METHOD FOR DETERMINATION OF EGR RATIO IN INTERNAL COMBUSTION ENGINE, AND DEVICE FOR CONTROL OF INTERNAL COMBUSTION ENGINE

The present invention makes it possible to accurately determine an EGR rate from an in-cylinder pressure. An EGR rate determination method for an internal combustion engine according to the present invention, a combustion period is calculated by using in-cylinder pressure data measured by an in-cylinder pressure sensor. An in-cylinder flame velocity is then calculated from the combustion period. Next, in accordance with prepared data indicative of the influence of an engine speed on the flame velocity, a portion of the flame velocity calculated from the combustion period that is affected by the engine speed is eliminated. Eventually, a current EGR rate is determined from the flame velocity from which the portion affected by the engine speed is eliminated.