Patent Publication Number: US-7913810-B2

Title: High-performance muffler assembly with multiple modes of operation

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM TO PRIORITY 
     This Application claims the benefit under 35 U.S.C. 119(e) of U.S. Application Ser. No. 11/713,106 filed Mar. 2, 2007, which claims benefit of U.S. Provisional Application No. 60/778,111 filed Mar. 2, 2006 by Meneely, V. et al. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mufflers for internal combustion engines in general, and, more particularly, to a high-performance muffler assembly including at least one valve assembly. 
     2. Description of the Prior Art 
     Typically, exhaust systems of internal combustion engines of all motor vehicles are equipped with a muffler for noise attenuation of the gases released from a combustion chamber of the internal combustion engines. Also, for internal combustion engines, especially diesel engines of large trucks, engine braking is an important feature for enhanced vehicle safety. For this reason, diesel engines in vehicles, particularly large trucks, are commonly equipped with an exhaust brake device for engine retarding. Exhaust brakes can be used on engines where compression release engine braking imparts too great of a load for the valve train. The exhaust brake device is characterized by increased sound level during engine braking operation. 
     The exhaust brake device consists of a restrictor element, such as a butterfly valve, mounted in the exhaust system upstream of a muffler. When this restrictor is closed, increasing exhaust backpressure resists the exit of gases during the exhaust cycle and provides a braking mode of operation. This system provides less braking power than a compression release engine brake, but also at less cost. With conventional fixed orifice exhaust brakes, the retarding power of an exhaust brake falls off sharply as engine speed decreases. This occurs because the restriction is typically optimized to generate maximum allowable backpressure at maximum engine speed. The optimized restriction is too large to be effective with the lower mass flow rates encountered at low engine speeds. In other words, the restriction is simply insufficient to be effective at the low engine speeds. 
     Typically, a range of engine operating speeds includes a low engine speed range (low engine speeds) and a high engine speed range (high engine speeds). Generally, the low engine speed range is defined as a speed range from an idle speed to a midrange speed, and high engine speed is defined as a speed range from the midrange speed to a maximum engine speed. In other words, the low engine speed is the engine speed at or near the lower end of the operating speed range of the engine, while the high engine speed is the engine speed at or near the upper end of the operating speed range of the engine. 
     While known exhaust systems of the internal combustion engines, including but not limited to those discussed above have proven to be acceptable for various vehicular applications, such devices are nevertheless susceptible to improvements that may enhance their performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel muffler assembly for an exhaust system of an internal combustion engine. The muffler assembly of the present invention comprises an elongated casing having an inlet port and an exit port, a first pipe disposed within the casing and having an inlet end in fluid communication with the inlet port and an outlet end selectively fluidly connected to the exit port of the casing, and a first valve mounted within the casing. The first valve is selectively movable between a closed position and an open position for regulating an exhaust gas flow through the first pipe. The muffler assembly is operable in a number of different modes of operation including a high-performance mode, an exhaust braking mode, a reverse-flow mode, etc., determined by the positions of the first valve of the muffler assembly. 
     According to a first exemplary embodiment of the present invention, the muffler assembly further comprises a pressure relief valve disposed inside the muffler casing upstream of the first valve and a second valve mounted within the muffler casing downstream of the first valve. The pressure relief valve is selectively movable between a closed position and an open position for selectively fluidly connecting the inlet end of the first pipe to the exit port by bypassing the first valve. The pressure relief valve moves into the open position when a pressure of exhaust gas acting on the pressure relief valve is higher than a predetermined value. The second valve is selectively movable between a closed position and an open position for preventing the exhaust gas flow through the outlet end of the first pipe when the second valve is in the closed position. The muffler assembly further comprises second and third pipes disposed within the casing and radially spaced from the first pipe, and first, second and third baffle plates dividing an internal cavity within the casing into a resonant chamber, an inlet chamber and a reverse-flow chamber. The muffler assembly of the first exemplary embodiment of the present invention is operable in a straight flow mode when both the first and second valves are in the open position, in an exhaust braking mode when both the first and second valves are in the closed position, in a reverse flow mode when the first valve is in the open position and the second valve is in the closed position, and in a warm-up mode during a cold start of the internal combustion engine when the first valve is in the closed position and the second valve is in the open position. 
     According to a second exemplary embodiment of the present invention, the muffler assembly further comprises a particulate filter disposed within the muffler casing. Preferably, the particulate filter is disposed downstream of the inlet end of the first pipe. The muffler assembly further includes at least one heating element activated when the muffler assembly operates in a regeneration mode for regenerating the particulate filter. 
     According to a third exemplary embodiment of the present invention, the muffler assembly further comprises second and third pipes disposed within the casing and radially spaced from the first pipe, and first, second and third baffle plates dividing an internal cavity within the casing into a resonant chamber, an inlet chamber and a reverse-flow chamber. The muffler assembly of the third exemplary embodiment of the present invention is operable in a straight flow mode when the first valve is in the open position and in a reverse flow mode when the first valve is in the closed position. 
     According to a fourth exemplary embodiment of the present invention, the muffler assembly further comprises a pressure relief valve disposed inside the muffler casing upstream of the first valve and a second valve mounted within the muffler casing downstream of the first valve. The pressure relief valve is selectively movable between a closed position and an open position for selectively fluidly connecting the inlet end of the first pipe to the exit port by bypassing the first valve. The pressure relief valve moves into the open position when a pressure of exhaust gas acting on the pressure relief valve is higher than a predetermined value. The second valve is selectively movable between a closed position and an open position for preventing the exhaust gas flow through the outlet end of the first pipe when the second valve is in the closed position. The muffler assembly further comprises first and second perforated baffle plates defining a resonant chamber between the first perforated baffle plate and the rear wall of the casing, an inlet chamber between the second perforated baffle plate and the front wall, and a central chamber therebetween. The first pipe further includes at least one aperture positioned between the first perforated baffle plate and the rear wall of the casing downstream of the second valve so as to provide fluid communication between the resonant chamber and the exit port through the outlet end of the first pipe, and at least one aperture positioned between the first and second valves so as to provide fluid communication between the central chamber and the first pipe between the first and second valves. The muffler assembly of the fourth exemplary embodiment of the present invention is operable in a straight flow mode when both the first and second valves are in the open position, in an exhaust braking mode when both the first and second valves are in the closed position, and in a bypass mode when the first valve is in the open position and the second valve is in the closed position. 
     According to a fifth exemplary embodiment of the present invention, the muffler assembly further comprises a perforated baffle plate defining a resonant chamber between the perforated baffle plate and the rear wall of the casing, and an inlet chamber between the first perforated baffle plate and the front wall. The first pipe further includes at least one aperture positioned between the first perforated baffle plate and the rear wall of the casing downstream of the first valve so as to provide fluid communication between the resonant chamber and the exit port through the outlet end of the first pipe, and at least one aperture positioned upstream of the first valve so as to provide fluid communication between the inlet chamber and the first pipe. The muffler assembly of the fifth exemplary embodiment of the present invention is operable in a straight flow mode when the first valve is in the open position and in a bypass mode when the first valve is in the closed position. 
     According to a sixth exemplary embodiment of the present invention, the muffler assembly further comprises a pressure relief valve disposed inside the muffler casing upstream of the first valve. The pressure relief valve is selectively movable between a closed position and an open position for selectively fluidly connecting the inlet end of the first pipe to the exit port by bypassing the first valve. The pressure relief valve moves into the open position when a pressure of exhaust gas acting on the pressure relief valve is higher than a predetermined value. The muffler assembly further comprises a perforated baffle plate defining a resonant chamber and an inlet chamber so that the inlet end of the first pipe is fluidly connected to the inlet chamber when the pressure relief valve in the open position. Moreover, the first pipe further includes at least one aperture positioned between the perforated baffle plate and a rear wall of the casing downstream of the first valve so as to provide fluid communication between the resonant chamber and the exit port through the outlet end of the first pipe. The muffler assembly of the sixth exemplary embodiment of the present invention is operable in the exhaust braking mode when the first valve is in the closed position, and in a straight flow mode when the first valve is in the open position. 
     According to a seventh exemplary embodiment of the present invention, the outlet end of the first pipe is closed and the muffler assembly further comprises a pressure relief valve disposed inside the muffler casing upstream of the first valve. The pressure relief valve is selectively movable between a closed position and an open position for selectively fluidly connecting the inlet end of the first pipe to the exit port by bypassing the first valve. The pressure relief valve moves into the open position when a pressure of exhaust gas acting on the pressure relief valve is higher than a predetermined value. The muffler assembly further comprises second and third pipes disposed within the casing and radially spaced from the first pipe, and first, second and third baffle plates dividing an internal cavity within the casing into a resonant chamber, an inlet chamber and a reverse-flow chamber. The muffler assembly of the seventh exemplary embodiment of the present invention is operable in an exhaust braking mode when the first valve is in the closed position and in a reverse flow mode when the first valve is in the open position. 
