Structural Lightweight Design Of Bus Frame

Weight lightening for bus body is one of the trends in bus development. Weight lightening for bus body not only can reduce the bus energy consumption, environmental pollution, automobile emission, but also can improve the power performance, operational stability, ride quality and vehicle safety capability. Bus body frame is an important part for bus load bearing, whose quality is about 20 percent to 40 percent of the total bus quality. Weight lightening for bus body frame plays an important part for reducing the entire bus quality.This paper first discusses the research significance of weight lightening for bus body, the approaches for weight lightening, and present situation of in-country and foreign studies. It analyzes the in-country studies of weight lightening for vehicles, its shortcomings and gaps with the foreign studies. It also analyzes the bus body frame and its weight-lightening design by the way of finite element method. This paper illustrates the fundamental theory, basic concept and basic steps of finite element method. It establishes the finite element model of the entire plate shell unit of bus body frame, analyzes the bus body frame under bending and torsional conditions with the methods of finite element and freedom modal, so as to acquire the bending rigidity and torsional rigidity of bus body frame, free frequency and vibration mode characteristics of first twenty steps. Therefore, we can get a certain idea of the basic performance of bus body frame, which will be the reference for the weight lightening of bus body.Based on topological optimization and sensitivity analysis, this paper makes an optimal design for weight lightening of bus body frame. The design first sets up the topological optimization interval of bus body. On this foundation, aiming at minimizing the quality of bus body frame, constrained by the rigidity, the topological optimization computational model of bus body frame is made. According to the results of topological optimization, the new bus body frame is designed. And then the performance between new and old bus body frames is contrasted and analyzed, to verify the satisfaction of newly designed bus body frame. If not satisfied, the topological optimization design will be carried out again until satisfied. If satisfied, the bus body is to be analyzed for its sensitivity.The design establishes the size optimization model of the new bus body frame. The designed thickness variables are 204 bus body frame members. It aims at minimizing the quality of bus body frame, and is constrained by the rigidity, to output the designed variables towards the threshold of sensitivity of objective function and constrain function. It will find out the frame members which are sensitive to the bus body quality and bus body rigidity. On the basis of the computation results and present bus body frame members, the design adjusts the thickness of the bus body frame members for new frames.We can carry out the finite element analysis and freedom modal analysis of the bus body frame under the bending and torsional conditions after the sensitivity analysis is done. And then the performance between new and old bus body frames is contrasted and analyzed, which finds that the bending rigidity and free frequency of the new bus body frame is superior to the old one. Although the torsional rigidity of the new bus body frame is reduced to some extent, it is still in the reasonable range. Compared to the old frame, the quality of new bus body frame is cut down by about 14.64 percent, to acquire a better result of weight lightening.