| 摘要 |
<P>PROBLEM TO BE SOLVED: To secure the conversion rate of exhaust gas when the air fuel ratio is rich with a relatively simple structure limiting operation loads. <P>SOLUTION: An open close valve 5 opening and closing an introduction path 4 introducing secondary air to an exhaust upstream of a three way catalyst is controlled by a control unit 6 to periodically increase and decrease flow rate of the introduced secondary air. Consequently, air fuel ratio of exhaust gas flowing in the three way catalyst 3 is alternated between lean air fuel ratio higher than a theoretical value and rich air fuel ratio lower than the theoretical value, and alternation cycle of air fuel ratio between lean and rich is changed by changing increase and decrease cycle of flow rate of secondary air based on a rotation speed of the engine 1. <P>COPYRIGHT: (C)2007,JPO&INPIT |
