| 摘要 |
PURPOSE:To decrease nitrogen oxides by providing a reduction catalyst layer for the nitrogen oxides to accelerate the reduction reaction of the nitrogen oxides on the outside surface of a platinum catalyst layer so that lean detection is executed on the richer side as the concn. of the nitrogen oxides is higher. CONSTITUTION:An inside electrode 2 and outside electrode 3 respectively consisting of platinum are formed to part of the inside and outside surfaces of a ceramics pipe 1 and a platinum catalyst layer 4 is deposited by evaporation on the outside surface of the pipe 1. The reduction catalyst layer 5 in which catalyst particles are made to co-exist with titanium oxide, etc., as a carrier is formed on the outside surface of the layer 4. The layer 5 accelerates the reaction between the nitrogen oxides NOX and the unburned components CO and HC in an exhaust as when the NOX arrives at the layer 5. The concn. of O2 increases correspondingly and the difference between the concn. of O2 on the inside of the pipe 1 and the concn. of O2 on the discharge side decreases. The leak detection is thus executed. The air-fuel ratio is, therefore, eventually controlled to the richer side as the concn. of NOX is higher if the feedback control of the air-fuel ratio is executed in accordance with the result of the detection. The increase in the amt. of the NOX to be discharged is thus suppressed. |
