A control apparatus for an internal combustion engine prevents variation of an air fuel ratio even upon introduction of purge air. A delay time occurring until the intake air detected, after having arrived at the combustion chamber through a surge tank, influences an air fuel ratio sensor, a delay time occurring until purge air containing evaporated fuel generated upon purging a canister, after having arrived at the combustion chamber through the surge tank, influences the air fuel ratio sensor, and a delay time occurring until fuel supplied by an injector, after having arrived at the combustion chamber, influences the air fuel ratio sensor, are represented by simplified physical models. A purge rate in the combustion chamber or in the neighborhood of the air fuel ratio sensor is calculated by using the physical models, and a purge air concentration and a fuel correction amount are calculated based on the purge rate thus obtained.
A control apparatus for an internal combustion engine, where a calculated fuel injection quantity is corrected with a purge-air-concentration learnt value calculated by subjecting a purge air concentration to purge-air-concentration filtering. A filtering effect in the purge-air-concentration filtering is changed in the direction of enhancing exhaust gas purification, when the purge air concentration is thick and when the purge air concentration is thin, whereby an air/fuel ratio introduced into the internal combustion engine is precisely controlled to a target air/fuel ratio so as to enhance the exhaust gas purification.
A butterfly valve restricts flow passage areas of a purge passage and a blow-by gas passage by the same degree. A first pressure sensor detects variation in pressure of the purge gas, which is generated by the butterfly valve. A second pressure sensor detects variation in pressure of the blow-by gas, which is generated by the butterfly valve. Since a fuel vapor concentration of the blow-by gas is lower than that of the purge gas, the blow-by gas can be treated as air of 100%. Hence, the fuel vapor concentration is calculated based on the variations in pressure detected by the first pressure sensor and the second pressure sensor.
