| 摘要 |
PROBLEM TO BE SOLVED: To conduct current detection exactly by suppressing sensor current appropriately in any other range than an oxygen concentration detection range. SOLUTION: An A/F sensor (limiting current type air-fuel ratio sensor) 30 outputs a linear A/F (air-fuel ratio) detection signal in proportion to an oxygen concentration in exhaust gas from an engine 10 according to applied voltage commanded from a microcomputer 20. The microcomputer 20 controls the applied voltage into the A/F sensor 30 so as to limit sensor current to a prescribed value in the area out of air-fuel detection range (out of oxygen concentration detection range). The applied voltage is controlled on a V-I coordinate by prescribed positive characteristics in the air-fuel detection range, and the applied voltage is controlled by characteristics different from the above positive characteristics out of air-fuel ratio detection range. On the rich side out of the air-fuel ratio detection range, the applied voltage is controlled so as to approach the maximum value (0.9V) of electromotive force of the A/F sensor 30. On the lean side out of the air-fuel ratio detection range, the applied voltage is controlled so as to approach the minimum value (0V) of the electromotive force of the sensor 30. |
