Abstract: An air-fuel ratio control apparatus for an internal combustion engine is provided which includes an air-fuel ratio determining circuit which determines an air-fuel ratio of exhaust gases flowing upstream of a catalytic converter for controlling the air-fuel ratio of the exhaust gases so as to agree with a target air-fuel ratio under feedback control, a sorbed substance amount determining circuit for determining the amount of substances sorbed in the catalytic converter, and a target air-fuel ratio determining circuit for determining said target air-fuel ratio so that the amount of substances determined by said sorbed substance amount determining means falls within a given range.

Abstract: A fuel supply amount control apparatus improves controllability during engine acceleration and deceleration and immediately after starting the operation of the engine, by enabling the setting of suitable parameters. An evaporation time constant indicating chronological changes in the fuel amount introduced into a cylinder from an intake system of the engine is computed by a predetermined computation equation. During this computation, the computation load is reduced by using an Aquino operator .alpha. and a stroke interval Aquino operator A.alpha. and computation for computing the fuel injection amount is executed at an interval shorter than the interval of two successive fuel injections, e.g., a crank angle of 60.degree.. During computation of the evaporation time constant, the evaporation time constant after full warm-up is corrected based on an average temperature weighted according to an adherence rate of fuel to the intake manifold and intake valve.