Patent Publication Number: US-2009229911-A1

Title: Variable geometry muffler for an exhaust system of an internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to a variable geometry muffler for an exhaust system of an internal combustion engine. 
     BACKGROUND ART 
     An internal combustion engine is provided with an exhaust system, which has the function of introducing into the atmosphere the gases produced by the combustion limiting both the noise and the content of polluting substances. A modern exhaust system comprises at least one muffler comprising a tubular body, which typically displays an elliptical section and is provided with an inlet opening and an outlet opening. A labyrinth which determines a path for the exhaust gases from the inlet opening to the outlet opening is defined within the tubular body; such labyrinth is normally formed by diaphragms (or baffles) arranged transversally (i.e. perpendicularly to the longitudinal axis of the tubular body) to define chambers within the tubular body and by tubes which connect the chambers to each other. 
     In a traditional muffler, the counterpressure generated by the muffler (i.e. the loss of pressure determined in the exhaust gases by the passage through the muffler) grows exponentially according as the engine speed increases (i.e. as the average speed of the exhaust gases increases). Consequently, in order to avoid excessively high counterpressure values at high engine speeds, it is necessary to penalise noise attenuation at low engine speeds. However, it would be preferable if the counterpressure generated by the muffler were more constant at varying engine speeds so as obtain both a good noise attenuation at low engine speeds and a limited counterpressure at high engine speeds. 
     In order to have a more constant counterpressure generated by the muffler at the variation of the engine speed, it has been suggested the use of at least one bypass valve, which is controlled by pressure (i.e. is passive being without a motor member) and has the function of modifying the geometry of the muffler labyrinth according to the exhaust gas pressure (i.e. according to the engine speed). An example of a bypass valve is provided in patent application WO2005059327A1. 
     A known bypass valve displays a lid, which is coupled to a bypass opening obtained through a diaphragm of the muffler and is mobile from a closed position of the bypass opening to an opening position of the bypass opening by effect of the exhaust gas pressure and against the bias of a spring which tends to maintain the lid in the closed position. The most common solution provides that the lid is hinged onto the diaphragm of the muffler and is coupled to a torsional spring. 
     It has been observed that the known bypass valves display a limited reliability in time, because the sliding couplings of the known bypass valves (i.e. the hinging points of the lid and the turns of the spring) tend to get jammed or however to work in a different manner from that provided in the design step by effect of the incrustations formed by the exhaust gases. 
     DISCLOSURE OF INVENTION 
     It is the object of the present invention to provide a variable geometry muffler for an exhaust system of an internal combustion engine, which muffler is free from the above-described drawbacks, and specifically is easy and cost-effective to manufacture. 
     According to the present invention, a variable geometry muffler for an exhaust system of an internal combustion engine is provided as claimed in the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limitative examples of embodiment thereof, in which: 
         FIG. 1  is a schematic and perspective view of a muffler made according to the present invention; 
         FIG. 2  is a schematic view of an internal labyrinth of the muffler in  FIG. 1 ; 
         FIG. 3  is a side section view of a bypass valve of the muffler in  FIG. 1 ; 
         FIG. 4  is a schematic and perspective view of a different embodiment of the bypass valve in  FIG. 3 ; 
         FIG. 5  is a schematic and perspective view of a further embodiment of the bypass valve in  FIG. 3 ; 
         FIG. 6  is a side elevated view of the bypass valve in  FIG. 5 ; 
         FIG. 7  is a perspective exploded view of the bypass valve in  FIG. 5 ; 
         FIG. 8  is a schematic and perspective view of a further embodiment of the bypass valve in  FIG. 3 ; 
         FIG. 9  is a side section view of the bypass valve in  FIG. 8 ; 
         FIG. 10  is a plan view of an annular accommodation seat of a wire-mesh ring; 
         FIG. 11  is a section view taken along line XI-XI of a detail in  FIG. 10 ; and 
         FIG. 12  is a section view take along line XII-XII of a detail in  FIG. 10 . 
     
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     In  FIG. 1 , numeral  1  indicates as a whole a muffler  1  for an exhaust system of an internal combustion engine (not shown). Muffler  1  comprises a tubular body  2 , which displays an elliptical section and is provided with an inlet opening  3 , through which the exhaust gases produced by the internal combustion engine enter tubular body  2 , and an outlet opening  4 , through which the exhaust gases exit from tubular body  2 . 
     As shown in  FIG. 2 , a labyrinth  5  which determines a path for the exhaust gases from inlet opening  3  to outlet opening  4  is defined inside tubular body  2 . Labyrinth  5  consists of diaphragms  6  (or baffles) arranged transversally (i.e. perpendicularly to a longitudinal axis  7  of tubular body  2 ) to define chambers  8  within tubular body  2  and of tubes  9  which connect chambers  8  to each other. 
