SYSTEM FOR DETERMINING DETERIORATION OF CATALYST

摘要

A system which accurately determines deterioration of a NOx storage reduction catalyst (4). This system for determining deterioration of a catalyst is provided with: a supply unit (5) which changes the air/fuel ratio of an exhaust passing through a NOx catalyst (4) by supplying a reducing agent to the NOx catalyst (4); an NH3 detection unit (8) which detects NH3 in the exhaust in the downstream of the NOx catalyst (4); a control unit (10) which controls the amount of the reducing agent so that the air/fuel ratio of the exhaust is at a predetermined rich air/fuel ratio; and a determination unit (10) which determines that the NOx catalyst (4) is deteriorated in cases when the value detected by the NH3 detection unit (8) is at the threshold value or higher when the reducing agent is supplied while controlling the amount of the reducing agent so that the air/fuel ratio of the exhaust is at the predetermined rich air/fuel ratio.