Patent Publication Number: US-7895832-B2

Title: Performance exhaust system

Description:
BACKGROUND 
     The invention relates to an exhaust system including a catalytic converter for motorcycle engines. 
     SUMMARY 
     In one construction, the invention provides an exhaust system for a motorcycle engine including a header having an upstream end adjacent a combustion chamber of the engine and having a downstream end opposite the upstream end. The exhaust system includes a catalytic converter positioned downstream of the combustion chamber and configured to improve the emissions quality of exhaust gases discharged from the combustion chamber. The exhaust system further includes a perforated section at least partially defining an exhaust passageway, the perforated section disposed adjacent the downstream end of the header. A resonator chamber is in fluid communication with the perforated section, the resonator chamber configured to allow expansion of the exhaust gases in the exhaust passageway through the perforated section. 
     In another aspect, the invention provides a motorcycle including an engine and components of the exhaust system described above. 
     In yet another aspect, the invention provides a muffler assembly for use with an engine. The muffler assembly has an upstream end for receiving exhaust gases from one or more headers and a downstream end for expelling exhaust gases to the atmosphere. The muffler assembly includes a sound-muffling section adjacent the downstream end and a catalytic converter having a quantity of catalyst capable of improving the emissions quality of the exhaust gases from the engine. An exhaust conduit at least partially defines an exhaust passageway upstream of the catalytic converter, the exhaust conduit having one or more apertures. A resonator chamber is configured to allow volumetric expansion of the exhaust gases within the exhaust passageway, the resonator chamber in fluid communication with the one or more apertures. The catalytic converter is positioned at the upstream end of the muffler assembly. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a motorcycle having an exhaust system embodying the present invention; 
         FIG. 2  is a partial cutaway perspective view of the exhaust system of  FIG. 1 . 
         FIG. 3  is a partial cutaway top view of a muffler assembly of the exhaust system shown in  FIG. 1 . 
         FIG. 4  is a partial cutaway side view of the muffler assembly of  FIG. 1 . 
         FIG. 5  is a graph representative of exhaust pressure versus crank angle illustrating the effect of the exhaust system of  FIG. 1 . 
         FIG. 6  is a graph representative of engine output versus engine speed illustrating the effect of the exhaust system. 
         FIG. 7  is a schematic view of another construction of an exhaust system embodying some aspects of the present invention. 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a motorcycle  10  having a twin-cylinder engine  14 . An air-fuel mixture is ignited in a combustion chamber (not shown) for each cylinder of the engine  14 . Following combustion in a given combustion chamber, the exhaust gases (containing mixed products of the combustion reaction and some residual, un-reacted components) are expelled through an exhaust port into an exhaust system  18  of the motorcycle. 
     The exhaust system  18 , as shown in  FIGS. 1-4 , includes brackets  20  for mounting to the motorcycle  10 . The exhaust system  18  includes a pair of header pipes (i.e., “headers”)  22 , a collector section  26 , a catalytic converter  30 , and a sound-muffling section  34 . The headers  22  are exhaust conduits leading directly from the engine  14 . The collector section  26 , catalytic converter  30 , and sound-muffling section  34  collectively define a muffler assembly  35 . 
     An upstream end  36 A of each header  22  is coupled to the engine  14  to receive exhaust gases from a respective exhaust port of the engine  14 . The headers  22  define exhaust flow passages that are separate from one another, each header  22  routing exhaust gases directly from an exhaust port of the engine  14  to a downstream exhaust component. A downstream end  36 B of each of the headers  22  leads into an upstream end  35 A of the muffler assembly  35 , specifically, the collector section  26 . The upstream end  35 A of the muffler assembly  35  is positioned generally forward of the engine  14 . The collector section  26  is an exhaust conduit defining a 2-into-1 exhaust flow passage joining the two separate exhaust flow passages of the headers  22  into a single, larger exhaust flow passage adjacent the catalytic converter  30 . Therefore, exhaust gases from both combustion chambers are treated by the catalytic converter  30 . 
     A connecting portion  35 C of the muffler assembly  35  is coupled to the upstream end  35 A to receive the exhaust gases from the upstream end  35 A, routing the exhaust gases from in front of the engine  14  along the underside of the engine  14  to a downstream end  35 B of the muffler assembly  35 . The downstream end  35 B, including the sound-muffling section  34 , is coupled to the connecting portion  35 C and positioned generally rearward of the engine  14 . A casing  35 D (made up of one or more pieces) extends from the upstream end  35 A to the downstream end  35 B, defining an outer surface of the muffler assembly  35 . 
