Apparatus and method for internal combustion engine control

A control apparatus for an internal combustion engine having an exhaust purifying catalytic device disposed in an exhaust passage for reducing emission of nitrogen oxides to atmosphere, the exhaust purifying catalytic device being operable to adsorb nitrogen oxides contained in exhaust gas discharged from the internal combustion engine when the engine is in a lean-combustion mode where an air-fuel ratio of an air-fuel mixture supplied to the engine is leaner than a theoretical air-fuel ratio, and to deoxidize adsorbed nitrogen oxides when the internal combustion engine is in a rich-combustion mode where the air-fuel ratio is equal to or richer than the theoretical air-fuel ratio, comprising:

• a burner, disposed near the exhaust purifying catalytic device, for heating the exhaust purifying catalytic device;
• adsorption amount estimating means for estimating an adsorption amount of purifying capability reducing substances, which decreases nitrogen oxide adsorbing ability of the exhaust purifying catalytic device, adsorbed by the exhaust purifying catalytic device, and for determining whether the estimated adsorption amount has reached a predetermined adsorption amount;
• and
• catalyst heating means for removing the purifying capability reducing substances from the exhaust purifying catalytic device by activating said burner when said adsorption amount estimating means judges that the adsorption amount of the purifying capability reducing substances has reached the predetermined adsorption amount.

An internal combustion engine control method for reducing emission of nitrogen oxides to atmosphere, by causing nitrogen oxides, contained in exhaust gas discharged from the internal combustion engine, to be adsorbed by an exhaust purifying catalytic device, disposed in an exhaust passage of the internal combustion engine, when the engine is in a lean-combustion mode where an air-fuel ratio of an air-fuel mixture supplied to the engine is leaner than a theoretical air-fuel ratio, and by deoxidizing adsorbed nitrogen oxides by means of the exhaust purifying catalytic device when the internal combustion engine is in a rich-combustion mode where the air-fuel ratio is equal to or richer than the theoretical air-fuel ratio, comprising the steps of:

• (a) estimating an adsorption amount of purifying capability reducing substances, which decreases nitrogen oxide adsorbing ability of the exhaust purifying catalytic device, adsorbed by the exhaust purifying catalytic device, and determining whether the estimated adsorption amount has reached a predetermined adsorption amount;
• and
• (b) removing the purifying capability reducing substances from the exhaust purifying catalytic device by increasing a temperature of the exhaust purifying catalytic device by changing an operating condition of the internal combustion engine so that an exhaust gas temperature increases when it is judged in said step (a) that the estimated adsorption amount has reached the predetermined adsorption amount.