Deterioration determining apparatus and deterioration determining method for oxygen sensor

A deterioration determining apparatus for an oxygen sensor, which is applied to an engine in which a feedback control of an air-fuel ratio is performed by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor, and a feedback center of the air-fuel ratio correction coefficient is adjusted by making response of the air-fuel ratio correction coefficient with respect to the output of the oxygen sensor different between when it is detected that the air-fuel ratio is richer than a target air-fuel ratio based on the output of the oxygen sensor, and when it is detected that the air-fuel ratio is leaner than the target air-fuel ratio based on the output of the oxygen sensor, comprising:

• a determining device which sets a deterioration determining value concerning a determination as to whether the oxygen sensor has deteriorated such that the deterioration determining value is variable according to a degree of adjustment of the feedback center of the air-fuel ratio correction coefficient, and makes the determination as to whether the oxygen sensor has deteriorated based on an inversion cycle of the output of the oxygen sensor and the deterioration determining value.

A deterioration determining method for an oxygen sensor, which is applied to an engine in which a feedback control of an air-fuel ratio is performed by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor, and response of the air-fuel ratio correction coefficient with respect to the output of the oxygen sensor is set so as to be variable, comprising the steps of:

• setting a deterioration determining value concerning a determination as to whether the oxygen sensor has deteriorated such that the deterioration determining value is variable according to the set response of the air-fuel ratio correction coefficient with respect to the output of the oxygen sensor;
• and
• making the determination as to whether the oxygen sensor has deteriorated based on an inversion cycle of the output of the oxygen sensor and the deterioration determining value.

A deterioration determining method for an oxygen sensor, which is applied to an engine in which a feedback control of an air-fuel ratio is performed by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor, and a feedback center of the air-fuel ratio correction coefficient is adjusted by making response of the air-fuel ratio correction coefficient with respect to the output of the oxygen sensor different between when it is detected that the air-fuel ratio is richer than a target air-fuel ratio based on the output of the oxygen sensor, and when it is detected that the air-fuel ratio is leaner than the target air-fuel ratio based on the output of the oxygen sensor, comprising the steps of:

• setting a deterioration determining value concerning a determination as to whether the oxygen sensor has deteriorated such that the deterioration determining value is variable according to a degree of adjustment of the feedback center of the air-fuel ratio correction coefficient;
• and
• making the determination as to whether the oxygen sensor has deteriorated based on an inversion cycle of the output of the oxygen sensor and the deterioration determining value.