INTER-CYLINDER AIR-FUEL RATIO VARIATION ABNORMALITY DETECTION DEVICE

摘要

PROBLEM TO BE SOLVED: To improve the detection accuracy of variation abnormality detection by using even an output of an air-fuel ratio sensor before forcibly generating an air-fuel ratio variation state.SOLUTION: A first parameter correlated to an output variation degree of the air-fuel sensor is calculated, and a possible range DB1 of a second parameter B indicating an inter-cylinder air-fuel ratio variation degree is decided on the basis of the first parameter. The first parameter is calculated by forcibly changing an air-fuel ratio of one prescribed cylinder, and a difference DX1 of the first parameter before and after the forcible change is calculated. A first characteristic LDXB1 indicating a relationship between the second parameter B and the difference DX is decided on the basis of the possible range DB1 of the second parameter and the difference DX1. Either of the determination value and the first parameter which is calculated before the forcible change is corrected on the basis of an inclination of the decided first characteristic LDXB1.