Patent ID: 8490385

Claim:
A catalyst deterioration diagnosis system for an exhaust gas purification device including an oxidation catalyst that oxidizes a component of an inflow exhaust gas and a reducing agent supply device that supplies a reducing agent into the exhaust gas that flows into the oxidation catalyst, the catalyst deterioration diagnosis system comprising: an electronic control unit that includes control logic, which when executed: detects or estimates an outflow exhaust gas temperature, which is a temperature of the exhaust gas that flows out of the oxidation catalyst or an outlet temperature of the oxidation catalyst; and performs a diagnosis of deterioration of the oxidation catalyst based on a detected value or an estimated value of the outflow exhaust gas temperature, wherein the electronic control unit performs the diagnosis of deterioration of the oxidation catalyst based on a high-temperature-inflow-condition exhaust gas temperature and a low-temperature-inflow-condition exhaust gas temperature, the high-temperature-inflow-condition exhaust gas temperature being a temperature detected or estimated by the electronic control unit while an inflow exhaust gas temperature, which is a temperature of the exhaust gas that flows into the oxidation catalyst or an inlet temperature of the oxidation catalyst, is in a high temperature region while the reducing agent is supplied from the reducing agent supply device, the low-temperature-inflow-condition exhaust gas temperature being a temperature detected or estimated by the electronic control unit while the inflow exhaust gas temperature is in a low temperature region, in which the inflow exhaust gas temperature is lower than the inflow exhaust gas temperature in the high temperature region, while the reducing agent is supplied from the reducing agent supply device.