Patent ID: 6877312

Claim:
An exhaust emission control system for purifying exhaust gas emitted from at least one combustion chamber of an internal combustion engine, comprising: an exhaust passage that comprises a first exhaust branch passage and a second exhaust branch passage, which join at downstream ends thereof into a common exhaust passage; a first NOx catalyst disposed in the first exhaust branch passage; a second NOx catalyst disposed in the second exhaust branch passage; a particulate filter disposed in the common exhaust passage and located downstream of a joining point of the first exhaust branch passage and the second exhaust branch passage; a first flow control valve that controls an amount of exhaust gas flowing through the first exhaust branch passage; and a second flow control valve that controls an amount of exhaust gas flowing through the second exhaust branch passage, wherein each of the first and second NOx catalysts stores NOx contained in the exhaust gas when an air/fuel ratio of the exhaust gas flowing into said each NOx catalyst is lean, and allows a reducing agent to reduce and remove the stored NOx when the air/fuel ratio of the exhaust gas flowing into said each NOx catalyst is rich; and the particulate filter traps particulates contained in the exhaust gas, and oxidizes and removes the trapped particulates.