     From the catalytic converter  30 , exhaust gases flow through a first passage of the connecting portion  35 C to the sound-muffling section  34 . As described above, the connecting portion  35 C extends longitudinally underneath the engine, but alternate shaping and positioning of the exhaust components on the motorcycle  10  are optional. The exhaust gases pass through the sound-muffling section  34  (changing direction at least twice) before exiting the muffler assembly  35  at a pair outlets  35 E, positioned at the downstream end  35 B. In some embodiments, at least a portion of the exhaust gases flow back from the sound-muffling section  34  into the connecting portion  35 C (into a resonator chamber, separate from the first passage of the connecting portion  35 C) before exiting the muffler assembly  35  at the outlets  35 E. 
     Returning now to the treatment of the exhaust gases at the upstream end  35 A, the catalytic converter  30  improves the emissions quality of the exhaust gases expelled from the engine  14  with the use of one or more known catalyst materials (referred to hereinafter simply as catalyst  38 ), which are contained within the catalytic converter  30 . The catalyst  38  reacts with undesirable exhaust gas components to produce more desirable products before being exhausted to the atmosphere via outlets  35 E. Specifically, nitrogen oxides (NO x ) can be converted to nitrogen (N 2 ) and oxygen (O 2 ), while carbon monoxide (CO) can be converted to carbon dioxide (CO 2 ). 
     The temperature of the catalyst  38  affects its performance. It is necessary to warm-up, or “light off”, the catalyst  38  above a minimum threshold temperature to obtain a desired level of performance from the catalytic converter  30  to effectively alter the undesirable exhaust gas components as described above. From a cold start of the engine  14 , the catalyst  38  is generally below the minimum threshold temperature, and therefore it is desirable to heat up the catalyst as quickly as possible to obtain sufficient or optimal performance. One way to get quicker light off of the catalyst  38  is to place the catalytic converter  30  close to the engine  14 , which is a source of heat via the hot exhaust gases flowing through the headers  22  to the catalytic converter  30 . 
     However, placing the catalytic converter  30  at the downstream ends  36  of the headers can have an undesirable effect on the exhaust gas pressure dynamics as compared to a placement further downstream. The undesirable effect can be somewhat reduced by using multiple catalytic converters  30  in parallel. However, the use of multiple catalytic converters  30  causes an undesirable increase in catalyst light off time (in addition to increasing cost, size, and weight). Regardless of its position in the exhaust system  18 , the catalyst  38  is a substantial obstruction in the flow passage and therefore, causes a sudden increase in flow resistance at its upstream end. This causes a positive pressure exhaust wave or pulse to be reflected back towards the engine  14  through the headers  22 . The dynamics of the exhaust gases coming from the engine  14  and the reflected waves moving towards the engine impacts the engine performance (i.e., horsepower and torque output). 
     Under certain operating conditions, a reflected exhaust pulse hinders the exhaust scavenging process as well as the ability for the cylinder to become charged with fresh intake air (which can also affect the input of fuel into the cylinder). If the exhaust wave that is reflected off the catalyst  38  arrives at either combustion chamber during valve overlap (the time that both the intake and exhaust valves are open), there is a significant performance loss due to decreased volumetric efficiency. With high exhaust gas pressure downstream of the combustion chamber, the net pressure differential that draws fresh air into the cylinder is reduced. Hence, less air and fuel fills the cylinder, and volumetric efficiency is spoiled, resulting in a “hole” in horsepower and torque output. The reduced output occurs over the range of engine speeds where the positive exhaust wave returns during valve overlap. Generally, a longer distance between the cylinders and the catalyst  38  results in power loss at lower engine speeds, and a shorter distance between the cylinders and the catalyst  38  results in power loss at higher engine speeds. 
     In the exhaust system  18 , the catalytic converter  30  is positioned within the first half of the total exhaust gas flow length between the engine  14  and the outlets  35 E. Furthermore, as shown in  FIGS. 2-4 , at least a portion of the collector section  26  is positioned within a resonator chamber  42 . Furthermore, the resonator chamber  42  substantially surrounds or encloses the catalytic converter  30 . In the illustrated embodiment, the catalytic converter  30  is entirely circumferentially enclosed within the resonator chamber  42  along the full length of the catalytic converter  30 . In some embodiments, the resonator chamber  42  does not fully surround or enclose the catalytic converter  30 , but rather is adjacent to or partially surrounding the catalytic converter  30 . One or more apertures or openings  46  define a perforated section  50  fluidly coupling the exhaust flow passage of the collector section  26  with the resonator chamber  42 , thus providing an expansion in the flow passage at the perforated section  50 . As shown in  FIGS. 2-4 , the openings  46  are circular in shape and are equally-spaced around the circumference of the collector section  26 . The openings  46  may have other shapes and/or other orientations in other embodiments. 
