Research On Static/Dynamic Characteristics Of Suspension Rubber Bushings And Its Application

Rubber bushings are mainly used to connect the vehicle body or between within the various components of the vehicle suspension system, primarily which can isolate vibrations and reduce noises. Meanwhile, the evaluation indexes of bushings are static/dynamic stiffness that not only impact the Kinematics and Compliance (K&C) of the suspension, but also impact the ride comfort or the other vehicle performances, etc. In this thesis, the comfort rubber bushing of McPherson suspension and the inclined rubber bushing of torsion beam suspension were used as the research objects, the main works are listed as follows.Firstly, based on the analysis of the hyperelastic constitutive relations of the rubber bushing material and its equations, the FEM models of two rubber bushings were built, and then the coefficients of the constitutive equation were estimated by simulation. The mechanical properties tests are the uniaxial/biaxial tension and planar tension, the three tests of the certain rubber material were fitted by using a variety of constitutive relations; the fitting results were compared with the three tests to establish the reasonable hyperelastic constitutive relations. After the coefficients of the constitutive equation were first selected, the preliminary simulation of the static characteristics was carried out, its results were the three axial stiffness compared with the results of the structural static stiffness test, some optimization objective functions were set by using the idea that the simulation approach to the test, a better constitutive equation coefficients were identified by using adaptive response surface optimization algorithm, further a more precise bushing model was established, a simulation was done to fit the stiffness about three axial by using the newer bushing model, so all the six static stiffness, which are the evaluation indexes of the bushing, were reorganized. In order to research the changing laws about the simulation curves of the axial or radial stiffness, some different radial shrinkages of the comfort rubber bushing were set, and through a comparison with the test values of the static stiffness, a better radial shrinkage could be determined. The structural strength analysis of two suspensions was carried out, the two suspensions are the torsion beam suspensions with the bushings included of all the six static stiffness and the one with the bushing based on rigid-flexible coupling, the availability of the bushing model with simple six stiffness could be decided by a comparison between the two maximum displacements & stresses of the simulation results.Secondly, from the time domain to the frequency domain, an analysis was done to build the viscoelastic constitutive relation of the rubber bushing material, then to determine that prony series was used for describing the viscoelastic characteristic, according to the bushing vibration principle of the dynamic characteristics, the boundary conditions of the rubber bushing were set, and the axis/radial displacement excitation were exerted in frequency domain, by setting initial values for the prony series coefficients, the first simulation of the dynamic characteristics was carried out, its results, which were the frequency correlation curves of axial/radial reaction force outputted, were compared with the results of the dynamic characteristic tests, a optimization objective function was set by using the idea that the simulation approach to the test, the more accurate prony series coefficients were identified by using an adaptive response surface optimization algorithm, further a more precise bushing model was established, a dynamic characteristic simulation was done again under some special frequencies to get the relation curves between the reaction forces and the displacements, the area bounded by closed curves is Hysteresis loop, it is the key parameter to calculate loss angle, by doing this, the reorganization of the bushing’s dynamic characteristic indexes will be ensured. In order to analyze the changing laws about the frequency correlation curves of the bushing axial/radial reaction force outputted, further some different radial shrinkages of the comfort rubber bushing were set, and through a comparison between the near-zero Hz axial/radial stiffness and the test values of static stiffness, a reasonable radial shrinkage could be determined for researching about the rubber bushing’s dynamic characteristics.Based on the importance of static/dynamic indexes for the rubber bushings in the analysis of vehicle performances, by listing the methods of suspension K&C analysis, some statistical data and movement laws from some kinds of tests and relative literature, which are related to the evaluation indexes of suspension K&C characteristics, were summarized as a quasi-evaluation criteria for this thesis’s research. The K&C analysis of the McPherson and torsion beam suspensions with rubber bushings were carried out, after comparing the corresponding simulation conclusions with the quasi-evaluation criteria, the reasonableness of the main indexes of the suspension K&C and its movement laws were judged. Further the positive & negative effects of six stiffness, which is the sensitivity, were identified by analyzing the indexes response of suspension K&C simulation, some stiffness with better sensitivity were used as the design variables to do the full factorial experimental design of torsion beam suspension’s K&C response, After obtaining the optimized values of the bushing stiffness and substituting them to the suspension model, then the K&C simulation was done again, the optimization of the bushing stiffness was evaluated by re-comparing the simulation results with quasi-evaluation criteria.Finally, a ride comfort simulation system with vehicle dynamics model was established, Based on the evaluation of the ride comfort’s indexes changing, By setting the assumptions that a rubber bushing was lacking or any one stiffness of the comfort rubber bushing was disabled, in the simulation of the ride comfort, the effectiveness of suspension rubber bushings on human’s subjective reactions was researched. After the simulation data processed in Matlab program were compared with the range table of ride comfort indexes, the sensitivity of any one bushing stiffness impacting on the uniaxial or total weighted acceleration root mean square value was analyzed.The Doctoral thesis was based on the rubber material mechanical properties test and structural static/dynamic test, by researching on the static/dynamic characteristics of the rubber bushings from McPherson and torsion beam suspensions, the coefficients of some hyperelastic or viscoelastic constitutive equations were identified and optimized to establish the precise bushing models, then all the static stiffness were mainly reorganized. And a new method of determining the reasonable radial shrinkage was given in the research about the static/dynamic characteristics of the rubber bushings, and the sensitivity from any one stiffness of the rubber bushings impacting on suspension K&C characteristics or vehicle ride comfort were analyzed, the second optimization of the bushing static stiffness was carried out in the suspension K&C simulation, the conclusion is satisfactory. The research results can provide a reliable theoretical guidance and useful reference for development of the suspension rubber bushing or other types of non-linear damping components and the reasonable matching of various vehicle performances.