Abstract: An air/fuel ratio estimator for estimating an air/fuel ratio of a mixture supplied to each cylinder of a multicylinder internal combustion engine through an output of an air/fuel ratio sensor installed at a confluence point of an exhaust system of the engine. The estimator includes first device for assuming the output of the air/fuel ratio sensor as an average value made up of a sum of products of past firing histories of each cylinder weighted by a predetermined value, and establishing a model using the air/fuel ratio as a state variable, a second device for obtaining a state equation with respect to the state variable. An observer is provided to estimate the unmeasured state variable indicative of the air/fuel ratio and the air/fuel ratio at each cylinder is estimated from an output of the observer. In the configuration upper and lower limit is established for the state variable such that it is replaced with its initial value if it exceeds either limit.

Abstract: Fuel metering control system in an internal combustion engine utilizing adaptive control having an intake manifold wall's fuel adherence plant. In the system, an actual air/fuel ratio in the individual cylinders is accurately estimated using an exhaust manifold model with an observer. Also, an actual cylinder air flow is estimated using a fluid model. Based on them, a desired cylinder fuel flow is determined by dividing the actual cylinder air flow by a desired air/fuel ratio and an actual cylinder fuel flow is determined by dividing the actual cylinder air flow by the estimated actual air/fuel ratio. The adaptive controller operates such that the actual cylinder fuel flow constantly coincides with the desired cylinder fuel flow.

Abstract: A system for controlling fuel metering in an internal combustion engine using a fluid dynamic model and the cylinder air flow past the throttle is determined therefrom. Based on the observation that the difference between a steady-state engine operating condition and a transient engine operating condition can be described as the difference in the effective throttle opening areas, the amount of fuel injection is determined from the product of the ratio between the areas and a basic fuel injection amount under the steady-state engine operating condition obtained by mapped data retrieval and by subtracting a correction amount corresponding to an air flow filling a chamber between the throttle and the cylinder from the product. Under steady-state engine operation, the correction amount becomes zero.