Patent Publication Number: US-2009229913-A1

Title: Dual Mode Exhaust Muffler

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 61/027,173 filed Feb. 8, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exhaust muffler for a vehicle that is shiftable between a quiet mode and a loud mode. 
     2. Background Art 
     Vehicle mufflers receive exhaust gases from an engine, such as an internal combustion engine or a diesel engine, for the purpose of attenuating the noise associated with the moving gas stream. Mufflers generally include a plurality of tubes and sound attenuating chambers formed by baffles and/or chambers within a shell. The walls of the tubes may include small openings to attenuate sound waves and reduce noise levels. While in most instances mufflers are designed to reduce noise and provide a low sound volume/low sound pressure level, absent undesirable resonance, some drivers of high performance vehicles prefer a louder sound and reduced back pressure. 
     A durable and reliably manufactured high performance exhaust muffler offering dual operating modes is provided by Applicants&#39; invention. As shown in the attached drawings, the following detailed description is of several illustrated embodiments. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a muffler assembly is provided for a vehicle. The muffler assembly comprises a shell, an inlet tube, a plurality of sound attenuating tubes, a valve, and an outlet tube. The inlet tube is disposed within the shell and extends from an inlet end to a first chamber. The inlet tube is a solid wall tube. All of the exhaust gases flow through the inlet tube from the inlet end to the first chamber. The plurality of sound attenuating tubes are disposed within the shell that have a plurality of sound attenuating orifices spaced along the length of the sound attenuating tubes. The sound attenuating tubes extend from the first chamber through a plurality of baffles disposed inside of the shell. The valve closure element directs the exhaust gases through the sound attenuating tubes in a first mode of operation. The valve closure element directs exhaust gases after flowing through the inlet tube that does not have sound attenuating orifices from the first chamber into a second chamber in a second mode of operation. The outlet tube receives exhaust gases that are routed through the sound attenuating tubes in the first mode of operation. The outlet tube has a direct flow port through which exhaust gases are received from the second chamber in the second mode of operation that have not been circulated through the sound attenuating tubes. The outlet tube discharges the exhaust gases from the muffler assembly in both modes. 
     According to another embodiment of the present invention, a dual transverse muffler assembly for a vehicle is provided that has a combined flow path. The dual transverse muffler assembly with a combined flow path comprises a first inlet tube through which exhaust gases flow into a shell. The first inlet tube is partially disposed within the shell and extends from the a first end wall to an interior chamber. A second inlet tube is partially disposed within the shell that extends from a second end wall to the interior chamber. A sound attenuating tube is disposed within the shell that has a first plurality of sound attenuating orifices spaced along its length, The sound attenuating tube extends from the interior chamber through a plurality of baffles disposed inside of the shell. A valve closure element directs the exhaust gases through the sound attenuating tube in a first mode of operation. The valve closure element directs exhaust gases from the first chamber into a second chamber in a second mode of operation. An outlet tube extends through the shell from a first outlet tube opening through the first end wall to a second outlet tube opening through the second end wall. The outlet tube receives exhaust gases that are received from the sound attenuating tube in the first mode of operation through a portion of the outlet tube that has a second plurality of sound attenuating orifices. The outlet tube also has a direct flow opening through which exhaust gases are received from the second chamber in the second mode of operation. Exhaust gases are discharged from the shell in both the first and second modes of operation through the first and second outlet openings. 
