Patent ID: 6530214
Filing Date: 2003-03-11
Classification: F02D

Abstract:
An air-fuel ratio control apparatus for an internal combustion engine having a catalyst comprising:an upstream-side exhaust gas sensor and a downstream-side exhaust gas sensor for detecting an air-fuel ratio or a rich/lean state of an exhaust gas at an upstream-side and a downstream-side of the catalyst for cleaning the exhaust gas, respectively; air-fuel ratio feedback control means for feedback-controlling a fuel injection amount so that an air-fuel ratio detected by the upstream-side exhaust gas sensor becomes equal to an upstream-side target air-fuel ratio; intermediate target value setting means for setting an intermediate target value on the basis of an air-fuel ratio previously detected by the downstream-side exhaust gas sensor and a final downstream-side target air-fuel ratio; sub-feedback control means for performing a sub-feedback control for correcting the upstream-side target air-fuel ratio on the basis of the air-fuel ratio detected by the downstream-side exhaust gas sensor and the intermediate target value; and return control means which performs, for a predetermined period of time, a return control for varying at least one of an update amount and an update rate of the intermediate target value, and a control gain, a control period and a control range of the sub-feedback control, when the catalyst is returned from a state of saturated adsorption.