Abstract: An improved internal combustion engine fuel control wherein a single oxygen sensor responsive to the combined exhaust gas flow of several engine cylinders is used both to control the overall or average air/fuel ratio, and to trim the air/fuel ratio in the individual engine cylinders. The oxygen sensor output is sampled in synchronism with the engine firing events, but at twice (or higher) the frequency, and filtered by an engine speed dependent high-pass filter to form a measure of the air/fuel ratio imbalance with respect to time. The imbalance signal, in turn, is parsed into an array of imbalance values that are associated with individual engine cylinders based on engine operating conditions, and the imbalance values are then used to develop correction factors for the respective engine cylinders that reduce the imbalance while preserving the overall or average air/fuel ratio of the engine.

Abstract: An improved fuel control in which the transfer function of a wide-range exhaust gas oxygen sensor is automatically and periodically learned or re-learned in the course of vehicle operation. The oxygen sensor is calibrated at two different operating conditions: at a stoichiometric air/fuel ratio, and at a fuel cut-off or free-air ratio. The first operating condition occurs during steady state operation when a switching sensor disposed in the exhaust gas stream downstream of the catalytic converter indicates that the engine is being fueled at the stoichiometric air/fuel ratio. The second operating condition occurs when engine fuel is shut off, either during vehicle deceleration, or when the engine is turned off. Once both calibration points have been determined, the transfer function of the wide range sensor is adjusted to match the stored voltages, and engine fueling is thereafter based on the adjusted transfer function.

Abstract: An improved individual cylinder fuel control method based on sampled readings of a single oxygen sensor responsive to the combined exhaust gas flow of several engine cylinders. The oxygen sensor output is sampled in synchronism with the engine firing events, a stored non-volatile table of offset values is used to correlate the sampled oxygen sensor values with individual engine cylinders, and a new offset value is determined and stored in place of a current offset value when the current offset value fails to reduce a measure of air/fuel ratio maldistribution among the engine cylinders. In systems having an oxygen sensor of the switching type, the measure of air/fuel ratio maldistribution is determined by filtering and integrating the oxygen sensor signal, and the new offset value is determined by repeatedly incrementing the stored offset value, and fueling the individual cylinders of the engine based on the incremented offset value, until the measure of air-fuel ratio maldistribution decreases.