Abstract:
An exhaust system for exhausting multiple cylinders of a small engine, wherein the exhaust system includes a plurality of exhaust units is described herein. Each exhaust unit of the exhaust system is operatively and fluidly connected to a separate cylinder of the small engine such that the exhaust gases from each cylinder remain separated as they pass through different exhaust units of the exhaust system. The exhaust system includes a canister having opposing end walls to define a volume therein. The exhaust system further includes at least two exhaust units, and each exhaust unit includes an inlet that is operatively and fluidly connected to a cylinder of the small engine, a primary chamber within the canister into which exhaust gases are introduced by the inlet, a primary stage transfer tube located at least partially within the primary chamber for fluidly connecting the primary chamber with an outlet through which exhaust gases are exhausted from the exhaust system. Each of the exhaust units is separated by an inner chamber wall that is shared by adjacent exhaust units yet prevents fluid communication between the adjacent exhaust units.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/311,965, filed Mar. 9, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to exhaust systems. More particularly, the invention relates to an exhaust system for a multi-cylinder internal combustion engine. 
       BACKGROUND 
       [0003]    Traction drive machines having small internal combustion engines, such as powered machines used for lawn care, commonly employ exhaust systems to convey the exhaust gas from the engine cylinders to the ambient environment. Small internal combustion engines are typically defined as engines having 25 horsepower or less. 
         [0004]    Small engines have higher concentrations of exhaust gas constituents requiring conversion. This is a result of the richer air:fuel ratios required in small engines for successful operation and engine cooling. The compact size of the exhaust catalyst, the high specific throughput (about 10 times higher than automotive), and the high concentration of emission constituents result in high heat generation rates and high catalyst temperatures. 
         [0005]    These exhaust systems typically do not include means to control the effects of “off nominal” conditions of engines. Off nominal conditions can be described as when one or more cylinders are not functioning properly (or optimally) such that the air:fuel exhaust gas mixtures entering the exhaust system are combustible mixtures and create excessively high exhaust gas and system temperatures if ignited. Sources of off nominal conditions include ignition misfiring, air:fuel cylinder-to-cylinder imbalance, and mechanical malfunction of an intake or exhaust valve. Sources of ignition include hot exhaust catalysts and exhaust gasses from a nominal cylinder. 
         [0006]    Therefore, off nominal conditions are very dangerous when the exhaust gasses from multiple cylinders are allowed to mix because the high exhaust gas and system temperatures from a nominal cylinder could ignite an unburned fuel mixture from an off nominal cylinder and cause unintended combustion and flames. For example, a V-twin air-cooled two cylinder engine with a dual-inlet single-outlet exhaust with catalysts normally has an exhaust gas temperature of 1350° F. However, if one sparkplug is caused to miss-fire, an unignited fuel:air exhaust gas mixture enters an exhaust chamber, mixes with ignited exhaust gasses from nominal cylinders, and ignites, which causes the exhaust gases to increase 1020° F. in 10 seconds to 2370° F. Further, off nominal conditions increase the risk of a meltdown of the catalyst substrate, which can result in catalytic deactivation and severe exhaust restriction. 
         [0007]    The exhaust temperatures which occurred during off nominal conditions in the scenario described above would be even higher if small engine designers attempted to achieve catalyst efficiencies approaching those of automotive catalysts. The high exhaust gas concentrations and high space velocities produced by a higher efficiency catalyst could create even higher heat loads and temperatures. Thus, in the scenario described above, it is necessary to limit the initial catalyst efficiency to protect the engine and exhaust system. 
         [0008]    It is known that some engine fuel management systems include oxygen sensors or temperature sensors that intend to limit the effects of off nominal conditions found during operation of engines, but these are typically expensive and create a machine control issue by reducing the overall engine power as quickly as possible when an off nominal condition is detected. 
         [0009]    Accordingly, a need exists for an inexpensive exhaust system that reduces the dangers of off nominal conditions. 
