초록 ▼

In an exhaust gas purification device, a catalytic converter containing selective reduction catalysts is disposed in an exhaust gas passage of an internal combustion engine capable of being operated at a lean air-fuel ratio. The catalytic converter includes a plurality of the selective reduction cat

In an exhaust gas purification device, a catalytic converter containing selective reduction catalysts is disposed in an exhaust gas passage of an internal combustion engine capable of being operated at a lean air-fuel ratio. The catalytic converter includes a plurality of the selective reduction catalysts disposed in series in the casing of the catalytic converter. Bypass passages which supply the exhaust gas to downstream selective reduction catalysts in the casing by bypassing the upstream catalysts are provided. When a reducing agent is supplied to the exhaust gas upstream of the converter, a part of the supplied reducing agent directly reaches the downstream selective reduction catalyst through the bypass passages without being oxidized by the upstream selective reduction catalysts. Therefore, the NO.sub.x purifying abilities of the downstream catalysts are improved and the formation of sulfates on the downstream catalysts is suppressed.

대표청구항 ▼

[What is claimed is:] [1.]a plurality of selective reduction catalysts disposed in series in the exhaust gas passage of the engine, wherein each of the selective reduction catalysts is capable of reducing NO.sub.x in the exhaust gas of the engine by selectively reacting NO.sub.x with a reducing agen

[What is claimed is:] [1.]a plurality of selective reduction catalysts disposed in series in the exhaust gas passage of the engine, wherein each of the selective reduction catalysts is capable of reducing NO.sub.x in the exhaust gas of the engine by selectively reacting NO.sub.x with a reducing agent in the exhaust gas even if the air-fuel ratio of the exhaust gas is lean;reducing agent supply means for supplying the reducing agent to the exhaust gas in the exhaust gas passage upstream of a first selective reduction catalyst disposed on the most upstream side in the selective reduction catalysts so that the exhaust gas containing the reducing agent is always supplied to the first selective reduction catalyst during operation of the engine; andbypass passage means for bypassing at least the first catalyst in such a manner that, during operation of the engine, a part of the exhaust gas containing the reducing agent always directly flows into selective reduction catalysts downstream of the first catalyst without flowing through the first catalyst.