Abstract: The shell main body for a muffler includes an inner shell in a cylindrical shape with a cross-section of an imperfect circle defined by small arc portions alternating with large arc portions; and an outer shell wrapping the inner shell and formed in a cylindrical shape similar to the inner shell. An end portion of the inner shell and an end portion of the outer shell are overlapped in a circumstantial direction of the shell main body to form a shell overlap portion that is capable of discharging vapor in a gap of the large arc portions formed between the inner shell and the outer shell into one of an outside and an inside of the shell main body. This shell overlapping portion is located in one of the small arc portions.

Abstract: The shell main body for a muffler includes an inner shell in a cylindrical shape with a cross-section of an imperfect circle defined by small arc portions alternating with large arc portions; and an outer shell wrapping the inner shell and formed in a cylindrical shape similar to the inner shell. An end portion of the inner shell and an end portion of the outer shell are overlapped in a circumstantial direction of the shell main body to form a shell overlap portion that is capable of discharging vapor in a gap of the large arc portions formed between the inner shell and the outer shell into one of an outside and an inside of the shell main body. This shell overlapping portion is located in one of the small arc portions.

Abstract: A flexible pipe unit for an exhaust pipe line of an internal combustion engine comprises a metal bellows which has a front open end adapted to be connected to a first exhaust pipe and a rear open end adapted to be connected to a second exhaust pipe. A cylindrical outer case of metal is coaxially disposed about the metal bellows in a manner to define therebetween a cylindrical space. A first structure is arranged between a front end of the outer case and a front end of the bellows to achieve a mechanical connection therebetween. A second structure is arranged between a rear end of the outer case and a rear end of the bellows to achieve a mechanical connection therebetween. At least one of the first and second structures comprises a spring member by which the bellows and the outer case are resiliently connected.