Air-fuel ratio control device for an engine

Abstract

The air-fuel ratio control device according to the present invention controls the air-fuel ratio of the engine in accordance with the output of the air-fuel ratio sensor disposed on the exhaust gas passage upstream of the three-way reducing and oxidizing catalyst. Further, to compensate for the change in the output characteristics of the upstream air-fuel ratio sensor, the output of the upstream air-fuel ratio sensor is corrected in accordance with the output of another air-fuel ratio sensor disposed on the exhaust gas passage downstream of the catalyst. Since the response of the downstream air-fuel ratio sensor is delayed due to the O.sub.2 storage capacity of the catalyst, the air-fuel ratio control device in the present invention predicts the future value, by a specified time, of the output of the downstream air-fuel ratio sensor based on the history of the change in the output of the upstream air-fuel ratio sensor and the present output of the downstream air-fuel ratio sensor. Since the output of the upstream air-fuel ratio sensor is corrected based on the predicted output of the downstream air-fuel ratio sensor, precise air-fuel ratio control can be achieved by eliminating the delay in the response of the downstream air-fuel ratio sensor caused by the O.sub.2 storage capacity of the catalyst.

Dependencies are inferred from the claim text.