Catalyst degradation detector judges degradation based on statistics value obtained from frequency data of each divided area of catalyst

摘要

A numeric unit (14) determines frequency data for each divided area of catalyst (4) according to value of degradation parameter obtained by comparing air fuel ratio measured by a pair of sensors (5,6). Based on frequency data, a statistic value is measured by a calculator (15) according to which degradation of catalyst is determined. A pair of sensors (5,6) are individually provided to upper and lower stream sides of catalyst (4) to measure air fuel ratio.