Patent ID: 7281369

Claim:
A deterioration diagnosing device for use with a particulate filter which is interposed on an exhaust passage of an internal combustion engine to trap a particulate matter contained in an exhaust gas, the filter comprising an oxidation catalyst which promotes oxidation of the particulate matter so that the filter is regenerated using the oxidation catalyst by burning the trapped particulate matter in a high-temperature atmosphere, the deterioration diagnosing device comprising: a first sensor which detects an oxygen concentration of the exhaust gas in the exhaust passage upstream of the filter as a first concentration; a second sensor which detects an oxygen concentration of the exhaust gas in the exhaust passage downstream of the filter as a second concentration; and a programmable controller programmed to: determine that a regeneration of the filter has substantially begun when the difference between an excess air factor corresponding to the first concentration and an excess air factor corresponding to the second concentration is not less than a predetermined value; determine that the regeneration of the filter has substantially ended when the difference falls below the predetermined value; and determine whether or not the oxidation catalyst has deteriorated in relation to a substantial regeneration period from the beginning of the substantial regeneration of the filter to the end of the substantial regeneration of the filter.