     According to an eighth exemplary embodiment of the present invention, the muffler assembly includes only one valve assembly mounted within a casing, and that a first pipe is centrally located within a second pipe which, in turn, is centrally located within the casing and extending substantially coaxially to a central axis of the casing between inlet and exit ports and thereof. The second pipe has a front perforated section adjacent to the front of the casing, a rear open section adjacent to the rear wall of the casing and a central section extending between the front and rear sections of the second pipe. The central section of the second pipe is impervious for exhaust gas flow. The muffler assembly  710  further comprises a baffle plate dividing the internal cavity within the muffler casing so as to define a resonant chamber and an inlet chamber. The baffle plate has one or more apertures so as to provide fluid communication between the inlet chamber and the resonant chamber. The muffler assembly further comprises one or more baffle members in the resonant chamber between the casing and the second pipe. The baffle members define a tortuous path of the exhaust gas flow through the resonant chamber. Preferably, the muffler assembly comprises a plurality of the baffle members each of the baffle members is in the form of a semi-annular plate disposed opposite to each other in an alternating manner. The muffler assembly of the eighth exemplary embodiment of the present invention is operable in a bypass mode when the valve is in the closed position and in a high-performance mode when the valve is in the open position. 
     The first and second valves are operatively controlled by an electronic control unit depending on at least one operating parameter of the muffler assembly and/or the internal combustion engine. 
     Therefore, the muffler assembly in accordance with the present invention allows for multiple modes of operation in order to improve and optimize operational characteristics of the internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a first exemplary embodiment of the present invention; 
         FIG. 2  is a sectional view of the muffler assembly according to the first exemplary embodiment of the present invention in a high-performance mode; 
         FIG. 3  is a sectional view of the muffler assembly in accordance with the first exemplary embodiment of the present invention in an exhaust braking mode; 
         FIG. 4  is a sectional view of the muffler assembly in accordance with the first exemplary embodiment of the present invention in a reverse flow mode; 
         FIG. 5  is a sectional view of the muffler assembly in accordance with the first exemplary embodiment of the present invention in a warm-up mode; 
         FIG. 6  is a cross-sectional view of a first valve assembly in a first pipe in a section taken along lines  6 - 6  in  FIG. 3 ; 
         FIG. 7  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a second exemplary embodiment of the present invention; 
         FIG. 8  is a sectional view of the muffler assembly according to the second exemplary embodiment of the present invention; 
         FIG. 9  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a third exemplary embodiment of the present invention; 
         FIG. 10  is a sectional view of a muffler assembly according to the third exemplary embodiment of the present invention in a reverse flow mode; 
         FIG. 11  is a sectional view of the muffler assembly in accordance with the third exemplary embodiment of the present invention in a high-performance mode; 
         FIG. 12  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a fourth exemplary embodiment of the present invention; 
         FIG. 13  is a sectional view of a muffler assembly according to the fourth exemplary embodiment of the present invention in a bypass mode; 
         FIG. 14  is a sectional view of the muffler assembly in accordance with the fourth exemplary embodiment of the present invention in an exhaust braking mode; 
         FIG. 15  is a sectional view of the muffler assembly in accordance with the fourth exemplary embodiment of the present invention in a high-performance mode; 
         FIG. 16  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a fifth exemplary embodiment of the present invention; 
         FIG. 17  is a sectional view of a muffler assembly according to the fifth exemplary embodiment of the present invention in a bypass mode; 
         FIG. 18  is a sectional view of the muffler assembly in accordance with the fifth exemplary embodiment of the present invention in a high-performance mode; 
         FIG. 19  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a sixth exemplary embodiment of the present invention; 
         FIG. 20  is a sectional view of a muffler assembly in accordance with the sixth exemplary embodiment of the present invention in a high-performance mode; 
         FIG. 21  is a sectional view of the muffler assembly in accordance with the sixth exemplary embodiment of the present invention in an exhaust braking mode; 
         FIG. 22  is a schematic view of an exhaust system of an internal combustion engine including a muffler assembly according to a seventh exemplary embodiment of the present invention; 
         FIG. 23  is a sectional view of a muffler assembly according to the seventh exemplary embodiment of the present invention in a reverse flow mode; 
         FIG. 24  is a sectional view of the muffler assembly in accordance with the seventh exemplary embodiment of the present invention in an exhaust braking mode; 
         FIG. 25  is a partial perspective view of a muffler assembly according to an eighth exemplary embodiment of the present invention; 
         FIG. 26  is a sectional view of a muffler assembly according to the eighth exemplary embodiment of the present invention in a bypass mode; 
         FIG. 27  is a sectional view of the muffler assembly in accordance with the eighth exemplary embodiment of the present invention in a high-performance mode. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described with the reference to accompanying drawings. 
     For purposes of the following description, certain terminology is used in the following description for convenience only and is not limiting. The words such as “front” and “rear”, “left” and “right”, “inwardly” and “outwardly” designate directions in the drawings to which reference is made. The words “smaller” and “larger” refer to relative size of elements of the apparatus of the present invention and designated portions thereof. The terminology includes the words specifically mentioned above, derivatives thereof and words of similar import. 
       FIG. 1  schematically depicts an exhaust system  1  according to a first exemplary embodiment of the present invention provided for an internal combustion engine (ICE)  2  equipped with a turbo-charger  4 . According to the preferred embodiment of the present invention, the internal combustion engine  2  is a diesel engine including a fuel injector  3 . As illustrated in  FIG. 1 , a compressor  4   a  of the turbocharger  4  supplies intake air under pressure to a combustion chamber of the engine  2  through an intercooler  6  where the compressed charge air is cooled before entering the combustion chamber of the engine  2 . Intake airflow is conventionally controlled by a throttle valve  8 . An exhaust gas flow from the combustion chamber of the engine  2  flows through a turbine  4   b  of the turbocharger  4  and an oxidation catalyst  9  into a high performance muffler assembly  10  according to the first exemplary embodiment of the present invention. As further illustrated in  FIG. 1 , the exhaust system  1  also comprises an exhaust gas recirculation (EGR) valve  12  selectively receiving a portion of the exhaust gas flow from the ICE  2  through an EGR cooler  14  for recirculation. The fuel injector  3 , the throttle valve  8  and EGR valve  12  are controlled by an electronic control unit  16  based on a one or more operating parameters of the internal combustion engine  2 , such as air pressure at inlet and outlet of the compressor  4   a  of the turbocharger  4  (sensors  5   a  and  5   b , respectively), a position of the throttle valve  8  (a throttle position sensor  8   a ), etc. 
     As illustrated in detail in  FIG. 2 , the high performance muffler assembly  10  according to the first exemplary embodiment of the present invention comprises an elongated casing (or shell)  20  defining an internal cavity  22  therein. The casing  20  is provided with an inlet pipe  24  guiding the exhaust gas flow from the ICE  2  into the casing  20  of the muffler assembly  10 , and an exit pipe  26  directing the exhaust gas flow out of the casing  20  of the muffler assembly  10 . Moreover, the casing  20  includes a continuous outer wall  28  extending along a central axis  21  of the casing  20 , a front wall  30  and a rear wall  32 . Preferably, the outer wall  28  of the casing  20  is substantially circular or elliptical in cross-section, while the front and rear walls  30 ,  32  are substantially planar. The inlet pipe  24  defines an inlet port  25  through the front wall  30  of the casing  20 , while the exit pipe  26  defines an exit port  27  through the rear wall  32  of the casing  20 . Both the inlet port  25  and exit port  27  are in fluid communication with the internal cavity  22  of the casing  20 . As further illustrated in  FIG. 2 , the muffler assembly  10  also comprises a first pipe  34  centrally located within the casing  20  and extending substantially coaxially to the central axis  21  of the casing  20  between the inlet and exit ports  25  and  27  thereof. More specifically, the first pipe  34  has an open inlet end  34   a  attached to the inlet port  25  and an open outlet end  34   b  in fluid communication with the exit port  27  of the casing  20 . 
     The casing  20  further includes a first, second and third baffle plates (or partition walls)  36 ,  38  and  40 , respectively, extending across the casing  20  between the outer wall  28  thereof. The baffle plates  36 ,  38  and  40  are spaced from each other along the central axis  21  of the casing  20 , and are axially spaced from the respective front and rear walls  30  and  32 . The baffle plates  36 ,  38  and  40  are fixed to the outer wall  28  of the casing  20  in any appropriate manner, such as by welding. As shown in  FIG. 2 , the first baffle plate  36  is disposed adjacent to the outlet end  34   b  of the first pipe  34  so as to define a resonant chamber  42  within the casing  20  between the first baffle plate  36  and the rear wall  32  of the casing  20 . The first baffle plate  36  has a central opening so as to provide fluid communication between the first pipe  34  and the resonant chamber  42 . In other words, the outlet end  34   b  of the first pipe  34  is open to the resonant chamber  42 . In turn, the resonant chamber  42  is in fluid communication with the exit port  27  of the casing  20 . The second baffle plate  38  is disposed adjacent to the inlet end  34   a  of the first pipe  34  and is axially spaced from the front wall  30  so as to define a substantially annular inlet chamber  44  within the casing  20  and about the first pipe  34  between the second baffle plate  38  and the front wall  30  of the casing  20 . As shown, the inlet chamber  44  is not in direct fluid communication with the inlet port  25 . The second baffle plate  38  has a central opening so as to receive the first pipe  34  therethrough. The third baffle plate  40  is disposed between the inlet and outlet ends  34   a  and  34   b  of the first pipe  34  so as to define a reverse-flow chamber  46  within the casing  20  between the first baffle plate  36  and the third baffle plate  40  of the casing  20 . The third baffle plate  40  has a central opening so as to receive the first pipe  34  therethrough. Thus, the first pipe  34  passes through the second and third baffle plates  38  and  40 , and engages the first baffle plate  36  at the outlet end  34   b  thereof. The first pipe  34  is also provided with a bypass opening  35  adjacent to the outlet end  34   b  thereof so as to provide fluid communication between the first pipe  34  and the reverse-flow chamber  46 . As illustrated, the bypass opening  35  of the first pipe  34  is open to the reverse-flow chamber  46 . 