       SUMMARY OF INVENTIVE FEATURES 
       [0010]    In one aspect of the present invention, an exhaust system for exhausting exhaust gases from a small engine having multiple cylinders is provided. The exhaust system includes at least two exhaust units. Each of said exhaust units includes a primary chamber, an inlet, an outlet, a primary stage transfer tube, and a catalyst. The inlet is fluidly connected to the primary chamber for introducing exhaust gases into the primary chamber. The outlet is fluidly connected to the primary chamber for exhausting exhaust gases from the primary chamber. At least a portion of the primary stage transfer tube is located within the primary chamber, and the primary stage transfer tube fluidly connects the primary chamber with the outlet. The catalyst is located within the primary chamber between the inlet and the outlet. Exhaust gases pass through the catalyst as the exhaust gases flow from the inlet to the outlet. Each of the at least two exhaust units is separated from at least one other of the at least two exhaust units by a common chamber wall, wherein the chamber wall maintains separation between exhaust gases flowing through each of the at least two exhaust units. 
         [0011]    In another aspect of the exhaust system of the present invention described above, at least two of the at least two exhaust units are disposed immediately adjacent to each other. 
         [0012]    In another aspect of the exhaust system of the present invention described above, the catalyst is disposed about a portion of the primary stage transfer tube, wherein the exhaust gases introduced into the primary chamber by way of the inlet pass through the catalyst prior to entering the primary stage transfer tube. 
         [0013]    In another aspect of the exhaust system of the present invention described above, the catalyst is disposed within the primary stage transfer tube, wherein the exhaust gases exiting the primary chamber pass through the catalyst prior to entering the outlet. 
         [0014]    In another aspect of the exhaust system of the present invention described above, the exhaust system further includes a canister, wherein at least a portion of the canister forms an outer wall of the primary chamber of each of the at least two exhaust units. 
         [0015]    In another aspect of the exhaust system of the present invention described above, at least one of the at least two exhaust units further comprises a secondary chamber located adjacent to the primary chamber, wherein the primary stage transfer tube fluidly connects the primary chamber and the secondary chamber. 
         [0016]    In another aspect of the exhaust system of the present invention described above, the primary stage transfer tube of at least one of the plurality of exhaust units directly fluidly connects the primary chamber to the outlet such that the exhaust gases are transferrable directly from the primary chamber to the outlet. 
         [0017]    In another aspect of the exhaust system of the present invention described above, the primary stage transfer tube of at least one of the plurality of exhaust units fluidly connects the primary chamber to the outlet such that the exhaust gases are transferrable indirectly from the primary chamber to the outlet such that the exhaust gases change direction of flow as the exhaust gases flow from the primary stage transfer tube to the outlet. 
         [0018]    In yet another aspect of the present invention, an exhaust system for exhausting exhaust gases from a small engine having multiple cylinders is provided. The exhaust system includes a plurality of exhaust units. Each of the exhaust units includes a primary chamber, an inlet, a secondary chamber, a primary stage transfer tube, an outlet, and a catalyst. The inlet is fluidly connected to the primary chamber for introducing exhaust gases into the primary chamber. At least a portion of the primary stage transfer tube is located within the primary chamber and at least a portion of the primary stage transfer tube is located within the secondary chamber. The primary stage transfer tube fluidly connects the primary chamber with the secondary chamber. The outlet is fluidly connected to the secondary chamber for exhausting the exhaust gases. The catalyst is located between the inlet and the outlet, wherein the exhaust gases are passable through the catalyst as the exhaust gases flow from the inlet to the outlet. 
         [0019]    In another aspect of the exhaust system of the present invention described above, each of the plurality of exhaust units is separable from another of the plurality of exhaust units by a shared chamber wall. 
         [0020]    In another aspect of the exhaust system of the present invention described above. 
