| Vehicle power battery packs are used as energy storage components for electric vehicles and often placed on the bottom of the vehicle body floor.They are extremely dangerous when they are hit by high-speed road rarity at the bottom,which may cause fire,explosion,and other safety accidents.Therefore,the research on the damage and influencing factors of the impact of the road rarity at the bottom of the battery pack is of great significance and application value for understanding the damage mechanism of the impact at the bottom of the battery pack and improving the driving safety of electric vehicles.Firstly,a case of an electric vehicle fire accident caused by the impact of road rarity at the bottom of the battery pack is dissected,and the conditions of the impact at the bottom of the battery pack and the relationship between the main influencing factors are analyzed.Based on the classification of road rarity and impact conditions at the bottom of the battery pack,three types of road rarity are extracted and modeled according to the damage form under the impact between the battery pack and the road rarity at the bottom.Then combined with the analysis of the electric vehicle fire accident and the characteristics of the bottom structure of electric vehicles,a common and high-risk model of road rarity impact at the bottom of the battery pack is constructed,and the main factors affecting the bottom impact force are discussed.The model and theoretical foundation are laid for the simulation analysis on the impact at the bottom of the battery pack with road rarity.Secondly,vertical squeeze tests are performed on rectangular aluminum-shell lithium batteries to study the vertical mechanical characteristics of the single cell and the battery core under the mechanical load,and it is found that there are four different deformation stages of the single cell during vertical loading.According to the relationship between the vertical deformation of the single cell and the change in voltage and temperature,a short-circuit failure determination criterion for rectangular aluminum-shell lithium batteries under the squeeze is established to achieve an accurate correlation between the battery deformation and the internal short circuit.In addition,the battery mechanical properties of the three directions are comprehensively compared and analyzed through the squeeze tests of the other two directions,and the three characteristics of the battery's plane compression load capacity,short-circuit failure mode and inner core deformation mode are obtained.Finally,based on the mechanical tests of the single cell,a homogenization model of the single cell and a refined model of the battery pack are established,and the validity of the models are verified respectively.Then,the established models are applied to impact conditions of a rod-shaped road rarity at the bottom of the battery pack and a cylindrical road rarity at the bottom of the battery pack.The deformation process of the battery pack under the impact of two different types of road rarity,the damage of the mechanical structure of the battery pack,and the damage of the battery module are analyzed.Several sets of simulation tests are established to study the factors affecting the damage of the battery pack case under two impact conditions,and several protection suggestions for battery packs under the impact of two different types of road rarity are given.These works in theoretical analysis conclusions of impact at the bottom of the battery pack with road rarity,the vertical failure mechanism of the single cell obtained by the mechanical test method,and the road rarity impact damage results at the bottom of the battery pack obtained by the numerical simulation have important reference significance and engineering application value for the development of the bottom impact evaluation system of battery packs and the understanding of the deformation process and damage mechanism of battery packs under the impact of different types of road rarity. |
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