Chassis Rubber Bushing Modeling For Automotive Durability Analysis

During the process of automotive durability analysis, boundary constraint load was obtained by Multi-body dynamics simulation to provide input conditions for the durability analysis. Therefore, accurate simulation about the force-configuration changes of the hard points on the system assembly or parts is the key to vehicle durability analysis simulation. At present, multi-body dynamics simulation models have been widely used in the analysis of handling stability and ride comfort for simulating the performance of vehicle or components in low frequency domain, but can't simulate the nonlinear characteristic well in the medium and high frequency domain for vehicle durability analysis. One of the main reasons is that rubber bushing modeling is not accurate enough.This paper focuses on the study of rubber bushing of vehicle suspension. Rubber bushing is an important part on chassis, which connects chassis to body and transmits vibrations to body from chassis. Experiments show that the mechanical properties of rubber bushing depends on frequency, amplitude, pre-load, temperature and many other variables, and its dynamic characteristics with variable stiffness, variable damping and nonlinearity are very complex. Multi-body dynamics analysis program such as ADAMS or DADS adopts the Kelvin-Voigt model for the bushing element. This model treats the bushing element as the linear combination of three translational spring-dampers and three rotational spring-dampers. However, this type of bushing model cannot generate the nonlinear hysteretic behavior of bushing element. So it is of great significance to establish an accurate model for the simulation of high frequency dynamic loads for durability analysis of vehicle.In this paper, modeling on the dynamic characteristics of rubber bushing is concerned. First of all, static and dynamic characteristics of rubber components are studied and researched, and the existing theoretical models are researched, Emphasis on the nonlinear model of hysteresis. Bouc-Wen model is proposed to describe the hysteresis friction of rubber components. In this study, the Bouc-Wen model being combined with a Standard Linear Solid (SLS) model is to establish one-dimensional modified Bouc-Wen model. According to the structure, rubber bushing is separated into two interconnected rigid body: inner rim and outer rim, the two steel rings are connect with the proposed model which is based on the modified Bouc-Wen model, thus the new dynamic model of rubber bushing is established.A method of parameters identification is studied. Adopting the optimization method of model parameters are achieved recognition. Large and complex as the model parameters, in order to obtain more accurate values of initial parameters, the modified Bouc-Wen model is separated into three relative simple models:Bouc-Wen model, Kelvin-Voigt model, and Standard Linear Solid Model. Simulation model is built respectively for numerical analysis. the parameters of models are analyzed to figure out the influence to the force-displacement curve caused by each parameter. Local sensitivity analysis is achieved to Overall parameters of model, determining the sensitivity of various parameters secondary sequence, providing initial conditions for model parameters initialization. In order to verify the dynamic properties of rubber component and obtain the parameters of model, Test data has been gotten from rubber bushing static, dynamic loading by using the VHF7D instron uniaxial test. Parameters were optimized with the test data and parameter analysis results of the model. Parameter optimization target function is the root mean square value poor between experimental data and simulation data for bushings force. Optimization theory is nonlinear least squares. Parameters identification was carried out based on the theory of least squares by Simulink Design Optimization tool of the MATLAB toolbox.In order to validate the validity of the proposed model, several different bushings theory model are built by MATLAB/Simulink modules, and numerical simulation is carried out to prove the validity of the model. It shows that the results with a modified Bouc-Wen model were in good agreement with experiment. Not only the proposed model can describes the influence about frequency, amplitude to the dynamic characteristics of the bushing rubber, but also it may express different dynamic characteristics on axle and radial direction. In particular, nonlinear characteristics under large amplitude excitation in radial can be expressed well. So nonlinear damping and nonlinear stiffness modeling were implemented, and simulation accuracy can meet the needs of the durability model.At last, The GFOSUB program of ADAMS software was used to construct the modified Bouc-Wen model. Simulation results were compared between the modified Bouc-Wen model and Kelvin-Voigt model with ADAMS and the rationality of the modified Bouc-Wen bushing model is given.