     The muffler assembly  10  further comprises second and third open ended pipes  48  and  50 , respectively, located within the casing  20  and extending generally in the direction between the inlet and exit ports  25  and  27  thereof. Preferably, the second and third pipes  48  and  50  extend substantially parallel to the central axis  21 . Moreover, the second and third pipes  48  and  50  are radially spaced from the first pipe  34 . The second pipe  48  extends between the first and second baffle plates  36 ,  38  and passes through an opening in the third baffle plate  40  so that an inlet end  48   a  of the second pipe  48  is open to (in fluid communication with) the inlet chamber  44  through an opening in the second baffle plate  38 , while an outlet end  48   b  is open to (in fluid communication with) the resonant chamber  42  through an opening  36   b  in the first baffle plate  36 . 
     The third pipe  50  extends between the second and third baffle plates  38  and  40  so that an inlet end  50   a  of the third pipe  50  is open to (in fluid communication with) the inlet chamber  44  through an opening in the second baffle plate  38 , while an outlet end  50   b  is open to (in fluid communication with) the reverse-flow chamber  46  through an opening in the third baffle plate  40 . Thus, the inlet chamber  44  is in fluid communication with the resonant chamber  42  through the second pipe  48 , and in fluid communication with the reverse-flow chamber  46  through the third pipe  50 . 
     Referring now to  FIGS. 1-6 , the muffler assembly  10  further comprises a first valve assembly  52  mounted within the casing  20 . According to the first exemplary embodiment of the present invention, the first valve assembly  52  functions as an exhaust brake device. The first valve assembly  52  includes a first valve  54  selectively movable between a closed position and an open position for regulating an exhaust gas flow through the first pipe  34 . Specifically, when the first valve  54  is in the open position, as illustrated in  FIGS. 2 and 4 , the exhaust gas flows through the first pipe  34 , while when the first valve  54  is in the closed position, as illustrated in  FIGS. 3 ,  5  and  6 , the exhaust gas is substantially prevented from flowing through the first pipe  34 . Preferably, the first valve  54  is a variable valve which can adapt fully closed position, fully open position and any intermediate position between the fully open and closed positions. At the same time, an orifice is provided between the first valve and the first pipe  34  to allow some exhaust gas flow through the first pipe  34  when the first valve  54  is in the closed position. 
     Preferably, the first valve  54  is an exhaust restrictor in the form of a butterfly valve mounted within the first pipe  34  for rotation about a shaft  55 . The first valve  54  is dimensioned so as to provide a gap (orifice)  39  (shown in  FIG. 6 ) between an inner peripheral surface of the first pipe  34  and a circumferential edge of the first valve  54  when the first valve  54  is in its closed position, as illustrated in  FIG. 6 . Preferably, the gap  39  is substantially annular in shape. Alternatively, or in addition to the gap  39 , the first valve  54  may also be provided with a vent opening  39 ′ therethrough. Therefore, in its open position shown in  FIGS. 2 and 4 , the first butterfly valve  54  is oriented substantially parallel to the central axis  21 , thereby producing only minimal resistance to the exhaust gas flow through the first pipe  34 . However, in its closed position shown in  FIGS. 3 ,  5  and  6 , the first butterfly valve  54  is oriented substantially perpendicular to the central axis  21 , thereby producing a maximum obstruction to the flow of the exhaust gas and therefore maximum exhaust gas backpressure. A restriction of the first valve  54  in the closed position thereof, thus the maximum exhaust gas backpressure, is determined by an area of the gap  39  around the first valve  54  and/or the optional vent opening  39 ′ therethrough. Further preferably, the first valve  54  is disposed adjacent to the inlet end  34   a  of the first pipe  34  but is axially spaced from the inlet port  25  of the casing  20 . 
     The first valve assembly  52  further includes a first actuator  56  provided for selectively moving the first valve  54  between the closed and open positions. It will be appreciated that the first actuator  56  may be in the form any appropriate device adapted for rotating the first valve  54  about the shaft  55 . Preferably, the first actuator  56  includes an actuator lever  57  and an actuator cylinder  58 . In a manner well know to those skilled in the art, a movable distal end of the actuator cylinder  58  is secured to a free end of the actuator lever  57  and can be actuated by the ECU  16 . In other words, the ECU  16  operatively controls the first valve assembly  52  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  10 , including engine speed and inlet and outlet exhaust gas pressure monitored by an engine speed sensor  7 , schematically depicted in  FIG. 1 , and pressure sensors  17  and  18 , respectively, shown in  FIGS. 1 and 2 . As illustrated in  FIGS. 1 and 2 , the exhaust gas inlet pressure sensor  17  is mounted to the inlet pipe  24  of the casing  20  adjacent to the inlet port  25  to monitor an inlet pressure of the exhaust gas entering the muffler assembly  10 , while exhaust gas outlet pressure sensor  18  is mounted to the exit pipe  26  of the casing  20  adjacent to the exit port  27  to monitor an outlet pressure of the exhaust gas exiting the muffler assembly  10 . Alternatively, the pressure sensors  17  and  18  could be mounted directly to the muffler casing  20 . Both the inlet and outlet exhaust gas pressure sensors  17  and  18  are electronically connected to the ECU  16 . Preferably, the actuator cylinder  58  is fluidly (e.g., pneumatically, hydraulically or vacuum) actuated by the ECU  16  through a solenoid valve  59  (shown in  FIG. 1 ), and is disposed outside the first pipe  34 . Alternatively, the first actuator  56  may be in the form of an electro-mechanical actuator or an electro-magnetic actuator. 
     Referring again to  FIGS. 1-6 , the muffler assembly  10  further comprises a second valve assembly  62  mounted within the casing  20 . According to the first exemplary embodiment of the present invention, the second valve assembly  62  functions as a diverter valve. Preferably, the second valve assembly  62  is substantially structurally similar to the first valve assembly  52  and includes a second valve  64  selectively movable between a closed position and an open position for preventing the exhaust gas flow through the outlet end  34   b  of the first pipe  34  when the second valve  64  is in the closed position. Specifically, when the second valve  64  is in the open position, as illustrated in  FIGS. 2 and 4 , the exhaust gas can flow out the first pipe  34 , while when the second valve  64  is in the closed position, as illustrated in  FIGS. 3 ,  5  and  6 , the exhaust gas is prevented from flowing through the outlet end  34   b  of the first pipe  34 . The second valve  64  is mounted within the first pipe  34  downstream of the first valve  54 . Preferably, the second valve assembly  62  is structurally substantially similar to the first valve assembly  52 . In the preferred embodiment, the second valve  64  is a variable exhaust restrictor in the form of butterfly valve mounted within the first pipe  34  for rotation about a shaft  65 . Further preferably, the second valve  64  is disposed adjacent to the outlet end  34   b  of the first pipe  34 . 
     The second valve assembly  62  further includes a second actuator  66  provided for selectively moving the second valve  64  between the closed and open positions. It will be appreciated that the second actuator  66  may be in the form any appropriate device adapted for rotating the second valve  64  about the shaft  65 . Preferably, the second actuator  66  includes an actuator lever  67  and an actuator cylinder  68 . In a manner well know to those skilled in the art, a movable distal end of the actuator cylinder  68  is secured to a free end of the actuator lever  67  and can be actuated by the ECU  16 . In other words, the ECU  16  operatively controls the second valve assembly  62  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  10 , including engine speed and the inlet and outlet exhaust gas pressures monitored by the engine speed sensor  7  and the pressure sensors  17  and  18 . Preferably, the actuator cylinder  68  is fluidly (e.g., pneumatically, hydraulically or vacuum) actuated by the ECU  16  through a solenoid valve  69  (shown in  FIG. 1 ), and is disposed outside the first pipe  34 . Alternatively, the second actuator  66  may be in the form of an electro-mechanical actuator or an electro-magnetic actuator. 
     The muffler assembly  10  further comprises an automatically, mechanically actuated pressure relief (or pressure regulator) valve  70  disposed inside the casing  20  upstream of the first valve  54 . The pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  34   a  of the first pipe  34  to the exit port  27  by bypassing the first valve  54 . More specifically, the pressure relief valve  70  fluidly connects the inlet end  34   a  of the first pipe  34  to the inlet chamber  44  when the pressure in the first pipe  34  reaches a predetermined high value. 
