| 摘要 |
The invention is intended to provide improved emission-cleaning performance by use of a three-way catalyst alone, without the need for a lean NOx catalyst, while ensuring a fuel economy improvement effect of lean burn operation. A multicylinder spark-ignition engine is constructed such that, in a pair of preceding and following cylinders whose exhaust and intake strokes overlap each other, burned gas discharged from the preceding cylinder ( 2 A, 2 D) which is currently in the exhaust stroke is introduced directly into the following cylinder ( 2 B, 2 C) which is currently in the intake stroke through an intercylinder gas channel ( 22 ) and gas discharged from only the following cylinder ( 2 B, 2 C) is led to an exhaust passage ( 20 ) provided with a three-way catalyst ( 24 ) in a low-load, low-speed operating range. Fuel supply to the individual cylinders is controlled in such a manner that combustion in the preceding cylinder ( 2 A, 2 D) is made under lean mixture conditions at an air-fuel ratio larger than the stoichiometric air-fuel ratio by a specific amount and combustion in the following cylinder ( 2 B, 2 C) is made under conditions of the stoichiometric air-fuel ratio created by supplying fuel to the burned gas introduced from the preceding cylinder ( 2 A, 2 D).
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