Catalyst monitor based on a thermal power model

Abstract

An on-board monitoring system for estimating the hydrocarbon conversion efficiency of a vehicle catalytic converter receives temperature signals from a plurality of temperature sensors positioned to detect the temperature of exhaust gas entering the catalytic converter and to detect the temperature of the catalyst substrate in the catalytic converter at spaced positions along the direction of flow. Diagnostic routine initiation tests are performed to determine if the vehicle is operating within an acceptable range, and if so, then a plurality of sets of temperature values are measured and stored over a plurality of time intervals. During the time intervals, several engine operating parameters are checked to determine if the vehicle is operating within a range which conforms approximately to the range of operation encountered in the Federal Test Procedure (FTP). Upon expiration of the time intervals, a total energy value, indicative of the thermal energy developed in the catalytic converter over the plurality of intervals is generated and compared to a predetermined value. If the calculated energy value deviates from the predetermined value by more than a predetermined deviation amount, a malfunction indicator light is set to indicate excessive deterioration of the catalytic converter.