Method and system for monitoring a catalytic converter

摘要

A method and system are provided for monitoring exhaust gas conversion efficiency of a catalytic converter during operation of an internal combustion engine coupled to the catalytic converter. The system includes an upstream exhaust gas sensor interposed the engine and the catalytic converter for generating a first signal based on the exhaust gas upstream of the converter. A downstream exhaust gas sensor is interposed the catalytic converter and atmosphere for generating a second signal based on the exhaust gas downstream of the converter. A phase shift detector is provided for estimating a phase shift between the first and second signals. A processor is provided for aligning the first and second signals such that the resulting phase shift between the first and second signals is substantially an integer multiple of pi radians and for determining conversion efficiency of the catalytic converter based such phase aligned first and second signals. With such method and system, average error of the calculated index ratio using such system and method and the theoretical average error in index ration (IR) is minimized when the phase shift between the upstream and downstream sensor signals is substantially an integer multiple of pi radians.