Patent Publication Number: US-6220387-B1

Title: Exhaust muffler

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to mufflers for attenuating the sound produced by the exhaust from internal combustion engines. More specifically, the present invention relates to mufflers that accelerate the flow of exhaust gases from internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     In recent years, it has become increasingly necessary to provide improved mufflers for the attenuation of the exhaust noise produced by internal combustion engines used in transportation vehicles, due to public outcry and the resulting government regulations. New regulations are almost continually being proposed which require ever more stringent noise standards. 
     Many types of exhaust systems utilizing combinations of headers, collectors, and mufflers, as well as other noise reducing devices have been developed to address this problem. One type of exhaust system, generally referred to as a collector, combines and directs exhaust gases from separate exhaust tubes into a common downstream exhaust pipe. An exhaust muffler is attached downstream of the outlet pipe of the collector to effect noise reduction of the exhaust gases. Additionally, a catalytic converter may be attached to the exhaust system to convert some of the pollutants of the exhaust gases into harmless compounds. Unfortunately, such collector/muffler/catalytic converter systems are not very effective at minimizing the complexity of the exhaust system due to their many separate components. Moreover, they create back pressure which results in reduced performance of the engine. This reduced performance, or reduced horsepower, is undesirable in most vehicles. 
     Some muffler systems include sound attenuating material disposed in an space defined by an interior casing, or a tube structure, and an outer casing of the muffler. Holes or perforations in the interior casing, or tube structure, provide paths for the transmission of reflected high frequency components of noise into the sound attenuating material so that the noise can be subsequently dissipated. Unfortunately, this sound absorbing material adds to the overall weight of the muffler system, restricts the flow of exhaust, and provides a medium for the buildup of heat. 
     Thus, what is needed is An exhaust muffler that is lightweight, inexpensive, durable under attack of hot and corrosive exhaust gases, and impervious to vibration. Moreover, what is needed is An exhaust muffler that provides efficient noise attenuation while not causing undue back pressure to the engine, that is, one that provides good muffling without degrading engine performance. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an advantage of the present invention to provide an exhaust muffler for an internal combustion engine. 
     Another advantage of the present invention is to provide an exhaust muffler that accelerates the extraction of exhaust gases from the engine. 
     Another advantage of the present invention is to provide an exhaust muffler that achieves a cooling effect on the muffler and subsequently the engine. 
     Yet another advantage of the present invention is to provide an exhaust muffler that is economical in construction, lightweight, reliable in operation, rugged and able to withstand automotive racing along with normal use for extended periods. 
     The above and other advantages of the present invention are carried out in one form by An exhaust muffler for an internal combustion engine. The muffler includes a tapered tube having an exhaust inlet end exhibiting a first diameter and an exhaust outlet end exhibiting a second diameter, the second diameter being less than the first diameter. The exhaust inlet end is configured to receive exhaust gases from the engine. An outer tube is axially aligned with and surrounds the tapered tube to form an annular passage between the tapered tube and the outer tube. The outer tube has an air inlet end and an air outlet end. The air inlet end is configured to receive air external to the engine to create an air flow in the annular passage for accelerating the receipt of exhaust gases from the engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, and: 
     FIG. 1 shows a perspective view of an exhaust muffler in accordance with the present invention; 
     FIG. 2 shows a side view of the exhaust muffler; 
     FIG. 3 shows a sectional view of the exhaust muffler along line  3 — 3  in FIG. 2; and 
     FIG. 4 shows a posterior view of the exhaust muffler as viewed at an exhaust outlet end of the muffler. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a perspective view of an exhaust muffler  20  in accordance with the present invention. Muffler  20  is shown coupled to a collector  22  which is secured to a plurality of exhaust tubes  24  each communicating and sealingly engaging with the upstream end of collector  22 . Exhaust tubes  24  are coupled to separate associated engine exhaust ports of an internal combustion engine  25 . 
