To prevent drop of NOx conversion performance even if the temperature of a NOx storage catalyst is low in engine start in a hybrid vehicle.
An exhaust emission control system for a hybrid vehicle has the NOx storage catalyst provided in an exhaust gas passage of an internal combustion engine. An ozone former is provided upstream of the NOx storage catalyst and supplies ozone (O3) to the upstream side of the NOx storage catalyst of the exhaust gas passage. Since the internal combustion engine stops during motor travel in which an electric motor is used for propelling force in the hybrid vehicle, the catalyst bed temperature of the NOx storage catalyst provided in the exhaust gas passage of the internal combustion engine drops and NO storage capacity drops in that period. Ozone, therefore, is supplied to the exhaust gas passage concurrently with or before start of the internal combustion engine. Ozone oxidizes NO in exhaust gas and converts the same to NO2. Since the NOx storage catalyst can convert NO2 even if the catalyst bed temperature is low, NOx conversion performance can be maintained.
HIROTA SHINYA
Koji Yamamoto
Tatsuo Egami
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