| 摘要 |
PURPOSE:To obtain a regularly stable exhaust purifying efficiency by providing, in the lower stream of a catalytic converter rhodium, a diagnostic sensor having two detecting elements for outputting electromotive forces according to oxygen concentration, with either of the elements having a nitrogen oxide reducing catalyst layer so that it can also sense the oxygen in nitrogen oxide. CONSTITUTION:A nitrogen oxide reducing catalyst layer is provided only on either of two oxygen concentration detecting elements of a diagnostic sensor (e) so that it can also sense the oxygen in nitrogen oxide. Thus, according to an increase in nitrogen oxide in the exhaust air, a difference is caused in the electromotive forces outputted from the two detecting elements of the diagnostic sensor (e). An abnormality detecting means (f) detects abnormality of nitrogen oxide exhaust quantity by this difference of the electromotive forces. When the abnormality is detected, the exhaust reflux quantity by an exhaust reflux control means (d) is increased and changed. Namely, when the nitrogen oxide in the exhaust air in the lower stream of a catalytic converter rhodium is increased, the exhaust reflux quantity is increased to reduce the combustion temperature, whereby the reduction effect of nitrogen oxide by exhaust reflux is stably ensured. |
