Abstract:
A sound attenuating exhaust muffler for an internal combustion engine is disclosed. The muffler has a body casing with an exhaust inlet at one end and an exhaust exit at the other end. Internally, three partitions define four serial chambers with a sound absorbing column located in the third chamber. The first and third partition fit closely to the body casing around their edges with apertures through the partitions, while the second partition fits closely in the height dimension but has gaps around each end in the width dimension. The second partition is bent at its middle to present two oblique surfaces towards the first partition.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to an automobile muffler. More specifically, this invention is an automobile muffler which performs the function of repressing engine noise while allowing a high flow rate of exhaust gases.  
       BACKGROUND OF THE INVENTION  
       [0002]     Internal combustion engines operate by compressing a charge of air, adding heat to that charge of air, and then harnessing the resulting expansion of the heated air to extract work from the expansion. In the case of engines operating on the Otto or Diesel cycles, the air charge is compressed in discrete quantities by pistons within cylinders, and the heat addition is accomplished by the combustion of fuel which has been mixed into the air charge. The combustion process is essentially a contained explosion, with the pistons also acting to extract work from the expanding gases of the air and combusted fuel. This process generates considerable noise, including additional noise resulting when the gases are further expanded by exhausting the cylinders to atmospheric pressure. To mitigate this noise the exhaust gases are piped from the engine to a muffler. A muffler serves to suppress the noise as the exhaust gases pass through it. Typical mufflers accomplish the noise suppression with chambers and baffles internal to the cannister body of the muffler.  
         [0003]     It is, of course, desirable to have an engine that operates quietly, but a balance is required. If the muffler restricts the flow of exhaust gases away from the engine too much, the resulting back pressure harms the engine&#39;s performance. In an extreme theoretical case, all of the work extracted from the expansion would be expended in exhausting the gases. In such a case, any additional load would stall the engine. As noted above, however, an engine with its cylinders exhausted directly to atmosphere would be too noisy for typical applications. The goal is to achieve noise suppression while minimizing the affect of back pressure on engine performance. This is particularly important for high performance engines where a maximum of power is desired.  
         [0004]     The present invention belongs to a class of mufflers comprising an enclosed cannister with chambers and baffles inside. The cannister can have various shapes and cross sections and the chambers and baffles are shaped and positioned in such a fashion that noise is reduced as the gases pass through. Frequently, as exhaust gases are routed through the muffler, locations of turbulence, and low pressure and high pressure will develop. Of particular concern are locations of turbulence and high pressure. A turbulent flow regime may be characterized by higher levels of fluid friction resulting in lower volume flow rates. Similarly, high pressure locations indicate where the flow of gases is being constricted, and the flow into the location is less encumbered than the flow away from the location. Both high friction flow regimes and constricted flow locations can affect upstream conditions in subsonic flow and for internal combustion engines that effect is higher back pressure and loss of performance power. The muffler of the present invention provides a balance between noise suppression and engine performance.  
       DESCRIPTION OF THE PRIOR ART  
       [0005]     A search of the prior art reveals a number of patents pertaining to mufflers in the general class of the present invention. The most relevant patent appears to be U.S. Pat. No. 4,574,914 by Flugger. The muffler in Flugger &#39;914 has a cannister body with a width and height dimension perpendicular to the overall direction of flow of the exhaust gases and its length dimension parallel to the overall flow. The width dimension of the cannister is substantially greater than the height dimension, and the length dimension is greater still than the width dimension. The exhaust is piped into a first end of the cannister and, after several deflections in its flow path, exits out a second end of the cannister.  
         [0006]     Partitions are arranged within the canister to alter the flow of the exhaust and attenuate noise. A first partition has the full height of the cannister but is shorter in the width dimension and has a gap at each side between its end and the sides of the cannister. The first partition is divided into two flat panels with a peak at its center and the panels extending from the peak to the sides. This first partition serves to split the exhaust flow and direct it to the sides of the cannister. A second partition follows which is formed to direct the flow into the central area of the partition where it is perforated to allow the flow of gases through the perforation. The first partition extends to the full height of the casing, but not its full width, while the second partition fits both the height and width of the casing.  
         [0007]     Another patent by Flugger, U.S. Pat. No. 4,809,812 is also relevant to the art. Flugger &#39;812 has a casing with an inlet and outlet. The inlet directs the exhaust gases onto a flow dividing partition within the casing. The exhaust gases are directed to either side of the casing to flow around the divider. On the backside of the divider are converging surfaces similar to the divider. Next in the casing is a second partition. This second partition fits the height and width of the casing and has surfaces shaped to direct the gases to the center of the second partition where a perforation allows the gases to pass through the partition. The spacing between the second partition and the converging surfaces on the back side of the dividing partition is such that nearly constant cross section passages are formed. This is intended to maintain smooth flow through the muffler without eddies forming to decrease the rate of flow. In one embodiment, Flugger &#39;812 directs the exhaust from the second partition onto a second dividing partition which is followed by similar set of constant cross section passages which guide the exhaust gases to the outlet.  
         [0008]     Another patent, also by Flugger, U.S. Pat. No. 5,123,502, claims a muffler having construction similar to those just described. This muffler, however, has features intended to burn off unburned fuel. Within the casing of the muffler, the first partition is a flow dividing partition like in the previous patents. This flow dividing partition is a simple one with two panels receding back from a central crease. A second, flow gathering partition follows this panel. It fits the height and width of the muffler casing, has a central panel and two side panels formed in it, and has a central perforation in the central panel to allow exhaust to pass through the partition. The two side panels bend forward from the central panel towards the first partition to gather the exhaust from the sides of the muffler to the central perforation. The shape and spacing of the first and second partition create a low pressure area in the muffler where unburned fuel collects. The first partition has a small aperture in its dividing crease. This aperture allows small amounts of combustion temperature exhaust gases to pass directly into the low pressure area to ignite and burn the unburned fuel collected there.  
         [0009]     As can be seen in the art discussed above, it is common to divide and converge the flow of exhaust gases through mufflers. Locations where the flow converges can be the site of turbulence and friction resulting in reduced flow rates. If, in addition to converging flow paths, a restriction is placed in the combined flow path, a high pressure location results which is indicative of resistance to flow and increased back pressure in the exhaust system. While some of the prior art attempts to avoid excessive turbulence in converging flow streams, the combined flow is forced through a restrictive aperture, necessarily producing a high pressure location. The present inventions avoids a single restrictive aperture.  
       SUMMARY OF THE INVENTION  
       [0010]     It is a primary objective of the present invention to provide a means for quieting an internal combustion engine.  
         [0011]     It is an additional objective of the present invention to provide a quieting means that allows a high flow rate of exhaust.  
         [0012]     It is a further objective of the present invention to provide a inexpensive means of quieting an internal combustion engine while allowing a high exhaust flow rate.  
         [0013]     The present invention is an improved muffler for an internal combustion engine. The invention comprises a casing with an inlet and exit. Within the casing are partitions forming several chambers. The partitions allow a high flow rate of exhaust gases while deflecting, reverberating, and absorbing the engine noises within the chambers of the muffler. A column within the third chamber of the muffler provides additional sound absorption.  
         [0014]     As discussed above, the method and device of the present invention overcomes the disadvantages inherent in prior art methods and devices. In the respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.  
         [0015]     Accordingly, those skilled in the art will appreciate that the conception upon which this invention is based may readily be utilized as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit of the present invention.  
         [0016]     Furthermore, the purpose of the foregoing Abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially including the practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection, the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the invention of the application, nor is it intended to be limiting to the scope of the invention in any way. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Additional utility and features of the invention will become more fully apparent to those skilled in the art by reference to the following drawings, which illustrate the primary features of the preferred embodiment.  
         [0018]      FIG. 1  shows the muffler of the present invention.  
         [0019]      FIG. 2  shows a cross section along the length and width of the muffler of the present invention, as indicated in  FIG. 1 .  
         [0020]      FIG. 3  shows a cross section near the exit end of the muffler as indicated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     The detailed description below is for preferred embodiments and is intended to explain the current invention. It is to be understood that a variety of other arrangements are also possible without departing from the spirit and scope of the invention.  
         [0022]      FIG. 1  shows the muffler of the present invention, indicated generally by  10 . The muffler  10  has an inlet pipe  15 , body  20  having an outer casing  25 , and an exit pipe  30 . The inlet pipe  15  would be connected to a pipe which would eventually lead to the exhaust manifold of an engine. The exhaust from the engine would enter the muffler  10  through the inlet pipe  15 , flow through the body  20  of the muffler  10  and leave via exit pipe  30 . First end plate  35  and second end plate  40  (shown in  FIG. 2 ) close the ends of outer casing  25  to complete the body  20  of muffler  10  leaving only inlet pipe  15  and exit pipe  30  for the flow of exhaust gas.  
         [0023]      FIG. 2  shows a cross section along the length and width of the muffler of the present invention, as indicated in  FIG. 1 . This shows the inner chambers and partitions of the muffler  10  and the paths of exhaust flow through it are indicated by arrows. The exhaust enters the muffler body  20  from inlet pipe  15  where it enters first chamber  45  defined by first end plate  35  and first partition  50 . First partition  50  has three panels, a center panel and a side panel at each side of the center panel. The side panels are defined by slight bends in first partition  50  with the side panels being bent slightly toward first end plate  35 . Overall, first partition  50  has the height and width of the inside of muffler body  20  so it closely fits within muffler body  20 , essentially allowing exhaust flow only through first central aperture  55 . First central aperture  55  is located in the center of first partition  50  and is round and has a diameter nearly as large as the height of first partition  50 .  
         [0024]     After passing through first central aperture  55 , the exhaust gases enter second chamber  60  defined by first partition  50  and second partition  65 . Second partition  65  is as tall as the inside of muffler body  20  but not as wide. Therefore, there is a gap between the ends of second partition  65  and the sides of muffler body  20 . Second partition  65  is divided into two panels by a central crease running from top to bottom. The central crease is aligned with first central aperture  55  and the two panels of second partition  65  recede away from central aperture  55  toward the sides of muffler body  20 . Thus, as the exhaust gases pass through first central aperture  55  the flow is split and directed to the sides of muffler body  20  and the ends of second partition  65 .  
