| 摘要 |
The exhaust duct 28 of a direct-injection engine 1 is provided with three-way catalyst 32 and a lean NOx catalyst 33 are arranged in that order from the upstream side. Switching between a stratified combustion state at a stratified combustion region (I) of low revolutions speeds and low loads and a homogeneous combustion state of substantially the theoretical air/fuel ratio at a warm lambd=1 region (II) adjacent thereto with higher revolution speeds or loads, a first oxygen concentration sensor 30 is arranged upstream from the three-way catalyst 32, and when the engine 1 shifts from the stratified combustion region (I) to the warm mu=1 region (II), the feedback control of the air/fuel ratio based on an output signal of that sensor 30 begins, and the target air/fuel ratio A/F is set to a range of 14.0<=A/F<14.7, so that the target air/fuel ratio A/F is slightly richer than the theoretical air/fuel ratio, thus preventing a temporary deterioration of the exhaust gas state. A second oxygen concentration sensor 34 is arranged between the catalysts 32 and 33, and the corrective control of the air/fuel ratio is terminated when the output signal from that sensor 34 is inverted to the richer side.
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