Method for detecting catalyst malfunctions
AssigneeFord Motor Company
InventorsDouglas R. Hamburg, Jeffrey A. Cook
Life of this patent
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Abstract
A method of detecting catalyst malfunction in a vehicle uses an exhaust gas oxygen sensor downstream of the catalyst. A feedback loop controls the air-fuel ratio as a function of the output signal from the exhaust gas oxygen sensor. The feedback gain is increased from low gain to high gain and then operational parameters are examined. In a first version the amplitude of the exhaust gas oxygen sensor is used as an indication. In a second version, the amplitude of the exhaust gas oxygen sensor reaches a predetermined limit and then the feedback gain is examined. In a third version, limit-cycle operation is reached and the frequency of the limit-cycle is examined with respect to a predetermined frequency.
Claims11
A method of detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including the steps of:
- providing a feedback loop to control air-fuel ratio as a function of the signal from the exhaust gas oxygen sensor;
- increasing feedback loop gain by altering operating parameters of the feedback loop until a desired characteristic of an output of the exhaust gas oxygen sensor is achieved;
- and
- establishing catalyst malfunction as a function of the output of the exhaust gas oxygen sensor and the feedback gain.
A method of detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including the steps of:
- applying a low gain to a feedback loop from the exhaust gas oxygen sensor downstream of the catalyst;
- examining the amplitude fluctuations of the exhaust gas oxygen sensor output;
- determining there is a high catalyst conversion efficiency if there are high amplitude fluctuations;
- determining there is a low catalyst conversion efficiency if there are low amplitude fluctuations;
- and
- establishing a catalyst failure when the amplitude fluctuations are below a predetermined amount.
A method of detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including the steps of:
- applying a low gain to a post-catalyst feedback loop;
- increasing the gain in the feedback loop until the amplitude fluctuations of the post-catalyst EGO sensor output reach a predetermined value;
- determining there is high conversion efficiency if a low gain is required to produce the predetermined value;
- determining there is a low conversion efficiency if a high gain is required to produce the predetermined value;
- determining the amount of gain required to produce the predetermined value;
- and
- establishing a catalyst failure when the gain is greater than a predetermined amount.
A method of detecting catalyst malfunction in a vehicle using exhaust gas oxygen sensor downstream of a catalyst including the steps of:
- applying a low gain to a post-catalyst feedback loop for controlling air-fuel ratio;
- increasing the gain in the feedback loop until the amplitude fluctuations of the post-catalyst EGO sensor output reach an air-fuel ratio limit-cycle operation;
- holding the gain constant at this level;
- measuring the limit-cycle frequency while the gain is held constant;
- and
- establishing a catalyst failure when the limit-cycle frequency is greater than a predetermined frequency.
An apparatus for detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including:
- a feedback loop to control air-fuel ratio as a function of the signal from the exhaust gas oxygen sensor;
- means for increasing the feedback gain until a desired fluctuation amplitude of the exhaust gas oxygen sensor is achieved;
- means for initially setting the gain of the post-catalyst feedback loop at a low value at the beginning of the catalyst testing interval to avoid a high amplitude limit-cycle oscillation which would saturate the exhaust gas oxygen sensor downstream of the catalyst,
- means for increasing the gain until a clearly defined limit-cycle oscillation is developed as indicated by the output of the exhaust gas oxygen sensor downstream of the catalyst;
- means for holding the gain constant during the remainder of the testing interval;
- means for determining the frequency of the limit-cycle;
- and
- means for establishing catalyst failure when the limit-cycle frequency is greater than a certain predetermined value.
An apparatus for detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including:
- means for applying a low gain to a feedback loop from the exhaust gas oxygen sensor downstream of the catalyst;
- means for examining the amplitude fluctuations of the exhaust gas oxygen sensor output;
- means for determining there is a high catalyst conversion efficiency if there are high amplitude fluctuations;
- means for determining there is a low catalyst conversion efficiency if there are low amplitude fluctuations;
- and
- means for establishing a catalyst failure when the amplitude fluctuations are below a predetermined amount.
An apparatus for detecting catalyst malfunction in a vehicle using an exhaust gas oxygen sensor downstream of the catalyst including:
- means for applying a low gain to a post-catalyst feedback loop;
- means for increasing the gain in the feedback loop until the amplitude fluctuations of the post-catalyst EGO sensor output reach a predetermined value;
- means for determining there is high conversion efficiency if a low gain is required to produce the predetermined value;
- means for determining there is a low conversion efficiency if a high gain is required to produce the predetermined value;
- means for determining the amount of gain required to produce the predetermined value;
- and
- means for establishing a catalyst failure when the gain is greater than a predetermined amount.
An apparatus for detecting catalyst malfunction in a vehicle using exhaust gas oxygen sensor downstream of the catalyst including:
- means for applying a low gain to a post-catalyst feedback loop;
- means for increasing the gain in the feedback loop until the amplitude fluctuations of the post-catalyst EGO sensor output reach an air-fuel ratio limit-cycle operation;
- means for holding the gain constant at this level;
- means for measuring the limit-cycle frequency while the gain is held constant;
- and
- means for establishing a catalyst failure when the limit-cycle frequency is greater than a predetermined frequency.
Dependencies are inferred from the claim text.