Abstract:
The present invention provides a muffler comprising a rotatable propeller within or adjacent to an expansion chamber to swirl exhaust gas towards the outlet. The muffler maintains the sound level of the exhaust within acceptable limits, while delivering improved power and/or fuel efficiency over that of standard mufflers.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention provides a muffler for internal combustion engines which delivers improved horsepower and/or fuel efficiency over standard mufflers.  
       BACKGROUND  
       [0002]     Due to environmental concerns, governmental entities have steadily imposed stricter limits on the amount and type of exhaust emitted by vehicles powered by the internal combustion engine. Moreover, the amount of noise produced by such engines must also meet stringent standards. While such limits may improve air quality and decrease noise pollution, such limits also produce severe drawbacks in increased fuel consumption and decreased power production by the affected engines. It is believed that such drawbacks are a result of back pressure of exhaust gas created by the very equipment that muffles the noise and cleans the exhaust gas. Accordingly, it is believed that such drawbacks can be mitigated by equipment that will increase exhaust flow-through.  
         [0003]     Various systems have been proposed to provide a more efficient means of reducing noise and/or air pollution from internal combustion engine exhaust. Some such proposed systems are found in U.S. Pat. No. 4,533,015 to Kojima; U.S. Pat. No. 4,339,918 to Michikawa; U.S. Pat. No. 4,331,213 to Taniguchi; U.S. Pat. No. 4,317,502 to Harris et al.; U.S. Pat. No. 4,303,143 to Taniguchi; U.S. Pat. No. 4,222,456 to Kasper; U.S. Pat. No. 4,129,196 to Everett; U.S. Pat. No. 4,109,753 to Lyman; U.S. Pat. No. 4,050,539 to Kashiwara et al.; and U.S. Pat. No. 3,016,692 to lapella et al. However, the quest to decrease noise and exhaust emissions, while off-setting the concomitant decreases in fuel efficiency and power production, proves to be an ongoing struggle.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention provides a muffler comprising a rotatable propeller within or adjacent to an expansion chamber to swirl exhaust gas towards the outlet. The muffler maintains the sound level of the exhaust within acceptable limits, while delivering improved power and/or fuel efficiency over that of standard mufflers. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0005]      FIG. 1  is a longitudinal cross-sectional view of an embodiment of a muffler according to the invention.  
         [0006]      FIG. 2  is an end view of an embodiment of a muffler according to the invention.  
         [0007]      FIG. 3  is side close-up view of the propeller of an embodiment of a muffler according to the invention.  
         [0008]      FIG. 4  is an end close-up view of the propeller of an embodiment a muffler according to the invention.  
         [0009]      FIG. 5  illustrates another embodiment of a muffler according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]     The invention is described by the following examples. It should be recognized that variations based on the inventive features disclosed herein are within the skill of the ordinary artisan, and that the scope of the invention should not be limited by the examples. To properly determine the scope of the invention, an interested party should consider the claims herein, and any equivalent thereof. In addition, all citations herein are incorporated by reference.  
         [0011]      FIG. 1  illustrates a cross-sectional view along the longitudinal axis of an embodiment of a muffler  10  according to the invention. Muffler  10  comprises an outer shell  16  having an inlet  162  at a tapered entry end  14  and an outlet  164  at tapered exit end  34 . In other embodiments, the outer shell has a substantially flat inlet end and/or outlet end. Materials used to form mufflers are well-known in the art. In an embodiment, the muffler casing and the relevant tubes are made from metals such as stainless steel. Methods of attaching the various components are also well-known. For example, coupling points can be formed integrally, or welded or brazed. Additional embodiments include mufflers having an oval cross-section having a round expansion area adjacent the propeller. The round expansion area may continue throughout the expansion chamber, or can elongate about an axis to conform with the outer oval cross-section.  
         [0012]     An inlet tube  12  is attached at a proximal end  122  to shell  16  at inlet  162 . A distal end  124  of inlet tube  12  is attached directly or indirectly to an exhaust gas source, such as an internal combustion engine (not shown). The interior  126  of inlet tube  12  opens up into an expansion chamber  18  defined by the interior of an expansion chamber tube  20 . The expansion chamber tube  20  is attached substantially coaxially to outer shell  16 . Although shown as attached to the outer shell so that a portion of the outer shell defines expansion chamber, expansion chamber tube  20  can be tapered at its ends, such that its opposing openings may also define inlet  162  and outlet  164 . Moreover, expansion chamber tube  20  is attached to outer shell  16  such that the exterior of the expansion chamber tube  20  and the interior of the outer shell  16  combine to define a sound suppression sleeve  22  that surrounds the expansion chamber  18 .  
