| 摘要 |
PURPOSE:To judge the concn. of oxygen irrespective of the temperature control of a sensor by a method wherein an AC voltage is applied to the oxygen sensor from an oscillator circuit and when a detection current becomes stable, the detection current is judged as a limiting current of the sensor. CONSTITUTION:A microcomputer 70 allows an oscillator circuit 41 to generate an AC voltage and a DC power source to generate a DC voltage so that they are outputted to a limiting current type oxygen sensor body 20. The DC voltage is determined at a level whereby a center of a variable amplitude of the AC voltage is maintained at a slightly plus side. A current detection circuit 50 detects a current flowing in the sensor 20 and the detected current is applied with an A/D conversion 60 to be inputted to the microcomputer 70. The microcomputer 70 varies the AC voltage applied to the sensor 20 in a wide range, thereby when current In-1 is equal to current In on a horizontal linear section of the voltage-current characteristic, the newest current In is set as the limiting current so that an oxygen, i.e., an air-fuel ratio is judged on the basis of concn. of oxygen-limiting current data. A calculating operation for the fuel ejection control is executed on the basis of the air-fuel ratio. |