     During operation, air is drawn into an intake manifold  27  of internal combustion engine  25  and directed into the internal combustion engine cylinders. The air drawn into intake manifold  27  mixes with fuel to enable the combustion process in the cylinders (not shown) of engine  25  in a conventional manner. The resulting product of this combustion process is exhaust gas which is discharged from the cylinders. These exhaust gases are subsequently received by exhaust tubes  24  (FIG. 1) and collected at collector  22  (FIG.  1 ). In the preferred embodiment, the exhaust gases pass from collector  22  through muffler  20  and are exhausted from muffler  20  at the rear of a vehicle (not shown), as a mixture of exhaust gases and air external to the internal combustion engine. This mixture of exhaust gases and external air is indicated generally by an arrow  26 , and will be described in detail below. 
     Exhaust tubes  24  and collector  22  are configured for attachment to an internal combustion engine of an automobile configured for racing. However, nothing in the present invention requires such a configuration. Rather, muffler  20  may be secured directly to the single exhaust tube of a conventional automobile, truck, van, motorcycle, speed boat, airplane, and the like. 
     Referring to FIGS. 2-3, FIG. 2 shows a side view of exhaust muffler  20  and FIG. 3 shows a sectional view of exhaust muffler  20  along line  3 — 3  in FIG.  2 . Muffler  20  includes a tapered tube  28  having an exhaust inlet end  30  exhibiting a first diameter  32  and an exhaust outlet end  34  exhibiting a second diameter  36 . A wall portion  37  of tapered tube  28  is located between exhaust inlet end  30  and exhaust outlet end  34 . 
     A straight tube  38  having an invariant diameter substantially equal to first diameter  32  is coupled to exhaust inlet end  30  of tapered tube  28 . Straight tube  38  is adapted for coupling to the exhaust outlet end of collector  22  (FIG.  1 ). This coupling may be achieved by welding, fasteners, crimping, coupling collar or fitting, or any other such mechanism that does not substantially interrupt the flow of exhaust gases from collector  22  (FIG. 1) into straight tube  38 . 
     Muffler  20  also includes an outer tube  40  surrounding tapered tube  28  to form an annular passage  42  between an inner surface  44  of outer tube  40  and an outer surface  46  of tapered tube  28 . Outer tube  40 , tapered tube  28 , and straight tube  38  are aligned about a common axis  48 , and an air inlet end  50  of outer tube  40  is disposed proximate exhaust inlet end  30  of tapered tube  28 . Likewise, an air outlet end  52  of outer tube  40  is disposed proximate exhaust outlet end  34  of tapered tube  28 . Air inlet end  50  is configured to receive air external to the internal combustion air, indicated generally by arrows  49 , to create a flow of external air  49  through annular passage  42  toward air outlet end  52 . 
     In a preferred embodiment, outer tube  40  is longer than tapered tube  28  so that outer tube  40  extends upstream from exhaust inlet end  30  of tapered tube  28  to surround a section  53  of straight tube  38 . Correspondingly, outer tube  40  extends downstream from exhaust outlet end  34  to form a hollow region  54  delineated by exhaust outlet end  34 , air outlet end  52  and inner surface  44  of outer tube  40 . 
     In the preferred embodiment, outer tube  40  is a reducing tube. In other words, a first tube diameter  55  of outer tube  40  at air inlet end  50  is greater than a second tube diameter  57  of outer tube  40  at air outlet end  52 . In addition, outer tube  40  further includes a reducing bell  56  coupled to air inlet end  50 . A mouth  59  of reducing bell  56  has a diameter that is greater than first tube diameter  55 . The purpose of reducing bell  56  and reducing outer tube  40  will be explained in detail below. 