         [0013]     Sound suppression sleeve  22  is packed with known sound suppression materials. Examples of such materials include fiberglass, glass wool, copper wool, copper strands, steel wool, etc. In an embodiment the sound suppression material is fiberglass. Tube  20  is perforated with apertures (not shown) so that the expansion chamber  18  is in communication with the materials in the sound suppression sleeve  22 . In an embodiment, tube  20  has about a 50% porosity. In another embodiment, tube  20  has between about 40 to about 80% porosity. In another embodiment, expansion chamber  18  has at least about 85% greater flow cross-sectional area than inlet tube  12 . In a further embodiment, expansion chamber  18  has at least about 75% greater flow cross-sectional area than inlet tube  12 . In yet another embodiment, expansion chamber  18  has between about 75% to about 90% greater flow cross-sectional area than inlet tube  12 .  
         [0014]     In an embodiment, within expansion chamber  18 , at an end proximal to inlet tube  12 , a propeller  24  (see  FIGS. 1, 3  and  4 ) is attached to the muffler by an rotational axis mount  28  to propeller support  26 . In an embodiment, the propeller comprises four blades  30 , each having about an 30 degree spiral twist  38 . Mount  28  securely attaches propeller  24  to propeller support  26 , but provides enough play for the propeller to rotate freely, as exhaust gas is forced out of inlet tube  12  into expansion chamber  18 . Alternatively, the blades have a turn of between about 20-60 degrees. There is no difference in performance if the blades are rotated clockwise or counterclockwise, as long as all blades are consistent with each other. In other embodiments, the propeller can have 2 to 8 blades. In another embodiment the propeller has 3 to 5 blades. In a preferred embodiment, the blades are relatively narrow. However, various blade widths may be utilized in the context of the invention.  
         [0015]     Various methods of mounting the propeller on the supports are known. In an embodiment, the propellers are mounted on a teflon-filled bronze bearing, which is, in turn, mounted on a standard shoulder screw, attached to the propeller support. In another embodiment, the propellers are mounted on a shoulder screw, which is mounted in a teflon-filled bronze bearing that is attached to the propeller support. The bearings and screws are also made of stainless steel or alloy steel. As shown in  FIG. 1 , propeller  24  can be fitted in front of support  26 . As shown in  FIG. 2 , the propeller (represented by blades  30 ) can also be fitted in back of support  26 .  
         [0016]     In  FIG. 1 , an arrow  40  in the interior  126  of inlet tube  12  represents gas traveling in a substantially linear direction in that area. When the gas reaches propeller  24 , the gas forces the propeller  24  to spin, which, in turn, causes the gas to spin (shown as arrow  32 ) as it passes through the expansion chamber  18 . The swirling effect forces the exhaust towards the tapered exit end  34  which maintains the spin-flow of the gasses to propel the gas out of the muffler through outlet tube  36 . The outlet tube  36  is attached at a proximal end  362  to outlet  164  and leads to the atmosphere at distal end  364 , either directly or indirectly (e.g. via a tailpipe). In an embodiment, outlet tube  36  has substantially the same interior diameter as inlet tube  12 . In another embodiment, the inlet tube  12  has a substantially smaller interior diameter than outlet tube  36 .  
         [0017]     In an alternative embodiment, propeller  24  is supported within the proximal end  122  of the inlet tube  12  ( FIG. 5 ). Note that in this embodiment, the proximal ends of inlet tube  12  and outlet tube  36  are shown as protruding into expansion chamber  18 . Different means to attach the inlet and outlet tubes are known, as are different means to attach the propeller to the muffler. Without being limited by any theory, it is believed that the propeller forces the exhaust to spin from a low volume space to a higher volume space, thereby improving throughput of the exhaust.  
         [0018]     It is found that the exemplary embodiments of the invention provide high performance propulsion mufflers that increase horsepower and/or fuel efficiency for internal combustion engines, while maintaining the sound level of the engine within acceptable levels. Without being limited by any particular theory, it is believed that as the exhaust gas enter the muffler, the propeller forces the gas to rotate into a tightly spun vortex, as the gas expands in the expansion chamber. This facilitates the flow of the gasses through the expansion chamber, and through the outlet tube. This effect creates a vacuum, which draws more gasses from the exhaust source, increasing the exhaust throughput of the engine.  
         [0019]     Relative to similar standard mufflers that do not have the propeller, it has been found that the horsepower of the engine can be increased by up to about 19%. In an embodiment, the horsepower was improved to between about 13 and about 19%. In another embodiment the fuel milage was increased by up to about 12% in city driving, and up to about 15% in highway driving. In a further embodiment, the fuel efficiency was improved to between about 5 to about 12% in the city. In yet another embodiment, the fuel efficiency was improved to between about 6 and about 15% on the highway. Vehicles that may benefit from such a muffler include trucks, automobiles, lawn mowers, boats, snowmobiles, power machinery, or other equipment driven by the internal combustion engine.