlet of the muffler along back-and-forth exhaust gas passages. The muffler also includes a central cylindrical passage between the muffler inlet and outlet and the latter is surrounded by the back-and-forth exhaust gas passages which are selectively provided with closed ends (sound reversal walls) for effecting sound dampening or attenuation at selected frequencies. 
     U.S. Pat. No. 6,089,347 granted on Jul. 18, 2000 to Ray T. Flugger discloses a muffler in which sound is reduced by incorporating a plurality of axially spaced cone-shaped partitions within a chamber of the muffler. Outward ends of the partitions defined between them spaces which are oriented with respect to the flow path of exhaust gasses so as to create a low pressure region within the spaces creating something of a venturi effect wherein exhaust gasses exteriorly of the partitions create low pressure regions between the partition walls. The orientation of the spaces between the partition walls with respect to the exhaust flow path exteriorly thereof is such that sound vibrations which enter the spaces and reflect off the partitions and the walls thereof as sound vibrations are attenuated between the partitions prior to exiting the muffler. 
     U.S. Pat. Nos. 5,530,214 and 6,105,716 issued respectively on Jun. 25, 1996 and Aug. 22, 2000, each in the name of Clyde A. Moorehead et al., disclose respectively a VENTURI MUFFLER and VENTURI MUFFLER HAVING PLURAL NOZZLES. In each case the venturi throat is sized to increase the speed of the gas flowing therethrough to decrease or attenuate noise. 
     U.S. Pat. No. 5,892,186 granted on Apr. 6, 1999 to Ray T. Flugger discloses a muffler for internal combustion engines which includes a central dispersion shell which tapers from an inlet to a minimum diameter at a restriction which is effective in attenuating noise by substantially reducing straight-through transmission of sound and by causing noise components to converge together thereby achieving sound frequency cancellation. A dispersion shell diverges from the restriction to an outlet and is surrounded by a perforated right-cylindrical shell which in turn is surrounded by a thermally insulating fiberglass layer and a ceramic fiber blanket. 
     U.S. Pat. Nos. 7,243,757 and 7,331,442 granted respectively on Jul. 17, 2007 and Feb. 19, 2008 to Karl Bernard Stuber and Alan Wall, respectively, are further examples of mufflers having inner passages provided with a variety of partitions, vanes, baffles or the like to reflect internal combustion exhaust gasses as they travel from inlet to outlet to reduce or attenuate exhaust noise. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a venturi muffler preferably formed of a plurality of substantially identical metallic, conical, stepped venturi-forming segments which are maintained in coaxial relationship to each other between an inlet and an outlet of the muffler. In a preferred form of the invention, each stepped segment includes at least a large outermost annular wall having a plurality of openings or holes therein, an inner cylindrical wall, an innermost smaller annular wall having openings or holes therein, and a substantially conical outlet wall progressively decreasing in size in the direction of the muffler outlet. The venturi-forming segments are stacked to form a plurality of coaxial axially adjacent outer and inner annular chambers which can be arranged such that exhaust gasses entering an outermost annular chamber flow into the next downstream inner annular chamber and from the latter chamber flow through a venturi passage into a main central exhaust passage of the muffler before exiting the muffler outlet. Alternatively, the inner and outer annular chambers are not in fluid communication with each other, whereby exhaust gasses at the muffler inlet pass through the openings in the outermost annular walls without entering the inner annular chambers and exit directly through the muffler outlet while other exhaust gasses enter the holes of the innermost annular walls into the inner annular chambers and pass therethrough and through the venturi passages into the main exhaust passage to the muffler outlet. In each case the plurality of venturi passages create a partial vacuum in the inner or both the inner and outer annular chambers and from one annular chamber to the other thereby creating a substantially continuous partial vacuum through the length of the combined segments through which sound waves cannot propagate from inlet to outlet thereby reducing the exhaust sound pressure waves and attenuating/reducing muffler exhaust noise. As exhaust gasses enter the outermost annular chambers through the openings in the outermost annular walls, they are reflected back (and forth) in each chamber to cancel out or attenuate incoming sound waves 180 degrees out of the phase with each other to reduce sound and absorb heat. In this way, each outermost annular chamber will have a different reflective frequency from the inlet to the outlet of the muffler to cancel out, lessen or attenuate the incoming pressure waves as the internal combustion engine revs at different RPM&#39;s. 