     A plurality of fins  58  and/or structural supports extends from an outer surface  60  of straight tube  38 . Fins  58  are configured to be removably secured to inner surface  44  of outer tube  40  to maintain outer tube  40  and tapered tube  28 , which is coupled to straight tube  38 , concentric. Fins  58  may be secured to inner surface  44  by threaded fasteners (not shown). Alternatively, fins  58  may be welded to inner surface  44 . In addition, fins  58  are strategically sized so as to permit a substantially unrestricted flow of external air  49  into annular passage  42 . 
     Wall portion  37  of tapered tube  28  includes a plurality of elliptical holes  62 . Each of elliptical holes  62  is characterized by a major axis  64  and a minor axis  66 , the major axis being longer than the minor axis. Each of elliptical holes  62  is positioned on tapered tube  28  such that its major axis  64  is substantially aligned with a longitudinal dimension of tapered tube  28 , generally referred to by an arrow  68 . 
     A first subset of elliptical holes  62  is arranged in a first row  70  encircling the circumference of tapered tube  28 . Likewise, a second subset of elliptical holes  62  is arranged in a second row  72  encircling the circumference of tapered tube  28 . 
     Referring to FIG. 4 in connection with FIG. 3, FIG. 4 shows a posterior view of exhaust muffler  20 , as observed at air outlet end  52  of muffler  20 . As best seen in FIG. 4, second row  72  is offset relative to first row  70  such that the center points of holes  62 , i.e., the intersection of major and minor axes  62  and  64 , respectively, of second row  72  are shifted a circumferential distance  74  relative to the center points of corresponding ones of holes  62  of first row  70 . In addition, major axis  64  and minor axis  66  of each of elliptical holes  62  are dimensioned so that when muffler  20  is viewed at air outlet end  52 , each of elliptical holes  62  appear as circles. Elliptical holes  62  may be formed by drilling through wall portion  37  of tapered tube  28  in a direction substantially perpendicular to the cross-section of tapered tube  28  to achieve the circular posterior appearance. Alternatively, elliptical holes  62  may be formed by laser cutting, electric discharge machine (EDM) cutting, water jet, and so forth. 
     In a preferred embodiment, tapered tube  28 , straight tube  38 , and fins  58  are machined from stainless steel and outer tube  40  is manufactured from aluminum or stainless steel. Consequently, the resulting assembly is inexpensive to manufacture, lightweight, durable under attack of hot and corrosive exhaust gases, and substantially impervious to vibration. 
     Referring back to FIG. 1-3 and as described previously, during operation internal combustion engine  25  draws air into an intake manifold  27  and directs a major portion of the air through the internal combustion engine cylinders. Exhaust gases discharged from the cylinders are received by exhaust tubes  24  (FIG. 1) which ae subsequently collected at collector  22  (FIG.  1 ). These exhaust gases, indicated generally by an arrow  76 , are received in straight tube  38 . Exhaust gases  76  are directed through straight tube  38  and into tapered tube  28  where exhaust gases  76  subsequently exit tapered tube  28  through holes  62  and exhaust outlet end  34  into region  54 . 
     When a vehicle, in which the engine located, is stationary or operating at a moderate speed, the pressure of the hot exhaust gases  76  discharging from exhaust outlet end  34  is reduced as exhaust gases  76  enter hollow region  54 . In other words, hollow region  54  located downstream from exhaust outlet end  34  of tapered tube  28 , exhibits a gas pressure that is less than a gas pressure upstream in tapered tube  28  proximate exhaust inlet end  30 . The result is a substantial increase in velocity of exhaust gases  76  as they leave tapered tube  28 . This high velocity exhaust gas  76  causes external air  49  to be drawn into reducing bell  56  to create a substantial flow of external air  49  through annular passage  42  toward air outlet end  52 . External air  49  and exhaust gases  76  mingle as exhaust gases flow from holes  62  and exhaust outlet end  34  of tapered tube  28 . This mixture of gases  26  is subsequently discharged from air outlet end  52  of outer tube  40 . 
