Apparatus and method for diagnosing degradation or malfunction of oxygen sensor
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United States of America Patent
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Jul 14, 1998
Grant Date -
N/A
app pub date -
Jun 4, 1996
filing date -
Jun 5, 1995
priority date (Note) -
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Abstract
An oxygen sensor has a detecting device unit for outputting a sensor current such as a limiting current of which a value is constant even though a sensing voltage applied to the oxygen sensor changes in a limiting current generating region and corresponds to an air-fuel ratio of a combustion gas and a heater for heating the detecting device unit to keep a resistance of the detecting device unit even though the oxygen sensor is degraded. When the sensing voltage is changed to a second sensing voltage of a resistance governing region, a current peak occurs in the sensor current, and a peak current value is detected. Because the peak current value decreases as the oxygen sensor is gradually degraded, when the peak current value is lower than a degradation judging value, it is judged that the oxygen sensor is degraded. Therefore, the diagnosis of the degradation of the oxygen sensor can be performed with a high accuracy.
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