Failure diagnostic apparatus and method for an air-fuel ratio sensor
First Claim
1. A failure diagnostic apparatus for an air-fuel ratio sensor, comprising:
- an air-fuel ratio sensor attached to an exhaust pipe of an internal combustion engine configured to detect an air-fuel ratio from an oxygen concentration of exhaust gas;
an offset power source configured to offset a ground-side voltage of the air-fuel ratio sensor;
means for judging whether the air-fuel ratio sensor is active;
means for judging for a failure from an offset-added output signal of the air-fuel ratio sensor in a period when the means for judging whether the air-fuel ratio sensor is active judges that the air-fuel ratio sensor is active;
means for switching a level of an input signal from the air-fuel ratio sensor when the means for judging for the failure has detected a failure in the air-fuel ratio sensor; and
means for inputting the input signal from the air-fuel ratio sensor through an A/D converter and determining whether the air-fuel ratio sensor is in a disconnection state or a ground fault state on the basis of a voltage level obtained when the means for switching a level of the input signal has switched the input signal level;
wherein an offset voltage of the offset power source is set higher than a maximum output voltage of the air-fuel ratio sensor and a maximum offset-added output voltage of the air-fuel ratio sensor is set lower than a maximum allowable input voltage of the A/D converter.
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Accused Products
Abstract
A failure diagnostic apparatus is provided with an offset power source for offsetting a ground-side voltage of an air-fuel ratio sensor, an activation state judging unit for judging whether the air-fuel ratio sensor is active, a failure diagnosing unit for judging for a failure from an offset-added output signal of the air-fuel ratio sensor in a period when the activation state judging unit judges that the air-fuel ratio sensor is active, an input resistance switching unit for switching the level of an input signal from the air-fuel ratio sensor when the failure diagnosing unit has detected a failure in the air-fuel ratio sensor, and a failure state judging unit for determining a type of failure of the air-fuel ratio sensor on the basis of a voltage level obtained when the input resistance switching unit has switched the input signal level.
26 Citations
6 Claims
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1. A failure diagnostic apparatus for an air-fuel ratio sensor, comprising:
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an air-fuel ratio sensor attached to an exhaust pipe of an internal combustion engine configured to detect an air-fuel ratio from an oxygen concentration of exhaust gas; an offset power source configured to offset a ground-side voltage of the air-fuel ratio sensor; means for judging whether the air-fuel ratio sensor is active; means for judging for a failure from an offset-added output signal of the air-fuel ratio sensor in a period when the means for judging whether the air-fuel ratio sensor is active judges that the air-fuel ratio sensor is active; means for switching a level of an input signal from the air-fuel ratio sensor when the means for judging for the failure has detected a failure in the air-fuel ratio sensor; and means for inputting the input signal from the air-fuel ratio sensor through an A/D converter and determining whether the air-fuel ratio sensor is in a disconnection state or a ground fault state on the basis of a voltage level obtained when the means for switching a level of the input signal has switched the input signal level; wherein an offset voltage of the offset power source is set higher than a maximum output voltage of the air-fuel ratio sensor and a maximum offset-added output voltage of the air-fuel ratio sensor is set lower than a maximum allowable input voltage of the A/D converter. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification