Method for estimating the oxygen concentration in internal combustion engines

A method for estimating the oxygen concentration in an internal combustion engine that includes, but is not limited to an intake manifold, an exhaust manifold, an EGR system, a throttle valve, an air mass sensor for measuring a fresh air flow ({dot over (m)}thr) entering the intake manifold through the throttle valve, and cylinders. The method includes, but is not limited to the steps of estimating the total gas flow ({dot over (m)}o) entering the cylinders, calculating the EGR gas flow ({dot over (m)}egr), calculating the air fraction (f-air-em) of the gas flowing in the exhaust manifold, calculating the air mass (mim-air) entering the cylinders based on the air fraction (f-air-em) in the exhaust manifold, on the total gas flow ({dot over (m)}o) entering the cylinders, on the EGR gas flow ({dot over (m)}egr) and on the fresh air flow ({dot over (m)}thr), calculating the total mass (mim) in the intake manifold based on the fresh air flow ({dot over (m)}thr), on the EGR gas flow ({dot over (m)}egr) and on the total gas flow ({dot over (m)}o) entering the cylinders, calculating the air fraction (fair-im) in the intake manifold based on the air mass (mim-air) entering the cylinders and the total mass (mim) in the intake manifold, and calculating the oxygen mass concentration ([O2]m-im) in the intake manifold based on the air fraction (fair-im) in the intake manifold.