     Whether the inner and outer annular chambers are in fluid communication with each other or not, in each case the innermost series of holes in the innermost annular walls supply exhaust to the succeeding conical shaped venturi passages. As the exhaust pressure increases, so too does the vacuum/partial vacuum in one or both sets of inner and outer annular chambers. As the exhaust pressure travels through the muffler from the inlet to the outlet, succeeding inner and/or outer annular vacuum chambers are progressively starved because the first set of innermost holes of the first venturi-forming segment limits the exhaust supply and there is a decreasing exhaust pressure supplied to the succeeding downstream innermost annular chambers. The partial vacuum is created in all venturi passages or channels because of the higher pressure of the exhaust gasses flowing relatively unimpeded along a center exhaust gas passage/flow path from the muffler inlet to the muffler outlet, except, of course, for the restriction caused by the conical exhaust outlet wall of each segment. 
     The venturi muffler of the invention further acts as a heat sink to remove heat from the engine exhaust as it passes therethrough and converts the heat into thermo-electrical power. Each of the venturi-forming segments and specifically each of the outermost cylindrical walls thereof form the exterior of the muffler or are in intimate surface-to-surface contact with an exterior outermost metallic sleeve. Thermo-electric modules are connected to the outermost annular walls of the segments or to the outermost metallic sleeve and the heat of the exhaust gasses which is extracted by each of the segments is conducted therethrough to the outermost annular walls of each segment and/or to the cylindrical outermost sleeve, wall or casing surrounding the same to which are connected thermal-electric modules for converting the exterior normally wasted heat to electrical power. Additionally, when heat is removed from the exhaust, energy is removed and the sound/noise of the exhaust is further lowered. The partial vacuum created by the exhaust gasses passing between inner and outer surfaces of the conical outlet walls of each venturi-forming segments also draws the hot exhaust gasses across the surfaces of both sides of each conical wall outlet to maximize heat extraction from the exhaust gasses and conduct the same to the exterior of the muffler. 
     In further accordance with the invention, the annular series of holes in the outermost and innermost annular walls of the segments also break up the sound waves into smaller Eddie currents which reduce sound as sound waves are introduced into each annular chamber causing reflection thereof progressively from the muffler inlet to the muffler outlet which dissipates sound energy without robbing engine power and saving fuel by lowering engine back pressure while at the same time converting normally wasted heat into thermo-electric power. Each venturi muffler can be “tuned” by varying the number of venturi-forming segments to efficiently dampen or attenuate the specific frequencies which are desired to be cancelled out of incoming sound waves. The venturi muffler can be further “tuned” by varying the size and number of the holes in the innermost and/or outermost annular walls, the axial length of the peripheral walls which varies the axial length of the innermost and/or outermost chambers and the length, angle of convergence and discharge opening of each of the conical venturi-forming walls. 
     With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an axial cross-sectional perspective view, and illustrates a venturi muffler of the invention having an inlet and an outlet and therebetween a plurality of substantially identical metallic venturi-forming segments assembled in axially stacked relationship in a manner to create a partial vacuum in one or both of a plurality of axially innermost and axially outermost annular sound-reflecting chambers thereby reducing/attenuating/eliminating and/or damping exhaust noise. 
         FIG. 2  is an exploded perspective view of two identical metallic, conical, stepped, venturi-forming segments, and illustrates outermost and innermost annular walls each having openings therein and a substantially conical venturi-forming outlet wall. 
         FIG. 3  is a fragmentary perspective view of the two venturi-forming or vacuum-forming segments of  FIG. 2 , and illustrates the two venturi-forming segments assembled in stacked relationship to each other and collectively defining an outermost annular chamber, an innermost annular chamber and a venturi passage between the conical venturi-forming outlet walls which create a partial vacuum in the innermost annular chamber for reducing, attenuating or dampening the noise of combustion engine exhaust flowing through the muffler. 
