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In a conventional fuel metering control system (speed density method) for an internal combustion engine, the fuel injection amount during transient operation is usually determined by using mapped data and various settings in a feedforward system predetermined through experimentation. However, this still does not necessarily represent the ideal level of compensation under a diverse range of environmental conditions. In order to satisfy various demanding requirements, such as reducing emissions, it is vital that the controllability of the air excess ratio(λ) be enhanced. The main technological obstacle that needs to be overcome is how best to determine accurately the required fuel amount from the engine in the feedforward system. To enable accurate prediction of the cylinder intake air volume, physical formulas of fluid dynamics were used to facilitate formulation of a model for the dynamic behavior of the intake air.

In this research project, modeling of the dynamic air excess ratio (λ) behavior in the exhaust gas at the confluence point in the exhaust manifold was performed. By applying an observer which is one method described by modern control system theory, estimation of the λ for each cylinder was carried out using one λ sensor. The estimated value was used to perform λ feedback control for each cylinder, allowing compensation of deviation in air-fuel ratio between cylinders and individual control of fuel injection volume for each cylinder, dramatically enhancing λ controllability.