During periods of vehicle deceleration, it would be desirable, from a fuel economy standpoint, to discontinue fuel delivery to the engine. However, present deceleration fuel shutoff strategies may cause engine harshness when refueling commences. In addition, the exhaust system's catalyst may be exposed to nearly pure air when fueling ceases. Because a catalyst absorbs oxygen, when refueling commences, the catalyst containing excess oxygen cannot effectively reduce nitrogen oxides (NO.sub.x) until the excess oxygen is purged. During the excess oxygen removal period, substantial quantities of NO.sub.x may break through the catalyst causing a vehicle to fall out of exhaust emission compliance.
USPTO Backgrounds
USPTO Backgrounds