Air-fuel ratio detecting apparatus and method
First Claim
1. An air-fuel ratio detecting apparatus comprising:
- an air-fuel ratio sensor having a sensor body which, upon application of a voltage to the sensor body, generates a limit current in accordance with at least one of an oxygen concentration and an unburned gas concentration in a detection-object gas;
a sensor body drive circuit that drives the sensor body;
element impedance detection means for detecting an impedance of an oxygen ion-conductive element provided in the sensor body by applying an AC voltage to the sensor body; and
diagnostic means for detecting and diagnosing faults based on the detected element impedance.
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Abstract
Under normal conditions, the temperature of an oxygen ion-conductive element provided in a sensor body is about 700° C., and the element impedance is about 30 Ω. If there is a fault in the sensor body or a sensor body drive circuit, the current becomes zero and the element impedance becomes infinite. If a heater has deteriorated, the element temperature rises only up to, for example, about 550° C., and the element impedance becomes about 150 Ω. If there is a fault in the heater or the heater drive circuit, the element is heated only by exhaust gas, so that the element temperature rises only up to about the temperature of exhaust gas and the element impedance becomes a value corresponding to an element temperature of about 300° C. Three reference values Z1, Z2, Z3 are set for comparison with the detected value of element impedance in order to perform fault diagnosis.
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Citations
16 Claims
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1. An air-fuel ratio detecting apparatus comprising:
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an air-fuel ratio sensor having a sensor body which, upon application of a voltage to the sensor body, generates a limit current in accordance with at least one of an oxygen concentration and an unburned gas concentration in a detection-object gas;
a sensor body drive circuit that drives the sensor body;
element impedance detection means for detecting an impedance of an oxygen ion-conductive element provided in the sensor body by applying an AC voltage to the sensor body; and
diagnostic means for detecting and diagnosing faults based on the detected element impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A control method for an air-fuel ratio detecting apparatus including an air-fuel ratio sensor having a sensor body that generates a limit current in accordance with at least one of an oxygen concentration and an unburned gas concentration of a detection-object gas upon application of a voltage to the sensor body, and a sensor body drive circuit that drives the sensor body, the method comprising the steps of:
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detecting an element impedance of an oxygen ion-conductive element provided in the sensor body by applying an AC voltage to the sensor body; and
detecting and diagnosing faults based on the element impedance detected by the element impedance detection means. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification