Abstract:
A device and method for muffling the sound from an internal combustion engine is described, wherein the device is a tube made of a suitable material such as rubber and is attached to the exhaust outlet of the vehicle. Further described is a method of muffling the sound of an internal combustion engine that is comprised of taking a length of tubing, having two ends and attaching one end of said tubing to the outlet of the exhaust of an internal combustion engine, and directing the other end of said tubing toward the ground surface, by forming an approximate ninety degree bend, such that this second end of the tubing is in close proximity with the ground surface, with the result that the sound level of the exhaust from the engine is substantially reduced.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to a device and method for reducing the exhaust noise of internal combustion engines, and more particularly to a method and apparatus for muffling the exhaust noise of vehicles, including particularly, but not limited to, four-stroke internal combustion engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    Beginning with the early days of internal combustion engines, there has been an effort to reduce the sound levels that are produced during operation of these devices. Typically, there are various sources of sound that are produced during operation. As the fuel/air mixture is detonated, there is the sound generated by the explosion. Internally, there are various moving parts that generate noise due to their interaction. During intake and exhaust, there is also the sound of fluid rushing in or rushing out of the engine.  
           [0003]    While some of the noises emanate from the metal casing of the engine itself, a substantial portion of these sounds may be heard through the exhaust stream of the engine. Accordingly, efforts have taken place to muffle the sounds traveling out of the engine through this pathway.  
           [0004]    Muffling devices have been developed with various methodologies for baffling the sound, thereby allowing the sound noise to dissipate, or to cancel itself out when sounds of opposite phase encounter each other. Mufflers are typically attached to all internal combustion engines that operate in public areas. Outside public areas, muffling has heretofore been of low priority, since the sounds have not been audible to a significant number of human beings.  
           [0005]    With growth of human population, and an increased amount of leisure time available, there are a larger number of people spending time in wilderness areas. In urban areas, the concentration of population has led to a substantial increase in the level of audible noise. In an effort to prevent a similar increase in sound in suburban and wilderness areas, an increased focus has recently been placed on quieter machines for operation in these areas.  
           [0006]    As sound waves spread out, their intensity decreases inversely with the square of the distance from their source. Thus there will be some attenuation due to this effect. However, the human ear does not respond linearly, so that doubling of sound intensity does not sound twice as loud to the human ear. For this reason, a logarithmic scale, or decibel scale, is used to measure sound pressure level with a typical minimum reference level of 2×10 −5  N/m 2  at 1 kHz being equal to zero decibels, which is barely audible for a normal hearing response.  
           [0007]    The sound level can be determined using the formula  
           20 log p 0 /p 0t  dB,  
           [0008]    where p 0t  is the sound pressure at the threshold of hearing at 1 kHz, and p 0  is the sound pressure under measurement.  
           [0009]    Thus, a sound of ten decibels is ten times louder, but  20  decibels is 100 times louder. For example, normal conversation is 60 decibels, while city traffic noise is in the 80-90 decibel range. While damage to the ear occurs with exposure to approximately 85 decibels or higher for long term periods, discomfort occurs at around 120 decibels. A jet engine is approximately 140 decibels. Mechanical damage to the ear occurs at approximately 160 decibels.  
           [0010]    The present invention began out of a need for a quieter All Terrain Vehicle (ATV). These vehicles are commonly used in off-road conditions, often into woods and other wilderness areas. It is desirable to reduce the noise emissions of such vehicles, in part to prevent disturbance to others and in part to allow for a stealthy approach to wildlife.  
           [0011]    The internal combustion engines of ATVs are usually four-stroke engines, otherwise known as Otto cycle engines. The present invention has been found to be particularly suited to reducing the sound noise of the emissions from such engines.  
           [0012]    Manufacturers of vehicles, particularly ATVs, are required to meet certain limits on noise. It may be necessary for the manufacturer to limit horsepower of the engine in order to meet these decibel limits. It is highly desirable for a manufacturer to be able to reduce decibels, particularly by non-restrictive means.  
           [0013]    There are various engine muffling devices and methods previously known, but which all are disadvantageous when compared to the present invention:  
           [0014]    U.S. Pat. No. 4,428,453 to Yuen et al. teaches a silencer device in which gases enter an upstream compartment of a silencer and flow through perforations in a tube and pipe into a chamber interior, then into an inverted trough through further perforations into a downstream compartment and an outlet. This describes a traditional muffler type device used on vehicles. While this may be adequate for some uses, particularly in urban areas, where there is much surrounding noise, it falls short in achieving a level of quietness desirable for wilderness areas.  
           [0015]    U.S. Pat. No. 6,158,214 to Kempka et al. teaches a four-chamber type of construction for very small passenger transporting motor vehicles, wherein a silencer system partition divides the silencer into a 3-pot main chamber and an additional chamber (resonator). This device is overly complicated as an add-on component to follow a standard muffler.  
           [0016]    U.S. Pat. No. 6,382,347 to Gerber teaches a muffler device with a single inlet pipe and single outlet pipe having perforations in a portion of a pipe within a muffler chamber. While generally simple in design, this device still requires more components than desirable.  
           [0017]    U.S. Pat. No. 4,848,513, issued Jul. 18, 1989 to Csaszar teaches “a compact noise abatement muffler for an internal combustion engine” wherein “exhaust gases passing through the muffler . . . achieve at least 4 changes of direction of gas flow”. While providing for a large reduction of about 10 decibels, the Csaszar patent requires complex construction in order to achieve four changes in direction of a gas flow.  
           [0018]    U.S. Pat. No. 4,284,162, issued Aug. 18, 1981 to Ishida teaches a “tail pipe [that] is rendered considerably long to effectively silencing [sic] exhaust noise”. This patent discloses the use of a reverse bend to add length to the tailpipe of the exhaust. Furthermore, it provides a second length within a muffler body to add length to the path that exhaust must travel. The Ishida device requires several components, increasing the cost of manufacture, and during tests of the present invention, it has been found that moderately lengthening a tailpipe does not noticeably reduce the sound level. While the present invention may derive benefit from some modest amount of sound reduction by virtue of extension of length, it is experimentally undetectable or measurable under the conditions of the tests performed.  
           [0019]    The fact that a conical opening can allow for expansion of gases and result in suppression of noise has been previously recognized. U.S. Pat. No. 6,158,546, issued Dec. 12, 2000 to Hanson et al. teaches “an outlet tube with a funnel shaped element having a large diameter end positioned in an expansion chamber”. While Hanson et al. disclose a conical exhaust section, the conical opening is an internal component that opens up into a chamber within the exhaust system itself. The tailpipe outlet from the exhaust system is not conical in shape.  
           [0020]    U.S. Pat. No. 5,214,253, issued May 25, 1993 to Houston, Jr. teaches “a flared expansion chamber”. In this patent, it is the expansion chamber that is flared, rather than the tailpipe as in the present invention. The flaring of the expansion chamber in a single dimension requires the addition of a plurality of tail pipes, significantly adding to the cost to practice the Houston, Jr. invention.  
           [0021]    Another possible method of sound reduction is the generation of vortices or eddy currents, which combine to cancel sound. Prior art does not take advantage of external surfaces to provide this effect. U.S. Pat. No. 5,428,954, issued Jul. 4, 1995 to Cowan, Sr. teaches generation of “vortices effective to dampen exhaust noise vibrations and to contain the same as they dissipate into the atmosphere”. This invention is applicable to jet engines and the exhaust is directed aftwardly, rather than towards the ground. Bypass ports around the engine are used to generate the vortex, contrary to the present invention, which is a single exhaust member extension, with direction to accomplish its noise reduction function.  
           [0022]    U.S. Pat. No. 4,220,219, issued Sep. 2, 1980 to Flugger teaches the “generation of sound dampening eddy currents in the chamber” and “the generation of eddy current therebetween is preferably formed proximate the outlet tube of the muffler”. This invention requires that gas streams combine coming from opposing directions, thereby creating the eddy currents, and thus requires two exhaust sources, or splitting of a single exhaust source.  
           [0023]    While some or all of the above referenced inventions may well be used on a vehicle, upstream of the present invention, to obtain a minimum level of noise reduction, they are disadvantageous in view of the present invention, wherein the present invention more adequately reduces the sound level and is less complicated.  
         BRIEF SUMMARY OF THE INVENTION  
         [0024]    Briefly described, the present invention overcomes the above-mentioned disadvantages and meets the recognized need for such a device by providing a method and apparatus for reducing exhaust noise of internal combustion engines, wherein the present invention causes a substantial reduction in such noise, particularly as to four-stroke internal combustion engines.  
           [0025]    According to its major aspects and broadly stated, the present invention in its preferred embodiment is a generally tubular exhaust extension directed in such a manner that the exhaust exits in close proximity to the ground. By orienting the extension in such a fashion that it is directed at and near the ground, in lieu of relying on extension length alone, a measurable noise reduction is achieved. By utilizing the ground surface for absorption and dampening of sound waves, such as grass or rough dirt, and by directing the exhaust tube directly downward into such surface, a muffling effect is achieved.  
           [0026]    More specifically, the present invention is a section of formed tubing, for exemplary purposes only, made of rubber or silicone rubber suitable for exhaust temperatures, wherein the end of the tubing enables exhaust to be directed downward into the ground, or at an angle to the ground, and in close proximity thereto. By directing the exhaust gases generally directly into the surface below, it is possible to achieve substantial noise reduction compared to a vehicle which lacks such a directed tube.  
           [0027]    The present invention relates to a device that could be used by hunters and outdoorsmen to quieten the sound of their vehicles. More particularly, any internal combustion engine may have its exhaust muffled through the use of the present invention.  
           [0028]    A feature and advantage of the present invention is its ability to provide a device that substantially reduces exhaust noise from internal combustion engines.  
           [0029]    A feature and advantage of the present invention is that manufacturers will have more design flexibility, since decibels will be reduced without the need for restrictive devices on the engines.  
           [0030]    An additional feature and advantage of the present invention is that manufacturers can use louder conventional mufflers and still reduce the overall sound with the present invention, thus increasing horsepower of the engine.  
           [0031]    A feature and advantage of the present invention is that it will give manufacturers an advantage over competitors that do not have the ability to use the present invention, at negligible additional cost.  
           [0032]    A further feature and advantage of the present invention is that, when utilized in combination with and All Terrain Vehicle, it enables the user to observe wildlife at closer proximity than is normally possible without the device.  
           [0033]    A feature and advantage of the present invention is its ability to provide for a quiet approach by a motor vehicle.  
           [0034]    A further feature and advantage of the present invention is that it is simple to manufacture and of low cost.  
           [0035]    A further feature and advantage of the present invention is its ability to reduce engine noise output levels by approximately 50%.  
           [0036]    A feature and advantage of the present invention that by reducing sound levels, it lessens or eliminates damage to the human ear.  
           [0037]    These and other objects, features and advantages of the present invention will become more apparent to one skilled in the art from the following description and claims when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    Having thus described the invention in general terms, the present invention will be better understood by reading the Detailed Description of the Preferred and Alternate Embodiments with reference to the accompanying drawing figures, which are not necessarily drawn to scale, and in which like reference numerals denote similar structures and refer to like elements throughout, and in which:  
         [0039]    [0039]FIG. 1 is a perspective view of a device according to a preferred embodiment of the present invention shown mounted on an All Terrain Vehicle.  
         [0040]    [0040]FIG. 2A is a side view of a device of the present invention, according to a preferred embodiment.  
         [0041]    [0041]FIG. 2B is a side view of a device of the present invention, according to an alternative embodiment, showing a modification to the outlet portion.  
         [0042]    [0042]FIG. 3A depicts an alternative embodiment of the invention in perspective view mounted on an All Terrain Vehicle.  
         [0043]    [0043]FIG. 3B is a side view of a device of the present invention, reflecting the alternative embodiment of FIG. 3A. 
     
    
     DETAILED DESCRIPTION  
       [0044]    In describing the preferred and alternate embodiments of the present invention, as illustrated in the Figures, specific terminology is employed for the sake of clarity. The invention, however, is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish similar functions.  
         [0045]    The present invention is suitable for reducing the sound level of exhaust emissions from internal combustion engines, particularly four-stroke internal combustion engines. While the present invention may be applied to other internal combustion engines, including two-stroke engines, the majority of sound from two-stroke engines emanates from the cylinder head and the exhaust system components themselves, rather than the exhaust gases and thus the reduction of noise by the present invention is less pronounced.  
         [0046]    Referring now to FIG. 1, muffling device  30  is preferably an elongated, generally cylindrically shaped tube, made for exemplary purposes only, of rubber, plastic, silicone rubber, metal or ceramic, or other suitable material. The tubing is of generally uniform diameter, but is not limited thereto. While of generally uniform diameter both internally and externally, the tubing is not limited thereto. Preferably the tube includes a fabric comprised of either synthetic or natural fiber woven and included into the material forming the tube. The tube must be of sufficient rigidity to hold its shape and position, and must be flexible enough to give when struck by objects on the travel surface. The tube must return to its original shape and position once the striking object is no longer in contact with it. While a generally cylindrical shape is preferred, other shapes could be utilized. Preferably muffling device  30  is installed on an ATV  10  as shown in FIG. 1, wherein first end  25  of muffling device  30  is dimensioned to enable adaptation to any known tailpipe  20  of a vehicle muffler  20 . Muffling device  30  is preferably configured with at least one bend  40  at a preferred approximate ninety-degree angle a suitable distance from rear of the vehicle to allow clearance, and is directed towards the ground surface  60  as seen FIG. 2A. Second end  50  of muffling device  30  is in close proximity to ground surface  60 , causing a reduction in sound level.  
         [0047]    For exemplary purposes only, the present invention was tested on a 2001 POLARIS™ SCRAMBLER™ series ATV and has been found to provide a significant reduction in exhaust noise, and thus overall noise, of the operation of this vehicle.  
         [0048]    It is noted that the quantity of sound reduction is a function of the character of the surface of the surrounding roadway, with grass surfaces providing the largest reduction, and rough dirt surfaces providing significant, but not as great as grass surface, reduction. While reduction could be achieved on hard surface roadways to some measure, it is less pronounced. Thus, with vehicular traffic on roadways, which is the typical mode of operation of internal combustion engines, there would not typically have been an opportunity to observe significant sound reduction and thus none would have been previously noted had the present invention been attempted therefor.  
         [0049]    It is particularly noted that when operating a vehicle equipped with the present invention, wildlife can be approached at a closer range than when operating without the muffling device. Deer, typically startled and seen running from a distance of about 100 feet, may be more closely approached, for example even as close as 30 feet, before they begin to run.  
         [0050]    In view of these observations of the unexpected benefits of the present invention, experiments were performed on the preferred embodiment, using a decibel meter and the results are shown in TABLE 1.  
                                                                     TABLE 1                       EXPERIMENTAL RESULTS       DECIBEL METER                   Slow speed conditions measured at distance of closest       approach of 8 feet                Stock muffler alone   82 dB           Muffler adapted with present invention   76 dB            Acceleration at full throttle from dead stop                Stock muffler alone   92 dB           Muffler adapted with present invention   88 dB            Stopped, snap opening of throttle                Stock muffler alone   89 dB           Muffler adapted with present invention   86 dB                                  
 
         [0051]    It is particularly noted that 85 dB is considered to be the threshold of sound at which damage begins to occur to a human ear, wherein hearing loss occurs when subjected to sound of this level for extended periods of time. Thus the ability of the present invention to reduce sound near this level or below advantageously lessens deterioration of hearing of individuals who are in close proximity to an internal combustion engine sound source.  
         [0052]    In determining the quantity of reduction of sound by the use of the present invention, it is instructive to calculate the reduction benefit derived from the use of the instant device. Decibel levels are logarithmic ratios; that is the ratio of the sound pressure is referenced to a standard sound pressure and the relative difference may be obtained. In the experimental results above for slow conditions, and a noise reduction from 82 dB to 76 dB, the reduction ratio derivation is as follows:  
         20 log  p   1   /p   0t =82  dB    
         20 log  p   2   /p   0t =76  dB,    
         [0053]    where p 0t  is the reference sound pressure, p 1  is the sound pressure under the test condition without the present invention and p 2  is the pressure recorded under the test condition using the present invention. Through calculation from the expressions above, a reduction in sound level of approximately 50% was obtained by use of the present invention at the experimental conditions reported.  
