Adaptive control of EGO sensor output
First Claim
1. An engine air/fuel control method for aligning a step change in output of an exhaust gas oxygen sensor which corresponds to a predetermined air/fuel ratio with the efficiency window of a catalytic converter positioned in the engine exhaust, comprising the steps of:
- generating an error signal related to a difference between the predetermined air/fuel ratio and the converter efficiency window;
shifting the step change and the corresponding predetermined air/fuel ratio towards the converter efficiency window by pumping current through an electrode of the sensor to reduce said error signal;
generating a correction factor related to a change in peak-to-peak excursion of said sensor output during a test period in which engine air/fuel operation is first forced sufficiently rich and then forced sufficiently lean of a preselected air/fuel ratio to saturate the EGO sensor output in its respective rich indicating state and lean indicating state; and
correcting said sensor output with said correction factor to reduce variations in said peak-to-peak excursion caused by said pumping of said current.
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Abstract
An engine air/fuel feedback control system adjusts the engine air/fuel ratio in response to a modified output of an exhaust gas oxygen sensor. A sensor output is compared to a reference at its nominal midpoint to develop a two-state signal indicating operation rich or lean of stoichiometry. This two-state or step output is shifted towards the peak efficiency window of a catalytic converter by pumping current through a sensor electrode in response to an error signal derived from a downstream sensor. Shifts in the upstream sensor amplitude caused by current pumping are corrected by a correction factor which is adaptively learned during a test cycle.
35 Citations
18 Claims
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1. An engine air/fuel control method for aligning a step change in output of an exhaust gas oxygen sensor which corresponds to a predetermined air/fuel ratio with the efficiency window of a catalytic converter positioned in the engine exhaust, comprising the steps of:
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generating an error signal related to a difference between the predetermined air/fuel ratio and the converter efficiency window; shifting the step change and the corresponding predetermined air/fuel ratio towards the converter efficiency window by pumping current through an electrode of the sensor to reduce said error signal; generating a correction factor related to a change in peak-to-peak excursion of said sensor output during a test period in which engine air/fuel operation is first forced sufficiently rich and then forced sufficiently lean of a preselected air/fuel ratio to saturate the EGO sensor output in its respective rich indicating state and lean indicating state; and correcting said sensor output with said correction factor to reduce variations in said peak-to-peak excursion caused by said pumping of said current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An engine air/fuel control method for aligning a midpoint in peak-to-peak excursion of a step change in output of an exhaust gas oxygen sensor which occurs at a predetermined air/fuel ratio with the efficiency window of a catalytic converter positioned in the engine exhaust, comprising the steps of:
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controlling the engine air/fuel ratio in response to a comparison of the sensor output with a reference value; generating an error signal related to a difference between the predetermined air/fuel ratio and the converter efficiency window; shifting the step change and the predetermined air/fuel ratio towards the converter efficiency window by pumping current through an electrode of the sensor to reduce said error signal; generating a correction factor related to a difference between a midpoint between the peak-to-peak amplitude of the sensor output and said reference value during a test period in which engine air/fuel operation is first forced sufficiently rich and then forced sufficiently lean of stoichiometric combustion to saturate the sensor output; and correcting the sensor output with said correction factor to reduce variations in the peak-to-peak excursion caused by said pumping of said current. - View Dependent Claims (12, 13, 14)
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15. An engine air/fuel control method for aligning a midpoint in peak-to-peak excursion of a step change in output of an exhaust gas oxygen sensor which occurs at a predetermined air/fuel ratio with the efficiency window of a catalytic converter positioned in the engine exhaust, comprising the steps of:
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generating an error signal related to a difference between the predetermined air/fuel ratio and the converter efficiency window; feedback control of the engine air/fuel ratio in response to a feedback variable derived by integrating a difference between the sensor output and a reference value, said feedback control also being responsive to said error signal; shifting the step change and the predetermined air/fuel ratio towards the converter efficiency window by pumping current through an electrode of the sensor to reduce said error signal; disabling said feedback and holding said pumping current at a constant value during a test period; forcing engine air/fuel operation lean for a predetermined time and rich for a preselected time during said test period; generating a correction ratio of a difference between a midpoint of the peak-to-peak excursion of the sensor output and said reference value to a stored value related to said pumping current during said test period; and correcting the sensor output with said correction ratio to reduce offsets in the peak-to-peak excursion caused by said pumping current. - View Dependent Claims (16, 17, 18)
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Specification