         [0021]    In still another aspect of the present invention, an exhaust system for exhausting exhaust gases from a small engine having multiple cylinders is provided. The exhaust system includes an elongated canister, a first exhaust unit, and a second exhaust unit. The elongated canister is formed of a substantially cylindrical skin, a first end wall and an opposing second end wall enclosing a volume therein. The first exhaust unit includes a first inlet, a first outlet, and a first catalyst, wherein an inner chamber wall is located within the cylindrical skin. The inner chamber wall, the first end wall, and a portion of the skin of the first exhaust unit define a first exhaust volume therein, and the first catalyst is located within the first exhaust volume. The first inlet and the first outlet operatively connected to the skin and fluidly connected to the first exhaust volume such that exhaust gases are introducible into the first exhaust volume through the first inlet. The exhaust gases are passable through the first catalyst when flowing from the first inlet to the first outlet, and the exhaust gases are exhaustible from the first exhaust volume through said the inlet. The second exhaust unit includes a second inlet, a second outlet, and a second catalyst, wherein the inner chamber wall disposed within the cylindrical skin, the second end wall, and a portion of the skin define a second exhaust volume therein. The second exhaust volume is located immediately adjacent to and separate from the first exhaust volume. The second inlet and the second outlet are operatively connected to the skin and fluidly connected to the second exhaust volume such that exhaust gases are introducible into the second exhaust volume through the second inlet and the exhaust gases are exhaustible from the second exhaust volume through the second outlet. The exhaust gases introducible into the first exhaust volume remain separate from exhaust gases introducible into the second exhaust volume by the inner chamber wall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The structure, operation, and advantages of the presently disclosed embodiment of the invention will become apparent when consideration of the following description taken in conjunction with the accompanying drawings wherein: 
           [0023]      FIG. 1  is a perspective view of one embodiment in accordance with the present invention. 
           [0024]      FIG. 2  is a perspective view of  FIG. 1  with the skin of the canister removed. 
           [0025]      FIG. 3  is a perspective view of a second embodiment in accordance with the present invention with the skin of the canister removed. 
           [0026]      FIG. 4  is a perspective view of a third embodiment in accordance with the present invention with the skin of the canister removed. 
           [0027]      FIG. 5  is a perspective view of a fourth embodiment in accordance with the present invention with the skin of the canister removed. 
           [0028]      FIG. 6  is a perspective view of a fifth embodiment in accordance with the present invention. 
       
    
    
       [0029]    Corresponding reference characters indicate corresponding parts throughout the views of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Reference will now be made in detail to various and alternative exemplary embodiments and to the accompanying drawings, with like numerals representing substantially identical structural elements. Each example is provided by way of explanation and not as a limitation. In fact, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope or spirit of the disclosure and claims. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure includes modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0031]      FIG. 1  shows an embodiment of exhaust system  100  having exhaust system inlets  102  and  202 , canister  150 , and outlets  135  and  235 . It is contemplated that inlets  102  and  202  can be headpipes or be in flow communication with headpipes. In the preferred embodiment, inlets  102  and  202  are headpipes of essentially the same length and diameter. It is contemplated that outlets  135  and  235  can be tailpipes or be in flow communication with tailpipes. In the preferred embodiment, outlets  135  and  235  are tailpipes. 
         [0032]      FIG. 2  shows exhaust system  100  with the skin of canister  150  removed. In this embodiment, exhaust system  100  has two exhaust units  101  and  201 . Exhaust units  101  and  201  include the volume within the skin of the canister ( FIG. 1 ) and are separated by inner chamber wall  145 , which prevents the mixing of exhaust gasses from exhaust units  101  and  201 . It is contemplated that other embodiments of exhaust system  100  may have two or more exhaust units to correspond to the same number of cylinders as the engine to which it is attached. 
