Air-fuel ratio control system for internal combustion engine

An air-fuel ratio control system for an internal combustion engine, comprising:

• upstream air-fuel ratio detecting means, provided upstream of a catalytic converter in an exhaust passage of the engine, for detecting a first air-fuel ratio of an air-fuel mixture based on exhaust gas upstream of the catalytic converter;
• downstream air-fuel ratio detecting means, provided downstream of the catalytic converter, for detecting a second air-fuel ratio of the air-fuel mixture based on the exhaust gas having passed through the catalytic converter;
• saturation determining means for determining saturation of said catalytic converter and a direction of said saturation based on said second air-fuel ratio;
• target air-fuel ratio setting means for correcting a target air-fuel ratio in a direction opposite to said direction of the saturation when said saturation determining means determines the saturation of the catalytic converter, said target air-fuel ratio setting means correcting said target air-fuel ratio by a given skip amount in a skipped manner;
• and
• fuel injection amount deriving means for deriving a fuel injection amount of a fuel injection valve at a given updating speed based on a differential between said first air-fuel ratio and said target air-fuel ratio.

An air-fuel ratio control system for an internal combustion engine, comprising:

• upstream air-fuel ratio detecting means, provided upstream of a catalytic converter in an exhaust passage of the engine, for detecting a first air-fuel ratio of an air-fuel mixture based on exhaust gas upstream of the catalytic converter;
• downstream air-fuel ratio detecting means, provided downstream of the catalytic converter, for detecting a second air-fuel ratio of the air-fuel mixture based on the exhaust gas having passed through the catalytic converter;
• saturation determining means for determining saturation of said catalytic converter and a direction of said saturation based on said second air-fuel ratio;
• adsorption amount deriving means for deriving a saturated adsorption amount of said catalytic converter;
• target air-fuel ratio setting means for setting the target air fuel ratio to a stoichiometric air-fuel ratio when no saturation is determined by said saturation determining means, and for continuously setting the target air-fuel ratio to a target value for a correction time when the saturation is determined by said saturation determining means, said target value and said correction time corresponding to said saturated adsorption amount derived by said adsorption amount deriving means;
• and
• fuel injection amount deriving means for deriving a fuel injection amount of a fuel injection valve at a given updating speed based on a differential between said first air-fuel ratio and said target air-fuel ratio.

An air-fuel ratio control system for an internal combustion engine, comprising:

• upstream air-fuel ratio detecting means, provided upstream of a catalytic converter in an exhaust passage of the engine, for detecting a first air-fuel ratio of an air-fuel mixture based on exhaust gas upstream of the catalytic converter;
• downstream air-fuel ratio detecting means, provided downstream of the catalytic converter, for detecting a second air-fuel ratio of the air-fuel mixture based on the exhaust gas having passed through the catalytic converter;
• inversion direction determining means for determining a direction of inversion of said second air-fuel ratio when said second air-fuel ratio has been inverted between rich and lean with respect to a stoichiometric air-fuel ratio;
• comparison value setting means for setting a comparison value on a side opposite to said direction of the inversion when determined by said inversion direction determining means;
• and
• fuel injection amount deriving means for deriving a fuel injection amount of a fuel injection valve based on a comparison between said first air-fuel ratio and said comparison value.