     As illustrated in detail in  FIGS. 2-5 , the pressure relief valve  70  is mounted to the first pipe  34  adjacent to the inlet end  34   a  thereof. Preferably, the pressure relief valve  70  is normally biased in a closed position by a calibrated spring  72 , and is movable between the closed position and an open position. In the normally closed position, the pressure relief valve  70  closes a relief opening  37  formed in the first pipe  34  adjacent to the inlet end  34   a  thereof so as to prevent fluid communication between the first pipe  34  and the inlet chamber  44 . However, when a pressure of the exhaust gas acting on the pressure relief valve  70  is higher than a predetermined value the pressure relief valve  70  moves into the open position. In the open position, the pressure relief valve  70  opens the relief opening  37  so as to provide fluid communication between the first pipe  34  and the inlet chamber  44 . It will be appreciated that the predetermined value of the exhaust gas pressure at which the pressure relief valve  70  opens depends on a spring rate of the compression spring  72 . Thus, the pressure relief valve  70  could easily be tuned by calibrating the spring rate of the compression spring  72 . 
     The muffler assembly  10  according to the first exemplary embodiment of the present invention is operable in a number of different modes of operation including a high-performance (or straight flow) mode, an exhaust braking mode, a reverse-flow mode, and a warm-up mode, determined by the positions of the first and second valve assemblies  52  and  62  of the muffler assembly  10 . As described hereinabove, the first and second valve assemblies  52  and  62  of the muffler assembly  10  are selectively and independently controlled by the ECU  16  in a closed or open loop depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  10 , including the inlet and outlet exhaust gas pressure, and the engine speed monitored by the pressure sensors  17  and  18 , and an engine speed sensor  7  schematically depicted in  FIG. 1 . 
     In the high-performance (or straight flow) mode illustrated in  FIG. 2 , both the first and second valves  54  and  64  are open. The exhaust gas flow freely passes directly through the first pipe  34 , as denoted by directional arrows F. The direct non-restricted exhaust gas flow through the muffler assembly  10  increases the exhaust flow of the engine  2 , reduces backpressure of the exhaust gas and increases efficiency of the turbocharger  4 . Lower restriction in the exhaust system  1  provides better fluid exchange in the combustion chamber, therefore the power output of the engine  2  increases. Specifically, the power output of the engine  2  increases by about 4-5% when the muffler assembly  10  operates in the high-performance muffler mode. Therefore, in the high-performance mode, the muffler assembly  10  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger and the engine  2  to breathe and function more efficiently. 
     In the exhaust braking mode illustrated in  FIG. 3 , both the first and second valves  54  and  64  are closed and the exhaust flow through the first pipe  34  is restricted. As a result, the exhaust gas back pressure is increased providing an exhaust brake function to the ICE  2 , thus providing the exhaust brake function to the motor vehicle. As the engine braking mainly occurs at lower engine speeds where exhaust pressures are lower, the restriction of the first valve  54  in the closed position (e.g., the area of the orifice  39  shown in  FIG. 4 ) is optimized to generate maximum allowable backpressure at the lower engine speeds. Thus, the optimized restriction of the first valve  54  is effective with the lower mass flow rates of the exhaust gas flow encountered at the lower engine speeds. 
     The exhaust gas backpressure increases generally proportionally to the engine speed. At high engine speeds the backpressure becomes higher than the maximum allowable exhaust backpressure. When the pressure of exhaust gas in the first pipe  34  acting on the pressure relief valve  70  becomes higher than a predetermined value (e.g. equal to the maximum allowable exhaust backpressure), the pressure relief valve  70  moves into its open position. Consequently, the exhaust gas flow F is forced to flow through the pressure relief valve  70  into the inlet chamber  44 , then through the second pipe  48  to the resonant chamber  42 , thus bypassing the first valve  54 . From the resonant chamber  42  the exhaust gas exits the muffler assembly  10  through the exit port  27 . Therefore, the pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  34   a  of the first pipe  34  to the exit port  27  by bypassing the first valve  54  in the exhaust braking mode. The pressure relief valve  70  usually operates only at high engine speeds where the exhaust gas backpressure is higher than the maximum allowable exhaust gas backpressure. In other words, the pressure relief valve  70  is provided to limit the maximum exhaust pressure developed within the first pipe  34  of the muffler assembly  10 . At higher than the maximum allowable exhaust backpressure the pressure relief valve  70  will open, controlled by the calibrated spring  72 . Thus, the pressure relief valve  70  controls the exhaust gas backpressure for maximum engine braking and is used to reduce the exhaust gas backpressure during higher engine speeds to increase the exhaust gas flow of the engine for higher performance. As a result, the muffler assembly  10  of the present invention is provided to optimize the retarding power of the exhaust brake over a wider range of the engine speeds than the existing exhaust brake devices. 
     The exhaust brake devices are characterized by increased sound level during the exhaust brake operation. For instance, due to the restriction of the closed exhaust brake valve  54  and the pressure differential therethrough, the velocity of the exhaust gas flowing through the orifice  39  around the first valve  54  (or the vent opening  39 ′) increases. The exhaust gas flowing at higher speed around the closed exhaust brake valve  54  has increased acoustical sound level compared to the exhaust gas flowing through an open exhaust pipe. However, as the exhaust brake device  52  is encapsulated in the casing  20  of the muffler assembly  10 , the sound level generated by the restricted exhaust gas flow is reduced and contained in the muffler assembly  10 . Evidently, the exhaust brake device  52  internal to the muffler assembly  10  provides a quieter exhaust brake when activated in comparison to conventional exhaust brake devices external to the muffler assemblies. Thus, being encapsulated by the muffler casing  20 , the noise associated with the exhaust brake operation is significantly reduced. 
     In the reverse-flow mode illustrated in  FIG. 4 , the first (exhaust brake) valve  54  is open, while the second (diverter) valve  64  is closed. The exhaust gas flows through the first pipe  34  until reaches the closed diverter valve  64 . The exhaust gas reverses its flow through the third pipe  50  and goes into the inlet chamber  44 , then through the second pipe  48  to the resonant chamber  42 . From the resonant chamber  42  the exhaust gas flows out of the casing  20  of the muffler assembly  10 . In the reverse-flow mode, the exhaust gas flows through a longer path inside the casing  20 , thus resulting in better muffling the exhaust gas noise by the muffler assembly  10 . 
     The warm-up mode illustrated in  FIG. 5 , is achieved by completely or partially closing the first (exhaust brake) valve  54  (as long as the maximum backpressure of the exhaust gas during idling of the engine  2  does not exceed the predetermine value), while opening the second (diverter) valve  64  at engine idle speed. The pressure relief valve  70  will open to prevent the overpressure during engine idling. The pressure relief valve  70  works as a safety valve to prevent overpressure and provide backpressure protection. The warm-up mode of the muffler assembly  10  of the engine  2  is useful for increasing the temperature of the engine in cold conditions, especially beneficial for diesel engines. Cold operating engines affect the combustion process in the combustions chamber generating unburned hydrocarbons and increase the wear of engine components. 
     Moreover, if the internal combustion engine  2  operates in an engine compression release braking mode, then the second valve  64  is closed during the engine compression release braking mode. 
     Furthermore, the first and second valve assemblies  52  and  62  control an amount of exhaust gas recirculation used in the engine  2 . The ECU  16  controls the closure of either one of the two valves  54  and  64  to obtain the desired exhaust gas recirculation for reducing the emissions of nitrogen oxides. 
       FIGS. 7 and 8  illustrate a second exemplary embodiment of a muffler assembly, generally depicted by the reference character  110 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 100 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     The muffler assembly  110  of  FIGS. 7 and 8  is structurally and functionally very similar to the muffler assembly  10  of  FIGS. 1-6 . A difference between the muffler assembly  110  of  FIGS. 7 and 8  and the muffler assembly  10  of  FIGS. 1-6  is that the muffler assembly  110  additionally includes a diesel particulate filter (DPF)  80  located within a casing  120  upstream of the inlet end  34   a  of the first pipe  34 . Specifically, as illustrated in  FIG. 8 , the DPF  80  is disposed in a cavity formed by an outer wall  128  between a front wall  130  and a filter wall  131  disposed adjacent to the inlet end  34   a  of the first pipe  34 . As shown in  FIG. 8 , the inlet chamber  44  is defined between the filter wall  131  and the first baffle plate  36 . The inlet end  34   a  of the first pipe  34  is in fluid communication with an inlet port  125  of the muffler assembly  110  through the DPF  80  so that all of the exhaust gas entering the casing  120  through the inlet port  125  flows into the inlet end  34   a  of the first pipe  34  by passing through the DPF  80 . The DPF  80  is used to filter soot particles from the exhaust gas flow of the diesel engine. The DPF  80  collects particulate matter without exceeding exhaust backpressure specifications determined by an engine manufacturer. 
     The muffler assembly  110  according to the second exemplary embodiment of the present invention is capable of operating in a regeneration mode in order to regenerate the particulate filter  80 . During operation in the regeneration mode, the temperature of the DPF  80  has to be increased for burning off the particulates trapped inside the DPF  80 . Both the first and second valves  54  and  64  are closed during the particulate filter regeneration. By closing the first valve  54  the high temperature exhaust gases from the engine  2  are trapped in the DPF  80 . The temperature increase of the DPF will help the regeneration process enabled by a regeneration strategy controlled by the ECU  16  shown in  FIG. 7 . The pressure relief valve  70  insures that the maximum exhaust gas backpressure allowable for the engine  2  is not exceeded during the regeneration process. 
