Lightweight Design Of Battery Pack Based On Driving Distance And Safety Performance

Power battery packs are the only power source for pure electric vehicles and are a decisive factor affecting the driving distance of electric vehicles.At the same time,the high energy density of battery packs also has an extremely important impact on the safety performance of electric vehicles.The lightweight design of battery packs can effectively reduce the energy loss of electric vehicles and improve driving economy,which is of great significance for increasing the driving range of electric vehicles.Based on the target driving distance of pure electric vehicles and the safety performance of the battery pack,this paper carries out a lightweight design of the battery pack system from two aspects: the number of battery modules and the optimization of the battery pack box structure.The specific work is as follows:(1)According to the design indicators of the power performance and driving distance of pure electric vehicles,the power system is designed to match the parameters.Through analysis and calcu lation,the number of battery modules is initially determined to be 78.Build simulation models of the whole vehicle,motor,drive train,and power battery in the Advisor software,select 60km/h constant speed working condition and CYC＿ECE＿EUDC urban road working condition for dynamic and economic analysis.Changing the number of battery modules,analyzing the driving distance and power performance of electric vehicles with different numbers of modules,and finally determined that the optimal number of batt ery modules that meet the driving distance and power requirements is 75.Compared with the initial calculation results,the number of battery modules has been reduced by 3,the total mass of the modules has been reduced by 7.605 kg,and the weight reduction ratio has reached 3.85%.(2)Determine the grouping and arrangement of battery modules,as well as the design scheme of the battery pack box,and establish the geometric model of the box.The finite element model of the battery pack is established accordi ng to the geometric model,and the modal,strength,stiffness and random vibration analysis of the battery pack are carried out based on Optistruct.The modal analysis results show that the low-order modal frequency of the box cover is lower than the road surface excitation frequency,and there is a greater risk of resonance.The simulation results of the strength,stiffness and random vibration of the battery pack meet the design requirements,but there is a large margin between the maximum stress or maxim um deformation and the safety value under various working conditions,indicating that the design of the battery pack box structure is too large.It is conservative and can be designed to be lightweight.(3)Optimize the top cover of the box.After the optimization,the frequency of the first six modes of the battery pack has been significantly improved,which effectively reduces the risk of resonance of the battery pack.(4)A combination of proxy model and finite element simulation is adopted to carry out lightweight design of the box.Taking the thickness of each component of the box as a design variable,and taking various static and dynamic mechanical properties of the battery pack as an output response,56 sets of sample data are generated through the optimal Latin hypercube test design.Through error analysis,the accuracy of the three proxy models of second-order response surface,kriging and radial basis function neural network is compared,and the second-order response surface model is selected as the model for subsequent optimization.Define the design variables,objective functions and constraints in the Isight software,use the NSGA-II algorithm for multi-objective optimization,and use the minimum total mass of the battery pack as the preference when solving,and select the optimal solution.In the end,the total mass of the optimized battery pack was reduced by 7.4Kg,and the weight reduction ratio of the design mass reached 12.7%.(5)Through simulation of collision,squeeze and bottom ball h it analysis,it is further verified that after the lightweight design,the safety performance of the battery pack system is good and meets the requirements of use.