Vibration Mitigation of Dynamic Skip Fire Engines with Flywheel Optimization and Torque Converter Clutch Slip

Dynamic Skip Fire (DSF) is an advanced cylinder deactivation technology to reduce fuel consumption and emissions of internal combustion engines. The firing sequence may vary dynamically depending on driver demanded torque with all cylinders capable of deactivation. This creates a challenge for managing noise vibration and harshness (NVH) caused by the low frequency excitation in the engine’s torque profile, especially in smaller engines with 3 or 4 cylinders. Due to the varying nature of firing sequences, the excitation is not limited to one or two engine orders and can vary with time, requiring broadband mitigation of the driveline. This work proposes the optimization of flywheel inertia combined with careful control of torque converter slip to overcome this challenge. Four different flywheel configurations and varying levels of torque converter slip were tested on a VW Jetta fitted with a 1.8L 4-cylinder engine with DSF control capability. For each configuration, DSF flyzone maps were generated and fuel consumption benefits were estimated. This paper covers a theoretical understanding of DSF excitations, vehicle NVH test results including torsional and seat vibration for various firing fractions with the different configurations, and fuel economy results with the optimized configuration. The methods developed here are extendable to other engines, platforms, and powertrain technologies like downsized, boosted engines with or without DSF/cylinder deactivation.