Optimization of Lightweight Gear Blanks to Improve NVH for an Electric Drive Unit

A single-speed electric drive unit (eDU) with multi-stage reduction can have high gear whine due to high pitch-line velocity in the absence of engine masking noise. A comprehensive investigation is conducted focusing on the optimization of the first-stage transfer gear blanks to improve NVH performance and reduce mass for EV applications. A multibody dynamic model of the eDU was constructed, incorporating asymmetric gear blank geometry, shaft elasticity, bearing stiffness, and housing flexibility, in order to characterize realistic operating conditions and simulate gear contact mechanics with high fidelity and computational efficiency. NVH excitation sources, including static transmission error and dynamic meshing force, were systematically evaluated for solid and slotted gear configurations. Based on a DOE optimization study, an 8-slot gear blank design is selected to balance mass reduction, stress, NVH, and manufacturing requirements. Micro-geometry optimization was conducted for the slotted gear blank design to reduce dynamic forces transmitted to the bearings and housing, thereby improving NVH performance. Prototype gears are built and tested for the baseline design with a solid blank and the lightweight 8-slot gear with two variants of optimized microgeometry designs. The predicted sound power at gear mesh correlates well with the test data over a range of torque levels in both drive and regenerative conditions, validating the fidelity of the analysis method. Auralization techniques, such as time-domain transfer path analysis and convolution, are used to predict radiated gear noise for a jury evaluation of sound quality. Analysis and test results confirm that the optimized gear blank achieve both lightweighting and NVH improvements for EV applications.