     Preferably, in order to facilitate heating of the DPF  80 , the muffler assembly  110  is provided with at least one heating element for heating exhaust gas in a regeneration mode thereof. According to the second exemplary embodiment of the present invention illustrated in  FIG. 8 , the muffler assembly  110  comprises a first heating element  82   a  disposed in the inlet pipe  124  upstream of the particulate filter  80 , and a second heating element  82   b  disposed in the casing  120  inside the DPF  80 . The heating elements  82   a  or  82   b  can be of any appropriate type, such as electrical resistance heaters. During the regeneration of the DPF  80 , the heating element heats up the exhaust gas flowing into the muffler casing  20 . The temperature of the particulate filter  80  has to be increased for burning off the particulates trapped inside. The first valve  54  is closed to insure that the heat from the exhaust gas flow and the heating elements  82   a  or  82   b  is contained in the DPF  80 . The regeneration can be done at idle speed of the engine  2  (or during engine or exhaust braking mode). 
     The first and second valve assemblies  52 ,  62  and the heating element  82   a ,  82   b  of the muffler assembly  110  are operatively controlled by the ECU  16  in closed loop based on one or more operating parameters of the muffler assembly  110 , including inlet and outlet exhaust gas pressure, acoustic frequencies generated by the muffler assembly  10 , acceleration, and exhaust gas temperature. In other words, the ECU  16  controls the first and second valve assemblies  52 ,  62  and the heating element  82   a ,  82   b  of the muffler assembly  110  based on readings from one or more sensors installed to the muffler assembly. It will be appreciated that closed loop systems are known in the art as systems that use feed-back from sensors internal to these systems. Alternatively, the first and second valve assemblies  52 ,  62  and the heating element  82   a ,  82   b  of the muffler assembly  110  are operatively controlled by the ECU  16  in open loop based on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  110 . 
     Accordingly, as illustrated in  FIGS. 7 and 8 , the muffler assembly  110  comprises inlet and outlet exhaust gas pressure sensors  17  and  18 , a temperature sensor  84 , an accelerometer (or vibration sensor)  85  detecting vibration of the muffler assembly  110 , and an acoustic sensor  86  detecting acoustic frequencies of sound waves generated by the muffler assembly  110 . As further illustrated in  FIGS. 7 and 8 , the exhaust gas inlet pressure sensor  17  is mounted to the inlet pipe  124  of the casing  120  adjacent to inlet port  125  to monitor an inlet pressure of the exhaust gas entering the muffler assembly  110 , while the exhaust gas outlet pressure sensor  18  is mounted to the exit pipe  126  of the casing  120  adjacent the exit port  127  to monitor an outlet pressure of the exhaust gas exiting the muffler assembly  110 . Alternatively, the exhaust gas pressure sensors  17  and  18  can be mounted to the muffler casing  120  adjacent to the corresponding inlet and outlet ports  125  and  127 , respectively, thereof. The temperature sensor  84  is mounted to the front wall  130  of the casing  120  adjacent to an inlet port  125  to monitor a temperature of the exhaust gas entering the muffler assembly  110 . Alternatively, the temperature sensor  84  can be mounted to the inlet pipe  124  of the casing  120 . The accelerometer  85  and the acoustic sensor  86  are mounted to the rear wall  132  of the casing  120  adjacent to an exit port  127  thereof. Alternatively, the accelerometer  85  and the acoustic sensor  86  could be mounted to the outer wall  28  of the casing  120  or to the exit pipe  126  of the casing  120 . 
     Based on readings of the sensors  17 ,  18 ,  84 ,  85  and  86 , the first and second valves  54  and  64  can also be controlled for various performance settings. Specifically, the ECU  16  reads the sensors  17 ,  18 ,  84 ,  85  and  86  from the inlet and the exit ports  125 ,  127  of the muffler assembly  110  and adjusts the position of the valves  54  and  64  (fully closed position, fully open position or any intermediate position between the fully open and closed positions) accordingly based on the feedback control. More specifically, the pressure readings from the inlet and outlet pressure sensors  17  and  18  allow a pressure differential across the muffler casing  120  to be determined and can be used to identify the need for DPF  80  to be regenerated (cleaned-up) or can be used for troubleshooting the muffler assembly  110  including the functioning of the first valve assembly  52  and the second valve assembly  62 . Based on the pressure differential between inlet and exit ports  125  and  127 , the regeneration mode of the DPF  80  can be enabled. Furthermore, the temperature reading from the temperature sensor  84  in the inlet side will modify the position of the first valve  54  and this feature can be used to control the temperature of the DPF filter  80 . The vibration sensor  85  or the acoustic sensor  86  can be used to partially open or close the second valve  64  to achieve a certain noise value for the muffler (noise control). 
       FIGS. 9-11  illustrate a third exemplary embodiment of a muffler assembly, generally depicted by the reference character  210 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 200 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  210  of  FIGS. 9-11  and the muffler assembly  10  of  FIGS. 1-6  is that in this case the muffler assembly  210  includes only one valve assembly  62  mounted within the casing  20 . According to the third exemplary embodiment of the present invention, the valve assembly  62  functions as a diverter valve. The valve assembly  62  includes a diverter valve  64  selectively movable between a closed position and an open position for preventing the exhaust gas flow through an outlet end  234   b  of a first pipe  234  when the diverter valve  64  is in the closed position. Specifically, when the diverter valve  64  is in the open position, as illustrated in  FIG. 11 , the exhaust gas can flow out the first pipe  234 , while when the diverter valve  64  is in the closed position, as illustrated in  FIG. 10 , the exhaust gas is prevented from flowing through the outlet end  234   b  of the first pipe  234 . In the preferred embodiment, the diverter valve  64  is an exhaust restrictor in the form of butterfly valve mounted within the first pipe  234  for rotation about a shaft  65 . The diverter valve  64  is disposed adjacent to the outlet end  234   b  of the first pipe  234 . 
     The valve assembly  62  includes an actuator  66  provided for selectively moving the diverter valve  64  between the closed and open positions. The actuator  66  may be in the form any appropriate device adapted for rotating the diverter valve  64  about the shaft  65 . The actuator  66  is actuated by the ECU  16 . In other words, the ECU  16  operatively controls the valve assembly  62  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  10 , including the inlet and outlet exhaust gas pressure. 
     The muffler assembly  210  according to the third exemplary embodiment of the present invention is operable in a number of different modes including a high-performance mode and a reverse-flow mode, determined by the positions of the valve assembly  262 . 
     In the high-performance mode illustrated in  FIG. 11 , the second valve  64  is open. The exhaust gas flow freely passes directly through the first pipe  234 , as denoted by directional arrows F. The direct non-restricted exhaust gas flow through the muffler assembly  210  increases the exhaust flow of the engine  2 , reduces backpressure of the exhaust gas and increases efficiency of the turbocharger  4 . Lower restriction in the exhaust system  201  provides better fluid exchange in the combustion chamber, therefore the power output of the engine  2  increases. Specifically, the power output of the engine  2  increases by about 4-5% when the muffler assembly  10  operates in the high-performance muffler mode. Therefore, in the high-performance mode, the muffler assembly  210  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger and the engine  2  to breathe and function more efficiently. 
     In the reverse-flow mode illustrated in  FIG. 10 , the diverter valve  64  is closed. The exhaust gas flows through the first pipe  234  until it reaches the closed diverter valve  64 . The exhaust gas reverses its flow through reverse-flow chamber  46  and the third pipe  50  into an inlet chamber  44 , and then goes through the second pipe  48  to the resonant chamber  42 . From the resonant chamber  42  the exhaust gas flows out of the casing  20  of the muffler assembly  210 . In the reverse-flow mode, the exhaust gas flows through longer path inside the casing  20 , thus resulting in better muffling the exhaust gas noise by the muffler assembly  210 . 
       FIGS. 12-15  illustrate a fourth exemplary embodiment of a muffler assembly, generally depicted by the reference character  310 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 300 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  310  of  FIGS. 12-15  with respect to the muffler assembly  10  of  FIGS. 1-6  is that in this case the muffler assembly  310  includes a single pipe  334  mounted within the casing  320  and centrally extending between front and rear walls  330  and  332  of a muffler casing  320  substantially coaxially to a central axis  321 . More specifically, the pipe  334  has an open inlet end  334   a  attached to an inlet port  325  and an open outlet end  334   b  attached to an exit port  327  of the casing  320 . In other words, the inlet and outlet distal ends  334   a ,  334   b  of the pipe  334  are attached to the inlet and exit pipes  324  and  326 , respectively. 
