Research On Design Technique Of Bus Rollover Safety Based On Deformation Distribution Control

In the prophase exploration, the research group finds that the enclosed skeleton of thebus during the rollover is the main structure bearing the impact load. Its main deformationpositions are the lower-waist beam joint, the window-waist beam joint and the tailor-weldedbeam joint which locates at the side wall and roof, and the large deformation of the jointabove is the main reason that causes the invasion to the passenger residual space.Consequently, how to distribute and control the joint deformation of the bus enclosedskeleton has the important significance on the rollover safety design of the bus structure.According to European regulation ECE R66, the rollover simulation model of a12-meter-long integral bus and a bus middle section are established. First, the rollover testprocess of the bus middle section is simply simulated. The good similarity betweensimulation results and the test shows that the rollover simulation method of the bus iseffective. Then the rollover process of the12-meter-long integral bus model is simulatedbased on the method.Analyzing the rollover deformation characteristics of the enclosed skeleton jointstructure of the12-meter-long integral bus shows that the localization form is the maindeformation characteristic of the joint structure. Because it may cause plastic hinge and it isbad for the energy absorption. The deformation localization of the joint structure of theenclosed skeleton should be controlled, and the deformation range should be enlarged toabsorb more energy. If the deformation localization of the lower-waist beam joint structureof the enclosed skeleton forms the plastic hinge, the passenger residual space will be invadedseverely. So how to control the deformation localization of the joint structure of the lower-waist beam, avoid the formation of the plastic hinge and lead deformation upward, willgreatly influence the improvement effect of the rollover safety performances of the busstructure.To reduce the research cycle, the body section structure which contains two enclosedskeleton is extracted in the12-meter-long integral bus. According to the simulation results ofthe bus rollover, the body section model is developed and the rollover process is simulated.First, the effect of the deformation characteristics of the body section structure is verified.Then considering the deformation characteristics of the lower-waist beam joint structure ofthe enclosed skeleton, an improved scheme is proposed. The scheme about moving thelower-waist beam down is to control the deformation localization of the joint structure of thelower waist beam. And the local reinforcement is welded in the inside of the sidewall pillarto cause the sidewall pillar and the local reinforcement to deform together and leaddeformation upward. The rollover simulation of the body section model indicates that theimprovement effect is notable. Further analysis about the body section structure deformation which contains thescheme mentioned above shows that the deformation localization of the window-waist beamjoint structure is enlarged and the plastic hinge is formed. To ensure the integrity of thepassenger residual space, the joint structure of the window-waist beam should be improvedto mate the joint structure stiffness of the lower-waist beam and control its deformationlocalization. Since it is hard to improve the joint structure of the window-waist beam of theenclosed skeleton, the contrastive analysis about the rollover safety performances of threekinds of window-waist beam joints that are often used in the domestic bus is made, and apreliminary rule about the influence of the rollover safety performances is obtained, based onthe body section model which contains the improved scheme of the lower waist beam jointstructure.Considering the deformation localization is bad for the energy absorption andenhancing the energy absorption ability of the window-waist beam superstructure can reducethe energy absorption of the structure that locates under window-waist beam of the enclosedskeleton. Therefore, the joint structure of the tailor-welded beam which locates at the sidewall and roof of the enclosed skeleton is improved, and the effect of the improved structureis verified, based on the body section model which contains the improved scheme of thelower-waist beam joint structure and the window-waist beam with a square cross section.To validate the effect of the enclosed skeleton joint structure that is improved by thedeformation distribution control technique, the improved structure is implanted in theenclosed skeleton structure of the12-meter-long integral bus model. Then the comparisonabout the rollover safety performances between original and improved structure of the12-meter-long integral bus is made by using CAE simulation technology. The results showthat the improved structure can improve the rollover safety performances of the originalstructure of the12-meter-long integral bus significantly, and the whole deformation of theimproved bus structure is well-distributed.Finally, a programmed evaluation method is proposed to appraise the rollover safetyperformances of the bus more quickly and accurately. Contrasting the results from theprogram that calculates the maximal decrease of the passenger space diagonal point distanceof the bus enclosed skeleton with the post-processing software show that the programmedevaluation method is feasible.