US Patent 7896127 Muffler unit for general-purpose engine

A muffler unit for a general-purpose engine includes a muffler (40) having a maze of sound-deadening chambers (101, 102, 103) defined therein and an inlet pipe (85) disposed inside the muffler. The inlet pipe has an open end (106) connected to an exhaust port of the engine via an exhaust pipe (43), a closed end (107) opposite to the open end, and perforations (108) provided near the open end and connecting an internal space of the inlet pipe and a first sound-deadening chamber (101). The closed end of the inlet pipe is exposed to the outside air, so that exhaust gasses are cooled when the gasses impinge on the closed end of the inlet pipe.