Exhaust gas purifying system for an internal-combustion engine

摘要

The invention relates to an exhaust gas purifying system (1) for an internal-combustion engine (10), comprising: an exhaust conduit (20) connectable to an exhaust port of the internal-combustion engine (10) for discharging exhaust gas; a first catalyzer (30) provided in a midway part of the exhaust conduit (20) for purifying the exhaust gas; a second catalyzer (40) provided in a midway part of the exhaust conduit (20) more downstream than the first catalyzer (30) for purifying exhaust gas flowed out from the first catalyzer (30); a third catalyzer (50) provided in a midway part of the exhaust conduit more downstream than the second catalyzer (40) for purifying exhaust gas flowed out from the second catalyzer (40); a secondary air introducing conduit (60) provided in the exhaust conduit (20) in a position between the second and the third catalyzers for introducing secondary air into the exhaust conduit (20).