| 摘要 |
PURPOSE:To enable to control air-fuel mixture to the theoretial air-fuel ratio, by changing the mode of control from feedback control to open-loop control by making judgement than an O2-sensor has become inactive just before the O2- sensor becomes inactive while controlling the mixture to the theoretical air-fuel ratio by way of feedback control. CONSTITUTION:The timer T is counted from the time instant to when an O2- sensor 5 is cooled during feedback control of the air-fuel ratio by continuing low-load operation of an engine for a long time and the output voltage V of the sensor 5 becomes lower than an ''inactive'' judging voltage VD that is set at a higher level than a rich-lean judging threshold voltage Vtau of the O2-sensor 5. When the time T reaches a prescribed time T1, a micro-computor in a control unit 11 makes judgement that the O2-sensor 5 is inactive. In this state, solenoids 2, 3 are controlled to operate at a prescribed duty ratio by changing the mode of control from feedback control to open-loop control. Thus, it is enabled to control the air-fuel ratio appropriately and to prevent degradation of the specific fuel consumption and adverse effect to the catalyst and exhaust gas by making air-fuel mixture rich. |
