Patent ID: 7497078

Claim:
An exhaust gas purifying system for an internal combustion engine, comprising: an exhaust-after-treatment device disposed in an exhaust system of the internal combustion engine, and including a particulate filter configured to collect particulates from exhaust gas, and an NO 2 generating unit upstream of or in the particulate filter; an excess air ratio frequency calculating unit configured to calculate an excess air ratio frequency at which an excess air ratio is equal to or less than a predetermined value during the operation of the internal combustion engine; a discharged particulate amount calculating unit configured to calculate an amount of discharged particulates on the basis of an excess air ratio frequency at which an excess air ratio is equal or less than a predetermined excess air ratio; a filter temperature frequency calculating unit configured to calculate a filter temperature frequency at which the temperature of exhaust gas in front of the particulate filter or the temperature of the particulate filter is equal to higher than a predetermined value; a burnt particulate amount calculating unit configured to calculate an amount of burnt particulates on the basis of the filter temperature frequency; and a particulate accumulation amount calculating unit configured to calculate an amount of particulates on the particulate filter on the basis of the calculated amount of discharged particulates and the calculated amount of burnt particulates.