Method to Compensate Fueling for Individual Firing Events in a Four-Cylinder Engine Operated with Dynamic Skip Fire

Cylinder deactivation in multicylinder spark-ignition (SI) engines leads to increased fuel efficiency at part load by allowing fired cylinders to operate closer to their peak thermal efficiency compared to all-cylinder operation. Unlike traditional cylinder deactivation strategies that are limited to deactivating only certain cylinders, Dynamic Skip Fire (DSF) is an advanced cylinder deactivation control strategy that makes deactivation decisions for every cylinder on an individual firing opportunity basis to best meet driver torque demand while saving fuel and mitigating noise, vibration, and harshness (NVH). During DSF operation, inducted charge air mass can vary for each firing event due to the firing sequence history. To maximize efficiency, cylinder fueling should be adjusted for each firing event in DSF based on the inducted charge air mass for that event. This article discusses the development of a control algorithm to compensate fueling for charge air mass variations of individual firing events in DSF on a 1.8-liter, four-cylinder SI engine with intake camshaft phasing using a production-type engine controller. The control algorithm architecture and calibration methodology are discussed. The final algorithm was evaluated by performing engine dynamometer testing with and without the compensation algorithm for selected DSF firing patterns at a range of engine load at 2000 rpm. Optimal fueling compensation in DSF resulted in more complete combustion, evidenced by an increase in brake-specific carbon dioxide emission of up to 1.9% and a decrease in brake-specific carbon monoxide emission of up to 48%. Reductions in brake-specific fuel consumption (BSFC) were also observed with fueling compensation, averaging up to 1.1% reduction in BSFC from 1 to 4 bar brake mean effective pressure (BMEP) depending on the firing sequence. Engine operation was very stable with and without the compensation algorithm in the operating ranges considered.