Electric Bus Body Structure Safety Analysis And Lightweight Optimization

Energy-saving,security and environment protection is the eternal theme of automobile manufacturing industry development.Automobile lightweight is of great significance to energy conservation and emissions reduction,however,during the lightweight design period the safety of the vehicle must be ensured at the same time.The bus plays an important role in the transport industry.It occupies a large proportion in the public traffic because of its large capacity,low unit transportation cost,flexible and convenient features.Currently,the bus body structure occupies almost 30%-50% of the complete vehicle kerb mass.According to the research datum,if the vehicle weight decrease 10%,the fuel efficiency can be increase 6%-8%.In no-load cases,about 70% of the energy consumes on the bodystructure mass.So,lightweight design is necessary without sacrificing the bus safety,especially for body structure lightweight.The total mass of Electric bus is heavier than traditional bus due to its dynamic system.Therefore the demand of lightweight design for electric bus is much stronger.In this paper an electric bus body structure lightweight design was done based on the bus rollover safety.The performances of the bus body structure before and after optimization were compared and analyzed to make sure the lightweight design is feasible.At first,the finite element model of the electric bus body structure was built up and the stiffness,strength and low order modes performance of the original bus body structure were analyzed.Second the finite element model of the rollover test platform was established according to the national standard,and then the bus rollover safety performance was estimated.Next analyzed each parts of the bus body structure contribution to bus rollover collision,and filtrated components which were sensitive to weight loss but not sensitive to rollover safety.Finally multi-objective optimization was done by choosing the thickness of the filtrated components as design variables,targeting the minimum mass of bus structure and the maximum of stiffness,and restraining the distance between side-body pillars and living space greater than zero at the maximum deformation moment.In this paper,a RBF approximation model was built up based on a series of sample points was obtained by DOE,and the result of the multi-objective optimization was gained by using NSGA-II method.At last a feasible lightweight plan of the bus body structure was designed keeping the stiffness,strength,and low order modes performance almost unchanged,at mean while the safety of the bus rollover was passed according to GB 17578-2013 “ Thestandard of the bus upper structure strength requirements and test methods”.As a result,the bus body structure obviously lose240 kg weight,loss weight ratio reach 9%.