Patent ID: 6856890

Claim:
An intake air amount estimation apparatus for an internal combustion engine, comprising: a first relational expression setter that sets a first relational expression between an intake pipe pressure and an amount of intake gas flowing into cylinders in the case of a first valve timing of the internal combustion engine wherein a valve timing can be changed in at least two stages between the first valve timing and a second valve timing and wherein an exhaust gas recirculation passage provided with a control valve is connected to an intake pipe downstream of a throttle valve; a second relational expression setter that sets a second relational expression between the intake pipe pressure and the intake gas amount in the case of the second valve timing; a first calculator that calculates, in the case of the first valve timing, an amount of recirculated exhaust gas flowing past the control valve which is based on an intake pipe pressure at the time when the control valve is at a specific opening degree, as an amount of intake exhaust gas flowing into the cylinders during steady operation of the engine; a second calculator that calculates, on the basis of the intake exhaust gas amount and by means of the first relational expression, an amount of intake air that is drawn via the throttle valve at the time when the control valve is at the specific opening degree in the case of the first valve timing; and a third calculator that calculates, on the basis of the intake exhaust gas amount and by means of the second relational expression, an intake air amount at the time when the control valve is at the specific opening degree in the case of the second valve timing, on the assumption that the intake exhaust gas amount for the specific opening degree based on the intake pipe pressure remains unchanged irrespective of a valve timing.