         FIG. 4  is a fragmentary axial cross-sectional view through the venturi muffler of  FIG. 1 , and diagrammatically illustrates the exhaust flow through the muffler from the inlet to the outlet creating a partial vacuum in the innermost annular chambers effecting sound dampening as exhaust is drawn through the venturi passages by the exhaust flow passing through the center of the muffler. 
         FIG. 5  is a fragmentary axial cross-sectional view of the venturi muffler of  FIGS. 1 through 4 , and illustrates the manner in which sound waves are reflected as they pass from the muffler inlet to the muffler outlet through the outer annular sound reflective chambers, the inner annular sound reflective chambers and the venturi passages with commensurate sound dampening created by the partial vacuum created in the innermost annular sound reflective chambers. 
         FIG. 6  is a fragmentary perspective view of two metallic, conical stepped, venturi-forming segments similar to the venturi-forming segments of  FIG. 3 , and illustrates an outermost annular chamber in fluid communication with an innermost annular chamber and the latter opening into a venturi passage which in turn opens into a central axial exhaust passage of the muffler. 
         FIG. 7  is a fragmentary axial cross-sectional view of a venturi muffler formed by stacking the venturi-forming segments of  FIG. 6 , and illustrates by headed arrows the exhaust flow therethrough including flow from each outermost annular chamber into an associated innermost annular chamber and through the associated venturi passages into the central exhaust passage of the muffler. 
         FIG. 8  is a fragmentary axial cross-sectional view of the venturi muffler of  FIG. 7 , and illustrates sound waves and the dampening thereof as exhaust flows from the muffler inlet to the muffler outlet. 
         FIG. 9  is a diagrammatic axial view of the venturi muffler of  FIG. 7 , and illustrates the manner in which heat from the exhaust gasses is extracted by the metallic venturi-forming segments and is conducted to outermost annular walls thereof which carry thermo-electric modules for transforming exhaust heat into electric power. 
         FIG. 10  is another venturi muffler of the invention, and illustrates a plurality of metallic, conical, stepped venturi-forming segments, each including at the end of an innermost conical venturi-forming wall an end wall having a plurality of openings therein. 
         FIG. 11  is a perspective view of one of the venturi-forming segments of the venturi muffler of  FIG. 10 , and illustrates details thereof. 
         FIG. 12  is another metallic, conical, stepped venturi-forming segment, and illustrates an innermost annular wall having four peripherally spaced axial ribs which project slightly beyond the innermost annular wall to maintain all innermost and outermost annular chambers in slightly spaced stacked relationship to each other. 
         FIG. 13  is a fragmentary axial cross-sectional view of another venturi muffler, and illustrates three identical metallic, conical, stepped venturi-forming segments with each pair of segments defining an annular outermost chamber, a venturi passage, and fins or vanes within each venturi passage for additionally creating a vortex or spiral flow of exhaust gasses flowing therethrough. 
         FIG. 14  is is a side perspective exploded view of the three assembled venturi-forming segments of  FIG. 13 , along with two additional venturi-forming segments, and illustrates the manner in which the same are progressively stacked individually or as groups of segments into an outermost metallic cylindrical sleeve defining a force-fit with an outermost peripheral wall of each venturi-forming segment to maintain the venturi muffler formed therefrom in assembled relationship. 
         FIG. 15  is an axial cross-sectional view of another venturi muffler and three venturi-forming segments thereof similar to the segments of  FIG. 1 , and illustrates the manner in which the same can be connected to a jet engine exhaust pipe to not only attenuate exhaust noise but also reduce its “heat signature” through heat dissipation by outside air passing through relatively large peripheral openings of an outermost annular wall of each segment and an exterior sleeve or acoustic material. 
         FIG. 16  is a perspective view of another venturi muffler of the invention, and illustrates a plurality of metallic stacked internested venturi-forming segments, each having a plurality of conical discharge nozzles with each pair of conical nozzles defining a substantially conical venturi passage. 
         FIG. 17  is an axial cross-sectional view through the venturi muffler of  FIG. 16 , and more clearly illustrates the plurality of internested venturi nozzles and the flow path of exhaust gasses therethrough which draw outside air into the venturi passages. 
