Patent ID: 6840235

Claim:
An internal exhaust gas recirculation amount estimation system of an internal combustion engine comprising: an exhaust valve closure timing in-cylinder temperature calculation section that calculates an in-cylinder temperature at an exhaust valve closure timing; an exhaust valve closure timing in-cylinder pressure calculation section that calculates an in-cylinder pressure at the exhaust valve closure timing; a gas constant calculation section that calculates a gas constant corresponding to a change in a composition of exhaust gas, based on an air-fuel mixture ratio; an exhaust valve closure timing in-cylinder residual gas amount calculation section that calculates an in-cylinder residual gas amount at the exhaust valve closure timing, based on at least the in-cylinder temperature, the in-cylinder pressure, and the gas constant; an valve overlap period blow-back gas amount calculation section that calculates a valve overlap period blow-back gas amount defined as a quantity of gas flow from one of intake and exhaust ports via a combustion chamber to the other port during a valve overlap period during which both of intake and exhaust valves are open together, the gas flow being created by a pressure difference between the intake and exhaust ports; and an internal EGR amount calculation section that calculates an internal exhaust gas recirculation amount based on the exhaust valve closure timing in-cylinder residual gas amount and the valve overlap period blow-back gas amount.