INTERNAL COMBUSTION ENGINE AIR-FUEL RATIO CONTROL APPARATUS AND METHOD

摘要

Internal combustion engine air-fuel ratio control apparatus and method are provided in which the target air-fuel ratio of exhaust gas flowing into an exhaust-gas purification catalyst unit (3) is controlled through at least proportional-integral control such that the correction amount per unit time of the oxygen amount in said catalyst unit (3) is maintained constant. When the intake air amount is smaller than a predetermined amount and the air-fuel ratio detected by an oxygen sensor (5) provided downstream of the catalyst unit (3) is rich, said target air-fuel ratio is controlled to suppress an increase in the air-fuel ratio in the exhaust-gas purification catalyst unit (3). Accordingly, even if rapid acceleration operation is performed in a state where the intake air amount is extremely small and the air-fuel ratio detected by the oxygen sensor (5) is rich, NOx in exhaust gas can be sufficiently removed through reduction reactions at the exhaust-gas purification catalyst unit (3).