Patent ID: 7134272

Claim:
A controlling method for an exhaust gas purifying system having an internal combustion engine, an exhaust passage of exhaust gas from the internal combustion engine, a hydrogen-catalyst provided in the exhaust passage to make at least a reaction for selectively removing CO by oxidation, and suppressing consumption of hydrogen, or a reaction for adsorbing CO, and transmitting hydrogen, the hydrogen-catalyst containing at least CeO 2 and precious metal, and an NOx purifying catalyst provided on a downstream of the hydrogen-catalyst of the exhaust passage to reduce nitrogen oxides, comprising the steps of: (a) detecting the amount of air sucked into the internal combustion engine which operates under lean conditions and intermittent rich conditions; (b) detecting a temperature of exhaust gas flowing into the hydrogen-catalyst; (c) reading prestored first to fourth data maps, the first data map indicating a relation between the amount of sucked air and the amount of adsorbed CO in the hydrogen-catalyst, the second data map indicating a relation between the exhaust gas temperature and the amount of adsorbed CO in the hydrogen-catalyst, the third data map indicating a relation between the amount of sucked air and the amount of reacted CO in the hydrogen-catalyst, and the fourth data map indicating a relation between the exhaust gas temperature and the amount of reacted CO in the hydrogen-catalyst; (d) reading the amount of adsorbed CO and the amount of reacted CO in the hydrogen-catalyst based on the detected amount of sucked air and the detected exhaust gas temperature by referring to the first to fourth data maps, and predicting the amount of CO consumption in the hydrogen-catalyst from the amount of adsorbed CO and the amount of reacted CO; (e) reading prestored fifth and sixth data maps, the fifth data map indicating a relation between the amount of CO consumption and an optimal amount of fuel injection with respect to the amount of CO consumption, and the sixth data map indicating the amount of CO consumption and an optimal time of fuel injection with respect to the amount of CO consumption; (f) deciding the optimal amount of fuel injection and an optimal time of fuel injection condition based on the predicted amount of CO consumption by referring to the fifth and sixth data maps; and (g) controlling an air/fuel ratio of mixed gas of fuel and air supplied to the internal combustion engine, which executes enrichment condition control for reducing an air/fuel ratio (A/F)r during enrichment to prolong a time of enrichment (tr) as a flow rate of exhaust gas emitted from the internal combustion engine is lowered in intermittent enrichment of the air/fuel ratio.