Individual Cylinder Fuel Control with a Switching Oxygen Sensor

In this paper we discuss in detail an algorithm that addresses cylinder-to-cylinder imbalance issues. Maintaining even equivalence-ratio (ϕ) control across all the cylinders of an engine is confounded by imbalances which include fuel-injector flow variations, fresh-air intake maldistribution and uneven distribution of Exhaust Gas Re-circulation (EGR). Moreover, in markets that are growing increasingly cost conscious, with ever tightening emissions regulations, correcting for such mismatches must not only be done, but done at little or no additional cost. To address this challenge, we developed an Individual Cylinder Fuel Control (ICFC) algorithm that estimates each cylinder's individual ϕ and then compensates to correct for any imbalance using only existing production hardware.

Prior work in this area exists^1,2, yet all disclosed production-intent work was performed using wide-range oxygen sensors, representing cost increases. In our production-bound algorithm, modeling and control of the cylinders' dynamic ϕ was performed using a single switching oxygen sensor. Our ICFC algorithm was developed on a 1996 Pontiac Grand Am with a production LD9 2.4L four-cylinder DOHC engine. It met internally defined performance requirements and LEV emissions. Other important contributions in this work include an analysis of exhaust gas transport and mixing phenomenon, and an analysis of digitally acquiring and post processing oxygen sensor data.