Abstract: An engine air/fuel control system responsive to an electrically heated exhaust gas oxygen sensor. Electrical power is supplied to the sensor by a feedback control system responsive to peak-to-peak measurement in the sensor output. Peak-to-peak measurements are averaged over a predetermined number of sample times and the resulting average value compared to a deadband. When the average measurement is above, within, or below the deadband, electrical power to the heater is, respectively, reduced, held constant, or decreased.

Abstract: An engine air/fuel controller (12) is responsive to a two-state exhaust gas oxygen sensor (16) positioned upstream of a three-way catalytic converter (20) and a proportional exhaust gas oxygen sensor (24) positioned downstream of the catalytic converter. A base fuel signal is trimmed by a feedback variable derived by integrating (402-428) the upstream (16) sensor output. The feedback variable is biased towards leaner air/fuel ratios when a distribution of the downstream sensor output amplitudes has a peak value indicating a rich air/fuel ratio. And the feedback variable is biased towards richer air/fuel ratios when the downstream sensor output distribution has a peak value indicating a lean air/fuel ratio (320-396).

Abstract: An engine air/fuel control system includes an apparatus and method for adaptively setting an initialization period preceding closed loop fuel control. During the initialization period, fuel delivered to the engine is modulated by a periodic waveform. A high voltage signal associated with the high output state of an exhaust gas oxygen sensor and a low voltage signal associated with the low voltage state of the exhaust gas oxygen sensor are sampled. When the difference between these signals exceeds a preselected value, the initialization period is terminated and closed loop fuel control is actuated.

Abstract: An engine air/fuel control system includes an apparatus and method for adaptively learning a reference voltage. Fuel delivered to the engine is trimmed by a feedback variable provided by integrating a two-state signal resulting from a comparison between the reference voltage and the exhaust gas oxygen sensor output. Each sample period of a microprocessor, a high voltage signal and low voltage signal are generated which track the outer envelope of the sensor signal. Calculation of a midpoint between high and low voltage signals provides the reference which instantaneously tracks the midpoint of the sensor signal.