| 摘要 |
PROBLEM TO BE SOLVED: To allow an output characteristic of an oxygen sensor to be changeable and capable of preventing a decrease in deterioration diagnosis accuracy of a catalyst due to a decrease in response properties of the oxygen sensor.SOLUTION: In a system in which a downstream oxygen sensor 21 is installed downstream of an upstream catalyst 18, output characteristics of the downstream oxygen sensor 21 can be changed by causing a constant current to flow between sensor electrodes by a constant current circuit provided outside the downstream oxygen sensor 21. A sensor response time of the downstream oxygen sensor 21 is detected during fuel cutting of an engine 11, and the constant current circuit is controlled so that the constant current flows by applying a voltage between the sensor electrodes of the downstream oxygen sensor 21 when the sensor response time exceeds a determination value. Accordingly, the output characteristics of the downstream oxygen sensor 21 are changed in a direction of reducing the sensor response time. The output characteristics of the downstream oxygen sensor 21 can be thereby changed in the direction of increasing the response properties when the response properties of the downstream oxygen sensor 21 decrease. |
