| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration of conversion efficiency due to a deviation in air-fuel ratio through catalyst, by optimumly making the air-fuel ratio lean in each of an adsorbing condition and a desorbing condition, in such a case that at least two of adsorbing catalyst devices are incorporated. SOLUTION: Conditions of adsorbing catalyst devices 17a, 17b, such as an adsorbing and desorbing condition, a catalyst activating condition, a degree of deterioration, a density of HC in during desorption and the like are determined in accordance with a lapsed time from a start, a catalyst temperature, a temperature of cooling water upon a start, a lapsed time from activation of catalyst and the like, and the engine air-fuel ratio is made to be lean so that the air-fuel ratios in respective catalyst devices which start their activation become a stoichiometric air-fuel ratio. With this arrangement, desorbed HC can be converted be effectively using the purification action of the catalyst, whereby it is possible to restrain deterioration of HC or NOx due to a deviation in air-fuel ratio during desorption.
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