Impact Response Analysis And Safety Evaluation Of The Bottom Of EV Battery Pack

As the power source of electric vehicles,the power battery pack is often installed on the bottom of the vehicle body.When the vehicle is running,the bottom of the vehicle collides with the road rarity,which will cause serious damage,fire and other accidents.Therefore,the bottom dynamic impact analysis of vehicle power battery pack and road rarity has important practical value and reference significance for understanding the bottom collision mechanism of battery pack and driving safety of electric vehicles.Taking a traffic accident caused by vehicle bottom collision in NAIS database as an example,this paper analyzes the corresponding relationship between road rarity and vehicle collision when vehicle bottom collision occurs.According to the corresponding relationship between road rarity and vehicle bottom collision,the collision forms are classified.Then,the geometric model of road rarity is parameterized,and the parametric models of three kinds of road rarity are compared.The cone model is selected to simulate the road rarity,which is characterized by the top angle and radius of the cone,and then the dynamic model of the collision between the model and the bottom of the battery pack is established.Quasi static compression and dynamic impact tests were carried out on square Li Fe PO₄cell and the inner core of the battery in Z direction to simulate the mechanical properties of the cell when the cell was vertically installed in the battery pack and the bottom impact occurred.According to the variation of force,temperature and voltage of single cell under quasi-static compression,the deformation process and short-circuit mechanism of single cell under compression are analyzed,and the short-circuit failure criterion of single cell under Z-direction extrusion is established.The mechanical properties and internal short-circuit failure of single cell and cell under different SOC and velocity impact are analyzed.The stress-strain model of the inner core of the battery under Z-direction coupling different SOC and velocity impact is obtained.The model is applied to the finite element modeling of single cell.The finite element model of single cell is applied to the battery pack,and the refined finite element model of battery pack is established,The finite element model of the battery pack and the road rarity model are used to analyze the bottom collision.The deformation process of the battery pack in the collision process and the damage of each part of the battery pack are analyzed.Then the bottom impact of the battery pack was carried out at different speeds,and the results were compared with those under quasi-static action.The top angle and top radius of different conical impactors are studied by parameterization,and the damage of battery pack under different impact angles is analyzed to reveal the influence of different parameters on the battery pack and the bottom impact of road rarity.Among the multi parameters that affect the impact of the bottom of the battery pack,seven factors with greater weight are selected,and the level value of each factor is selected according to the actual situation.The orthogonal table of L₂₇（3⁷）was established by orthogonal test method to simulate 27 groups of tests of bottom impact of battery pack and road rarity.The invasion amount of road rarity when battery pack was damaged was taken as the safety evaluation index.The range analysis method is used to evaluate the safety of the battery pack,and the weight relationship of each parameter is obtained when the battery pack of electric vehicle impacts the bottom of road rarity.