Patent ID: 7216480

Claim:
An exhaust emission control system for a vehicle including a primary engine and a secondary engine having a displacement smaller than that of the primary engine, the exhaust emission control system comprising: an exhaust passage having a junction portion at which exhaust gas discharged from the primary engine and exhaust gas discharged from the secondary engine join together; an exhaust emission purifying device that purifies the exhaust gas joined at the junction portion in the exhaust passage; a first air/fuel ratio detection unit provided between the primary engine and the junction portion for detecting an air/fuel ratio of exhaust gas; a second air/fuel ratio detection unit provided downstream of the exhaust emission purifying device for detecting an air/fuel ratio of the exhaust gas; and a controller that controls an air/fuel ratio of air/fuel mixture each admitted into the primary engine and the secondary engine based on the air/fuel ratio detected by the first air/fuel ratio detection unit and the air/fuel ratio detected by the secon air/fuel ratio detection unit, respectively, wherein: an activated state of the exhaust emission purifying device is determined; and when it is determined that the exhaust emission purifying device is not in the activated state, the secondary engine is started.