Method for obtaining exhaust gas flow quantity, exhaust gas flow measurement apparatus, and exhaust gas recirculation control system

An exhaust recirculation control system of the internal combustion engine computes an oxygen concentration in total intake air containing recirculation exhaust gas in a cylinder and the ratio between an oxygen quantity in the total intake air and a fuel injection quantity (oxygen quantity/fuel injection quantity ratio). The computed values are compared with target values which are pre-set according to engine operating conditions and, based on the result of the comparison, at least an EGR valve or a fuel injection quantity. In order to perform such a control with high accuracy, a correcting means corrects a recirculation exhaust gas mass flow signal from a gas mass flowmeter on the basis of a predicted exhaust gas component concentration. And, by using the corrected recirculation exhaust gas mass flow, oxygen concentration in total intake air containing the recirculation exhaust gas in the cylinder and the ratio between the oxygen quantity in the total intake air and the fuel injection quantity (target oxygen quantity/fuel injection quantity ratio) are computed to perform EGR control.