     The resonator chamber  42  serves a “dead end” expansion volume in that the only passageways into and out of the resonator chamber  42  are the openings  46 . Thus, all the exhaust gases that enter the resonator chamber  42  through the openings  46  eventually flow out of the resonator chamber  42  through the openings  46  and subsequently pass through the catalytic converter  30 . On the other hand, the exhaust gases that do not enter the resonator chamber  42  can pass directly into and through the catalytic converter  30 . Flow into the catalytic converter  30  is unobstructed in that there are no physical obstructions to prevent exhaust flow straight from the headers  22  and through the catalytic converter  30 , only the flow-restrictive nature of the catalytic converter  30 , itself. 
     In the illustrated embodiment, the collector section  26  does not form a substantial length of the exhaust system  18 . This is in contrast to an exhaust system with a long collector section, which typically runs from the front or alongside the engine to a location rearward of the engine. Rather, the collector section  26  of the illustrated exhaust system  18  serves to consolidate the exhaust gas flow passages of the headers  22  over a short length such that the perforated section  50  and the catalytic converter  30  are positioned at or substantially adjacent the downstream ends  36  of each of the headers  22  and within about the first 40% of the total flow length between the engine exhaust ports and the outlets  35 E. For example, the length from the rear cylinder exhaust port to the perforated section  50  is about 612 millimeters, and the length from the perforated section  50  to the outlets  35 E is about 950 millimeters. 
     The above description highlights some of the difficulties with simply taking a catalytic converter from a downstream location and moving it to a far upstream location for quicker light off. The resonator chamber  42  and the perforated section  50  of the present invention enable both quick light off and satisfactory power output of the engine  14 . 
     When the exhaust valve (not shown) of one cylinder opens, a high pressure wave propagates down the associated header pipe  22 . When this wave arrives at the perforated section  50 , its pressure is dissipated by the expansion of the resonator chamber  42 . A secondary wave (the remaining component of the original high pressure wave) is incident on the catalyst  38 . A portion of the secondary wave of exhaust gases passes through the catalytic converter  30  to the muffler sound-muffling section  34 . The portion of the secondary wave that does not go through the catalytic converter  30  is reflected off the catalyst  38  and back toward the engine  14 . Before propagating to the upstream ends  36 A of the headers  22 , the pressure of the reflected wave is further diminished by expansion that occurs as the reflected wave encounters the perforated section  50 . Therefore, the reflected wave that eventually makes it back toward the engine  14  is dissipated through expansions at the perforated section  50  (in addition to the portion which is passed through the catalytic converter  30 ). In addition to dissipation, a wave cancellation effect occurs under certain operating conditions and is tuned at least in part by the number of openings  46  and the size of the volume within the resonator chamber  42 . In the occurrence of wave cancellation, two waves traveling in opposite directions are incident upon one another and at least one of the waves is cancelled out. For example, a wave of fresh exhaust gases from the engine  14  can cancel the effect of a reflected wave traveling from the collector section  26  toward the engine  14 . 
     In the twin-cylinder engine  14  of the illustrated embodiment, in which both cylinders feed the single catalytic converter  30 , the reflected wave off of the catalyst  38  is split at the collector section  26  and continues up both header pipes  22 . In any exhaust configuration with multiple header pipes feeding a single catalytic converter, the reflected wave off of the catalyst is split at the collector among the header pipes. Therefore, the combination of the perforated section  50  and the resonator chamber  42  can deliver particularly good performance in twin-cylinder, shared exhaust setups, such as on the motorcycle  10  of  FIG. 1 . Although the exhaust system  18  is shown and primarily described for operation with a 2-into-1 setup, it is also useful for single-cylinder engines, and multi-cylinder engines with separated or shared exhaust systems. 
