Passenger Car Sub Frame Structure Analysis And Lightweight

A passenger car auxiliary frame appeared strong vibration in the process of road testscorresponding a certain engine speed and appear crack failure. In this paper, causes forthe vibration and crack problem has been analysis, structure improvement and lightweightdesign is put forward. The method is:Firstly，vice frame geometric model is set up by using UG which is one kind of3DCAD software, then to clean up and simplify the geometry,imported into Hyper meshsoftware to establish finite element analysis model of frame.12kinds of working condition of Vice frame can be obtained through the workingcondition of the corresponding models,finite element static analysis for twelve kinds ofworking condition is carried out by the solver MSC. NASTRAN. and then Compare thecalculation results,according to the distribution of stress to draw a conclusion thatbraking and acceleration is two relatively dangerous working condition of sub-frame.At the same time by the comprehensive analysis of weak parts and strengthen parts of thesub frame. Lay the foundation for structural improvement.To validates the finite elementanalysis model,connection methods，boundary conditions and so on,the stress-strain testfor the sub-frame is carried out, Arrangement of measuring point is according to theposition of the crack and other parts which need to take more attation, the test experiment,the test is carried out with the help of a sub-frame bench test.bench test experimentalsimulation two dangerous working condition of the subframe. with the help of a fatiguetest bench, comparing the results of the experiment and the finite element analysis,verifing the finite element analysis model.The analysis of free modal and Constraint modal are carried out on the cradle.knowfrom the analysis of vibration isolation theory, the first-order natural frequency of thecradle is closed to vibration frequency of the phase generated by the engine, do not meetthe requirement of vibration isolation, thus finding the cause of the vibration problem. Bymeans of the modal theory about further analysis, it can be concluded that the naturalfrequency can be improved by the means of increasing the static stiffness of thesub-frame, thus achieve the purpose of avoiding resonance frequency bands. Introducingthe stiffness quality coefficient for analysis, The unreasonable bending rigidity of thesub-frame is the main cause of cracking,improving the bending stiffness by adjustingStructural parameter of the sub-frame, in order to achieve the purpose of the vibrationabsorber.the problems of Cracking and vibration are resolved.finite element static analysis for two relatively dangerous working condition ofsub-frame,to analyze static characteristics of the improved structure.from the analysis of claw structure we can drawn that this part is the place need to be strengthen,Stiffnessanalysis is performed for the sub-frame torsional deformation, in the form ofdeformation by the vice frame rigidity analysis. At the same time, through the analysis andadjustment of design parameters, the plan of lightweight improvement is put forwardwithout affecting the matching of overall stiffness. then to analyze static characteristics ofthe improved structure. the bench test and road test are carried out for the improvedsub-frame confirmed that the improved structure successfully to full fill the goal-theLightweight improvement.