To prevent a fuel consumption from worsening and a catalyst from deteriorating owing to an excessive detoxication of sulfur poisoning of the catalyst.
When a sulfur estimated deposit amount SOXMILE equals to or more than a threshold SOXFUL by estimating the sulfur deposit amount SOXMILE corresponding to a traveling distance, a poison detoxicating starts. A sulfur subtracted value RSMILE in poison detoxicating is adjusted by a factor k calculated based on the ratio of a traveling distance HMILE with high-octane gasoline to a traveling distance RMILE with regular gasoline. The higher the distance with high-octane gasoline which is low in sulfur content, the greater the sulfur subtracted value RSMILE becomes. The sulfur deposit amount SOXMILE is reduced based on the sulfur subtracted value RSMILE per unit time to stop poison detoxication when SOXMILE=0.
SATO KENICHI
OTAKE YOSHIYUKI