         FIG. 18  is an axial cross-sectional view of a venturi muffler similar to the venturi muffler of  FIG. 17 , and illustrates an external cylindrical metallic sleeve preventing outside air from being introduced into the venturi passages to create a partial vacuum in outermost annular and inner conical vacuum chambers and thermo-electric modules on the exterior of the sleeve. 
         FIG. 19  is an axial cross-sectional perspective view of another venturi muffler, and illustrates venturi-forming segments with each adjacent pair of segments defining outermost, medial and innermost annular sound-reflective chambers with each of the latter opening through a venturi passage into a central exhaust flow passage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A venturi muffler constructed in accordance with this invention is fully illustrated in  FIG. 1  of the drawings and is generally designated by the reference numeral  10 . The venturi muffler  10  includes an exhaust inlet Ei, an exhaust outlet Eo, and therebetween a medial sound damping or sound attenuating section  12  which dampens, reduces, attenuates or muffles the noise caused by the sudden expansion of internal combustion chamber exhaust gasses of a conventional internal combustion engine (not shown) connected to the exhaust inlet Ei. 
     The sound damping section  12  is, for illustrative purposes, formed by seven vacuum or partial vacuum-forming/venturi-forming segments  13  through  19 , though more or less such venturi-forming segments may be utilized depending upon the particular application. The venturi-forming segments  13  and  14  of  FIGS. 1 through 3  will be described in detail and the description thereof is equally applicable to the remaining venturi-forming segments  15  through  19 . 
     Each of the venturi-forming segments  13 ,  14  is defined by a metallic highly heat conductive, tubular stepped member  20 . Each tubular stepped member  20  is defined from an exhaust entrance opening  21  ( FIG. 3 ) to an exhaust exit opening  22  by an outermost peripheral wall  23 , a peripheral radius or shoulder  24 , an outermost annular wall  25 , a peripheral shoulder or radius  26 , an annular wall  27 , a peripheral radius or shoulder  28 , an innermost annular wall  29 , a peripheral shoulder or radius  30  and an innermost venturi-forming or venturi passage forming wall  31  converging in a direction from the peripheral shoulder or radius  30  to the exhaust exit opening  22  of each tubular stepped member  20 . The outermost annular wall  25  includes a plurality of circular openings or holes  33  in equally spaced relationship to each other. The innermost annular wall  29  likewise includes a plurality of substantially equally spaced openings or holes  34 . 
     The sound damping section  12  ( FIG. 1 ) is formed by internesting or stacking adjacent pairs of the tubular stepped members  20  of the venturi-forming segments  13  through  19  in substantially internested coaxially aligned relationship, as is evident in  FIG. 1  of the drawings, which establishes between any two adjacent tubular stepped members  20  of the venturi-forming segments  13  through  19  an outermost annular sound-reflective/reflecting chamber  35 , an innermost annular sound-reflective/reflecting chamber  36  and an annular venturi passage  37  defined between the conical venturi-forming converging outlet walls  31  of adjacent sound damping sections  13 ,  14 ;  14 ,  15 ;  15 ,  16 ;  16 ,  17 ;  17 ,  18  and  18 ,  19  ( FIG. 1 ). The holes or openings  33  in the outermost annular walls  25  of all of the sound damping tubular stepped members  20  are in axial alignment, as are the holes or openings  34  ion the inner annular walls  29  of the tubular stepped members  20 . As is best illustrated in  FIG. 3 , the shoulder or radius  28  of each upstream tubular stepped member  20 , as viewed in the direction of exhaust flow from the exhaust entrance opening  21  to the exhaust exit opening  22 , contacts the shoulder or radius  26  of the next adjacent downstream tubular stepped member  20 . The contact between the radiuses or shoulders  28 ,  26 , as is best illustrated in  FIG. 3 , essentially closes off fluid communication between the annular sound-reflective chambers  35 ,  36 . When the venturi muffler  10  is assembled in the manner illustrated in  FIG. 1  of the drawings, the tubular stepped members  20  of the venturi-forming segments  13  through  19  are welded or rolled sealed to each other and to the exhaust inlet entrance opening or inlet Ei and the exhaust outlet Eo. 
