Research On Lightweight Design Of City Coach Body Based On Bar-Shell Finite Element Model

Production and sales of coach in China has got the first place continuously for 13 years in the world up to 2015.With the increase of output and sales volume of coach,the ownership,fuel consumption,emission of greenhouse gases and NOX compounds and other polluting gases increased dramatically.At present,lightweight design as an important method to lowering fuel consumption,energy conservation and emission reduction and improving charactertics of vehicle has received more and more attention.On the base of the principle of simplification,this paper established geometric model of city bus body in 6120 city,and then built the finite element model based on the beam-shell element.Simply for building the beam element,preliminary work is small and speeding fast,the shell element reflected loading condition of coach skeleton.And this paper built the finite element model of coach skeleton by shell element and suspension model by the beam and spring-damp element.According to city bus working condition,calculating and analyzing the statics specialty in 6120 city based on bending mode and twist operating condition,introducing briefly evaluation index and loading of finite element.The statics analysis result showed that under the four conditions,there are more rods with smaller maximum equivalent stress in the body structure,material yield limit as objective function optimized.According to the static condition calculation results,selection of chassis,front cover part structure and side upper angle as the size optimization object,to structure the thickness as design variables,the material yield limit as constraint function,the minimum volume as the objective function to optimize the dimensions.The inherent modal characteristics of a city bus body before and after dimensional optimization are compared and analyzed.The result of analysis and optimization indicated that stiffness characteristic of city coach body is good and the quality of design objects lowered 22.81 kg.Also meeting strength and maximum VMS requirements of material yield limit under four working condition.Low order intrinsic frequency of city coach body is no obvious change,avoid the rang of excitation frequency,and intrinsic mode has no mutation.There is little effect on dynamic behavior on the base of size optimization.