         [0033]    Exhaust unit  101  includes an inlet  102 , outlet  135 , primary chamber  115 , and secondary chamber  120 . Inlet  102  is in fluid communication with the primary chamber  115  of exhaust unit  101  for introducing exhaust gases from the engine into the primary chamber  115 . Primary chamber  115  contains catalyst  110  and at least a portion of a primary stage transfer tube  105  therein. The primary stage transfer tube  105  extends between the primary chamber  115  and the secondary chamber  120  and fluidly connects these chambers. Exhaust gasses are exhaustible from the secondary chamber  120  into the atmosphere through outlet  135 . It is contemplated that primary chamber  115  and secondary chamber  120  can be various sizes and can be equipped with various configurations of baffles that reflect and absorb selected sound power while maintaining separation of exhaust gasses. 
         [0034]    In operation, exhaust gasses are introduced from a first internal combustion engine cylinder (not shown) into the primary chamber  115  of exhaust unit  101  through the inlet  102 . Primary chamber  115  is defined by the first chamber wall  130 , inner chamber wall  145 , and a portion of the skin of canister  150 . The exhaust gasses then exit the inlet  102 , pass through the catalyst  110 , and then enter a first end of the primary stage transfer tube  105 . In the preferred embodiment, exhaust gasses enter primary stage transfer tube  105  through helical perforations  106  which cause the direction of flow of the exhaust gasses to turn. Primary stage transfer tube  105  extends between the primary chamber  115  and the secondary chamber  120  to fluidly connect these chambers and allow exhaust gasses to flow through the first chamber wall  130  that separates the primary and secondary chambers  115 ,  120 . In the preferred embodiment, catalyst  110  is located as close as practical to inlet  102 , and more particularly, the catalyst  110  is located between the skin of canister  150  and the outside of primary transfer tube  105 . In an alternative embodiment depicted in  FIG. 3 , catalyst  110  is located within a portion of the primary stage transfer tube  105  disposed within the primary chamber  115 , and exhaust gasses pass through catalyst  110  while flowing through primary stage transfer tube  105  en route to secondary chamber  120 . Secondary chamber  120  is defined by the first chamber wall  130 , a portion of the skin of canister  150 , and a first end wall  125 . The exhaust gasses exit secondary chamber  120  through the outlet  135 . 
         [0035]    Exhaust unit  201  includes an inlet  202 , outlet  235 , primary chamber  215 , and secondary chamber  220 . Inlet  202  is in fluid communication with the primary chamber  215  of exhaust unit  201  for introducing exhaust gases from the engine into the primary chamber  215 . Primary chamber  215  contains catalyst  210  and at least a portion of a primary stage transfer tube  205  therein. The primary stage transfer tube  205  extends between the primary chamber  215  and the secondary chamber  220  and fluidly connects these chambers. Exhaust gasses are exhaustible from the secondary chamber  220  into the atmosphere through outlet  235 . It is contemplated that primary chamber  215  and secondary chamber  220  can be various sizes and can be equipped with various configurations of baffles that reflect and absorb selected sound power while maintaining separation of exhaust gasses. 
         [0036]    In operation, exhaust gasses are introduced from a first internal combustion engine cylinder (not shown) to the primary chamber  215  of exhaust unit  201  through the inlet  202 . Primary chamber  215  is defined by a first chamber wall  230 , inner chamber wall  145 , and a portion of the skin of canister  150 . The exhaust gasses then exit the inlet  202 , pass through the catalyst  210  and then enter a first end of the primary stage transfer tube  205 . In the preferred embodiment, exhaust gasses enter primary stage transfer tube  205  through helical perforations  206  which cause the direction of flow of the exhaust gasses to turn. Primary stage transfer tube  205  extends between the primary chamber  215  and the secondary chamber  220  to fluidly connect these chambers and allow exhaust gasses to flow through the first chamber wall  230  that separates the primary and secondary chambers  215 ,  220 . In the preferred embodiment, catalyst  210  is located as close as practical to inlet  202 , and more particularly, the catalyst  210  is located between the skin of canister  150  and the outside of primary transfer tube  205 . In an alternative embodiment depicted in  FIG. 3 , catalyst  210  is located within a portion of the primary stage transfer tube  205  disposed within the primary chamber  215 , and exhaust gasses pass through catalyst  210  while flowing through primary stage transfer tube  205  en route to secondary chamber  220 . Secondary chamber  220  is defined by the first chamber wall  230 , a portion of the skin of canister  250 , and a second end wall  225 . The exhaust gasses exit secondary chamber  220  through outlet  235 . 