     Two perforated baffle plates  336  and  338  along with the front and rear walls  330  and  332  divide an internal cavity  322  of the casing  320  into three chambers  342 ,  344  and  346 . As shown in  FIGS. 13-15 , the first baffle plate  336  is disposed adjacent to the outlet end  334   b  of the pipe  334  so as to define a first (resonant) chamber  342  within the casing  320  about the pipe  334  between the first baffle plate  336  and the rear wall  332  of the casing  320 . The first baffle plate  336  has a central opening so as to receive the pipe  334  therethrough. The second baffle plate  338  is disposed adjacent to the inlet end  334   a  of the pipe  334  and is axially spaced from the front wall  330  so as to define a second (inlet) chamber  344  within the casing  320  and about the pipe  334  between the second baffle plate  338  and the front wall  330  of the casing  320 . As shown, the inlet chamber  344  is not in direct fluid communication with the inlet port  325 . The second baffle plate  338  has a central opening so as to receive the pipe  334  therethrough. The third (central) chamber  346  is defined within the casing  320  about the pipe  334  between the first and second baffle plates  336  and  338 . Thus, the pipe  334  passes through the first and second baffle plates  336  and  338 , and is connected to the inlet and exit ports  325  and  327  at the opposite ends  334   a  and  334   b  thereof. 
     The pipe  334  also comprises a first perforated section  334   c  positioned between the first and second baffle plates  336  and  338 , and a second perforated section  334   d  positioned between the first baffle plate  336  and the rear wall  332  of the muffler casing  320 . Thus, the pipe  334  is in fluid communication with the resonant chamber  342  and the central chamber  346 . In other words, the outlet end  334   b  of the pipe  334  is open to the resonant chamber  342 . In turn, the resonant chamber  342  is in fluid communication with the exit port  327  of the casing  320 . As a result, the exhaust gasses entering the pipe  334  of the muffler casing  320  through the inlet pipe  324  can expand into the central chamber  346  between the baffle plates  336  and  338 , and into the resonant chamber  342  between the first baffle plate  336  and the rear wall  332  of the muffler casing  320 . The pipe  334  is also provided with a relief opening  337  disposed between the inlet end  334   a  thereof and the second baffle plate  338  so as to provide fluid communication between the pipe  334  and the inlet chamber  344 . 
     The muffler assembly  310  further comprises a first valve assembly  52  and a second valve assembly  62  both mounted within the casing  320 . Preferably, the first and second valve assemblies  52  and  62  are substantially similar. 
     The first valve assembly  52  functions as an exhaust brake device and includes a first valve  54  selectively movable between a closed position and an open position for regulating an exhaust gas flow through the pipe  334 . Preferably, the first valve  54  is an exhaust restrictor in the form of butterfly valve mounted within the pipe  334  for rotation about a shaft  55 . In its open position shown in  FIGS. 13 and 15 , the first butterfly valve  54  is oriented substantially parallel to a central axis  321 , thereby producing only minimal resistance to the exhaust gas flow through the pipe  334 . However, in its closed position shown in  FIG. 14 , the first butterfly valve  54  is oriented substantially perpendicular to the central axis  321 , thereby producing a maximum obstruction to the flow of the exhaust gas. At the same time, an orifice is provided between the first valve  54  and the pipe  334  to allow some exhaust gas flow through the pipe  334  when the first valve  54  is in the closed position. More specifically, the first valve  54  is dimensioned so as to provide a gap (orifice) between an inner peripheral surface of the pipe  334  and a circumferential edge of the first valve  54  when the first valve  54  is in its closed position (similarly to the orifice  39  of the embodiment illustrated in  FIG. 6 ). Preferably, the orifice is substantially annular in shape. Further preferably, the first valve  54  is disposed adjacent to the inlet end  334   a  of the pipe  334  but is axially spaced from the inlet port  325  of the casing  320 . The first valve assembly  52  further includes a first actuator  56  provided for selectively moving the first valve  54  between the closed and open positions. In a manner well know to those skilled in the art, a movable distal of the actuator  56  can be actuated by the ECU  16 . The first valve  54  is positioned upstream of the first perforated section  434   c.    
     The second valve assembly  62  functions as a diverter device and includes a second valve  64  selectively movable between a closed position and an open position for regulating an exhaust gas flow through the pipe  334 . Preferably, the second valve  64  is a restrictor in the form of butterfly valve mounted within the pipe  334  for rotation about a shaft  65 . In its open position shown in  FIG. 15 , the second butterfly valve  64  is oriented substantially parallel to a central axis  321 , thereby producing only minimal resistance to the exhaust gas flow through the pipe  334 . However, in its closed position shown in  FIGS. 13 and 14 , the second butterfly valve  64  is oriented substantially perpendicular to the central axis  321 , thereby producing a maximum obstruction to the flow of the exhaust gas and therefore maximum exhaust gas backpressure. Further preferably, the second valve  64  is disposed adjacent to the outlet end  334   b  of the pipe  334  but is axially spaced from the outlet port  327  of the casing  320 . Also, the second valve  64  is disposed between the first and second perforated sections  334   c  and  334   d . The second valve assembly  62  further includes a second actuator  66  provided for selectively moving the second valve  64  between the closed and open positions. The actuator  66  is actuated by the ECU  16 . In other words, the ECU  16  operatively controls the first and second valve assemblies  52  and  62  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  310 , including inlet and outlet exhaust gas pressure monitored by pressure sensors  17  and  18 , respectively, shown in  FIG. 12 . 
     The muffler assembly  310  further comprises an automatically, mechanically actuated pressure relief (or pressure regulator) valve  70  disposed inside the casing  320  upstream of the first valve  54 . The pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  334   a  of the pipe  334  to the exit port  327  by bypassing the first valve  54 . More specifically, the pressure relief valve  70  fluidly connecting the inlet end  334   a  of the pipe  334  to the inlet chamber  344  when the pressure in the pipe  334  reaches a predetermined high value. 
     The muffler assembly  310  according to the fourth exemplary embodiment of the present invention is operable in a number of different modes including a high-performance mode, a bypass mode, and an exhaust braking mode, determined by the positions of the first and second valve assemblies  52  and  62  of the muffler assembly  310 . As described hereinabove, the first and second valve assemblies  52  and  62  of the muffler assembly  10  are selectively and independently controlled by the ECU  16  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  310 , including the inlet and outlet exhaust gas pressure monitored by the pressure sensors  17  and  18 . 
     In the exhaust braking mode illustrated in  FIG. 14 , both the first and second valves  54  and  64  are closed and the exhaust flow through the pipe  334  is restricted. As a result, the exhaust gas back pressure is increased providing an exhaust brake function to the ICE  2 , thus providing the exhaust brake function to the motor vehicle. When the pressure of exhaust gas in the pipe  334  acting on the pressure relief valve  70  becomes higher than a predetermined value the pressure relief valve  70  moves into its open position. Consequently, the exhaust gas flow F is forced to flow through the pressure relief valve  70  into the inlet chamber  344 , then through the second perforated baffle plate  338  into the central chamber  346 , thus bypassing the first valve  54 . From the central chamber  346  the exhaust gas flows into the resonant chamber  342  through the first perforated baffle plate  336 . Then, the exhaust gas flows into the pipe  334  through the second perforated section  334   d  and exits the muffler assembly  310  through the exit port  327 . Therefore, the pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  334   a  of the pipe  334  to the exit port  325  by bypassing the first valve  54  in the exhaust braking mode. 
     In the bypass mode illustrated in  FIG. 13 , the first valve  54  is open, while the second valve  64  is closed. The exhaust gas passes the open first valve  54  and flows through the pipe  334  until reaches the closed second valve  64 . The exhaust gas bypasses the second valve  64  and flows first into the central chamber  346  through the first perforated section  334   c , and then through the first perforated baffle plate  336  into the resonant chamber  342 . From the resonant chamber  342  the exhaust gas flows out of the muffler casing  320  through the second perforated section  334   d  and the exit port  327 . 
     In the high-performance mode illustrated in  FIG. 15 , both the first and second valves  54  and  64  are open. The exhaust gas flow freely passes directly through the pipe  334 , as denoted by directional arrows F. The direct non-restricted exhaust gas flow through the muffler assembly  310  increases the exhaust flow of the engine  2 , reduces backpressure of the exhaust gas and increases efficiency of the turbocharger  4 . Lower restriction in the exhaust system  301  provides better fluid exchange in the combustion chamber, therefore the power output of the engine  2  increases. Specifically, the power output of the engine  2  increases by about 4-5% when the muffler assembly  310  operates in the high-performance muffler mode. Therefore, in the high-performance mode, the muffler assembly  310  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger and the engine  2  to breathe and function more efficiently. 
       FIGS. 16-18  illustrate a fifth exemplary embodiment of a muffler assembly, generally depicted by the reference character  410 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 400 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  410  of  FIGS. 16-18  with respect to the muffler assembly  310  of  FIGS. 12-15  is that the muffler assembly  410  includes only one valve assembly  62  mounted within the casing  420 , only one perforated baffle plate  436 , and lacks a pressure relief valve  70  mounted to a central pipe  434 . According to the fifth exemplary embodiment of the present invention, the valve assembly  62  functions as a diverter valve. The valve assembly  62  includes a diverter valve  64  selectively movable between a closed position and an open position for preventing the exhaust gas flow through an outlet end  434   b  of the central pipe  434  when the diverter valve  64  is in the closed position. Specifically, when the diverter valve  64  is in the open position, as illustrated in  FIG. 18 , the exhaust gas can flow out the pipe  434 , while when the diverter valve  64  is in the closed position, as illustrated in  FIG. 17 , the exhaust gas is prevented from flowing through the outlet end  434   b  of the pipe  434 . In the preferred embodiment, the diverter valve  64  is in the form of butterfly valve mounted within the pipe  434  for rotation about a shaft  65 . The diverter valve  64  is disposed adjacent to the outlet end  434   b  of the pipe  434 . 