       FIGS. 5 and 6  illustrate the enhanced performance afforded by features of the exhaust system  18 .  FIG. 5  is a computer-simulated graph representative of exhaust pressure (at the port) versus crankshaft angle of the engine  14  while operating at a relatively high engine speed, such as 8000 RPM. One pressure plot in  FIG. 5  is for a baseline configuration with a catalytic converter positioned similarly to the catalytic converter  30  in the muffler assembly  35  of the illustrated exhaust system  18 . The baseline configuration, which is represented by a solid line, does not include the perforated section  50  or the resonator chamber  42 , but is otherwise identical to the illustrated exhaust system  18 . A second pressure plot in  FIG. 5 , indicated by the dashed line, is for the engine  14  with the exhaust system  18 , including the perforated section  50  and the resonator chamber  42 . The plots on the graph of  FIG. 5  illustrate the effect of a reflected exhaust wave arriving at the exhaust port during valve overlap, generally around top dead center (TDC, 360 degrees as indicated in  FIG. 5 ). The exhaust system  18  having the perforated section  50  and the resonator chamber  42  experiences a much lower exhaust pressure during valve overlap. The comparatively high exhaust pressure during valve overlap for the baseline configuration leads to decreased volumetric efficiency and decreased engine output as described above. Due to the location of the catalytic converter  30  adjacent the downstream ends  36  of the headers  22  (i.e., short exhaust length between the engine  14  and the catalyst  38 ), the reflected exhaust wave is present at the exhaust port during valve overlap at these relatively high engine speeds. 
       FIG. 6  is a computer-simulated graph illustrating the resulting power loss for an engine operating at speeds at which a reflected exhaust wave arrives at the exhaust port during valve overlap. The solid line on the graph of  FIG. 6  represents the engine  14  with the theoretical baseline configuration described above, which serves as a basis for comparison. The dashed line represents the engine  14  with the illustrated exhaust system  18 , including the perforated section  50  and the resonator chamber  42 . Between 5500 rpm and 9000 rpm, the perforated section  50  and the resonator chamber  42  of the exhaust system  18  allow the engine to generate between 2 and 4 more horsepower. This represents up to about a 5 percent increase in power (measured at about 6000 rpm). 
       FIG. 7  illustrates another construction of an exhaust system  80  having a pair of headers  82 , a resonator chamber  84 , a catalytic converter  86 , a perforated section  88  associated with each of the headers  82 , and a sound-muffling portion  89 . A collector section  90  combines two exhaust flow passages defined by the headers  82  into a single exhaust flow passage. The perforated sections  88  fluidly couple the header exhaust flow passages with an interior volume of the resonator chamber  84 . The resonator chamber  84  is configured to surround the collector section  90 , the perforated sections  88 , and the catalytic converter  86 . In alternate embodiments, the catalytic converter  86  is either positioned outside the resonator chamber  84  or positioned partially within the resonator chamber  84 . 
     The perforated sections  88  are defined by one or more openings or apertures  92  in each of the headers  82 . The openings  92  are circular and equally-spaced around circumferences of the headers  82  in the illustrated embodiment, but other shapes and orientations are possible. Although the exhaust system  80  of  FIG. 7  differs from the exhaust system  18  of  FIGS. 2-4  by positioning of the perforated sections  88  in the headers  82  rather than the single perforated section  50  in the collector section  26 , the location of the perforated sections  88  with respect to the catalytic converter  86  is generally the same as in the exhaust system  18 . Because the perforated sections  88  are positioned at the downstream ends of the headers  82  and because the collector section  90  does not span a considerable length, the catalytic converter  86  is immediately downstream of the perforated sections  88 . The exhaust system  80  operates with the engine  14  to have similar operation and performance as the exhaust system  18  described above. 
     In addition to having two separate perforated sections  88 , the exhaust system  80  of  FIG. 7  differs from the exhaust system  18  of  FIGS. 2-4  by being positioned substantially alongside the engine  14 , rather than underneath the forward portion of the engine  14 . The aspects of mounting to the side of the engine  14  and having two perforated sections  88  do not have to be incorporated together, but are both included in  FIG. 7  for clarity. Either one of the design aspects of  FIG. 7  can be incorporated with the exhaust system  18  of  FIGS. 2-4  without the other. 
     The areas  94  indicated by the arrows in  FIG. 7  represent alternate locations for the perforated sections  88 . Rather than forming the openings  92  only in the headers  82 , additional openings  92  may be formed in the collector section  90 . This location of the perforated sections  88  is somewhat of a hybrid of the exhaust system  18  of  FIGS. 2-4  and the exhaust system  80  of  FIG. 7  in that there are multiple perforated sections  88  that are formed in the collector section  90 .