     According to yet another embodiment of the present invention, a dual transverse muffler assembly for a vehicle is provided that has a dual independent flow path. The dual transverse muffler assembly with a dual independent flow path comprises a shell that is divided by a central baffle that divides the shell into two parts. First and second sets of muffler components are provided within the shell on opposite sides of the central baffle with one set of muffler components being provided in each of the two parts. Each set of muffler components has a first baffle provided within the shell proximate the end wall, a second baffle provided within the shell at a spaced location relative to the first baffle on the opposite side of the first baffle from the end wall, an a third baffle provided within the shell between the second baffle and the central baffle. An inlet tube directs the flow of exhaust gases into the shell through the first and second baffles to an interior chamber. A sound attenuating tube is disposed within the shell that has a first plurality of sound attenuating orifices spaced along the length of the sound attenuating tube. The first sound attenuating tube extends from an inlet that opens into the interior chamber through the first and second baffles to a first end chamber defined between the end wall and the first baffle. A valve opening ring is disposed in the third baffle and is provided with a valve closure element. The valve closure element directs the exhaust gases through the sound attenuating tube in a quiet mode of operation. The valve closure element directs exhaust gases from the first interior chamber through the valve opening ring and into a direct exhaust chamber defined between the third baffle and the central baffle in a loud mode of operation. An outlet tube extends through the shell from a outlet tube opening through the first end wall to the central baffle, the outlet tube has a plurality of sound attenuating orifices that receive exhaust gases that pass through the first plurality of sound attenuating orifices of the sound attenuating tube in the quiet mode of operation. The outlet tube has at least one direct flow opening through which exhaust gases are received from the direct exhaust chamber in the loud mode of operation that have not been circulated through the sound attenuating tube. Exhaust gases are discharged from the shell in both the first and second modes of operation through the tailpipe opening. 
     The above features and other advantageous features of the present invention will be better understood in view of the attached drawings and the following detailed description of the disclosed embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exhaust muffler assembly; 
         FIG. 2  is a perspective view of an exhaust muffler assembly with the shell removed; 
         FIG. 3  is an exploded perspective of the exhaust muffler assembly; 
         FIG. 4  is a plan view of an exhaust muffler assembly; 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 4 ; 
         FIG. 6  is a plan view of an exhaust muffler assembly with the shell removed and operating in a quiet mode; 
         FIG. 7  is a plan view of an exhaust muffler assembly with the shell removed and operating in a loud mode; 
         FIG. 8  is a diagrammatic plan view of a dual transverse driver controlled exhaust having two independent exhaust flow streams operating in a quiet mode; 
         FIG. 9  is a diagrammatic plan view of a dual transverse driver controlled exhaust having two independent exhaust flow streams operating in a loud mode; 
         FIG. 10  is a diagrammatic plan view of a dual transverse driver controlled exhaust system having a combined exhaust gas flow stream operating in a quiet mode; 
         FIG. 11  is a diagrammatic plan view of a dual transverse driver controlled exhaust system having a combined exhaust gas flow stream operating in a loud mode; 
         FIG. 12  is a diagrammatic plan view of a vacuum switch in an open position; and 
         FIG. 13  is a diagrammatic plan view of a vacuum switch in a closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring to  FIG. 1 , a muffler assembly  10  is illustrated that is made in accordance with one embodiment of the present invention. Other embodiments of the invention are possible within the scope of the present invention. The muffler assembly  10  includes a shell  12  that may be oval, circular or oblong in shape. The component parts of the muffler assembly  10  may be formed of stainless steel or ferritic stainless steel to eliminate or minimize corrosion. An inlet end wall  16  is assembled to one end of the shell  12  by welding or by a hem flange connection. An inlet tube  18  is received in the inlet end wall  16 . A vacuum diaphragm actuator  20  is also assembled to the inlet end wall  16 . Instead of the illustrated vacuum diaphragm actuator  20 , a manual actuator or an electrical solenoid actuator may be provided. An outlet end wall  22  is provided at the opposite end of the shell  12  from inlet end wall  16 . An outlet tube  24  is received in the outlet end wall  22 . A return spring adjustment mechanism  26  is assembled to outlet end wall  22 . The internal components and structure of the muffler assembly  10  that are enclosed by the shell  12  will be more specifically described with reference to  FIGS. 2-7  below. 
     Referring to  FIG. 2 , portions of the muffler assembly  10  are shown with the shell  12  removed. The inlet tube  18  extends through the inlet end wall  16  and also through an inlet end interior baffle  30 . An inlet tube extension  28  extends from the inlet tube  18  between inlet end interior baffle  30  and an intermediate interior baffle  32 . Inlet tube  18  and inlet tube extension  28  may be formed from a single piece of tubing or may be made from different pieces of tubing and assembled together. A valve opening ring  40  is provided on a valve plate baffle  34  that defines a valve opening  36 . The valve opening is adapted to be opened and closed by means of a valve closure element  38 , or valve closure plate. The valve closure element  38  engages the valve opening  36  when the muffler assembly is in its normal, or quiet, mode of operation. The valve closure element  38  may be flat, curved or partially spherical in shape to facilitate better sealing against the valve opening ring  40 . A first reticulated tube  42  and a second reticulated tube  44  are oriented parallel to the inlet tube extension  28  and extend between the inlet end interior baffle  30  and the intermediate interior baffle  32 . A plurality of openings  48  are formed in the first and second reticulated tubes  42 ,  44 . The openings  48  form small outlets in the walls of the tubes  42  and  44  through which exhaust gases may flow. The flow of exhaust gases into the openings  48  attenuates sound waves of various wavelength and reduces the noise emitted from muffler assembly  10 . 
