mDSF: Improved Fuel Efficiency, Drivability and Vibrations via Dynamic Skip Fire and Miller Cycle Synergies 2019-01-0227

mDSF is a novel cylinder deactivation technology developed at Tula Technology, which combines the torque control of Dynamic Skip Fire (DSF) with Miller cycle engines to optimize fuel efficiency at minimal cost. mDSF employs a valvetrain with variable valve lift plus deactivation and novel control algorithms founded on Tula’s proven DSF technology. This allows cylinders to dynamically alternate among 3 potential states: high-charge fire, low-charge fire, and skip (deactivation). The low-charge fire state is achieved through an aggressive Miller cycle with Early Intake Valve Closing (EIVC). The three operating states in mDSF can be used to simultaneously optimize engine efficiency and driveline vibrations. Acceleration performance is retained using the all-cylinder, high-charge firing mode.

Although mDSF can be implemented with a variety of valvetrains, the most cost-efficient solution for mDSF is comprised of asymmetric intake valve lifts and/or ports, with one high-flow power charging port and one high-efficiency Miller port. The power charging port is deactivated independently, whereas the Miller port deactivation is coupled to the exhaust valves. High-charge firing is realized with all four valves active, low-charge firing is realized with the power valve deactivated, and skip is realized with all four valves deactivated.

The mDSF asymmetric valve strategy was compared to the baseline symmetric valve strategy through dynamometer tests in a production Miller cycle engine and minimal degradation in efficiency was observed. Maximum torque was reduced by 3-8% for mDSF, but it is expected that this can be recovered with combustion system optimization. Engine fuel consumption maps were generated based on experimental data and mDSF “flyzones” were estimated using Tula’s extensive noise, vibration and harshness (NVH) database and experience. Compared with a production state-of-the-art Miller cycle engine baseline, mDSF was projected to reduce fuel consumption by 9.5% in the US City-Highway cycle and 7.5% in the WLTC (Class 3). Combined with a relatively low added cost of the proposed valvetrain design, mDSF presents an unparalleled cost-benefit ratio in the market with relatively short-term production viability.