| 摘要 |
PROBLEM TO BE SOLVED: To change output characteristics of an oxygen sensor, and to prevent occurrence of trouble caused by output voltage variation due to internal resistance of the oxygen sensor during supply of a constant current.SOLUTION: Output characteristics of an oxygen sensor 21 can be changed by allowing a constant current circuit formed on the outside of the oxygen sensor 21 to flow a constant current between sensor electrodes. When a predetermined current switching permission condition is formed, a current value of a current flowing between the sensor electrodes is switched, a direct current resistance value (internal resistance value) of the oxygen sensor 21 is calculated from a difference between outputs of the oxygen sensor 21 before and after the switching and a difference between current values. In constant current supply (namely when changing the output characteristics of the oxygen sensor 21) for allowing the constant current to flow between the sensor electrodes, output voltage variation is found out from the constant current value and the direct current resistance value, and the output of the oxygen sensor 21 is corrected by using the output voltage variation. Consequently, air-fuel ratio control based on the output of the oxygen sensor 21 can be accurately performed. |