         [0037]    In some embodiments, tail pipes  135  and  235  are equipped with permanent or removable spark arrestors  140  and  240 , which can reduce the emission of carbon particles and flames from outlets  135  and  235 . In the preferred embodiment, exhaust gasses enter the outlets  135  and  235  through helical perforations  136  and  236  which cause the direction of flow of the exhaust gasses to turn. Additionally, in some embodiments, outlets  135  and  235  are fixed in place, while in other embodiments, outlets  135  and  235  are removable, which simplifies periodic cleaning. 
         [0038]    As can be seen, it is contemplated that catalysts  110  and  210  can be a variety of shapes and may be placed in various locations between inlets  102  and  202  and outlets  135  and  235 . Further, it is contemplated that some embodiments of exhaust system  100  may not use catalysts. 
         [0039]    Because exhaust units  101  and  201  are not in fluid communication with each other within the canister, exhaust gasses within exhaust units  101  and  201  do not mix within the volume defined by the canister. This separation of exhaust gasses prevents the creation of a thermal run-away during an off nominal condition in which exhaust gasses from different cylinders mix and ignite, potentially reaching a temperature of over 2300° F. 
         [0040]    Under certain circumstances, unignited exhaust gasses can ignite when passing through catalysts  110  and  210 . In some embodiments, outlets  135  and  235  are aligned with primary stage transfer tubes  105  and  205 , as is shown in  FIG. 4 , which does little to hinder any flames passing through primary stage transfer tubes  105  and  205  from exiting outlets  135  and  235 . However, as depicted in  FIGS. 3 and 4  outlets  135  and  235  in other embodiments are oriented at an angle relative to the primary stage transfer tubes  105  and  205 , which forces any resulting flames exiting primary stage transfer tube  105  and  205  to change direction prior to exiting outlet  135  and  235 . Further, helical perforations  136  and  236  in outlets  135  and  235  require the flames to turn an additional 180 degrees in order to enter outlets  135  and  235 . These additional turns and length that the exhaust must travel serves to quench the flames and stop the reaction in the catalysts. 
         [0041]    Further, tests have shown that exhaust gasses emitted from embodiments of exhaust system  100  containing non-optimized catalysts have HC+NO X  readings of 4.90, which approach the Blue Sky emissions level of 4.0. Accordingly, since exhaust system  100  reduces the dangers of off nominal conditions, the catalyst efficiency can be increased and optimized to achieve a Blue Sky HC+NO X  emissions level. 
         [0042]      FIG. 5  shows another embodiment of exhaust system  100  with the skin of canister  150  removed. In this embodiment, exhaust system  100  has two exhaust units  101  and  201 . Exhaust units  101  and  201  are separated by inner chamber wall  145 , which prevents the mixing of exhaust gasses from exhaust units  101  and  201 . 
         [0043]    Exhaust unit  101  includes an inlet  102 , an outlet  135 , and primary chamber  115 . Inlet  102  is in fluid communication with the primary chamber  115  of exhaust unit  101  for introducing exhaust gases from one cylinder of the engine (not shown) into the primary chamber  115 . Primary chamber  115  contains catalyst  110  and at least a portion of the primary stage transfer tube  105  therein. Outlet  135  vents exhaust gasses into the environment and can be an extension of primary stage transfer tube  105 . It is contemplated that outlet  135  can be removable or fixed to canister  150 . It is contemplated that primary chamber  115  can be various sizes and can be equipped with various configurations of baffles that reflect and absorb selected sound power while maintaining separation of exhaust gasses. 