     Referring to  FIG. 3 , the muffler assembly  10  is shown in an exploded perspective view. The muffler assembly includes the shell  12  which encloses all of the other components of the muffler assembly  10  located between the inlet end wall  16  and the outlet end wall  22 . Inlet tube  18  is connected to the inlet tube extension  28 . Alternatively, the inlet tube  18  and inlet tube extension  28  may be formed from a single piece of tubing, as previously noted. The inlet tube  18  extends through the inlet end wall  16  through an inlet tube opening  50 . The inlet tube extension  28  extends through a tube receiving opening  52  formed in the inlet end interior baffle  30 . Additional tube receiving openings  52  are formed in the inlet end interior baffle  30  to receive the reticulated tubes  42  and  44 . Additional tube receiving openings  54  are formed in the intermediate interior baffle  32 . In this way, the inlet tube extension  28  and first and second reticulated tubes  42  and  44  are supported on opposite ends by the inlet end interior baffle  30  and the intermediate interior baffle  32 . 
     A support bracket  60  is assembled to the inlet end wall  16 . The vacuum diaphragm actuator  20  is assembled to a bracket  60  to hold it in a fixed relationship relative to the inlet end wall  16 . The support bracket  60  includes an actuator rod opening  62  through which an actuator rod  64  is connected to the vacuum diaphragm actuator  20 . A clevis  66  is attached to the actuator rod  64  and to an operator  68  that is moved by the vacuum diaphragm actuator  20 . The operator  68  moves axially relative to the vacuum diaphragm actuator  20  to in turn move the actuator rod  64  in a generally axial direction. The actuator rod  64  extends from the return spring adjustment mechanism  26  located on the outer side of the outlet end wall  22  to the clevis  66 . The valve closure element  38  is secured to the actuator rod  64  by two collars  69 . The actuator rod  64  extends through the first reticulated tube  42  and the outlet end wall  22 , valve plate baffle  34 , intermediate interior baffle  32 , the inlet end interior baffle  30  and the inlet end wall  16 . The actuator rod  64  may be disposed at an angle relative to the central axis of the first reticulated tube  42 . 
     The valve plate baffle  34  includes a tube receiving opening  70  that receives an extended portion  72  of the second reticulated tube  44 . The extended portion  22  does not include openings  48 . The extended portion  72  is received over a necked down portion  74  of the outlet tube  24 . The outlet tube  24  is received in an outlet opening  76  formed in the outlet end wall  22 . Direct flow ports  78  are provided in the outlet tube  24  through which exhaust gases may flow directly from the inlet tube  18  through the inlet tube extension  28  and the valve opening ring  40  when the valve closure element  38  is shifted to its open position. 
     Referring to  FIG. 4 , the muffler assembly  10  is shown in a plan view with the shell  12  assembled over the internal components of the muffler assembly  10 . The inlet tube  18  is assembled to the inlet end wall  16 . The vacuum diaphragm actuator  20  is attached by means of the support bracket  60  to the inlet end wall  16 . The clevis  66  is secured by a pin or other appropriate connector to the operator  68  of the vacuum diaphragm actuator  20 . The outlet tube  24  and return spring adjustment mechanism  26  are both connected to the outlet end wall  22 . 
