| 摘要 |
The present invention relates to a diagnostic device which performs highly accurate diagnosis of the deterioration of a diesel oxidation catalyst (DOC). The present invention is provided with: a DOC (15) for oxidizing hydrocarbons (HC) and nitrogen monoxide (NO) in an exhaust gas; a selective catalytic reduction (SCR) catalyst (22) for reducing and purifying NOx included in the exhaust gas; a NOx-purification-rate calculation unit (41) which calculates, on the basis of NOx values at an upstream side and a downstream side of the SCR catalyst (22), a low-temperature-side NOx purification rate and a high-temperature-side NOx purification rate; a HC heat-generation-rate calculation unit (42) which calculates a HC purification rate on the basis of at least the difference between the exhaust-gas heat quantities at an upstream side and a downstream side of the DOC (15); and a deterioration determination unit (45) which determines the deterioration in the NO2 generation performance of the DOC (15), on the basis of the calculated low-temperature-side NOx purification rate, the calculated high-temperature-side NOx purification rate, and the calculated HC purification rate. |
