| abstract |
In an internal combustion engine, an NO X selective reduction catalyst (15) is arranged in the engine exhaust passage, and a urea aqueous solution feed valve (17) is arranged in the engine exhaust passage upstream of the NO X selective reduction catalyst (15). Based on the detections results of an NO X purification rate detecting means for detecting the NO X purification rate by the NO X selective reduction catalyst (15), a urea aqueous solution feed amount detecting means for detecting the amount of feed of the urea aqueous solution, and a urea aqueous solution concentration detecting means for detecting the concentration of the urea aqueous solution, abnormalities in the NO X selective reduction catalyst (15), urea aqueous solution feed system, and urea aqueous solution are judged. |