Patent ID: 6622477
Filing Date: 2003-09-23
Classification: F01N,F02D,Y02T

Abstract:
An air/fuel ratio control device for an internal combustion engine, comprising:a catalyst provided in an exhaust gas pipe of the internal combustion engine, the catalyst having an oxygen storage function in which oxygen in the exhaust gas is adsorbed or released in response to the air/fuel ratio of the exhaust gas; an air/fuel ratio sensor disposed upstream of the catalyst in the exhaust gas pipe; an air/fuel ratio sensor disposed downstream of the catalyst in the exhaust gas pipe; and a controller which controls the air/fuel ratio, the controller functioning to: estimate an oxygen storage amount of the catalyst based on the output of the air/fuel ratio sensor upstream of the catalyst; control the air/fuel ratio so that the oxygen storage amount coincides with a target value; perform a variable setting the determination time on the output of the air/fuel ratio sensor downstream of the catalyst in response to operating conditions of the internal combustion engine; and correct the output of the upstream air/fuel ratio sensor when the continuous time after the output of the air/fuel ratio sensor downstream of the catalyst switches to a rich or a lean value exceeds the determination time, wherein a correction on the output of the upstream air/fuel ratio sensor is performed towards lean values when the output of the downstream air/fuel ratio sensor is rich, and when the output of the downstream air/fuel ratio sensor is lean, it is corrected towards rich values.