| 摘要 |
PROBLEM TO BE SOLVED: To promote refreshing of a catalyst while suppressing deterioration of the fuel consumption in a spark ignition type direct injection engine provided with a catalyst of NOx absorbing type in an exhaust passage, being operated by changing-over between the stratified combustion mode and uniform combustion mode, and switched to the rich operation forcedly, when the NOx absorbing amount of the catalyst increases. SOLUTION: When an engine 1 is switched forcedly into rich operation, the closing motion of a throttle valve, in association with changing-over from the stratified combustion mode to the uniform combustion mode, is delayed to temporarily generate a condition in which the oxygen concentration in the exhaust gas is low and the flow rate of the exhaust gas is sufficiently high (SA15 and 16). The amount of fuel injection is increased, so that the excess air ratio in the combustion chamber does not becomeλ=1 to 1.3. Similar control is conducted for promoting the release of NOx from the catalyst, when the engine is in acceleration operation.
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