초록 ▼

A catalyst 3 which has oxygen storage performance is installed in an engine exhaust passage 2, an oxygen storage amount is estimated based on the output of an upstream air-fuel ratio sensor 4 installed in the upstream of the catalyst 3, and an air-fuel ratio is controlled so that this oxygen storage

A catalyst 3 which has oxygen storage performance is installed in an engine exhaust passage 2, an oxygen storage amount is estimated based on the output of an upstream air-fuel ratio sensor 4 installed in the upstream of the catalyst 3, and an air-fuel ratio is controlled so that this oxygen storage amount coincides with a target value. When the output of a downstream air-fuel ratio sensor 5 has become lean or rich for longer than a fixed time, the output of the upstream air-fuel ratio sensor 4 is corrected based on the output of the downstream air-fuel ratio sensor 5 placed in the downstream of the catalyst 3. In this way, the output fluctuation due to deterioration of the air-fuel ratio sensor 4 upstream of the catalyst is corrected, and the catalyst oxygen storage amount is always precisely controlled to the target value.

대표청구항 ▼

1. 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 f

1. 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.