     Referring to  FIG. 5 , the arrangement of the inlet tube extension  28 , first and second reticulated tubes  42  and  44  and the shell  12  are shown in cross-section. The openings  48  of the first and second reticulated tubes  42  and  44  are provided with louvers  80  that are arcuate or linear recesses in the first and second reticulated tubes  42  and  44  formed adjacent to and in conjunction with the openings  48 . As gas flows through the reticulated tubes  42 ,  44 , a portion of the exhaust gases flowing through the tubes may be diverted into the space between the inlet end interior baffle  30  and the intermediate interior baffle  32 . This space may also be filled with an acoustic absorption medium  82 . The acoustic absorption medium  82  may be glass wool, steel wool, stainless steel wool, ceramic wool, or the like. Combinations of different acoustic absorption materials may be used and various pre-formed media may also be used. The acoustic absorption medium  82  serves to absorb acoustic energy from the exhaust gas flow and deaden or quiet the noise emitted from the muffler assembly when the exhaust gases flow through the first and second reticulated tubes  42  and  44 . A stainless steel wool sock  83 , or tube, may be assembled over the reticulated tubes  42  and  44  to inhibit particles of the acoustic absorption medium  82  from flowing into the reticulated tubes  42  and  44 . 
     Referring to  FIG. 6 , operation of the muffler assembly  10  in a quiet mode is illustrated. In the quiet mode, exhaust gases are received in the inlet tube  18  that directs the exhaust gases through the inlet tube extension  28  that extends between the inlet end interior baffle  30  and the intermediate interior baffle  32 . Exhaust gas flow is shown diagrammatically by means of the phantom arrows  84 . The exhaust gas flow reverses direction after passing through the intermediate interior baffle  32  and is directed through the first reticulated tube  42 . The gas flow then reverses direction again as it passes between inlet end wall  16  and the inlet end interior baffle  30 . After reversing direction, the exhaust flow path  84  flows through the second reticulated tube  44  and into the extended portion  72 , and ultimately through the outlet tube  24 . As the exhaust gases flow through the first and second reticulated tubes  42  and  44 , a portion of the exhaust gases pass through the openings  48  and into the space defined between inlet end interior baffle  30  and the intermediate interior baffle  32 . The acoustic absorption medium  82  is preferably wrapped or assembled around the tubes  42  and  44  to provide additional sound attenuation and desired acoustic properties. 
     Referring to  FIG. 7 , the muffler assembly  10  is shown in its loud mode with the valve closure element  38  shifted by the vacuum diaphragm actuator  20  to open the valve opening  36  (shown in  FIG. 3 ). In the loud mode, exhaust gases flow into the inlet tube  18  and through the inlet end wall  16  and inlet end interior baffle  30  to the inlet tube extension  28 . A loud mode exhaust flow path  86  is shown by phantom arrows in  FIG. 7 . As shown in  FIG. 7 , the exhaust flows from the inlet tube extension  28  into the space between the intermediate interior baffle  32  and the valve plate baffle  34 . The exhaust gas flow is then directed through the valve opening ring  40 . The valve closure element  38  is separated from the valve opening ring  40  and closes off the reticulated tube  42  to direct the exhaust gases to flow through the valve opening  36  and into the space defined between valve plate baffle  34  and the outlet end wall  22 . An exhaust flow path  86  then flows into the direct flow ports  78  formed in the outlet tube  24  and through the outlet tube  24 . In the loud mode shown in  FIG. 7 , exhaust flow is not directed through the reticulated tubes  42  and  44 . No portion of the acoustic energy is absorbed by the openings  48  or the acoustic absorption medium  82  and no sound attenuation is provided by the inlet end interior baffle  30  or the intermediate interior baffle  32 . A limited amount of sound attenuation is obtained as the loud mode exhaust flow path  86  flows through the inlet tube extension  28  and through the valve opening ring  40  to the direct flow port  78 . 
     The driver of the vehicle can shift the muffler assembly  10  from the quiet mode shown in  FIG. 6  to the loud mode shown in  FIG. 7  by selectively porting vacuum from the engine or other vacuum source to the vacuum diaphragm actuator  20 . A vacuum valve control, such as that illustrated in  FIGS. 12 and 13 , or an electrical switch (not shown) may be assembled to the dashboard of the vehicle (not shown) may be actuated to provide vacuum to the vacuum diaphragm actuator  20 . 
     In  FIG. 7 , vacuum provided to the vacuum diaphragm actuator  20  retracts the operator  68  into the actuator  20 . This movement of the operator  68  is communicated through the clevis  66  to the actuator rod  64 . The actuator rod  64  is shifted toward actuator  20  when vacuum is provided. Shifting the actuator rod  64  causes the return spring adjustment mechanism  26  to compress a spring  88  of the return spring adjustment mechanism  26 . When the actuator rod  64  shifts, the valve closure element  38  is moved into engagement with one end of the reticulated tube  42 . This shifts the gas flow from flowing through the reticulated tubes  42  and  44  to cause the gas to flow through the valve opening ring  40 , as previously described. 
