Method for measuring conversion efficiency of catalyst and detecting deterioration thereof with air/fuel ratio sensors

摘要

The invention provides a method for accurately and precisely measuring a converted rate of a catalyst for HC/CO/NOx, NOx, and HC/CO and detecting deterioration using two air/fuel ratio sensors disposed on the upstream and downstream sides of the catalyst. The converted rate of the catalyst is determined based on a predetermined relationship between the mean converted rate and a reduction ratio of output amplitudes of the downstream sensor to the upstream sensor. The catalyst is determined to be deteriorating when the reduction ratio becomes less than a predetermined value.