     As exhaust or exhaust gasses from an internal combustion engine (not shown) enter the exhaust inlet Ei and the exhaust entrance opening  21  of the venturi-forming segment  13 , several distinct exhaust flow paths are established, namely, a plurality of outermost exhaust flow paths FPo ( FIG. 4 ) passing through all of the aligned holes or openings  33 , into and out of the outermost sound-reflective annular chambers  35  and exiting into the exhaust outlet Eo. A similar intermediate exhaust flow path FPi flows through all of the axially aligned holes or openings  34  of the annular walls  29 , into and through the innermost annular reflective chambers  36  and both exit the last series of holes or openings  34  in the venturi-forming segment  19  or flow through each venturi passage  37  under the influence of an axial or central exhaust flow path FPc from the exhaust inlet Ei to the exhaust outlet Eo which creates a vacuum or partial vacuum in each of the innermost annular reflective chambers  36  through which sound cannot propagate thereby reducing, damping or attenuating the exhaust sound pressure waves in the manner diagrammatically illustrated in  FIG. 5  of the drawings. Referring specifically to  FIG. 5 , the lower unnumbered headed arrows indicate the manner in which sound waves pass through the openings  33  and  34  and are reflected back (and forth) by the annular walls  25  and  29 . As each sound wave is reflected in a direction back toward the exhaust inlet Ei, it meets and cancels out an on-coming sound wave 180 degrees out of phase to both reduce sound and absorb heat, as is depicted in the upper illustrated portions of the annular sound wave reflecting or reflective chambers  35  and  36 , the amplitude or height of which is illustrated as decreasing from the sound-reflective chamber  35  defined between the venturi-forming segments  13  and  14  and the last sound-reflective chamber  35  defined between the venturi-forming segments  18  and  19 . Additionally and most importantly, the flow of exhaust along the central exhaust flow path or flow passage FPc ( FIG. 4 ) creates an increasing partial vacuum in each of the innermost annular chambers  36  toward the exhaust outlet Eo as exhaust gasses are drawn through the venturi passage  37  by and into the central exhaust flow path FPc. Therefore, all annular sound-reflective chambers  35 ,  36  reduce sound by reflecting sound waves between the respective annular walls  25  and  29  thereof, and additional sound dampening occurs in the innermost sound reflective chambers  36  by the partial vacuum formed therein. Therefore, the exhaust sound or noise is reduced, attenuated or dampened by (1) the cancellation of sound waves 180 degrees out of phase with each other when moving axially through all of the annular chambers  35 ,  36  by reflection between the respective annular walls  25  and  29 , (2) the creation in the annular chambers  36  of a partial vacuum through which sound cannot propagate or propagates minimally, and (3) by the heat removed by all of the venturi-forming segments  13  through  19 . An increase in the cancellation of sound waves in the annular sound-reflective chambers  35  and  36  can be effected by eliminating the holes or openings  33 ,  34  in the respective annular walls  25 ,  29  of the last tubular stepped member  20  of the last venturi-forming segment  19 . Additionally, the holes or openings  34  in the annular wall  29  of the tubular stepped member  20  of the first venturi-forming segment  13  are sized to limit the exhaust flow along the exhaust flow path FPi ( FIG. 4 ) so that the substantially higher rate of flow of the exhaust along the central exhaust flow path FPc draws the gasses from the innermost annular chambers  36  via the venturi passages  37  thereby assuring the creation of sound dampening partial vacuums in each of the annular chambers  36  which progressively increase from chamber to chamber in the direction of exhaust flow until exiting into the exhaust outlet Eo. The last venturi-forming wall  31  adjacent the exhaust outlet  12  also functions as a check valve which prevents atmospheric pressure from entering the venturi muffler  10  which saves back pressure efficiencies of the associated internal combustion engine (not shown). Thus, the venturi muffler  10  saves fuel by lowering engine back pressure in addition to cancelling out or damping incoming combustion engine noise/sound waves over a wide frequency range. 
