Apparatus and method for diagnosing degradation or malfunction of oxygen sensor
First Claim
1. A method for diagnosing degradation of an oxygen sensor from which a limiting current corresponding to an oxygen concentration is output according to a voltage-current characteristic by applying a sensing voltage placed in a limiting current generating region, comprising the steps of:
- changing the sensing voltage applied to the oxygen sensor from a first sensing voltage to a second sensing voltage which is placed outside the limiting current generating region to output a sensing current having a current peak from the oxygen sensor;
detecting a peak current value of the sensing current output from the oxygen sensor;
judging whether or not the peak current value of the sensing current is within a normal range; and
diagnosing the oxygen sensor to be degraded in cases where it is judged that the peak current value of the sensing current is not within the normal range.
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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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Citations
16 Claims
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1. A method for diagnosing degradation of an oxygen sensor from which a limiting current corresponding to an oxygen concentration is output according to a voltage-current characteristic by applying a sensing voltage placed in a limiting current generating region, comprising the steps of:
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changing the sensing voltage applied to the oxygen sensor from a first sensing voltage to a second sensing voltage which is placed outside the limiting current generating region to output a sensing current having a current peak from the oxygen sensor; detecting a peak current value of the sensing current output from the oxygen sensor; judging whether or not the peak current value of the sensing current is within a normal range; and diagnosing the oxygen sensor to be degraded in cases where it is judged that the peak current value of the sensing current is not within the normal range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for diagnosing malfunction of an oxygen sensor from which a limiting current corresponding to an oxygen concentration is output according to a voltage-current characteristic by applying a sensing voltage placed in a limiting current generating region, comprising the steps of:
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setting a particular sensing voltage at a positive or negative value outside the limiting current generating region; applying the particular sensing voltage to the oxygen sensor; detecting a particular sensing current output from the oxygen sensor; judging whether or not a value of the particular sensing current is within a desired current value range; and informing of a malfunction of the oxygen sensor in cases where the value of the particular sensing current is not within the desired current value range. - View Dependent Claims (13, 14, 15)
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16. An apparatus for diagnosing degradation of an oxygen sensor from which a limiting current corresponding to an oxygen concentration is output according to a voltage-current characteristic by applying a sensing voltage placed in a limiting current generating region, comprising:
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voltage changing means for changing the sensing voltage applied to the oxygen sensor from a first sensing voltage to a second sensing voltage which is placed outside the limiting current generating region; current change detecting means for detecting a change of the sensor current output from the oxygen sensor to which the second sensing voltage is applied by the voltage changing means and detecting a peak current value of the sensing current; degradation diagnosing means for diagnosing degradation of the oxygen sensor according to the peak current value detected by the current change detecting means by judging whether or not the peak current value of the sensing current is within a normal range; degradation judging means for judging that the oxygen sensor is degraded in cases where it is judged by the degradation diagnosing means that the peak current value of the sensing current is not within the normal range and outputting a degradation judging signal; and alarming means for displaying the degradation of the oxygen sensor according to the degradation judging signal output from the degradation judging means.
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Specification