     A bypass valve  10 , which is adapted to modify the geometry of labyrinth  5  according to the pressure of the exhaust gases is arranged within tubular body  2 ; specifically, in the embodiment shown in  FIG. 2 , bypass valve  10  is coupled to a diaphragm  6  and according to the exhaust gas pressure is adapted to put two chambers  8  which are, normally, reciprocally isolated by diaphragm  6  itself into direct communication. 
     As shown in  FIG. 3 , bypass valve  10  comprises a lid  11 , which is coupled to a bypass opening  12  and is mobile from a closed position (shown by a solid line in  FIG. 3 ) of bypass opening  12  to an opening position (shown by a dotted line in  FIG. 3 ) of bypass opening  12  by effect of the exhaust gas pressure and against the bias of an elastic body which tends to maintain lid  11  in the closed position. 
     The elastic body consists of an elastic foil  13 , which is folded as a “U” and displays a mobile end  14  coupled to lid  11  and a fixed end  15  which is opposite to mobile end  14  and integral with a fixed part of muffler  1  (specifically with diaphragm  6  in which bypass valve  10  is mounted). 
     According to the embodiment shown in  FIGS. 2 ,  3 ,  4 ,  8  and  9 , mobile end  14  of elastic foil  13  supports lid  11 . According to the embodiment shown in  FIGS. 2 and 3 , lid  11  consists of an extension of mobile end  14  of elastic foil  13  and forms a monolithic body with elastic foil  13  itself; instead, according to the embodiments shown in  FIGS. 4 ,  8  and  9 , mobile end  14  of elastic foil  13  is connected to lid  11  by means of rivets, fitting and/or welding. According to a different embodiment (not shown), mobile end  14  of elastic foil  13  supports lid  11  by means of the interposition of a connecting element, which is fixed both to mobile end  14  and to lid  11 . 
     According to the embodiment shown in  FIGS. 2 and 3 , fixed end  15  of elastic foil  13  is arranged by the side of bypass opening  12  and is directly fixed (typically screwed, riveted or welded) to diaphragm  6  in which bypass valve  10  is mounted. 
     According to the embodiments shown in  FIGS. 4-9 , fixed end  15  of elastic foil  13  is arranged by the side of bypass opening  12  and is fixed to a support  16  (typically screwed, riveted or welded) to diaphragm  6  in which bypass valve  10  is mounted. According to the embodiment shown in  FIGS. 8 and 9 , support  16  displays a flat plate, which is arranged over bypass opening  12  and displays a through hole  17  obtained at bypass opening  12  itself. According to the embodiments shown in  FIGS. 4-7 , support  16  is shaped as an inverted “U”. 
     According to the embodiment shown in  FIGS. 5-7 , lid  11  is hinged to support  16 , which is fixed (typically screwed, riveted or welded) to diaphragm  6  in which bypass valve  10  is mounted; in this manner, lid  11  is rotationally mounted to turn about an axis of rotation between the closed position and the opening position. In this embodiment, mobile end  14  of elastic foil  13  rests on lid  11 , while fixed end  15  of elastic foil  13  is coupled to (i.e. received by) support  16 . Preferably, lid  11  is hinged to support  6  by means of a hinge pin  18 , which is integral with support  16  (i.e. lid  11  turns with respect to pin  18 ); furthermore, elastic foil  13  partially envelops pin  18 . 
     According to a preferred embodiment, bypass valve  10  comprises a wire-mesh ring  19 , which is arranged about bypass opening  12  to define an abutting element against which lid  11  rests in the closed position. According to the embodiment shown in  FIGS. 2 and 3 , bypass opening  12  is obtained through diaphragm  6 , which displays an annular accommodation seat  20  of wire-mesh ring  19 . According to the embodiment shown in  FIGS. 8 and 9 , support  16  displays annular accommodation seat  20  of wire-mesh ring  19 . 
     In the embodiment shown in  FIGS. 2 and 3 , wire-mesh ring  19  displays a rectangular section and accommodation seat  20  consists of a “U”-shaped fold of diaphragm  6  squashed to clamp a lower portion of wire-mesh ring  19 . In the embodiments shown in  FIGS. 8-12 , wire-mesh ring  19  displays a “L”-shaped section and accommodation seat  20  is formed so as to clamp a lower horizontal portion of wire-mesh ring  19 . 
       FIGS. 10-12  show a possible embodiment of annular accommodation seat  20  of wire-mesh ring  19 ; specifically, accommodation seat  20  shown in  FIGS. 10-12  consists of a plurality of portions  21  of diaphragm  6 , each of which is arranged to delimit bypass opening  12  and is deformed to catch a horizontal portion of wire-mesh ring  19 . Portions  21  of diaphragm  6  are alternatively deformed in opposite directions to catch opposite sides of the horizontal portion of wire-mesh ring  19 . 
     The above-described Muffler  1  displays a number of advantages, because it is simple and cost-effective to make and at the same time displays a high reliability in time; such result is obtained in virtue of the fact that the use of elastic foil  13  allows to make bypass valve  10  essentially insensitive to the incrustations formed by the exhaust gases.