INNOVATIVE AIR ESTIMATION AND LUENBERGER OBSERVERS IN MODEL BASED A/F CONTROL

In this paper it has been demonstrated as the closed loop air fuel ratio (A/F) control system, equipped with a linear oxygen sensor (UEGO), can be improved with an innovative reformulation of the fuel injection control by means of a model based approach. the A/F control, within a rigorous speed throttle logic (which avoids the use of the air flow meters and of the pressure sensor inside the intake manifold), can be designed using a Luenberger type observer which includes the dominant dynamics of air, fuel and oxygen lambda sensor. The control has been developed and experimented on a research one cylinder spark ingnition engine (AVL 5401). The air mass reference can be supplied either by a stationary map or, in substitution, by means of a physical gas dynamic code (Method of transfer function, MTF) which is able to compute cycle by cycle the pressure pumping fluctiations and the cylinder filling (volumetric efficiency). The experimental campaign on AVL5401 has tested the control erformances in transient conditions determmined by moderate and severe unsteady maneuvers concerning both the load and engine speeds. The robustness of the control is demonstrated and also the possibility to replace the maps with the MTF approach. The controlis able to keep the A/F in the most part of the transients around the stechiometric value, with errors bounded within 3-4 %in presence of critical throttle maneuvers which are more sever than those in the usual operarive conditions.