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Root Cause Analysis and Structural Optimization of E-Drive Transmission
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 30, 2020 by SAE International in United States
Event: 11th International Styrian Noise, Vibration & Harshness Congress: The European Automotive Noise Conference
We face a growing demand for so-called eAxles (electric axle drive) in vehicle development. An eAxle is a compact electric drive solution for full electric vehicles (and P4 hybrids) with integrated electric machine and transmission. The transmission can be rather simple using fixed gear with cylindrical gear steps but increasing demands on power and speed range as well as efficiency increase its complexity with planetary stages or switchable gear steps. Such an electro-mechanic system has different behavior than the classical ICE-driven powertrains, for example regarding NVH, where high frequency and tonal noise from gear whining and electro-magnetic excitation is an important comfort issue that needs to be understood and controlled. As knowledge base for such drives is currently low, development needs to be supported by methodologies, which are not only on high predictive level for NVH responses, but also allow a detailed understanding and insight into the causes and reasons of a certain behavior to identify noise effects and to accelerate learning for such systems. In addition, such methods should lead to the possibility to improve and optimize the design. This paper describes the simulation tool chain serving to design and optimize the transmission of an electric axle drive from concept to final design. A two-stage transmission of an eAxle is designed from scratch by initial layout of gears and shafts, including optimization of gear micro geometry. After shaft system and bearings are defined, concept design of transmission housing is evaluated with help of a basic topology optimization regarding stiffness and certain eigenfrequencies. In the next step fully flexible multi-body dynamic (MBD) and acoustic analysis of the transmission is performed using internally calculated excitations due to gear contact and bearing interaction with shaft and gear dynamics for entire speed and load range. Critical operating conditions in terms of NVH (shaft dynamics, structure borne noise and noise radiation) are evaluated and selected as target for optimization in the following steps. Critical operating conditions are detected by detailed root cause analysis (RCA) including operational modal analysis of assembled transmission, modal and panel contribution evaluation, operational deflection shape analysis (ODS), numerical transfer path analysis (NTPA) and transfer function (TF) evaluation. Based on RCA result the transmission housing design is exposed to the new optimization loop using different methods and tools and based on the dynamic loads. Design is optimized with target to reduce emitted noise. Final housing design is verified by repeating MBD and acoustic analysis. The developed simulation methodology and tools can successfully identify the main noise sources from the e-drive transmission. Followed by design optimization the emitted noise is reduced and design can be improved.