| 摘要 |
PURPOSE:To enable to control the air-fuel ratio corresponding to pump current to a value in the vicinity of the theoretical air-fuel ratio, by feedback controlling the air-fuel ratio such that the pump current passed through an oxygen pump of an air-fuel ratio sensor is lower than a prescribed value. CONSTITUTION:Providing that the air-fuel ratio at time t0 is richer than the theoretical air-fuel ratio, the air-fuel ratio is controlled to become lean, so that correction data I and driving time T1 are reduced gradually and the air-fuel ratio is decreased gradually to the theoretical air-fuel ratio. Then, at time t1 when the air-fuel ratio becomes equal to the theoretical air-fuel ratio, current IP is inversely increased and air-fuel ratio data PI is also inversely increased. Subsequently, when the data PI becomes higher than a prescribed value alpha at time t2, the air-fuel ratio is controlled to become rich by inverting the correction data I and thereby increasing the driving time T1 gradually. Further, when the data PI becomes higher than the value alpha again at time t4, the driving time T1 is decreased gradually by inverting the correction data I. Thus, the current IP is kept lower than an upperlimit control value and the air-fuel ratio of an engine 20 is controlled to be within a prescribed range. |
