Multi-objective Lightweight Design Of Pure Electric Bus Body Frame

Pure electric vehicle has the advantage of zero pollution,low noise,high energy conversion efficiency,simple structure,convenient use and maintenance etc.for the use of power battery and motor drive,and has become the main direction of the development of city bus.Because of the specific energy of electric vehicle is not high,it is necessary to increase the number of batteries in order to improve the driving range.The weight of the bus body frame accounted for about 30%~40% of the total weight,so as to reduce the quality of electric vehicle,structure optimization of the body is an effective way to reduce bus body bone mass,and has important significance to extend bus mileage,and improve power.This paper studies the main content includes the following aspects:First of all,the object of research of this paper is the 6.6 meter pure electric bus developed by a company.According to the three-dimensional UG model provided by the company,the finite element model of the bus frame is established in the finite element software Hypermesh.Static analysis and modal analysis are conducted in Radioss software including horizontal bending,ultimate torsion,emergency braking and emergency turning.Then,the strength test was carried out in Dingyuan proving ground,and the data of resistance strain gauges were recorded and processed,the finite element model was verified in the range of error tolerance.Secondly,carring out parts of the floor of the bus body frame,the top cover and the left and right side of the skeleton.According to the symmetry of the body structure and function similarity component grouping,the thickness of the component acts as variables,the sensitivity analysis was carried out to choose design variables which were sensitive to the skeleton quality but not sensitive to body performance components to improve the efficiency of optimization parameters of side member thickness.Secondly,the sensitivity analysis of the floor,the top cover and the left and right side frame parts of the bus body frame is carried out.The part thickness parameters are served as the optimization variables,The components which are sensitive to the skeleton quality but not sensitive to the body frame are selected,and the thickness parameters of the parts are taken as the variables of the optimization design to improve the optimization efficiency.Then,multi-objective optimization was performed in the Hyperstudy software,with using experimental design method for sampling ham SRE in the design variable space of each sampling point.Based on the finite element simulation data,the radial basis function(RBF)neural network is used to establish the approximate model of the body mass,stiffness and modal performance.Finally,the multi-objective optimization method is used to optimize the bus skeleton.The body frame quality minimum and torsional stiffness act as the optimization goal,the first-order torsion modal frequency and the first bending mode frequency act as constraints,genetic algorithm is used to optimize the body frame for multi objective optimization.The performances of the body frame of before and after optimization were compared.The final weight loss is 146 Kg,body frame mass was reduced from 1321 kg to 1175 kg,lightweight degree is 11.05%,the effect of weight loss is remarkable,at the same time,the performances of the bus body frame structure still meet the requirements.