Catalyst deterioration diagnosis method, method for purification of exhaust gas using the diagnosis method, catalyst deterioration diagnosis apparatus, and apparatus for purification of exhaust gas using the diagnosis apparatus

An apparatus for purification of exhaust gas, comprising:

• a catalyst for purification of exhaust gas disposed in an exhaust gas flow path through which the exhaust gas flows;
• and
• a catalyst deterioration diagnosis apparatus for diagnosing deterioration of the catalyst for purification of exhaust gas, the catalyst deterioration diagnosis apparatus comprising:
• a test catalyst disposed in the exhaust gas flow path through which the exhaust gas flows;
• and
• an electronic control unit configured to:
• invert an air-fuel ratio of the exhaust gas in the flow path from a lean side to a rich side or from a rich side to a lean side;
• measure a change over time in electrical resistance of the test catalyst at the inversion of the air-fuel ratio and find a resistance change ratio of the test catalyst;
• and
• determine deterioration of the test catalyst based on the resistance change ratio.

A catalyst deterioration diagnosis method for diagnosing deterioration of a catalyst for purification of exhaust gas by using a test catalyst disposed in an exhaust gas flow path through which the exhaust gas flows, the method comprising:

• a flowing step of flowing the exhaust gas into contact with the test catalyst;
• an exhaust gas control step of inverting an air-fuel ratio of the exhaust gas in the flow path from a lean side to a rich side or from a rich side to a lean side;
• a measurement step of measuring a change over time in electrical resistance of the test catalyst at the inversion of the air-fuel ratio and finding a resistance change ratio of the test catalyst;
• and
• a determination step of determining deterioration of the test catalyst based on the resistance change ratio.