| 摘要 |
<p>PURPOSE:To improve the accuracy for judgement of deterioration of a catalyst converter by inhibiting operation of a catalyst deterioration detecting means when any abnormal condition of an exhaust return flow means is detected. CONSTITUTION:In an ECU 5 (electronic control unit), engine operation condition is judged, and a control signal is supplied to a solenoid valve 22 so as to set, to 0 level, the deviation between the valve opening degree command value of an exhaust return flow valve which is set according to internal-intake pipe absolute pressure PBA and the number of engine rotational speed NE and the real valve opening value of the exhaust return flow valve 19 detected by a lift sensor 24. In the ECU 5 under process of such solenoid valve control, it is judged whether the absolute value of the deviation between a real valve opening degree and the valve opening command value is larger than a specific dead zone value or not, abnormal condition of the exhaust return flow valve 19 is diagnosed when large condition thereof continues for a specific time, and the change is not generated during this period. When such abnormal condition diagnosis is protised, deterioration judgement of a catalyst converter 14 is inhibited by the ECU 5. It is thus possible to prevent fluctuation of a judgement time caused by exhaust return flow, and also to improve the accuracy of deterioration judgement.</p> |
