MUFFLER FOR AN INTERNAL COMBUSTION ENGINE

摘要

A muffler for an internal combustion engine having a valve disc for closing and/or opening an opening end of a bypass inner pipe, wherein the opening and/or closing operation of the valve disc is properly performed by virtue of the pressure of exhaust gas without being influenced by an external factor, said muffler having a simple construction and being easy to mount, said muffler being characterized in that the valve disc (32) is pivotally mounted on a fixed shaft (36) supported in the vicinity of the opening end (28a) of the bypass inner pipe (28) and is biassed toward the opening end (28a) by means of a coil spring (42) to thereby close the opening end (28) in close contact with a flange portion (38). When the number of revolutions of the internal combustion engine is low, the pressure inside the bypass inner pipe (28) is smaller than an operation force which is a sum of the biassing force of the coil spring (42) and an external pressure, and therefore the opening end (28a) is kept closed, while when the number of revolutions increases and the pressure is increased to a predetermined pressure, the relationship between the two factors is reversed, whereby the valve disc (32) is separated form the opening end (28a), the bypass inner pipe (28) being thereby put in a communicating state.