Undercarriage impact occurs when vehicle’s ground clearance is incompatible with obstacle on the road. This kind of accidents are particularly dangerous for electric vehicles as battery pack is usually integrated into the vehicle floor. In case of an undercarriage collision, the battery pack could be ploughed through by the obstacle on the road, which could cause damage to battery cells in the packand occurance of internal short circuit and thermal runaway. To tackle this new problem, damage assessment method is needed to guide design of protective structure of battery pack.&nbsp;The present paper documents an analysis of battery damages in undercarriage collisions and a development of a sled test method for evaluating undercarriage collisions. We first used a simplified finite element model of battery pack and conducted computer simulations to understand the influences of a few key parameters. Through some simplifications, the load case and the boundary condition close to that in undercarriage collision were set in the model. The battery pack model included blade battery cells that had no module-level assemblies. A homogenized model of deformable battery cells was adopted for assessing the damage extent. The parametric analysis was focused on the influences of initial collision velocity (also representing initial kinetic energy) and intial overlap height between the obstacle and the battery pack. The deformation and energy absorption of battery cells from different cases were compared. The results show that the deformation and energy absorption in the central zone (impact zone) are greater than that in the side zone, and the battery damage is highly localized along the ploughing area. When the initial overlap height increases, the battery pack as a whole dissipates more energy, and the energy absorption ratio of the battery pack housing and the battery cell casing becomes greater while the energy absorption ratio of the battery cells becomes lower. &nbsp;&nbsp;Based on the learning from the finite element analysis, we then developed a generic sled test method for evaluating undercarriage collisions. The test method needs to be &nbsp;repeatable and adaptable for evaluating a wide range of electric vehicle undercarriage collision. It is also required that, as the sled moves forward with a specified speed, the undercarriage loading device shall hit and plough through the battery pack from the proximal zone to the distal zone with sufficient length. A variety of undercarriage collision test mechanisms were designed and several sled tests with battery pack were conducted. The tests showed that the undercarriage collision caused highly localized damage, and the battery pack was properly ploughed through by the loading mechanism. After the test, the damaged battery pack and battery cells were examined. It was shown that the test method and device are suitable to different sizes of electric vehicles and different types of battery packs. Besides, it can be configured with different test arrangements according to test requirements. Hopefully, this test method can become a unified and standard method for evaluating battery pack damage in undercarriage collisions and guide design of protection structures for enhancing safety performance of battery packs.

Damage Assessment Method of Battery Pack of Electric Vehicle in Undercarriage Collision

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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