     The perforated baffle plate  436  divides an internal cavity  422  of the casing  420  into two chambers  442  and  444 . A first (resonant) chamber  442  is defined within the casing  420  about the pipe  434  between the baffle plate  436  and a rear wall  432  of the casing  420 . The baffle plate  436  has a central opening so as to receive the pipe  434  therethrough. A second (inlet) chamber  444  is defined within the casing  420  and about the pipe  434  between the baffle plate  436  and a front wall  430  of the casing  420 . The inlet chamber  444  is in fluid communication with the resonant chamber  442  through the perforated baffle plate  436 . 
     The pipe  434  also comprises a first perforated section  434   c  positioned between the front wall  430  of the muffler casing  420  and the baffle plate  436 , and a second perforated section  434   d  positioned between the baffle plate  436  and the rear wall  432  of the muffler casing  420 . In other words, the first perforated section  434   c  is positioned upstream of the diverter valve  64 , while the second perforated section  434   d  is positioned downstream of the diverter valve  64 . Thus, the pipe  434  is in fluid communication with the resonant chamber  442  and the inlet chamber  444 . In other words, the outlet end  434   b  of the pipe  434  is open to the resonant chamber  442 . In turn, the resonant chamber  442  is in fluid communication with the exit port  427  of the casing  420 . As a result, the exhaust gasses entering the pipe  434  of the muffler casing  420  through the inlet pipe  424  can expand into the inlet chamber  444  and into the resonant chamber  442  of the muffler casing  420 . 
     The muffler assembly  410  according to the fifth exemplary embodiment of the present invention is operable in a number of different modes including a high-performance mode and a bypass mode, determined by the positions of the valve  64 . As described hereinabove, the valve assembly  62  is selectively and independently controlled by the ECU  16  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  410 , including the inlet and outlet exhaust gas pressure monitored by the pressure sensors  17  and  18  (shown in  FIG. 16 ). 
     In the bypass mode illustrated in  FIG. 17 , the valve  64  is closed. The exhaust gas flows through the pipe  434  until reaches the closed valve  64 . The exhaust gas bypasses the diverter valve  64  and flows first into the inlet chamber  444  through the first perforated section  434   c , then through the perforated baffle plate  436  into the resonant chamber  442 . From the resonant chamber  442  the exhaust gas flows out of the muffler casing  420  through the second perforated section  434   d  and the exit port  427 . 
     In the high-performance mode illustrated in  FIG. 18 , the valve  64  is open. The exhaust gas flow freely passes directly through the pipe  434 , as denoted by directional arrows F. The direct non-restricted exhaust gas flow through the muffler assembly  410  increases the exhaust flow of the engine  2 , reduces backpressure of the exhaust gas and increases efficiency of the turbocharger  4 . Lower restriction in the exhaust system  401  provides better fluid exchange in the combustion chamber, therefore the power output of the engine  2  increases. Therefore, in the high-performance mode, the muffler assembly  410  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger  4  and the engine  2  to breathe and function more efficiently. 
       FIGS. 19-21  illustrate a sixth exemplary embodiment of a muffler assembly, generally depicted by the reference character  510 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 500 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  510  of  FIGS. 19-21  with respect to the muffler assembly  10  of  FIGS. 1-6  is that in this case the muffler assembly  510  includes a single pipe  534  mounted within the casing  520  and only one valve assembly  52  mounted within the pipe  534 . The pipe  534  extends between front and rear walls  530  and  532  of the muffler casing  520  substantially coaxially to a central axis  521 . More specifically, the pipe  534  has an open inlet end  534   a  attached to an inlet port  525  and an open outlet end  534   b  attached to an exit port  527  of the casing  520 . In other words, the inlet and outlet distal ends  534   a ,  534   b  of the pipe  534  are attached to the inlet and exit pipes  524  and  526 , respectively. 
     A perforated baffle plate  536  divides an internal cavity  522  of the casing  520  into two chambers  542  and  544 . The first (resonant) chamber  542  is defined within the casing  520  about the pipe  534  between the baffle plate  536  and a rear wall  532  of the casing  520 . The baffle plate  536  has a central opening so as to receive the pipe  534  therethrough. The second (inlet) chamber  544  is defined within the casing  520  and about the pipe  534  between the baffle plate  536  and a front wall  530  of the casing  520 . The inlet chamber  544  is in fluid communication with the resonant chamber  542  through the perforated baffle plate  536 . The inlet chamber  544  is not in direct fluid communication with the inlet port  525 . The pipe  534  also comprises a perforated section (or at least one aperture)  534   c  positioned between the baffle plate  536  and the rear wall  532  of the muffler casing  520 . Thus, the resonant chamber  542  is in fluid communication with the exit port  527 . 
     According to the sixth exemplary embodiment of the present invention, the valve assembly  52  functions as an exhaust brake device. Preferably, the valve assembly  52  includes an exhaust valve  54  selectively movable between a closed position and an open position for preventing the exhaust gas flow through an outlet end  534   b  of the pipe  534  when the exhaust valve  54  is in the closed position. Specifically, when the exhaust valve  54  is in the open position, as illustrated in  FIG. 20 , the exhaust gas can flow out the pipe  534 , while when the exhaust valve  54  is in the closed position, as illustrated in  FIG. 21 , the exhaust gas is prevented from flowing through the outlet end  534   b  of the pipe  534 . At the same time, similarly to the first exemplary embodiment of the present invention, an orifice is provided between the exhaust valve  54  and the pipe  534  to allow some exhaust gas flow through the pipe  534  when the exhaust valve  54  is in the closed position. In the preferred embodiment, the exhaust valve  54  is an exhaust restrictor in the form of butterfly valve mounted within the pipe  534  for rotation about a shaft  55 . The first valve  54  is dimensioned so as to provide a gap (orifice) between an inner peripheral surface of the pipe  534  and a circumferential edge of the first valve  54  when the first valve  54  is in its closed position (similarly to the orifice  39  of the embodiment illustrated in  FIG. 6 ). Preferably, the orifice is substantially annular in shape. 
     The muffler assembly  510  further comprises an automatically, mechanically actuated pressure relief (or pressure regulator) valve  70  disposed inside the casing  520  upstream of the exhaust valve  54 . The pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  334   a  of the pipe  534  to the exit port  427  by bypassing the exhaust valve  54 . More specifically, the pressure relief valve  70  fluidly connecting the inlet end  534   a  of the pipe  534  to the inlet chamber  544  when the pressure in the pipe  534  reaches a predetermined high value. 
     The muffler assembly  510  according to the sixth exemplary embodiment of the present invention is operable in a number of different modes including a high-performance mode, and an exhaust braking mode, determined by the positions of the valve assembly  52  of the muffler assembly  510 . As described hereinabove and illustrated in  FIG. 19 , the valve assembly  52  is selectively and independently controlled by the ECU  16  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  510 , including the inlet and outlet exhaust gas pressure monitored by the pressure sensors  17  and  18 . 
     In the high-performance mode illustrated in  FIG. 20 , the exhaust valve  54  is open. The exhaust gas flow freely passes directly through the pipe  534 , as denoted by directional arrows F. The direct non-restricted exhaust gas flow through the muffler assembly  510  increases the exhaust flow of the engine  2 , reduces backpressure of the exhaust gas and increases efficiency of the turbocharger  4 . Lower restriction in the exhaust system  501  provides better fluid exchange in the combustion chamber, therefore the power output of the engine  2  increases. Specifically, the power output of the engine  2  increases by about 4-5% when the muffler assembly  510  operates in the high-performance muffler mode. Therefore, in the high-performance mode, the muffler assembly  510  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger and the engine  2  to breathe and function more efficiently. 
     In the exhaust braking mode illustrated in  FIG. 21 , the exhaust valve  54  is closed and the exhaust flow through the pipe  534  is restricted. As a result, the exhaust gas back pressure is increased providing an exhaust brake function to the ICE  2 , thus providing the exhaust brake function to the motor vehicle. When the pressure of exhaust gas in the pipe  534  acting on the pressure relief valve  70  becomes higher than a predetermined value the pressure relief valve  70  moves into its open position. Consequently, the exhaust gas flow F is forced to flow through the pressure relief valve  70  into the inlet chamber  544 , then through the perforated baffle plate  536  into the resonant chamber  542 , thus bypassing the exhaust valve  54 . Then, the exhaust gas flows into the pipe  534  through the perforated section  534   c  and exits the muffler assembly  510  through the exit port  527 . Therefore, the pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  534   a  of the pipe  534  to the exit port  525  by bypassing the exhaust valve  54  in the exhaust braking mode. 
       FIGS. 22-24  illustrate a seventh exemplary embodiment of a muffler assembly, generally depicted by the reference character  610 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 600 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  610  of  FIGS. 22-24  with respect to the muffler assembly  10  of  FIGS. 1-6  is that in this case the muffler assembly  610  includes only one valve assembly  52  mounted within the casing  620 , and that a first pipe  634  centrally located within the casing  620  and extending substantially coaxially to a central axis  621  of the casing  620  between inlet and exit ports  625  and  627  thereof, has an open inlet end  634   a  attached to the inlet port  625  but a closed outlet end  634   b  engaging a first baffle plate  636 . In other words, the outlet end  634   b  of the first pipe  634  is closed to a resonant chamber  642 . 
