| 摘要 |
PURPOSE:To prevent air-fuel ratio control from deteriorating in accuracy by correcting air-fuel ratio detection characteristics into specific characteristic when air or specific gas which differs in oxygen concentration is supplied. CONSTITUTION:The intake side of an oxygen sensor 2 is connected to supply paths 27 and 28 for gaseous N2 and air through a cross valve 25, whose opening/closing state is switched by a solenoid valve regulating circuit 29 to supply the gaseous N2 or air to the sensor 2 selectively by an air pump 21. Then, the output voltage V1 of a reference electrode 13 and a zero-point adjusting voltage VR developed by a variable resistance VR1 are inputted to a comparator, which compares both voltage values to calibrate the detection characteristics. Therefore, even if the oxygen concentration detected value of a sensing electrode 14 deviates slightly in a state before the calibration, the comparator output becomes zero in an ideal air-fuel ratio artificial state in which there is no oxygen at the time of gaseous N2 supply, so that the actual detected value is also calibrated to the zero level. Further, the point of air 100% (oxygen concentration: 21%) is specified accurately based on the zero level, so the air-fuel ratio detection characteristics which vary accurately corresponding to the actual air-fuel ratio are obtained over the entire range from the zero level to the 21% air concentration are obtained. |
