Patent ID: 7409821

Claim:
A catalytic converter degradation determining system comprising: a temperature detecting section configured to detect a temperature of a catalytic converter that traps NOx in exhaust gas when a lean air-fuel mixture is used for combustion and that cleans and releases trapped NOx when a stoichiometric air-fuel mixture or a rich air-fuel mixture is used for combustion; a pre-degradation NOx adsorption efficiency establishing section configured to establish a pre-degradation NOx adsorption efficiency of the catalytic converter corresponding to conditions under which the catalytic converter is new based on the temperature of the catalytic converter; a pre-degradation trapped NOx estimating section configured to estimate a pre-degradation NOx trapping amount using the pre-degradation NOx adsorption efficiency; a post-degradation NOx adsorption efficiency establishing section configured to establish a post-degradation NOx adsorption efficiency of the catalytic converter corresponding to conditions under which the catalytic converter is degraded based on the temperature of the catalytic converter; a post-degradation trapped NOx estimating section configured to estimate a post-degradation NOx trapping amount using the post-degradation NOx adsorption efficiency; and a degradation determining section configured to determine that the catalytic converter is degraded when a difference between the pre-degradation NOx trapping amount and the post-degradation NOx trapping amount is below a prescribed value, the pre-degradation trapped NOx estimating section being further configured to calculate a pre-degradation trapped NOx rate by multiplying the pre-degradation NOx adsorption efficiency by an exhaust gas NOx quantity in the exhaust gas, and to estimate the pre-degradation NOx trapping amount by summing individual values of the pre-degradation trapped NOx rate over a prescribed amount of time, and the post-degradation trapped NOx estimating section being further configured to calculate a post-degradation trapped NOx rate by multiplying the post-degradation NOx adsorption efficiency by the exhaust gas NOx quantity in the exhaust gas, and to estimate the post-degradation NOx trapping amount by summing individual values of the post-degradation trapped NOx rate over a prescribed amount of time.