     The return spring adjustment mechanism  26  may be adjusted by tightening a nut  90  or other conventional adjustment mechanism to locate the valve closure element  38 . The return spring adjustment mechanism  26  should be adjusted to facilitate sealing between the valve closure element  38  and the valve opening ring  40  in the quiet mode shown in  FIG. 6 . The return spring adjustment mechanism  26  should also be adjusted to facilitate sealing between the valve closure element  38  and the end of the reticulated tube  42  in the loud mode. 
     The clevis  66  is connected to the operator  68  of the vacuum diaphragm actuator  20  by means of a pin  92  that accommodates the slight axial offset of the actuator rod  64  relative to actuator  20 . The pin  92  and clevis  66  permits the actuator  20  to be connected to the actuator rod  64  without binding or restriction because the clevis  66  is permitted to pivot on the pin  92 . The position of the valve closure element  38  may be adjusted by manipulating the clevis  66 , pin  92  and actuator rod  64 . These three parts together constitute an adjustable actuator connector. 
     The dual transverse muffler  100  is described with reference to the left side of the muffler  100  shown in  FIGS. 8 and 9 . The right and left sides of the dual transverse muffler  100  are essentially mirror images of each other and the description of the right side is not repeated for brevity. The same reference numerals are used to describe the internal parts on the left side of the muffler  100  as are used on the right side of the muffler  100 . 
     Referring to  FIG. 8 , a dual transverse muffler having two independent flow paths is illustrated in a quiet mode. The muffler  100  includes a shell  102  that is closed on one end by a first end wall  104  and on the opposite end by a second end wall  106 . A first inlet tube  108  is partially disposed within the shell  102  and extends through the first end wall  104 . A second inlet tube  110  is partially disposed in the shell  102  and extends through the second wall  106 . A first outlet tube  112  is partially disposed within the shell  102  and extends through the first end wall  104 . A second outlet tube  114  is partially disposed within the shell  102  and is inserted through the second end wall  106 . 
     A first baffle  116  is assembled within the shell  102  to be the baffle that is closest to the first end wall  104 . A second baffle  118  is assembled within the shell  102  inboard of the first baffle  116 . A third baffle  120  is assembled within the shell  102  between second baffle  118  and a central baffle  122 . The baffles  116 ,  118 ,  120  and  122  divide the internal space within the shell  102  into chambers. 
     An intermediate reticulated tube  126  is assembled to the first baffle  116  and the second baffle  118 . A plurality of sound attenuating ports  128  are provided in the intermediate reticulated tube  126 . The sound attenuating ports  128  may also be referred to as openings that are provided with louvers that define arcuate or linear recesses, as previously described with reference to  FIGS. 1-7 . An intermediate section  130 , or intermediate chamber, is defined between the first baffle  116  and the second baffle  118 . A plurality of sound attenuating ports  132  are provided in the intermediate section  130 . A valve opening ring  134  defines an opening (not shown) through the third baffle  120  that is similar to the opening  36  in the embodiment of  FIGS. 1-7 . A valve closure plate  136 , or valve closure element, is provided to open and close the valve opening ring  134  depending upon whether the muffler  100  is to be operated in the quiet mode or loud mode. 
     A rod  138  is assembled to the valve closure plate  136  and extends through the intermediate reticulated tube  126  and the first end wall  104 . For the right hand side, the rod  138  extends through the second end wall  106 . Vacuum diaphragm actuators  140  are provided on each of the first end wall  104  and the second end wall  106 . The rod  138  is connected to the vacuum diaphragm actuator  140  on one end of the rod  138 . The other end of the rod  138  is provided with a return spring  142 . Return spring  142  is attached to the central baffle  122  on the opposite side of the central baffle  122  from the remainder of the rod  138 . The first and second outlet tubes  112 ,  114  define direct flow ports  146  between the third baffle  120  and the central baffle  122 . An inlet end  148  of the intermediate reticulated tube  126  is selectively opened and closed by the valve closure plate  136  depending upon whether the dual transverse muffler  100  is in the quiet mode or in the loud mode. The reticulated tube  126  and intermediate section  130  may be wrapped in a stainless steel wool sock and an acoustic absorption medium as previously described with reference to  FIG. 5 . 
