| 摘要 |
<p>PURPOSE:To enhance the reliability of deterioration diagnosis by providing air-fuel ratio sensors on the upstream side and the downstream side of a catalytic converter, performing the deterioration judgement on the basis of signals of the air-fuel ratio sensors when it is judged that an engine meets the diagnosis conditions, and raising the exhaust gas temperature through the process of forcibly delaying the ignition time. CONSTITUTION:A catalytic converter 17 is interposed in an air exhaust passage 13, and O2 sensors 18, 19 are provided as air-fuel ratio sensors on the upstream side and the downstream side so as to input signals into a control unit 23. The control unit 23 performs the catalyst deterioration diagnosis from output signals of the O2 sensors 18, 19 after judging the fact that the fixed diagnosis conditions are met from a water temperature sensor 11, a crank angle sensor 21, a car speed sensor 22, etc. At this time, the exhaust temperature is raised by delaying the injection amount control of a fuel injection valve 14 and delaying the ignition time later than the optimum ignition time. Thus, the temperature of the catalytic converter 17 can be kept high, and the reliability of the diagnosis is enhanced without decreasing the opportunity and the frequency of the catalyst deterioration diagnosis.</p> |