         [0025]     The exhaust gases exit second chamber  60  by flowing around the ends of second partition  65  where the exhaust gases enter third chamber  70  defined by second partition  65  and third partition  75 . Third partition  75  has three panels, a center panel and a side panel at each side of the center panel. The side panels are defined by slight bends in third partition  75  with the side panels being bent slightly toward second partition  65 . Overall, third partition  75  has the height and width of the inside of muffler body  20  so it closely fits within muffler body  20 , essentially allowing exhaust flow only through apertures in third partition  75 . Located in the center of third partition  75  is second central aperture  80  and located in the center of the two side panels of third partition  75  are auxiliary apertures  85 . Second central aperture  80  is located in the center of third partition  75  and in the preferred embodiment, said aperture is round and has a diameter approximately two-thirds of the height of third partition  75  in this embodiment. One auxiliary aperture  85  is located in the center of each side panel of third partition  75 . The auxiliary apertures  85  have the same diameter which is approximately one-fifth of the height of third partition  75 . Centrally located in third chamber  70  is column  90 . Column  90  has four sides and is the same height as the inside of muffler body  20 . Two sides of column  90  are essentially parallel to the two panels of second partition  65  with an obtuse angle between them while the other two sides opposite those are slightly longer, resulting in the other four angles being acute, although the exact angles are not critical.  
         [0026]     The exhaust gases pass through third partition  75  via second central aperture  80  and auxiliary apertures  85  into fourth chamber  95  defined by third partition  75  and second end plate  40 . From there, the exhaust gases exit muffler body  20  from exit pipe  30 . As shown in  FIG. 1  and  FIG. 2 , exit pipe  30  is placed at one side of second end plate  40 .  
         [0027]      FIG. 3  shows the cross section indicated in  FIG. 2 . Second central aperture  80  is larger and allows more exhaust gas flow than auxiliary apertures  85  located centrally in the side panels of third partition  75 . However, the presence of the auxiliary holes  85  boosts flow rate while maintaining the sound barrier presented by third partition  75 .  
         [0028]     Returning to  FIG. 2  to discuss how the muffler of the present invention achieves a balance of sound attenuation with a high flow rate, it is noted that sound, while a form of wave energy, travels in essentially straight lines through a physical medium. Hence, the present invention places partitions in the linear path of the sound waves while providing non-linear flow paths for the exhaust gases. The apertures, gaps, and channels created by partitions  50 ,  65 , and  75  and outer casing  25  are sized large enough to accommodate a high flow rate.  
         [0029]     The exhaust gases exit inlet pipe  15  and expand out into first chamber  45 . Similarly, sounds exiting inlet pipe  15  disperse into the broader cross section of first chamber  45 . Some portion of the sound impacts first partition  50  and reverberates. Another portion passes through first central aperture  55 . Finally, another fraction of the sound will impart first partition  50  and transmit through it. The latter two portions of the sound will travel into second chamber  60  and impact upon the oblique surfaces of second partition  65 , where the oblique angles will allow less of the sound to transmit through second partition  65  and cause it to reverberate within second chamber  60 . Sound which does pass into third chamber  70  will be obstructed by column  90  which has space within it for further trapping transmitted noise. Finally, third partition  75 , while generally perpendicular to the exhaust flow though muffler  10  will present surfaces not perpendicular to second partition  65  and column  90 . Although separated from second partition  65 , column  90  also serves to define the flow paths between column  90  and third partition  75  into channels, reducing the amount of turbulence in the flow in that section. As the exhaust gases flow through these channels towards convergence at second central aperture  80 , auxiliary apertures  85  allow a portion of the exhaust gases to pass through third partition  75 , reducing the pressure at second aperture  80 . This reduces back pressure in the exhaust system. By providing generous flow paths for exhaust gases while presenting internal sound barriers the present invention achieves the desired balance of sound attenuation with high flow rate and low back pressure.  
         [0030]     While not shown in the drawings, other embodiments utilizing multiple inlets and outlets are possible. Using two inlets would allow the exhaust from two separate banks of engine cylinders to pipe directly into the muffler. This would avoid merging the individual exhaust pipes into a single pipe before joining the muffler, an arrangement that can result in restrictive flow in the single pipe. Using two outlets would increase the flow rate out of the muffler and further reduce back pressure.  
         [0031]     Other embodiments not illustrated involve variations in the column located in the third chamber. One of these embodiments uses a round column. This provides certain advantages in the manufacture of the muffler as well its performance. Other variations on the column would tune the muffler as its overall size changes. Frequently, changing a system&#39;s overall size does not result in all dimensions changing in direct proportion to each other. Similarly, the angles between the sides of a polygonal column may change to tune the muffler.  
         [0032]     Having provided detailed descriptions of the preferred embodiment, it should be noted that there are several means to vary the specific sizing and spacing but still accomplish the construction of the invention. It should be obvious from this that there are numerous embodiments subsumed in the present invention and the scope of this invention should not be limited by the discussion of the preferred embodiment above.