Motorcycle exhaust system

Abstract

An exhaust system for a motorcycle engine includes a muffler assembly. The muffler assembly includes a downstream attenuation portion adapted to be positioned substantially rearward of the motorcycle engine and having a first height, an upstream portion adapted to be positioned substantially forward of the motorcycle engine and having a second height, and an intermediate attenuation portion between the upstream portion and the downstream attenuation portion. The intermediate attenuation portion is adapted to be positioned substantially below the motorcycle engine and has a third height less than half the first height. In some embodiments, a motorcycle is provided, in which the motorcycle engine is positioned substantially within a recess of the muffler assembly to a depth greater than the third height.

1 . A muffler assembly for a motorcycle engine, the muffler assembly comprising:
 a downstream attenuation portion adapted to be positioned substantially rearward of the motorcycle engine and having a first height;   an upstream portion adapted to be positioned substantially forward of the motorcycle engine and having a second height; and   an intermediate attenuation portion between the upstream portion and the downstream attenuation portion, the intermediate attenuation portion being adapted to be positioned substantially below the motorcycle engine and having a third height less than half the first height.   
   
   
       2 . The muffler assembly of  claim 1 , further comprising a shell encasing the upstream portion, the downstream attenuation portion, and the intermediate attenuation portion. 
   
   
       3 . The muffler assembly of  claim 1 , wherein the upstream portion includes a catalytic converter. 
   
   
       4 . The muffler assembly of  claim 1 , wherein the downstream attenuation portion includes first, second, and third bulkheads at least partially defining first, second, and third chambers. 
   
   
       5 . The muffler assembly of  claim 1 , wherein the intermediate attenuation portion includes a chamber configured to receive exhaust gases from the downstream attenuation portion. 
   
   
       6 . The muffler assembly of  claim 1 , wherein the third height is about 33 percent of the first height and about 40 percent of the second height. 
   
   
       7 . A motorcycle comprising:
 an engine;   a transmission coupled to the engine and configured to receive power from the engine;   a rear wheel coupled to the transmission and configured to receive engine power through the transmission; and   a muffler assembly coupled to the engine and in communication therewith to receive exhaust gases from the engine, the muffler assembly including
 a downstream attenuation portion positioned between the transmission and the rear wheel, and 
 an intermediate attenuation portion positioned forwardly of the downstream attenuation portion, the intermediate attenuation portion extending along an underside of the engine. 
   
   
   
       8 . The exhaust system of  claim 7 , further comprising an upstream portion of the muffler assembly including a catalytic converter. 
   
   
       9 . The exhaust system of  claim 8 , wherein the downstream attenuation portion includes a plurality of chambers configured to receive exhaust gases from the upstream portion via a first passage. 
   
   
       10 . The exhaust system of  claim 9 , wherein the intermediate attenuation portion includes a chamber configured to receive exhaust gases from the downstream attenuation portion via a second passage. 
   
   
       11 . The exhaust system of  claim 7 , wherein the engine includes a crankcase, the muffler assembly being shaped to conform to a front portion, a bottom portion, and a rear portion of the crankcase. 
   
   
       12 . The exhaust system of  claim 7 , wherein the intermediate attenuation portion has a height less than half of a height of the downstream attenuation portion. 
   
   
       13 . The exhaust system of  claim 7 , wherein the height of the intermediate attenuation portion is about 33 percent of the height of the downstream attenuation portion. 
   
   
       14 . A motorcycle comprising:
 an engine;   two wheels defining a central axis of the motorcycle; and   a muffler assembly in communication with the engine to receive exhaust gases from the engine, the muffler assembly being positioned substantially along the central axis and including
 a downstream attenuation portion, 
 an upstream portion, 
 an intermediate attenuation portion positioned substantially under the engine, the intermediate attenuation portion having a height, and 
 a recess at least partially defined by the downstream attenuation portion and the intermediate attenuation portion, wherein the recess has a depth greater than the height of the intermediate attenuation portion, the engine being positioned substantially within the recess. 
   
   
   
       15 . The motorcycle of  claim 14 , further comprising a muffler shell defining a substantially continuous outer surface of the muffler assembly, the muffler shell extending from the upstream portion to the downstream attenuation portion. 
   
   
       16 . The motorcycle of  claim 15 , wherein the muffler shell at least partially defines a plurality of chambers of the downstream attenuation portion and a chamber of the intermediate attenuation portion. 
   
   
       17 . The motorcycle of  claim 15 , wherein the upstream portion includes a catalytic converter. 
   
   
       18 . The motorcycle of  claim 17 , wherein the muffler shell at least partially defines an expansion chamber, the catalytic converter being positioned within the expansion chamber. 
   
   
       19 . The motorcycle of  claim 14 , wherein the height of the intermediate attenuation portion is about half the depth of the recess. 
   
   
       20 . The motorcycle of  claim 19 , wherein the recess is formed by a contour substantially matching a lower contour of the engine.