     Reference is made to  FIGS. 6 through 9  of the drawings in which a venturi muffler  10 ′ ( FIGS. 7 through 9 ) is illustrated and all components thereof corresponding to the components of the venturi muffler  10  have been identically numbered and primed. 
     The muffler  10 ′ includes a sound damping section  12 ′ between an exhaust inlet Ei and an exhaust outlet Eo. The sound damping section  12 ′ is defined by venturi-forming segments  13 ′ through  18 ′, each being in the form of a metallic tubular stepped member  20 ′ ( FIG. 6 ), and when internested in the manner illustrated in  FIGS. 6 through 9 , the radiuses or shoulders  26 ′,  28 ′ are slightly spaced from each other, as opposed to the sealing contact between the shoulders or radius portions  26 ,  28  of the tubular stepped embers  20  of the venturi muffler  10 . Accordingly, an annular gap  39  ( FIGS. 7 through 9 ) between each of the radiuses or shoulders  26 ′,  28 ′ places all adjacent annular reflective chambers  35 ′,  36 ′ in fluid communication and the venturi effect created via the venturi passages  37  earlier described with respect to the exhaust flow paths of  FIG. 4  create a partial vacuum in both the outermost annular chambers  35 ′ and the innermost annular chambers  36 ′ ( FIG. 7 ) thereby increasing the sound dampening of the exhaust gasses. 
     The venturi muffler  10 ′ of  FIG. 9  also includes against the outer surface (unnumbered) of the outermost annular walls  23 ′ of each metallic tubular stepped member  20 ′ thermo-electric modules  40  substantially surrounding the entirety of the sound damping section  12 ′ which absorb the heat of the exhaust gasses conducted or convected thereto, as indicated by the unnumbered headed arrows in  FIG. 9 , to convert exhaust gas heat into thermo-electrical power. 
     Another venturi muffler  10 ″ ( FIG. 10 ) is substantially identical to the venturi muffler  10  and like components have been identified by identical reference numerals which have been double primed. The difference in the venturi muffler  10 ″ is that each metallic tubular stepped conical member  20 ″ ( FIG. 11 ) does not include a single exhaust exit opening, such as the opening  22  ( FIG. 2 ) at the venturi-forming outlet wall  31  of each tubular stepped conical member  20 . Instead, the venturi-forming outlet walls  31  of the venturi muffler  10  are closed in the venturi muffler  10 ″ by a wall  51  ( FIG. 11 ) having a plurality of holes or openings  52  with the holes or openings  52  being in axial alignment ( FIG. 10 ). In operation, the muffler  10 ″ functions as heretofore described with respect to the venturi muffler  10 , but in addition thereto all adjacent pairs of end walls  51  define sound reflective chambers  59  which reflect the sound waves to achieve further cancellation/damping of exhaust gas noise in the manner described with respect to  FIGS. 4 and 5  of the drawings. 
     In  FIG. 3  of the drawings, the shoulders of radiuses  26 ,  28  are illustrated in contacting/sealing relationship though obviously within tolerance some minor leakage might occur therebetween resulting in slight exhaust flow from the outermost annular sound-reflective chambers  35  into the innermost sound-reflective chambers  36 . In  FIG. 6 , the radiuses or shoulders  26 ,  28  are appreciably spaced from each other to define the annular flow passages  39  ( FIGS. 6 and 8 ). Obviously, the pressure of internal combustion engine exhaust gasses can create variations in sizes of the passages  39  or create varying degrees of “leakage” between the shoulders  26 ,  28 . In order to maintain a specific minimum sized passage  39 , a metallic tubular conical stepped member  20 ′″ shown in  FIG. 12  includes four equally spaced ribs  55 , each projecting radially outwardly from the innermost annular wall  27 ′″ and projecting axially slightly beyond the shoulder or radius  28 ′″ in the form of a nose  56 . When such stepped members  20 ′″ are stacked in the manner heretofore described with respect to the venturi muffler  10  of  FIG. 1 , the ribs  55  and noses  56  maintain desired and exact minimum spacing in the area of the passage  39  ( FIG. 8 ) particularly under varying exhaust pressures as the speed of an associated internal combustion engine is varied. 