     Operation of the dual transverse muffler  100  in the quiet mode is described with continuing reference to  FIG. 8 . The dual transverse muffler  100  operating in the quiet mode creates an exhaust flow path identified by reference numeral  150  in  FIG. 8 . The exhaust flow path  150  is introduced into the first inlet tube  108  that directs the exhaust gases through the first end wall  104 , first baffle  116 , and second baffle  118 . The valve closure plate  136  closes the annular valve opening ring  134  which causes the exhaust gases to flow into the intermediate reticulated tube  126 . Exhaust gases flow in an intermediate flow path  152  from the sound attenuating ports  128  in the intermediate reticulated tube  126  through the intermediate section  130  to the sound attenuating ports  132  formed in the first outlet tube  112 . Exhaust gases then flow through the first outlet tube  112  and out of the muffler into the atmosphere. 
     Operation of the dual transverse muffler  100  is described in the loud mode with reference to  FIG. 9 . In the loud mode, the exhaust gases flow through the first inlet tube  108  through the first end wall  104 , the first baffle  116 , and the second baffle  118 . In the loud mode, the valve closure plate  136  is moved to close the inlet end  148  of the intermediate reticulated tube  126 . The valve closure plate  136  is moved by the vacuum diaphragm actuator  140  and the rod  138 . An exhaust gas flow path in the loud mode is indicated by reference numeral  154 . After the exhaust gases flow through the inlet tube  108 , they flow through the chamber defined by the second baffle  118  and the third baffle  120  through the valve opening ring  134 . The exhaust gas then flows through the chamber defined between the third baffle  120  and the central baffle  122  to the direct flow ports  146  that are formed in the first outlet tube  112 . Exhaust gases then flow through the first outlet tube  112  and into the atmosphere. 
     Referring to  FIG. 10 , a dual transverse muffler  160  having a combined exhaust flow path is described. The dual transverse muffler  160  is shown in the quiet mode in  FIG. 10 . The dual transverse muffler  160  is shown in the loud mode in  FIG. 11 . 
     The dual transverse muffler  160  includes a shell  162  that is closed on one side by a first end wall  162  and is closed on the opposite lateral side by a second end wall  166 . A first inlet tube  168  is partially disposed within the shell  162  and extends through the first end wall  164 . A second inlet tube  170  is partially disposed within the shell  162  and extends through the second wall  166 . A first outlet tube  172  extends through the shell  162  and also through the first and second end walls  164  and  166 . 
     A first baffle  176  is assembled inside the shell  162  near the first end wall  164 . A second baffle  178  is provided within the shell  162  near the inner end of the first inlet tube  168 . A third baffle  180  is provided within the shell  162  between the second baffle  178  and the second end wall  166 . The inner end of the second inlet tube  170  extends through the third baffle  180 . The baffles may be solid walls or may have openings depending upon the performance requirements for the muffler. 
     An intermediate reticulated tube  182  is assembled within the shell and is connected through the first baffle  176  and second baffle  178 . A plurality of sound attenuating ports  184  are provided in the intermediate reticulated tube  182  in an intermediate section  186  of the intermediate reticulated tube  182 . The intermediate section  186 , or intermediate chamber, is defined within the shell between the first baffle  176  and the second baffle  178 . A plurality of sound attenuating ports  188  are provided in the outlet tube  172 . A valve opening ring  190  is provided in the third baffle  180 . A valve closure plate  192  closes the valve opening ring  190  when operating in the quiet mode as shown in  FIG. 10 . A rod  194  connects the valve closure plate  192  to a vacuum diaphragm actuator  196  and a return spring  198 . The vacuum diaphragm actuator  196  is assembled to the first end wall  164 . The return spring  198  is assembled to the rod  194  and the second end wall  166 . 
