Muffler for stratified scavenging engine

Abstract

A cost-effective muffler for a stratified scavenging engine capable of reducing the number of cells with no exhaust gas flowing in a columnar catalyst as much as possible to create a uniform exhaust gas flow in the columnar catalyst and thus obtaining a desired exhaust gas purification rate, so that THC emissions can be effectively curbed, without substantial alteration or dimensional changes to an existing muffler body and columnar catalyst. At least one of distances: from introduction port to partitioning wall plate; from front wall surface of front chamber to front end surface of the columnar catalyst; and from partitioning wall plate to front end surface of the columnar catalyst is within a predetermined range to prevent gas flow introduced into the front chamber through the introduction port and hitting against the partitioning wall plate to be reversed from bypassing cells in the upper end portion of the columnar catalyst as much as possible.

What is claimed is: 
     
         1 . A muffler for a stratified scavenging engine, comprising:
 a muffler body that introduces and discharges an exhaust gas from a stratified scavenging engine;   a partitioning wall plate disposed inside the muffler body vertically to a direction in which the exhaust gas is introduced, the partitioning wall plate hermetically partitioning the muffler body into a front chamber and a rear chamber on a downstream side of the front chamber, an upper half portion of the front chamber provided with an introduction port for introducing the exhaust gas; and   a columnar catalyst for exhaust gas purification attached to roughly a lower half portion of the partitioning wall plate so as to extend over the front chamber and the rear chamber, with an axis of the columnar catalyst orthogonal to the partitioning wall plate,   wherein   the columnar catalyst is a monolithic form catalyst provided with multiple cells in a grid pattern, each cell having a linear passage that allows the front chamber and the rear chamber to communicate with each other, and   at least one of a distance A from the introduction port to the partitioning wall plate, a distance D from a front wall surface of the front chamber to a front end surface of the columnar catalyst, or a distance T from the partitioning wall plate to the front end surface of the columnar catalyst is set to be within a predetermined range so as to prevent a gas flow introduced into the front chamber through the introduction port and hitting against the partitioning wall plate to be reversed from bypassing the cells in an upper end portion of the columnar catalyst as much as possible.   
     
     
         2 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 part of the gas flow reversed also enters the cells in the upper end portion of the columnar catalyst while being guided to an outer periphery surface of a cylindrical shell provided in an outer periphery of the columnar catalyst.   
     
     
         3 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 the columnar catalyst is an oxidation catalyst, a redox catalyst, or a three-way catalyst capable of oxidation combusting at least an uncombusted fuel component contained in the exhaust gas.   
     
     
         4 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 a catalyst attachment portion is provided in roughly the lower half portion of the partitioning wall plate, the catalyst attachment portion having a circular insertion hole for enabling the columnar catalyst to be secured at any position in a direction orthogonal to the partitioning wall plate.   
     
     
         5 . The muffler for a stratified scavenging engine according to  claim 4 , wherein
 the columnar catalyst is hermetically attached to the catalyst attachment portion through welding.   
     
     
         6 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 a capacity of the front chamber is set to four to six times a displacement of the stratified scavenging engine.   
     
     
         7 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 the distance A from the introduction port to the partitioning wall plate is set to be within a range of 21.5 mm or greater, the distance D from the front wall surface of the front chamber to the front end surface of the columnar catalyst is set to be within a range of 5 mm or greater, the distance T from the partitioning wall plate to the front end surface of the columnar catalyst is set to be within a range of 7 mm or greater, and a distance H from a lower end of the introduction port to an upper end of the columnar catalyst is set to be within a range of 9 mm or greater.   
     
     
         8 . The muffler for a stratified scavenging engine according to  claim 7 , wherein
 the distance A from the introduction port to the partitioning wall plate is set to be within a range of 25 to 30 mm, the distance D from the front wall surface of the front chamber to the front end surface of the columnar catalyst is set to be within a range of 5 to 20 mm, the distance T from the partitioning wall plate to the front end surface of the columnar catalyst is set to be within a range of 7 to 16 mm, and the distance H from the lower end of the introduction port to the upper end of the columnar catalyst is set to be within a range of 9 to 20 mm.   
     
     
         9 . The muffler for a stratified scavenging engine according to  claim 1 , wherein
 a displacement of the stratified scavenging engine is within a range of 20 to 40 cc and a diameter C and a length L of the columnar catalyst are within a range of 25 to 50 mm and a range of 15 to 35 mm, respectively.