     Another venturi muffler  110  ( FIGS. 13 and 14 ) is similar to the venturi muffler  10  and like components have been identified by identical reference numerals preceded by  100 . The major difference between the venturi muffler  10  and the venturi muffler  110  is that the conical venturi-forming outlet wall  131  of each tubular annular step member  120  has welded thereto an exterior spiral vane or fin  60 , the circumferential and axial length of which can vary but in all cases the function thereof is to create a spiral vortex Sv of the exhaust gasses as they flow through the venturi passages  137  from the inner sound-reflective annular chambers  136 . As is most readily apparent from a comparison of  FIGS. 4 and 13 , the spiral vortex exhaust gasses Sv travel a greater distance between the annular reflective chambers  136  and the exhaust exit opening  122  of each venturi-forming wall  131  as compared to the same distance of exhaust gas flow through the venturi passages  37  of the venturi muffler  10 . The greater distance of travel of the exhaust gasses along the spiral vortex Sv further lessens or attenuates sounds and additional heat can be extracted therefrom by the spiral vanes  60  which further increases the power that can be derived therefrom when the venturi muffler  110  utilizes thermo-couples  40 , as in the case of the venturi muffler  10 ′ ( FIG. 9 ). Two other differences in the venturi muffler  110 , as compared to the venturi muffler  10 , is that the venturi muffler  110  only includes the inner sound-reflective annular chambers  136  (excluding the outer annular sound-reflective chambers  35  of the venturi muffler  10 , and the holes or openings  133  are elongated and arcuate to augment the formation of the spiral vortex exhaust gasses Sv as they are drawn through the venturi passages  137 . 
     The venturi muffler  110  is also manufactured in the manner heretofore described with respect to the venturi muffler  10  by stacking or axially assembling tubular metallic stepped members  120  in the manner best illustrated in  FIG. 14  of the drawings. However, rather than welding the tubular stepped members  120  to each other, a metallic tubular sleeve  70  is expanded at a temperature well beyond the temperature of exhaust gasses which flow through the venturi muffler  110 . When the metallic cylindrical sleeve  70  is so expanded, venturi segments  113  through  117 , etc., are inserted under a forced fit into the expanded sleeve  70  which when cooled, maintains all of the tubular stepped members  120  in assembled relationship. 
     Reference is made to  FIG. 15  of the drawings in which a venturi muffler  210  is illustrated and all components thereof corresponding to the components of the venturi muffler  10  have been identically numbered and preceded by “200.” The venturi muffler  210  is illustrated conventionally connected to an exhaust pipe EP of an aircraft jet engine (not shown) by which sound damping or attenuation is achieved in a manner heretofore described with respect to the venturi muffler  10 . However, a major function achieved by the venturi muffler  210  is the reduction of the “heat signature” of the jet engine through (1) conduction of heat through the metallic tubular step members  220  radially outwardly and into a heat-absorbing sleeve  201  of acoustic material (fiberglass, porous ceramic, etc.) and (2) forming the openings  233  larger than the openings  33  of the of the venturi muffler  10  such that outside air Oa passing therethrough additionally cools each of the metallic tubular stepped members  220  achieving a reduction of the jet engine&#39;s “heat signature” which is advantageous in military aircraft which are vulnerable to heat-seeking missiles. 
     Another venturi muffler constructed in accordance with this invention is illustrated in  FIGS. 16 and 17  of the drawings and is generally designated by the reference numeral  310  with components thereof corresponding to the venturi muffler  10  being preceded by reference number “300. ” The venturi muffler  310  is designed for use with smaller internal combustion engines, typical of which might be garden riding mowers. The venturi muffler  310  is formed from a plurality of stamped metallic tubular stepped members  320 , each defined by an annular wall or flange  329 , a peripheral shoulder or radius  330 , a venturi-forming wall  331  and a plurality of conical exhaust discharge nozzles  80 , each having a nozzle outlet  81  and projections or bumps  82  which maintain adjacent venturi forming walls  331  in spaced relationship to each other to define therebetween a plurality of conical venturi passages  337  through which exterior air Ea is drawn from atmosphere into each annular chamber  336 , its associated venturi passage  337  and outwardly therefrom under the influence of exhaust gasses passing through the nested discharge nozzles  80 . A plurality of nuts, bolts and washers, collectively identified by the reference numeral  85 , are associated with holes or openings  86  in the annular walls  329  to maintain the annular walls  329  in spaced relationship so that exterior air Ea can be drawn therebetween to both cool the metallic tubular stepped members  320  and create a limited partial vacuum within the annular and conical chambers  336  and along the venturi passages  337 . 