     A plurality of direct flow ports  202  are provided in the outlet tube  172  between the third baffle  180  and the second end wall  166 . The inlet end  204  of the intermediate reticulated tube  182  is open as shown in  FIG. 10 . The valve closure plate  192  is disposed in a sealing relationship over the valve opening ring  190  leaving the inlet end  204  open. A quiet exhaust flow path is identified by reference numeral  206  in  FIG. 10 . Exhaust gases are introduced into the muffler  160  through the first inlet tube  168  and the second inlet tube  170 . Exhaust gases flow from the inlet tubes into the chamber formed between the second baffle  178  and the third baffle  180 . With the valve closure plate closing the valve opening ring  190 , exhaust gases are directed through the inlet end  204  of the intermediate reticulated tube  182 . Exhaust gases flow through the sound attenuating ports  184  in the intermediate reticulated tube  182  through the intermediate section  186  to the sound attenuating ports  188  formed in the outlet tube  172 . The reticulated tube  182  and outlet tube  172  may be wrapped in a stainless steel wool sock and an acoustic absorption medium as previously described with reference to  FIG. 5 . Exhaust gases then flow through both ends of the outlet tube  172  and into the atmosphere. 
     Referring to  FIG. 11 , a loud exhaust flow path is indicted by reference to the flow path arrows by reference numeral  208 . In the loud mode, exhaust gases are introduced into the muffler  160  through the first inlet tube  168  and the second inlet tube  170 . Exhaust gases flow from the inlet tubes into the chamber defined between the second baffle  178  and the third baffle  180 . In the loud mode of operation, the valve closure plate  192  closes or seals the inlet end  204  of the intermediate reticulated tube  182 . The exhaust gases flow through the valve opening ring  190  into the chamber defined between the third baffle  180  and the second end wall  166 . From there, the exhaust gases flow into the flow ports  202  formed in the outlet tube  172 . The exhaust gases then flow out of both ends of the outlet tube  172  into the atmosphere. 
     Referring to  FIG. 12 , a vacuum switch  212  is illustrated that may be used to operate the vacuum diaphragm actuator in any of the above embodiments. The vacuum switch  212  is supplied from a vacuum source such as the inlet manifold of an internal combustion engine, or the like. Vacuum is provided through tubing (not shown) to the vacuum diaphragm actuator  20 ,  140 ,  196  to shift the muffler  10 ,  100 ,  160  from the quiet to the loud mode of operation. The vacuum switch  212  is actuated by moving a control rod  220 . The vacuum switch  212  includes a housing  224  and a valve body  226  that is shiftable within the housing  224 . A chamber  228  is defined between the valve body  226  and the housing  224  that selectively allows vacuum to be provided from the vacuum source port  216  to the vacuum supply port  218 . 
     In the loud mode position shown in  FIG. 12 , the valve body  226  is shifted to the right end of the housing  224  by pulling the control rod  220 . An oval ring seal  230  is provided that also, in part, defines the chamber  228  and forms a seal between the housing  224  and the valve body  226 . In this position, vacuum is ported from the vacuum source port  216  to the vacuum supply port  218 . Vacuum is provided to the vacuum diaphragm actuators  20 ,  140 ,  196  that holds the valve closure elements  38 ,  136 ,  196  over the inlet opening of the intermediate reticulated tubes  42 ,  126 ,  182  and opens the respective valve openings  36 ,  134 ,  190 . 
     Referring to  FIG. 13 , the vacuum switch  212  is shown in the quiet operation mode. In the quiet mode, the valve closure elements  38 ,  136 ,  196  close the respective valve openings  36 ,  134 ,  190  and open the inlet opening of the intermediate reticulated tubes  42 ,  126 ,  182 . A circular seal ring  232  is provided to seal the vacuum source port  216  between the housing  224  and valve body  226 . The circular seal ring  232  seals the gap between the housing  224  and the valve body  226  when the control rod  220  is pushed to shift the valve body  226  to the left side of the housing  224  as shown in  FIG. 13 . In this position, vacuum supplied through the vacuum source port  216  is sealed by the circular seal ring  232 . 
     The vacuum switch  212  is normally set to the quiet mode operation. It should be understood that the normal mode of operation could be reversed, however, it is preferred that the muffler be in the quiet mode of operation when vacuum is not provided to the various diaphragm actuators so that in the event of a system failure the muffler would operate in the quiet mode. The system could also be operated on a pressurized fluid basis by connecting the switch  212  to a pressure source and providing a pressure diaphragm actuator to operate the mufflers. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.