Failure determination method for O.sub.2 sensor
First Claim
1. A failure determination method for an O2 sensor which detects oxygen concentration of an exhaust gas from an internal combustion engine, comprising the steps of:
- (a) maintaining an air-fuel ratio of a mixture supplied to the internal combustion engine at a rich or lean value, with respect to a stoichiometric air-fuel ratio, for a first predetermined time period;
(b) forcibly subjecting the air-fuel ratio to an oscillatory change such that the air-fuel ratio alternately varies between a rich value with respect to the stoichiometric air-fuel ratio and a lean value with respect to the stoichiometric air-fuel ratio after a lapse of said first predetermined time period;
(c) detecting change of an output voltage of the O2 sensor during the forcibly subjected oscillatory change of the air-fuel ratio; and
(d) determining abnormality of the O2 sensor based on the detected change of the output voltage of the O2 sensor.
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Abstract
A failure determination method for an O2 sensor is provided wherein the air-fuel ratio of a mixture is maintained at a value which produces a leaner or richer air-fuel ratio than a stoichiometric ratio by a predetermined value, for a predetermined time after an engine starts operating in an idle region, to thereby make the oxygen concentration of exhaust gas surrounding the O2 sensor uniform. Subsequently, the air-fuel ratio is forcibly subjected to an oscillatory change with a predetermined amplitude of ±10 to 15% of the stoichiometric ratio with respect to the stoichiometric ratio at a predetermined frequency of several Hz, to determine abnormality of the O2 sensor based on the change of the output voltage of the O2 sensor.
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Citations
12 Claims
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1. A failure determination method for an O2 sensor which detects oxygen concentration of an exhaust gas from an internal combustion engine, comprising the steps of:
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(a) maintaining an air-fuel ratio of a mixture supplied to the internal combustion engine at a rich or lean value, with respect to a stoichiometric air-fuel ratio, for a first predetermined time period; (b) forcibly subjecting the air-fuel ratio to an oscillatory change such that the air-fuel ratio alternately varies between a rich value with respect to the stoichiometric air-fuel ratio and a lean value with respect to the stoichiometric air-fuel ratio after a lapse of said first predetermined time period; (c) detecting change of an output voltage of the O2 sensor during the forcibly subjected oscillatory change of the air-fuel ratio; and (d) determining abnormality of the O2 sensor based on the detected change of the output voltage of the O2 sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification