Patent ID: 7448204

Claim:
An engine system, comprising: an exhaust port for releasing combusted gas from an engine; an exhaust system comprising: an exhaust pipe coupled with the exhaust port, the exhaust pipe comprising a first location having a first cross-sectional area, a second location having a second cross-sectional area, and a third location having a third cross-sectional area; a first catalyst disposed at the first location in the exhaust pipe, the first catalyst configured to provide a reduction action; a second catalyst disposed at the second location in the exhaust pipe a set distance downstream of the first catalyst, the second catalyst configured to provide an oxidation action; a secondary air induction pipe for introducing air into the exhaust pipe at the third location, the secondary air induction pipe being connected to the exhaust pipe between the first and the second catalysts at a location where the secondary air induction pipe is in fluid communication with the first catalyst and a temperature difference between the first and the second catalysts in a cold start transient phase is within a predetermined range; and a muffler that surrounds a portion of the exhaust pipe, wherein the first catalyst is disposed upstream of the muffler, and the second catalyst is disposed inside the muffler; wherein the third cross-sectional area is less than at least one of the first and the second cross-sectional areas.