| 摘要 |
An exhaust system has main passageways (2#1-2#4), respectively, coupled corresponding to cylinders(#1-#4). The main exhaust passageways (2#1-2#4) merge to intermediate main passageways (3a,3b) and then into a single downstream main passageway (7). A main catalytic converter (8) is inserted midway of the downstream main passageway (7). Bypass passageways (11#1-11#4) branch from the respective upstream main passageways (2#1-2#4) and then merge into a single downstream bypass passageway (16), in which a bypass catalytic converter (18) is provided. An exhaust recirculation passageway (20) branches from a downstream side of the bypass catalytic converter (18). A bypass control valve (4) is closed only in the cold operating state, thereby to shift the exhaust gas flow. Even when the bypass control valve (4) is open, the exhaust gas flows through the bypass catalytic converter (18) inasmuch as exhaust gas recirculation is underway. Consequently, the catalyst deterioration diagnosis can be accomplished in accordance with detected signals of upstream and downstream air-fuel ratio sensors (21,22). |
