ENGINE AIR-FUEL RATIO CONTROL DEVICE

PURPOSE:To effectively use the performance of a ternary catalyst so as to aim at enhancing the composition of exhaust gas during acceleration by biasing the air-fuel ratio toward the rich side or the lean side in view of the components of exhaust gas produced during acceleration. CONSTITUTION:A calculating means 3 calculates a basic fuel injection amount Tp in accordance with an intake-air amount (engine load) and an engine rotation speed detected by sensors 1, 2, and a calculating means 5 calculates a feed-back compensating value alpha in accordance with a deviation between an air-fuel ratio detected by an oxygen sensor 4 and a stoichiometric air-fuel ratio while a calculating means 6 obtains a fuel injection amount Ti=TpXalpha. In this arrangement, when a determining means 7 determines the time of acceleration, a feed- back constant setting means 8 sets a feed-back constant for calculating a feed back compensating value alpha in accordance with an elapse from the time of acceleration so that the air-fuel ratio is biased from the stoichiometric air-fuel ratio. Thereby it is possible to effectively use the performance of a ternary catalyst so as to improve the composition of exhaust gas upon acceleration.