Patent ID: 6494038
Filing Date: 2002-12-17
Classification: F01N,F02D

Abstract:
An engine air-fuel ratio controller, comprising:a catalyst installed in an exhaust passage which absorbs oxygen when an exhaust air-fuel ratio is lean, and releases the absorbed oxygen when the exhaust air-fuel ratio is rich; means for detecting an air-fuel ratio upstream of the catalyst; means for detecting an air-fuel ratio downstream of the catalyst; means for controlling a fuel supply amount of the engine to obtain the stoichiometric air-fuel ratio, which is a target air-fuel ratio, based on the detection value of the upstream air-fuel ratio; means for estimating the oxygen storage amount absorbed by the catalyst based on the detection value of the upstream air-fuel ratio; means for modifying the target air-fuel ratio so that the estimated oxygen storage amount coincides with the target value; means for determining whether or not there is an error in the output of the upstream air-fuel ratio detecting means based on the detection value of the downstream air-fuel ratio; means for correcting the detection value of the upstream air-fuel ratio detecting means according to the determination result; and means for determining that there is a fault in the upstream air-fuel ratio sensor when the absolute value of the integral of the detection values of the upstream air-fuel ratio sensor exceeds a predetermined value.