Air-fuel ratio control manner of the internal combustion engine and degradation method of detection null of the exhaust air concentration sensor which is used for its air-fuel ratio control

摘要

PURPOSE:To detect surely the degradation degree of an exhaust concentration sensor by calculating the average values of air-fuel ratio correction factors for a plurality of set values of desired air-fuel ratio and comparing a plurality of calculated average values with each other to detect the degradation degree of the exhaust concentration sensor. CONSTITUTION:An oxygen concentration sensor 15 is attached to the upstream side of a ternary catalyst 14 in an exhaust pipe 13 to input the output together with the outputs of other various sensors to an ECU 5 and calculate fuel injection timing TOUT according to the engine running condition. That is, basic fuel injection timing Ti determined on the basis of the engine condition is correctively calculated to obtain TOUT according to a desired air-fuel ratio correction factor, air fuel ratio correction factor and other correction factors based on various engine parameter signals. Then, the average values of the air fuel ratio correction factors are calculated respectively in a plurality of set values of desired air-fuel ratio to compare a plurality of calculated average values with each other and detect the degradation degree of the sensor 15. The output value of the sensor 15 is corrected according to the degradation degree.