Patent ID: 7089106

Claim:
An in-cylinder air amount estimation apparatus which is applied to an internal combustion engine where pulsation of a pressure occurs in an intake pipe due to opening/closing of an intake valve, and which calculates an inflow air amount that is an amount of air flowing into the intake pipe, and estimates an in-cylinder air amount using the inflow air amount, comprising: a reduction amount calculation device which performs quantization of an output of a pressure sensor for detecting the pressure in the intake pipe using analogue to digital conversion in a predetermined sampling cycle, and calculates a pressure reduction amount that is an amount of reduction in the pressure in the intake pipe due to opening of the intake valve using a value obtained by the quantization as the pressure in the intake pipe; an excess air amount calculation device which calculates an excess air amount that is an amount of air charged into a cylinder due to the pulsation of the pressure, based on the pressure reduction amount; and an in-cylinder air amount estimation device which estimates the in-cylinder air amount based on the inflow air amount and the excess air amount, wherein the reduction amount calculation device calculates, as the pressure reduction amount for calculating the excess air amount, an average value of the pressure reduction amount in plural opening/closing cycles of the intake valve; and the reduction amount calculation device obtains the average value of the pressure reduction amount using an averaging method with high accuracy in a case where a ratio of a length of a pulsation cycle of the pressure to a length of the sampling cycle for the analogue to digital conversion is less than a predetermined level, as compared to a case where the ratio of the length of the pulsation cycle of the pressure to the length of the sampling cycle for the analogue to digital conversion is equal to or greater than the predetermined level.