To maintain stability of an air-fuel ratio targeted at release of a purifying capacity reducing substance depositing on a catalyst.
An exhaust emission control device for an engine comprises a means 11 for estimating a deposition quantity of a purifying capacity reducing substance on the catalyst 7 disposed in an exhaust passage of an engine, a determining means 11 for determining whether or not timing is reached for releasing the purifying capacity reducing substance depositing on the catalyst according to the estimated deposition quantity, a temperature increasing means 6 for increasing the temperature of the catalyst when the determining means determines the timing for releasing the purifying capacity reducing substance depositing on the catalyst, an air-fuel ratio controlling means 5, 11, 14 and 15 for maintaining an exhaust air-fuel ratio of the catalyst near to the stoichiometric air-fuel ratio likewise at the timing for releasing the purifying capacity reducing substance depositing on the catalyst, and a means 5 and 15 for enriching the exhaust air-fuel ratio over the stoichiometric air-fuel ratio after the air-fuel ratio controlling means maintains the exhaust air-fuel ratio near to the stoichiometric air-fuel ratio.
ISHIZUKA YASUJI
SATO KENICHI