     The structure of tapered tube  28  and the offset row configuration of elliptical holes  62  allows a smooth flow of exhaust gases  76  from tapered tube  28  to be mixed with external air  49 . In other words, exhaust gases  76  do not substantially change direction as they are directed through tapered tube  28 . The smooth flow of exhaust gases  76  from elliptical holes  62  and the mixing action of the hot exhaust gases  76  with the cooler external air  49  results in effective noise attenuation of the high pressure sound wave produced when exhaust valves (not shown) open. Moreover, elliptical holes  62  achieve the benefit of substantially reventing backflow of exhaust gases back into the internal combustion engine which has the undesirable affect of degrading engine performance. 
     In addition to preventing undesirable backflow, an additional benefit of the cooperative relationship between outer tube  40  and tapered tube  28  is the ability of muffler  20  to draw exhaust gases  76  from the internal combustion engine. Reducing bell  56  and air inlet end  50  of outer tube  40  face forward relative to the vehicle, and exhaust mixture  26  is discharged rearward relative to the vehicle. Accordingly, as the vehicle moves faster, more external air  49  is captured by reducing bell  56  and rammed into annular passage  42 . 
     In addition, the structure of reducing bell  56  and the tapered configuration of outer tube  40  serve to further increase the velocity of external air  49 . The velocity of external air  49  flowing through annular passage  42  into hollow region  54  approaches the velocity of exhaust gases  76  being discharged from tapered tube  28 . The result is a greater pressure differential between the pressure in hollow region  54  and the pressure in tapered tube  28 . The consequence of this greater pressure differential is to accelerate the receipt of exhaust gases  76  from the engine and increase engine power as external air flow velocity increases due to increased vehicle speed. The accelerated receipt of exhaust gases  76  from the engine causes the engine to run cooler. In other words, the hot exhaust gases  76  are discharged quickly before the heat of exhaust gases  76  can be transferred to the engine components, thus reducing engine wear. 
     Tests have indicated, however, that there is a desired relationship between first diameter  32  of exhaust inlet end  30  and first tube diameter  55  of air inlet end  50  for effectively accelerating receipt of exhaust gases  76  from the engine. In other words, the difference between first diameter  32  and first tube diameter  55  is equivalent to the width of annular passage  42 . Tests have indicated that if the width of annular passage  42  is too great, the resulting velocity of external air  49  flowing through annular passage  42  is too high, resulting in the undesirable backflow of exhaust gases  76  into the engine. However, if the width of annular passage  42  is too small, the benefit of accelerating the receipt of exhaust gases will not be achieved. Accordingly, tests have determined that when first diameter  32  of exhaust inlet end  30  is in a range of approximately fifteen to forty percent smaller than first tube diameter  55 , effective acceleration of exhaust gases  76  is achieved without the undesirable effect of backflow. 
     In summary, the present invention teaches of an exhaust muffler for an internal combustion engine. The exhaust muffler draws air external to the internal combustion engine along an annular passage surrounding a tapered tube configured to receive exhaust gases from the engine. The velocity of the external air produces a low pressure region downstream of the exhaust gases to accelerate the extraction of exhaust gases from the engine. The accelerated extraction of exhaust gases achieves a cooling effect on the muffler and subsequently the engine by drawing out the hot exhaust gases before heat is transferred from the exhaust gases back to the engine. In addition, exhaust gases smoothly flow through elliptical holes located in the tapered tube to mix with the external air. This smooth flow and effective mixing results in noise attenuation without the undesirable effect of backflow of exhaust gases into the engine. The structure of the exhaust muffler is economical in construction, lightweight, reliable in operation, rugged and able to withstand automotive racing use for extended periods. 
     Although the preferred embodiments of the invention have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. For example, the exhaust muffler may be used with a catalytic converter system. In addition, the elliptical holes in the exhaust muffler may be configured as circular holes. Alternatively, the elliptical holes may be absent from the tapered tube. Such a configuration would still result in noise attenuation, although, perhaps at the expense of decreased engine performance due to the increased potential for backflow.