Efficient and Integrated Desing of Underbody and Battery Pack for Battery Electric Vehicles

Climate change and the consequent more restrictive regulations are pushing the industry towards higher efficiency and lower emissions means of transport. The road transport sector is deeply affected, leading the main Original Equipment Manufacturers (OEMs) to start the transition to alternative powertrains, among which Battery Electric Vehicles (BEVs) are the faster-growing. The large, heavy, and safety-critical battery pack asks for a specific optimized solution for a lightweight and high-performance vehicle platform. In this research, a first benchmarking analysis is presented to study the current state-of-the-art for BEV underbody and battery pack designs. Following this investigation, a classification scheme was designed to allow easier comparison between different solutions, pointing out the most relevant characteristics and best design choices. Starting from the results of the benchmarking analysis, the study followed with a series of Finite Element Analyses (FEAs), on different simplified platform models, organized through a fractional factorial Design of Experiment (DOE). The responses of the experiments were the torsional stiffness and bending stiffness and first resonance mode, evaluated together with the mass of the system. These investigations revealed that the most influential factors for the analyzed performance outputs were the torque box and rocker rail internal structures, together with the material of the battery pack. Other parameters were less influential, but the study was still able to highlight the more favourable configurations. Through two additional analyses the battery pack was found to heavily affect the structure static stiffness, but both the battery pack and floor panels needed appropriate stiffening to avoid low-frequency resonance. The conducted analysis allowed the development of a linear regression model and the execution of a design optimization which delivered two different optimized solutions, showing good performance and high weight efficiency. After the discussion of the gathered results, validated design guidelines were created to provide a starting point for the development of future dedicated and integrated BEV underbodies and battery packs.