COMBUSTION STATE PARAMETER CALCULATION METHOD FOR INTERNAL COMBUSTION ENGINE

A combustion state parameter calculation method for an internal combustion engine, which is capable of continuously calculating a combustion state parameter while properly maintaining the accuracy of the calculated parameter even when part of in-cylinder pressure sensors is in failure. In the combustion state parameter calculation method, as a combustion state parameter, a first combustion state parameter dependent on the magnitude of in-cylinder pressure is calculated based on a detection value from an in-cylinder pressure sensor, on a cylinder-by-cylinder basis. When it is determined that a characteristic abnormality failure in which the magnitude of the detection value deviates from the actual in-cylinder pressure has occurred in part of the in-cylinder pressure sensors and has not occurred in the other in-cylinder pressure sensors, the first combustion state parameter of a failure-determined cylinder is calculated based on the detection value from the other in-cylinder pressure sensors.