     The first pipe  634  passes through the second and third baffle plates  38  and  40 , and engages the first baffle plate  636  at the outlet end  634   b  thereof. The first pipe  634  is also provided with a bypass opening  635  adjacent to the outlet end  634   b  thereof so as to provide fluid communication between the first pipe  634  and a reverse-flow chamber  646 . 
     According to the sixth exemplary embodiment of the present invention, the valve assembly  52  functions as an exhaust brake device. Preferably, the valve assembly  52  includes an exhaust valve  54  selectively movable between a closed position and an open position for preventing the exhaust gas from flowing through the first pipe  634  when the exhaust valve  54  is in the closed position. Specifically, when the exhaust valve  54  is in the open position, as illustrated in  FIG. 23 , the exhaust gas can flow out the first pipe  634 , while when the exhaust valve  54  is in the closed position, as illustrated in  FIG. 214  the exhaust gas is prevented from flowing through the first pipe  634 . At the same time, similarly to the first exemplary embodiment of the present invention, an orifice is provided between the exhaust valve  54  and the first pipe  634  to allow some exhaust gas flow through the first pipe  634  when the exhaust valve  54  is in the closed position. In the preferred embodiment, the exhaust valve  54  is an exhaust restrictor is a butterfly valve mounted within the first pipe  634  for rotation about a shaft  55 . The first valve  54  is dimensioned so as to provide a gap (orifice) between an inner peripheral surface of the first pipe  634  and a circumferential edge of the first valve  54  when the first valve  54  is in its closed position (similarly to the orifice  39  of the embodiment illustrated in  FIG. 6 ). Preferably, the orifice is substantially annular in shape. 
     The muffler assembly  610  further comprises an automatically, mechanically actuated pressure relief (or pressure regulator) valve  70  disposed inside the casing  620  upstream of the exhaust valve  54 . The pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  634   a  of the first pipe  634  to the inlet and resonant chambers  44  and  642 , respectively, by bypassing the exhaust valve  54 . More specifically, the pressure relief valve  70  fluidly connecting the inlet end  634   a  of the pipe  634  to the inlet chamber  44  when the pressure in the first pipe  634  reaches a predetermined high value. As illustrated in  FIGS. 23 and 24 , the pressure relief valve  70  is mounted to the first pipe  634  adjacent to the inlet end  634   a  thereof upstream of the exhaust valve  54 . 
     The muffler assembly  610  according to the sixth exemplary embodiment of the present invention is operable in a number of different modes including a reverse-flow mode, and an exhaust braking mode, determined by the positions of the valve assembly  52  of the muffler assembly  610 . As described hereinabove and illustrated in  FIG. 22 , the valve assembly  52  is selectively and independently controlled by the ECU  16  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  610 , including the inlet and outlet exhaust gas pressure monitored by the pressure sensors  17  and  18 . 
     In the reverse-flow mode illustrated in  FIG. 23 , the exhaust brake valve  54  is open. The exhaust gas flows through the first pipe  634  until reaches the closed outlet end  634   b  thereof. The exhaust gas reverses its flow through the third pipe  50  into the inlet chamber  44 , and then goes through the second pipe  48  to the resonant chamber  642 . From the resonant chamber  642  the exhaust gas flows out of the casing  620  of the muffler assembly  610 . In the reverse-flow mode, the exhaust gas flows through longer path inside the casing  20 , thus resulting in better muffling the exhaust gas noise by the muffler assembly  610 . 
     In the exhaust braking mode illustrated in  FIG. 24 , the exhaust brake valve  54  is closed and the exhaust flow through the first pipe  634  is restricted. As a result, the exhaust gas back pressure is increased providing an exhaust brake function to the ICE  2 , thus providing the exhaust brake function to the motor vehicle. When the pressure of exhaust gas in the first pipe  634  acting on the pressure relief valve  70  becomes higher than the predetermined value the pressure relief valve  70  moves into its open position. Consequently, the exhaust gas flow F is forced to flow through the pressure relief valve  70  into the inlet chamber  44 , then through the third pipe  48  into the resonant chamber  642 , thus bypassing the exhaust brake valve  54 . From the resonant chamber  642  the exhaust gas exits the muffler assembly  610  through the exit port  627 . Therefore, the pressure relief valve  70  is provided for selectively fluidly connecting the inlet end  634   a  of the first pipe  634  to the exit port  627  by bypassing the exhaust brake valve  54  in the exhaust braking mode. 
       FIGS. 25-27  illustrate an eighth exemplary embodiment of a muffler assembly, generally depicted by the reference character  710 . Components, which are unchanged from the first exemplary embodiment of the present invention, are labeled with the same reference characters. Components, which function in the same way as in the first exemplary embodiment of the present invention depicted in  FIGS. 1-6  are designated by the same reference numerals to some of which 700 has been added, sometimes without being described in detail since similarities between the corresponding parts in the two embodiments will be readily perceived by the reader. 
     A difference between the muffler assembly  710  of  FIGS. 25-27  and the muffler assembly  10  of  FIGS. 1-6  is that the muffler assembly  710  includes only one valve assembly  52  mounted within a casing  720 , and that a first pipe  734  is centrally located within a second pipe  735  which, in turn, is centrally located within the casing  720  and extending substantially coaxially to a central axis  721  of the casing  720  between inlet and exit ports  725  and  727  thereof. 
     The first pipe  734  has an open inlet end  734   a  axially spaced from the front wall  730  of the casing  720  and an open outlet end  734   b  axially spaced from the rear wall  730  thereof. The second pipe  735  has an open inlet end  735   a  attached to the inlet port  725  and an open outlet end  735   b  attached to the exit port  727 . Moreover, the second pipe  735  has a front section  737  adjacent to the front wall  730  of the casing  720  and upstream of a first valve  54 , a rear section  741  adjacent to the rear wall  732  of the casing  720  and a central section  739  extending between the front and rear sections  737  and  741  of the second pipe  735 . The front section  737  of the second pipe  735  has one or more apertures  737   a  so as to provide fluid communication between the second pipe  735  and an internal cavity  722  within the casing  720 . Preferably, the front section  737  of the second pipe  735  is perforated, as shown in  FIGS. 26 and 27 . The rear section  741  of the second pipe  735  has one or more apertures (or window)  743  so as to provide fluid communication between the second pipe  735  and the internal cavity  722  within the casing  720 . The central section  739  of the second pipe  735  is impervious for exhaust gas flow. 
     The muffler assembly  710  further comprises a baffle plate  736  dividing the internal cavity  722  within the muffler casing  720  so as to define a resonant chamber  742  between the baffle plate  736  and the rear wall  732  of the casing  720  and an inlet chamber  744  between the baffle plate  736  and the front wall  730  of the casing  720 . The baffle plate  736  has one or more apertures  736   a  and  736   b  so as to provide fluid communication between the inlet chamber  744  and the resonant chamber  742 . 
     The muffler assembly  710  further comprises one or more baffle members  740  in the resonant chamber  742  between the outer wall  728  of the casing  720  and the second pipe  735 . The baffle members  740  define a tortuous path of the exhaust gas flow through the resonant chamber  742 . Preferably, the muffler assembly comprises a plurality of the baffle members  738  each of the baffle members  738  is in the form of a semi-annular (half-moon) plate disposed opposite to each other in an alternating manner, as illustrated in  FIG. 25 . 
     The muffler assembly  710  according to the eighth exemplary embodiment of the present invention is operable in a number of different modes including a high-performance mode and a bypass mode, determined by the positions of the valve  64 . As described hereinabove, the valve assembly  62  is selectively and independently controlled by the ECU  16  depending on one or more operating parameters of the internal combustion engine  2  and/or the muffler assembly  710 , including the inlet and outlet exhaust gas pressure monitored by the pressure sensors  17  and  18 . 
     In the bypass mode illustrated in  FIG. 27 , the valve  64  is closed. The exhaust gas flows through the second pipe  735  into the first pipe  734  until reaches the closed valve  64 . The exhaust gas bypasses the diverter valve  64  and flows first into the inlet chamber  744  through the front perforated section  737 , then through the apertures  736   a  and  736   b  in the baffle plate  736  into the resonant chamber  742 . The exhaust gas flows through the resonant chamber  742  in the tortuous path by deflecting from the semi-annular baffle members  740 , as illustrated in  FIG. 27 . From the resonant chamber  742  the exhaust gas flows out of the muffler casing  720  through the windows  743  in the rear section  741  and the exit port  727 . 
     In the high-performance mode illustrated in  FIG. 26 , the valve  64  is open. The exhaust gas flow freely passes directly through the first and second pipes  734  and  735 , as denoted by directional arrows F. In the high-performance mode, the muffler assembly  710  allows for a higher flow of the exhaust gas and lower exhaust gas backpressure that, in turn, allows the turbocharger and the engine to breathe and function more efficiently. 
     Therefore, the muffler assembly in accordance with the present invention allows for multiple modes of operation in order to improve and optimize operational characteristics of the internal combustion engine. 
     The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.