Design Optimization of Torsional Coupling Through Transient Torsional Vibration Analysis

Control of powertrain torsional vibration has always been important consideration to improve NVH performance of vehicle. Torsional couplings are used between engine flywheel and motor generator to isolate downstream driveline components from harmful and damaging torsional vibration. Low torsional stiffness of these coupling helps to isolate the torsional vibration during normal engine operation. But due to lower torsional stiffness, torsional mode of the coupling gets resonated during engine start and shutdown, which may result into coupling failures. Vehicle with engine auto start-stop feature is resulting into frequent engine starting event than traditionally observed, which results into more resonant cycles in coupling. The problem becomes more severe in hybrid electric vehicles where high inertia motor generator is directly coupled to engine. Traditionally damping has been used to control magnitude of torque peak at resonance. This study is focused on simulating transient torsional vibration to predict coupling resonance during engine start and shutdown for medium duty commercial hybrid electric vehicle. Sensitivity study has been done to understand impact of coupling torsional stiffness, driveline inertia and rate of combustion energy input on maximum dynamic torque in coupling. Torsional vibration measurement was conducted to calibrate the analytical model which was subsequently used for further design optimization. This paper presents the analysis methodology, coupling design optimization process and comparative result assessment.