Development of a weight-optimized battery housing structure for volume vehicles

Development of a weight-optimized battery housing structure for volume vehicles

Current developments often show that individual requirements are realized by separate subsystems. Therefore, some systems only fulfill a single function, and as a result, the weight of the structure usually increases while the available space for the batteries decreases. The approach of this project is therefore to reduce the weight of the protective structure on a full vehicle level by functionally integrating structural body components in the battery housing. These components are in particular the vehicle floor and a part of the vehicle sill. Compared to the reference structure, the total weight of the body and battery housing can be reduced and the package space for battery cells increased at the same time.

There are several load cases, which have to be considered to investigate the mechanical behavior of the integrated battery housing. On a system level, the crush test based on GB/T 31467.3 and ECE R100 standards, the underfloor intrusion test and the drop test (also based on GB/T 31467.3 standard) are to be mentioned. The according results are shown in Fig. 1.

None of these tests may result in a damage of the battery cells. By the means of simulation, this is ensured by allowing the structure to deform, while maintaining the integrity of the structure itself. Contact between the deforming component and the battery cells should be avoided at any time. Based on a reference vehicle model, suitable for mass production, the load cases are set up on a full vehicle level according to Euro NCAP protocol. These include the side pole impact, the frontal crash with full coverage and the side impact with a mobile deformable barrier (Fig. 2). Especially the side pole impact is the most demanding load case for the battery housing and therefore used as a main design criteria for the integrated structure.

The major requirement for the full vehicle load cases is that the battery cells do not experience any deformation. Therefore, a contact between the cells and the structure is avoided. The procedure is similar to one on a system level. Maximizing the performance of a functionally integrated structure can only be achieved by designing the joining technology precisely. In the present project, the investigation of innovative joining techniques is carried out by the Laboratory for Materials and Joining Technology (LWF) in Paderborn. With regard to battery housing structures, high requirements exist towards leak tightness and corrosion resistance. Therefore, hybrid joining techniques, consisting of a mechanical joining element and an adhesive bond, are ideally suited for lightweight structures, especially when it comes to multi-material lightweight design. The LWF is conducting investigations on hybrid joints. The results will be incorporated into the development of the battery housing structure.