         [0054]    A second set of experiments were performed to determine the distance at which sound was no longer heard by a human observer from an operating ATV with and without a device of the present invention. For this test, the ATV was operated at a fixed speed around a central point, while the observer walked away from it. The test results are shown in TABLE 2.  
                                 TABLE 2                       EXPERIMENTAL RESULTS       SUBJECTIVE AUDIBILITY TEST       Audible distance test (point at which no further sound can be       detected, while ATV was driven at constant speed around a       fixed point)                                    Stock muffler alone   &gt;730   feet           Muffler adapted with present invention   312   feet                                  
 
         [0055]    Although sound was still observed with the stock muffler at a distance of 730 feet, due to lack of room to continue the distance test it was estimated from the above data that sound would disappear at approximately 830 feet.  
         [0056]    [0056]FIG. 2B shows the device with a modification thereto. In this alternate embodiment, muffing device  30  has, proximate to second end  50 , an expanded diameter area relative to body of muffling device  30 , wherein a cone-shaped region  70  is defined. The wide base of cone-shaped region  70  is positioned proximate to ground surface  60 , such that exhaust gases exit in close proximity to ground surface  60 , causing a sound muffling effect.  
         [0057]    It is contemplated in an alternative embodiment that second end  50  of muffling device  30  will define the shape of a rectangle at its opening, once again positioned proximate to ground surface  60 . It is further envisioned rectangular shape of second end  50  will be larger than the dimensions of the body of muffling device  30  itself, thus forming a pyramid shape, the base of which pyramid is facing the ground surface  60 .  
         [0058]    [0058]FIG. 3A shows an alternative embodiment, wherein first end  25  of muffling device  30  extends aft from existing muffler tail pipe  20  of an All Terrain Vehicle, but then traverses in arcuate bend  40  downward, such that it bends at an angle less than ninety degrees. Muffling device  30  may practically comprise a bend  40  through an angle between thirty and less than ninety degrees. By then cutting second end  50  of muffling device  30 , which is in proximity to the ground  60 , in a plane parallel to ground  60 , as shown in FIG. 3B, an oval opening in second end  50  of muffling device  30  is formed. A support member  80  is mounted to frame  5  of ATV  10  providing support by attaching to muffling device  30  by use of a clamping means  90 , and holds muffling device  30  at the correct angle. Support member  80  is secured to the frame  5  of ATV  10  by securing means  95 , typically in the form of a threaded nut.  
         [0059]    The tubing used for the present invention may be of any suitable material that is resistant to high temperatures, such as those described above, and may also be reinforced using a fabric of natural fibers or synthetic materials. In particular, high temperature silicone rubber hoses have been found most suitable. The material must be of a semi-rigid material, that is a material rigid enough to hold its form and position, yet flexible enough to give when obstructed by physical objects such as rocks in the travel path.  
         [0060]    In order to attach the tubing that comprises the muffling device  10  to the outlet pipe of the exhaust system of the internal combustion engine of an ATV, any suitable device, such as, for exemplary purposes only, a hose clamp, may be used.  
         [0061]    In an alternative embodiment, it is envisioned that muffling device  10  may be bent through other angles.  
         [0062]    It is further envisioned in an alternative embodiment that muffling device  10  may comprise more than one bend.  
         [0063]    In addition, in an alternative embodiment, muffling device  10  may comprise bends within its interior while having a straight form to its exterior.  
         [0064]    In an additional alternative embodiment, muffling device  10  may comprise a tube made from multiple components fitted together.  
         [0065]    In still further an alternative embodiment, muffling device  10  may be fabricated integrally to the exhaust outlet of the muffler of an internal combustion engine.  
         [0066]    Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only, and that various other alternatives, adaptations, and modifications may be made within the scope of the present invention. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Accordingly, the present invention is not limited to the specific embodiments illustrated herein, but is limited only by the following claims.