To prevent the torque shock or deterioration of fuel consumption by injecting fuel directly into a combustion chamber during compression stroke so that the air-fuel ratio of an engine is close to a theoretical air-fuel ratio to execute a stratified combustion in the release of the occluded NOX from a NOX occlusion type catalytic device.
It is judged in an ECU 40 whether NOX is leaked or not from an exhaust emission purifying catalytic device 30 on the basis of the output of a NOX sensor 32. When the NOX to be occluded in an occlusion type NOX catalyst 30a is leaked, and the output from the NOX sensor 32 reaches a judgment threshold X1, resulting the judgment of YES, NOX purge is executed. Namely, the fuel regulated so that the air-fuel ratio of the engine is close to the theoretical air-fuel ratio is injected into a combustion chamber 8 through a fuel injection valve 6 in compression stroke to perform a stratified combustion. According to this, at the time of executing the stratified combustion in an extremely lean air-fuel ratio, this stratified combustion is kept to prevent a torque shock caused by the change of combustion form.
OKADA KOJIRO
TAMURA YASUKI
NAKAYAMA OSAMU
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