| 摘要 |
<p>An engine has a first cylinder group (1) and a second cylinder group (2). The first cylinder group (1) and the second cylinder group (2) are connected to a common NOx storage reduction catalyst (13) via their corresponding exhaust passageways (7, 10) and their corresponding three-way catalysts (9, 12), respectively. When the temperature of the NOx storage reduction catalyst (13) is to be raised, the average air-fuel ratio of the first cylinder group (1) is made rich, and the average air-fuel ratio of the second cylinder group (2) is made lean. At this time, in the first cylinder group (1), the air-fuel ratio of two cylinders is made rich and the air-fuel ratio of one cylinder is made lean, and in the second cylinder group (2), the air-fuel ratio of two cylinders is made lean and the air-fuel ratio of one cylinder is made rich, in accordance with an embodiment.</p> |