     Another venturi muffler  410  is illustrated in  FIG. 18  of the drawings and like reference numerals have been applied thereto preceded by “400. ” The venturi muffler  410  includes a cylindrical outer highly heat-conductive metallic sleeve  90  which closes the annular chambers  436  to outside atmosphere precluding the introduction of exterior air Ea therein, as in the case of the venturi muffler  310 . In this fashion, the annular chambers  436 , as well as the conical partial vacuum chambers  436 , are under a greater partial vacuum during the operation of an internal combustion engine with which the venturi muffler  410  is associated. Additionally, thermo-electric modules  440  substantially surround the entirety of the cylindrical heat-conductive sleeve  90  which absorb the heat of the exhaust gasses conducted or convected thereto thereby converting exhaust gas heat into thermo-electric power. 
     Another venturi muffler  510  is illustrated in  FIGS. 19 and 20  of the drawings and components corresponding to those of the venturi muffler  10  have been applied thereto preceded by numeral “500. ” The venturi muffler  510  includes an exhaust inlet  511 , an exhaust outlet  512  and therebetween a medial sound damping or sound attenuating section  512 . 
     The sound damping section  512  is formed of five vacuum-forming/venturi-forming segments  513  through  517 , each defined by a metallic highly heat-conductive tubular stepped member  520 . 
     Each tubular step member  520  includes an outermost peripheral wall  523 , a peripheral radius or shoulder  524 , an outermost annular wall  525  having holes or openings  533  therein, and a shoulder or radius  526 . Each tubular stepped member  520  also includes from an exhaust exit opening  522  a conical venturi-forming outlet wall  531 , a peripheral radius or shoulder  530 , an annular wall  529  having holes or openings  534  and a peripheral shoulder or radius  528 . The shoulders or radii  526  and  528  are joined by an annular wall  91 , a peripheral shoulder or radius  92 , an annular wall  93  having holes or openings  94 , a peripheral shoulder or radius  95  and an annular wall  96  collectively defining an intermediate annular reflective chamber  97  between all adjacent pairs of the tubular stepped members  520  thereby collectively defining between each pair of tubular step members  520  an outermost annular sound-reflective chamber  535 , an intermediate sound-reflective chamber  97  and an innermost sound-reflective chamber  536  with the latter opening through an annular venturi passage  537  to create a partial vacuum in each of the annular chambers  535 ,  97  and  536 . 
     Variations in the venturi mufflers heretofore described can be made in keeping with the present disclosure. As an example, the vanes or fins  60  of the venturi muffler  110  ( FIGS. 13 and 14 ) can be utilized in the venturi muffler  210  of  FIG. 15  which, as heretofore described, not only reduces noise, but reduces the “heat signature” of an associated jet engine of a jet aircraft. The vortex creates a spinning exhaust flow to disrupt on-coming sound waves that are traveling in a straight line from the engine such that the exhaust flow along the central axial flow passage is converted to spiral flow therethrough, as is illustrated in  FIG. 13 . The faster the jet aircraft flies, the faster the internal spin or vortex (Sv) that is influenced by outside air pressure being sucked and pushed into the engine muffler and centrifugally spun therethrough causing a reduction of pressure at the core of the spin. Therefore, the venturi muffler  210  can additionally dampen sound while also reducing the heat signature by providing each of the conical tapered outlet walls  231  with an external fin or vane, such as the fin or vane  60  of  FIG. 13 , resulting in the air flow diagrammatically illustrated therein. 
     Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.