Dynamic Skip Fire (DSF) is a proven cylinder deactivation strategy developed at Tula Technology that, in production, has proven to deliver significant fuel consumption improvements across engine and vehicle platforms. DSF allows cylinders to operate near optimal efficiency by reducing pumping losses and improving combustion stability. The Atkinson cycle is also a well-known strategy to improve thermodynamic efficiency by reducing pumping losses and over-expanding combustion gases. This strategy is commonly implemented with long duration intake cams and late intake valve closing. The Atkinson cycle sacrifices power density in a naturally aspirated engine so displacement is commonly increased. The upsized Atkinson cycle engine still shows significant reduction in fuel consumption at high load but has a fuel consumption penalty at low loads due to increased friction and throttling losses. This paper introduces a new synergistic engine concept that employs DSF with Atkinson cycle to operate firing cylinders at peak efficiency and minimize the low load penalty of the Atkinson cycle engine.
Engine simulations were used to derive all-cylinder firing engine fuel maps for a state-of-the-art baseline (4-cylinder, 2.0 l) and an upsized Atkinson cycle engine (4-cylinder, 2.5 l) with cooled EGR (CEGR). Simulations for a D-segment vehicle with a 6-speed transmission in the WLTC were used to determine four weighted engine speed/load points with high fuel and time share that represent the total fuel consumed on the drive cycle. The DSF and Atkinson DSF engines were optimized at these conditions, considering appropriate noise, vibration, and harshness constraints, and the estimated cycle fuel consumption was calculated. Compared with the baseline, the Atkinson 2.5L CEGR engine showed a fuel consumption improvement of 0.9%, whereas the baseline DSF engine reduced fuel consumption by 6.1%. The Atkinson-CEGR engine with DSF reduced fuel consumption by 8.4%, exhibiting a synergy of 1.4% that would otherwise not be obtained from each individual technology. DSF improvements include simulated steady state fuel consumption reduction and estimated deceleration cylinder cut-out benefit.