| 摘要 |
PROBLEM TO BE SOLVED: To provide a diagnosis device for an internal combustion engine, utilizing cylinder pressure detecting means for calculating the deviation amount of an air-fuel ratio between cylinders including regions richer than a theoretical air-fuel ratio or calculating an air-fuel ratio index value.SOLUTION: The diagnosis device for the internal combustion engine includes cylinder pressure sensors 30. A discrimination of whether the cylinders each correspond to a rich cylinder or a lean cylinder is made. A cylinder pressure detected by each of the cylinder pressure sensors 30 is used for calculating a polytropic index m in an expansion stroke in each of the cylinders. On the basis of the polytropic index m in the expansion stroke in a reference lean cylinder where the lean degree of an air-fuel ratio is estimated and the lean degree, a m-AF curve and the polytropic index m in the expansion stroke in the reference lean cylinder are associated with each other. On the basis of the polytropic index m in the expansion stroke in the reference cylinder, the m-AF curve after associated therewith, and the polytropic index m in the expansion stroke in another cylinder than the reference lean cylinder, the deviation amount of the air-fuel ratio between the cylinders is calculated. |
