| 摘要 |
PURPOSE:To prevent shift to lean air-fuel ratio controlled, by driving an exhaust system air-fuel ratio controlling actuator after the lapse of a prescribed delay time, if the exhaust air-fuel ratio is judged rich. CONSTITUTION:When the output of an oxygen concentration sensor 18 which is arranged in the downstream part of an exhaust manifold and detects the exhaust air-fuel ratio from the residual oxygen concentration in exhaust gas varies, with a fixed comparison voltage as center, the actuator driving current I is set 0 until a prescribed delay time T is lapsed, in the case when rich is judged according to the result or rich-lean judgement in a fixed comparator 32 in accordance with output, and after the lapse of the pescribed dealy time T, the actuator driving current is increased with the rich-side integration constant of a rich-side integration circuit 36, and secondary air is supplied. Therefore, the secondary- air feeding time is reduced, and the secondary-air feeding amount is reduced, so also the controlled air-fuel ratio becomes close to the thoretical air-fuel ratio, and the exhaust-gas purifying performance is improved. |
