Abstract: The muffler comprises a resonator (6) which communicates by way of an outlet orifice (14) with a chamber (5). A flexible valve member (16) regulates the section of the passage through this orifice in accordance with the rate of flow of the gas through the outlet of the resonator under the action, for example, of the pressure prevailing in the resonator. When the running speed of the engine decreases, the valve member reduces the section of the passage through the orifice (16) and modifies the acoustic attenuation in the resonator. The valve member may be controlled by other parameters of the flow of the exhaust gas inside the muffler.

Abstract: At least one of the ends of the silencer an end chamber is defined between an intermediate planar dished wall and an end dished wall which is provided with a rounded and hollow boss. The boss substantially extends two exhaust gas tubes in front of which it is located and its apex is spaced from the intermediate dished wall by a distance which is slightly greater than the radius of the tubes so that the boss guides the change in direction of the gas flow between the tubes.