Individual cylinder fuel control having adaptive transport delay index

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. In systems having a wide-range oxygen sensor, the measure of air/fuel ratio maldistribution is determined by summing the air/fuel ratio errors identified by the sensor, and the new offset value is determined by alternately toggling a selected cylinder rich and lean, and sampling the oxygen sensor signal to identify the selected cylinder. Either way, the control adapts the stored offset values for changes that occur over time due to component degradation and variation and changes in engine hardware.

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