| 摘要 |
PURPOSE:To obtain an optimal air-fuel ratio at the time of full-cylinder operation and also at the time of partial-cylinder operation of an engine, by providing an O2-sensor respectively in an exhaust passage for cylinders that are always kept in operation and in an exhaust passage for cylinders that can be rendered inoperative, and controlling the air-fuel ratio for these two sets of cylinders independently according to the output signals of the two O2-sensors. CONSTITUTION:An exhaust passage 1 connected to both of cylinder-group #1-#3 that can be rendered inoperative by stopping fuel supply in a low-load region and cylinder- group #4-#6 that are alway kept in operation is divided into an exhaust passage 2 for the cylinders #1-#3 and an exhaust passage #4-#6 at an intermediate portion of the passage 1. A first catalyst 7 is disposed in the exhaust passage 3 while a second catalyst 8 is disposed on the downstream side of the position where the two exhaust passages 2 and 3 are joined. Further, a first O2-sensor 9 is disposed in the exhaust passage 3 at the position on the upstream side of the first catalyst 7 while a second O2-sensor 10 is disposed in the exhaust passage 2. During the operation of an engine, the air-fuel ratio of the cylinders #1-#3 and that for the cylinders #4-#6 are controlled independently from each other by furnishing the output signals of the two sensors 9, 10 to a control means. |
