| 摘要 |
A front A/F sensor (4) which detects an air-fuel ratio of exhaust flowing into a first three-way catalyst (3a), a first rear O2 sensor (5a) which detects an oxygen concentration of exhaust flowing out of the first three-way catalyst, a second three-way catalyst (3b) interposed downstream of the first three-way catalyst, and a second rear O2 sensor (5b) which detects an oxygen concentration of the exhaust flowing out of the second three-way catalyst (3b), are provided. During normal running, the oxygen storage amount of the first three-way catalyst (3a) is computed based on the detected air-fuel ratio, and the air-fuel ratio of the engine is controlled based on the computed oxygen storage amount so that the oxygen storage amount of the first three-way catalyst (3a) is a target amount. However, after running at a lean air-fuel ratio due to fuel cut, the air-fuel ratio is controlled based on the oxygen concentration detected by the second rear O2 sensor (5b) so that the oxygen storage amounts of the catalysts are target values. |
