Exhaust pipe

Abstract

An exhaust pipe includes a tubular portion and a space forming portion. The tubular portion forms an exhaust flow path in an exhaust system of an internal combustion engine. The tubular portion has a tubular shape. The space forming portion is provided along at least one of an inner surface and an outer surface of the tubular portion and forms at least one branch space between the space forming portion and the tubular portion. The at least one branch space communicates with the exhaust flow path and has a function as a side-branch muffler. The at least one branch space includes a space with a length that is one third or more of an entire length of the exhaust system.

What is claimed is: 
     
         1 . An exhaust pipe comprising:
 a tubular portion forming an exhaust flow path in an exhaust system of an internal combustion engine; and   a space forming portion provided along at least one of an inner surface and an outer surface of the tubular portion and forming at least one branch space between the space forming portion and the tubular portion, the at least one branch space communicating with the exhaust flow path and having a function as a side-branch muffler,   wherein the at least one branch space comprises a space with a length that is one fifth or more of an entire length of the exhaust system.   
     
     
         2 . The exhaust pipe according to  claim 1 ,
 wherein the tubular portion is a longest tubular portion of a tubular body forming the exhaust flow path in the exhaust system.   
     
     
         3 . The exhaust pipe according to  claim 1 ,
 wherein the at least one branch space comprises a space with a length that is one third or more of the entire length of the exhaust system.   
     
     
         4 . The exhaust pipe according to  claim 1 ,
 wherein the at least one branch space comprises two branch spaces with lengths different from each other.   
     
     
         5 . The exhaust pipe according to  claim 1 ,
 wherein the at least one branch space comprises two branch spaces each having a length that is one fifth or more of the entire length of the exhaust system.   
     
     
         6 . The exhaust pipe according to  claim 1 ,
 wherein the space forming portion is provided along the inner surface of the tubular portion.   
     
     
         7 . The exhaust pipe according to  claim 1 ,
 wherein the space forming portion comprises a tubular inner pipe member disposed inside the tubular portion and forming a double-wall pipe together with the tubular portion,   wherein the inner pipe member comprises:
 an attached portion attached to the inner surface of the tubular portion; and 
 a separated portion spaced apart from the inner surface of the tubular portion, and 
   wherein the at least one branch space comprises a space formed between the separated portion and the tubular portion.   
     
     
         8 . The exhaust pipe according to  claim 7 ,
 wherein an area defined by an outer edge of the separated portion in a cross-section perpendicular to an axial direction of the double-wall pipe is encompassed by an area defined by an outer edge of the attached portion in the cross-section.   
     
     
         9 . The exhaust pipe according to  claim 1 ,
 wherein the tubular portion comprises a curved portion forming a curve in the exhaust flow path.