Abstract

An air fuel ratio management system having a calibration correction for the pressure differentials between the exhaust and intake manifolds of the engine is disclosed. The differential calibration corrects the air/fuel ratio of the system for the variable internal exhaust gas recirculation occasioned by changing restrictions to flow found in the intake and exhaust manifolds. In one implementation a differential pressure sensor communicates with both the intake and exhaust manifolds to develop a differential pressure signal. The differential pressure signal is thereafter applied to a function circuit which generates a pressure correction signal. An electronic control unit receives the pressure correction signal and utilizes it to modify the air/fuel ratio calibration according to the functional conversion. In the preferred embodiment the function circuit comprises a voltage controlled linear current source. In another implementation individual pressure sensors are used for each manifold to generate signals to a difference circuit which subtracts the intake manifold absolute pressure from the exhaust manifold absolute pressure to form the differential pressure signal. In either implementation incremental or proportional modification of a variable duration fuel pulse from the electronic control unit can be obtained by the pressure correction signal.