Dual-sensor type air fuel ratio control system for internal combustion engine and catalytic converter diagnosis apparatus for the same

摘要

A dual-sensor type air-fuel ratio control system for an internal combustion engine. A catalytic converter disposed within an exhaust pipe is flanked by first and second upstream and downstream air-fuel ratio sensors 11, 12. An apparatus for detecting deterioration of the catalytic converter includes a deterioration decision circuit 54 for determining deterioration of the catalyst on the basis of at least the second air-fuel ratio sensor signal, a filter circuit 50 for filtering the second sensor signal, and a comparison circuit 51 for comparing the second sensor filtered and unfiltered signals. The deterioration decision circuit compares a deterioration parameter value derived from the result of the comparison with a predetermined value corresponding to a detected operation state of the engine to determine deterioration of the catalyst when the deterioration parameter value exceeds the predetermined value.