| 摘要 |
PURPOSE:To markedly reduce a time period while the concn. of oxygen can not be judged, by a method wherein the density of oxygen is judged when the difference of currents of the oxygen sensor in applying different voltages thereto is roughly zero. CONSTITUTION:In response to a control level Vm from a microcomputer 60, a voltage-applying circuit 70 alternatively generates rectangular waveform voltages A, B to apply them to a limiting current type oxygen sensor body 20 so that a current detection circuit 40 detects a current flowing in the sensor 20. When a falling and trailing edge level of a detection current is not equal to a rising and trailing edge succeeding thereto, the microcomputer 60 controls a rectangular waveform voltage so as to vary it to a voltage corresponding to a specific section of a limiting current in a current-voltage characteristic of the sensor 20. Consequently, when they are equal to each other, the falling and trailing edge is set with the limiting current and the concn. of oxygen, i.e., an air-fuel ratio is judged. In consideration of the air-fuel ratio, the injection control 80 of fuel is executed. The air-fuel ratio is judged irrespective of the heating control of the sensor 20. |
