Lightweight Design And Fatigue Life Analysis Of Electric Vehicle Bridge

At present,driven by new traction such as electrification,intelligence and networking,the transformation and upgrading of traditional fuel vehicles to the new energy field accelerated.Pure electric vehicles are far better than traditional fuel vehicles in energy saving and consumption reduction.However,as the heat of pure electric vehicles continues to heat up,the problems in its use are also gradually highlighted,especially the low integration and heavy weight of the drive axle.As an important type of pure electric vehicle bridge,direct electric drive bridge is developed by continuous technological innovation in recent years.It adopts coaxial structure to solve the problem of non-coaxial and low integration of electric drive bridge.However,the corresponding evaluation criteria and technical route for engineering application need to be established.In this paper,the direct-connected electric drive bridge of pure electric vehicles is taken as research object to improve driving comfort and driving range.Firstly,the three-dimensional solid model of the direct-connected electric drive bridge is established according to the design parameters.Combined with the actual road load,the finite element analysis model is established by simplifying the solid model,and the simulation analysis is carried out under the extreme working conditions.The results show that the strength and stiffness meet the requirements,and there is a large margin.Then,the first 6 modal shapes of the bridge shell are obtained by modal analysis,and the modal test is carried out by hammering method.The accuracy of the results is verified by comparing the test and simulation results.The modal analysis results show that the direct-connected electric drive bridge vibrates up and down at low frequency,and at high frequency it vibrates up and down and also produces torsion.The low-order modal natural frequency is 53.075 Hz.Usually,the excitation frequency range caused by road roughness is 0～50Hz.The natural frequency of the low-order mode is very close to 50 Hz of the road excitation,and there is a risk of resonance.Therefore,the wall thickness of the bridge shell is selected as the design variable for optimization.After optimization,the low order modal frequency is increased by about 12 Hz to avoid the risk of resonance with external excitation.Aiming at the weight redundancy problem of the overall structure of the direct-connected electric drive bridge,the lightweight design of the bridge shell is carried out.Firstly,the weight and fatigue life of the bridge shell are taken as the optimization objectives to construct the lightweight optimization model of the bridge shell.By coordinating the two target values,the non-dominated sorting genetic algorithm with the elite strategy is used to conduct the multi-objective optimization of the direct-connected electric drive bridge shell based on the fatigue life,and the optimized compromise solution set is obtained.The optimal scheme is selected.After optimization,the weight of the direct-connected electric drive bridge shell is reduced by 6.64 %,and the lightweight effect is obvious.Then,the nominal stress method is used to analyze the fatigue life of the bridge shell before and after optimization,according to Miner damage theory,combined with the modified S-N curve and the vertical random load spectrum obtained from the combined pavement test.The results show that the fatigue performance of the optimized structure of the direct-connected electric drive bridge is better than that before optimization,and both meet the requirements of the specification.Finally,according to the results of lightweight design,the test samples were made for vertical bending fatigue test and metallographic structure test.The feasibility of the proposed multi-objective lightweight design method for direct drive axle housing based on fatigue life is verified.The above research provides a reference for the structural design of pure electric vehicle axles,provides theoretical and technical basis for the optimal design of electric drive axle housing,and has strong practical engineering value.