Patent ID: 6918463

Claim:
A muffler for an engine having an exhaust passage, the muffler comprising: a casing; an exhaust pipe penetrating and extending through the casing, the exhaust pipe adapted to be connected with the exhaust passage of the engine; an enlarged chamber having a volume and formed in the exhaust pipe positioned in the casing, the enlarged chamber being adapted to accommodate therein a particulate filter for collecting particulates contained in exhaust gas flowing into the enlarged chamber or a catalyst; an upstream side communicating passage communicating an exhaust gas chamber, which is defined between an outer wall surface of the exhaust pipe and an inner wall surface of the casing, and the exhaust pipe upstream of the enlarged chamber with each other; a downstream side communicating passage communicating the exhaust gas chamber and the exhaust pipe downstream of the enlarged chamber with each other; and a communication control means for closing the upstream side communicating passage until the pressure in the exhaust pipe upstream of the enlarged chamber reaches a predetermined threshold value and for opening the upstream side communicating passage when the above-mentioned pressure reaches the threshold value, wherein when the upstream side communicating passage is closed, the exhaust gas flows through the enlarged chamber, and when the upstream side communicating passage is opened, a part of the exhaust gas flows out from the exhaust pipe, via the upstream side communicating passage, into the exhaust gas chamber, and then bypasses the enlarged chamber and returns into the exhaust pipe via the downstream side communicating passage.