         [0044]    In operation, exhaust gasses are introduced from a first internal combustion engine cylinder (not shown) into the primary chamber  115  of exhaust unit  101  through inlet  102 . Primary chamber  115  is defined by the first chamber wall  130 , inner chamber wall  145 , and a portion of the skin of canister  150 . The exhaust gasses then exit the inlet  102 , pass through catalyst  110 , and then enter a first end of the primary stage transfer tube  105 . In the preferred embodiment, exhaust gasses enter primary stage transfer tube  105  through helical perforations  106  which cause the direction of flow of the exhaust gasses to turn. Primary stage transfer tube  105  extends between the primary chamber  115  and the outlet  135  and fluidly connects the primary chamber  115  with the outlet  135  to allow exhaust gasses to flow through the first chamber wall  130  and into outlet  135  through which exhaust gasses into the environment. In the preferred embodiment, catalyst  110  is situated as close as practical to inlet  102  and located between the skin of canister  150  and the outside of primary stage transfer tube  105 . 
         [0045]    Exhaust unit  201  includes an inlet  202 , outlet  235 , and primary chamber  215 . Inlet  202  is in fluid communication with the primary chamber  215  of exhaust unit  201  for introducing exhaust gases from the engine into the primary chamber  215 . Primary chamber  215  contains catalyst  210  and at least a portion of the primary stage transfer tube  205  therein. Outlet  235  vents exhaust gasses into the environment and can be an extension of primary stage transfer tube  205 . It is contemplated that outlet  235  can be removable or fixed to canister  150 . It is contemplated that primary chamber  215  can be various sizes and can be equipped with various configurations of baffles that reflect and absorb selected sound power while maintaining separation of exhaust gasses. 
         [0046]    In operation, exhaust gasses are introduced from a first internal combustion engine cylinder (not shown) into the primary chamber  215  of exhaust unit  201  through inlet  202 . Primary chamber  215  is defined by the first chamber wall  230 , inner chamber wall  145 , and a portion of the skin of canister  150 . The exhaust gasses then exit the inlet  102 , pass through the catalyst  210 , and then enter a first end of the primary stage transfer tube  205 . In the preferred embodiment, exhaust gasses enter primary stage transfer tube  205  through helical perforations  206  which cause the direction of flow of the exhaust gasses to turn. Primary stage transfer tube  205  extends between the primary chamber  115  and the outlet  235  to fluidly connect these members and allow exhaust gasses to flow through the first chamber wall  230  and into outlet  235  through which exhaust gasses enter the environment. In the preferred embodiment, catalyst  210  is located as close as practical to inlet  202 , and more particularly, the catalyst  210  is located between the skin of canister  250  and the outer surface of primary stage transfer tube  205 . 
         [0047]    Further, as depicted in  FIGS. 2-5 , it is contemplated that canister  150  contains the primary chambers, and secondary chambers if present, of each exhaust unit that comprise exhaust system  100 . It is further contemplated that the first and second exhaust units  101 ,  201  are located immediately adjacent to each other, and if the exhaust system includes more than two exhaust units, each of the exhaust units is located immediately adjacent to at least one other exhaust unit and separated therefrom by an inner chamber wall  145 . 
         [0048]    In  FIG. 6  it is contemplated that some embodiments of exhaust system  100  include shroud  160  which covers and surrounds exhaust system inlets  102  and  202 , canister  150 , and at least a portion of outlets  135  and  235 . Shroud  160  has air intakes  165  and  170  and air egresses  175  and  275 , which promote air circulation under shroud  160 , thereby reducing the temperature of exhaust system  100  and exhaust gasses and providing for flame quenching during off-nominal conditions. This system also provides for exhaust dilution to further reduce the average temperature of the exhaust. 
         [0049]    While this invention has been described in conjunction with the specific embodiments described above, it is evident that many alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the preferred embodiments of this invention, as set forth above are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of this invention.