Finite Element And Dynamics Modeling And Simulation Of Gradual Stifness Leaf Spring Rear Suspension

Multi-body dynamics modeling, simulation and analysis are all based on the suspension model. Because of Gradual stiffness leaf spring's multi role as a spring, control device and shock absorber in rear suspension, and its nonlinearity of large deformation and stiffness, the multi-body dynamics modeling of it is one of the difficulty and key point in the vehicle dynamics simulation analysis area. To accurately create multi-body dynamics model of Gradual stiffness leaf spring suspension, suspension characteristics test data or precise calculating result of finite element method is required, based on which to adjust the model. In order to reduce development costs and shorten the development cycle of suspension system, the modeling of suspension system using the finite element method is a very effective way. Relevant aspects of these are mainly researched with a certain minibus chassis devolopment project of SGMW Co.Ltd in this paper.Firstly, a stiffness characteristic and KnC characteristics finite element calculation model are both established by using Abaqus, a large non-linear finite element analysis software. The rear lug and the bushings are added to the stiffness characteristic calculation model of the leaf spring in which the geometric nonlinearity and the non-linear boundary conditions in contact areas are taken into account, meanwhile, and by correctly setting a certain steps, the assembling and clamping process of leaf spring before loaded is simulated. Comparisons between the calculation results of this model and the bench test results show that the model can accurately simulate the stiffness of the gradual stiffness leaf spring rear suspension. The KnC characteristics calculation model, a model of bilateral suspension, is built on the basis of the unilateral suspension stiffness calculation model. Using this finite element model, the KnC characteristics of gradual stiffness leaf spring rear suspension are analyzed. By the forces at the wheel center point and the wheel alignment parameters calculated by the history output variables related to the displacements of the reference points near the wheel center point and the displacements of the wheel center itself, the values of KnC characteristics of rear suspension finite element model are solved. Utilizing the single-axis KnC characteristics testrig developed by ADSL of JLU, tests of rear suspension KnC characteristics are carried out. Comparisons between the calculation results of the finite element model and the test results show that the Finite element rear suspension model for KnC characteristic can accurately simulate the KnC characteristics of leaf spring rear suspension, and then a benchmark for the multi-body dynamics modeling and analysis of gradual stiffness leaf spring rear suspension is established.Then, from the perspective of multi-body dynamics modeling, comparative study of three current widespread used modeling methods of leaf spring and their respective advantages and disadvantages are carried out, results of which show that the most reasonable method for building the multi-body dynamics model of gradual stiffness leaf spring used for vehicle dynamics simulation is the discrete beam method. Similar to the concepts of the finite element method, single leaf spring is divided into discrete blocks in the model built by this method, which are counted as rigid parts. A massless cell called Beam in Adams is enforced between each two adjacent blocks, by which all interaction forces between them are transmitted. A multi-body dynamics model of gradual stiffness leaf spring rear suspension is established by the discrete beam method, using a secondary development modeling plug-in unit about Adams/Car. Based on this model, simulations on stiffness and KnC characteristics of rear suspension are implemented and simulation results are contrasted to the finite element calculation results verified by experimental results, the comparison shows that the multi-body dynamics model possesses high accuracy, accordingly the foundation of simulation of vehicle performance laid.Finally, based on the multi-body dynamic model of leaf spring rear suspension subsystems verified by the finite element calculation results, the subsystems of the front suspension system, steering system, stabilizer bar in the front suspension, vehicle body, power and transmission system, brake system and front and rear tires are established, and then the vehicle assembly for Adams simulation model is established. According to relevant test standards about the vehicle dynamics, the simulations are conducted under fixed steer wheel angle steady state steering test, step steer transient state steering test and pulse input running test for ride comfort. Comparisons between the simulation results and test results of the benchmark vehicle are carried out and also evaluations are given for this: the vehicle has good performances in fixed steer wheel angle steady state steering test and pulse input running test for ride comfort, which achieve the level of the benchmark vehicle, but the response times of the yaw velocity and the lateral acceleration in step steer transient state steering test are a little longer than the benchmark vehicle, then, suggestions can be given for the following chassis development jobs.