Abstract: An air/fuel control system for an engine (10) provides an air/fuel indicating signal linearly related to average engine air/fuel operation from a two-state exhaust gas oxygen sensor (76). Fuel delivered to the engine is modulated with a periodic or modulation signal (244). The modulation signal is offset in either a fuel increasing or a fuel decreasing direction when the air/fuel indicating signal is respectively saturated at either a lean or a rich value (394-420).

Abstract: An air/fuel control system for an engine (28) provides an air/fuel indicating signal linearly related to average engine air/fuel operation from a two-state exhaust gas oxygen sensor (44). Fuel delivered to the engine is modulated with a periodic signal (144). A reference value corresponding to a desired air/fuel ratio is subtracted from a rolling average of the exhaust gas oxygen sensor output to provide an error signal (148-152). A feedback variable (FV) for adjusting the engine air/fuel ratio is generated from a proportional plus integral controller having the error signal as its input (156). In this manner, average engine air/fuel ratio is maintained at the desired air/fuel ratio and the rolling average of the exhaust gas oxygen sensor output provides an air/fuel indicating signal.

Abstract: An engine air/fuel control system and method is provided having feedback control responsive to an exhaust gas oxygen sensor. A fuel command responsive to the EGO sensor is modulated (312) and the modulation disabled in response to detection of an air/fuel transient period (502-510, 610). In addition, feedback control gain is increased (514, 614) and the modulation signal held at a value opposite the state of the EGO sensor occurring upon initiation of the air/fuel transient period (510, 610). An indication is provided that the air/fuel transient is terminated when the EGO sensor switching frequency resumes a normal condition (522-528, 622-628). Modulation is thereafter resumed and the feedback gain restored (532-538, 632-638).

Abstract: An engine air/fuel control system modulates the flow of fuel delivered to the engine with a modulation signal (100, 144) The feedback variable generated (210-228) from a two-state exhaust gas oxygen sensor (16) corrects the fuel flow (156). During each of a plurality of pre-determined intervals, the fuel flow is biased with a rich offset (342). Amplitude of the modulation signal is corrected by a difference between the feedback variable generated during two successive occurrences of the predetermined interval (346-378).

Abstract: An air/fuel control system for an engine (28) provides an air/fuel indicating signal linearly related to average engine air/fuel operation from a two-state exhaust gas oxygen sensor (44). Fuel delivered to the engine is modulated with a periodic signal (144). Adaptive feedback control (steps 200-280) adaptively learns a desired amplitude for the periodic signal to generate the air/fuel indicating signal with desired sensitivity and operating range.

Abstract: A fuel control system operating under closed-loop control senses the oxygen content of the combustion products of an internal combustion engine along with the engine angular velocity and air flow through the intake manifold. The fuel control system supplies an air/fuel modulation signal to modify a fueling value which is calculated as a function of the engine angular velocity and air flow. An oxygen sensor monitoring test is performed periodically to determine the efficacy of the oxygen sensor. The total switching time of the oxygen sensor, comprising the lean-to-rich and rich-to-lean switching times, is determined and checked against a range. If the total switching time is within the range then the difference between the lean-to-rich and rich-to-lean switching times, is determined and checked against a second range. If the difference is within the second range the oxygen sensor is determined to be operating effectively and the test is terminated.