ABNORMALITY DIAGNOSIS APPARATUS FOR EXHAUST GAS PURIFICATION APPARATUS

摘要

The present invention provides an abnormality diagnosis apparatus for an exhaust gas purification apparatus having an SCR catalyst, with which a misdiagnosis of an abnormality in the SCR catalyst even though the SCR catalyst is normal can be suppressed. In the present invention, a NO X purification ratio is determined using an estimated NO X inflow amount as a parameter, and an abnormality in the SCR catalyst is diagnosed on the basis of the NO X purification ratio. According to the present invention, a minimum NH 3 adsorption amount is determined as an NH 3 adsorption amount of the SCR catalyst in a condition where an actual NO X inflow amount reaches a maximum. When the minimum NH 3 adsorption amount equals or exceeds a predetermined amount, a determination is made as to whether or not a NO X purification ability of the SCR catalyst has deteriorated from a normal condition by comparing the NO X purification ratio with a first threshold. When the minimum NH 3 adsorption amount is smaller than the predetermined amount, a determination is made as to whether or not the NO X purification ability of the SCR catalyst has been completely lost by comparing the NO X purification ratio with a second threshold that is smaller than the first threshold.