Research And Application Of Vehicle Vibration Modeling Method Based On Reduction Technology

Vibration performance is one of the important performances of vehicles.Under the background of "lightweight vehicle" and "low idle speed engine" of commercial vehicles,vehicle structure flexibility is enhanced,idle excitation frequency is decreased.The above two impacts tend to deteriorate vehicle vibration performance.This research focuses on the practical problems of vehicle vibration-performance development.To comply with the technical trend of "structural flexibility,computational efficiency and connection nonlinearity" in the field of vehicle vibration research,a set of theory and modeling method for establishing rigid-flexible coupled vehicle vibration model is proposed.The whole research focuses on the application of model reduction technology.Firstly,the reduction of large-scale finite element structure is carried out.Code is programmed to iedntify the mass and stiffness matrices and carry out high-dimensional matrix operation of finite element model,and complete the model reduction of typical vehicle structure.In order to balance the reduction accuracy and computational efficiency of the super large model,IRS reduction is carried out on the basis of a smallscale Guyan reduction model.As a result of this,the degree-of-freedom of the redutcion model is furtherly decreased.Considering the huge consumption of computational resources in the reduction process,the boundary condition treatment approaches of the reduced model is discussed based on the reuse of the reduced model.It includes the most commonly used fixed boundary conditions,prescribed motion boundaries and coupling boundaries.It is found that for the fixed boundary conditions,only Guyan reduction model can be reused;no matter what reduction method is used,the model should be reduced to suit for different prescribed displacement boundaries,and the reduced model can not be reused;for coupled boundaries,the reduced models can restore the dynamic characteristics of the original coupling model through appropriate dynamic and kinematic constraints.Secondly,the dynamic and static stiffness characteristics of leaf spring are studied by experiments.It is found that the hysteresis is positively related to the amplitude of loading,but is not affected by the loading frequency.On the basis of verification,the influence factors of leaf spring hysteresis characteristics are analyzed by using finite element method.Results show that the surface friction coefficient,tangential damping,contact area and axial load have an important influence on the hysteresis characteristics of leaf spring,and some guiding suggestions are given to reduce the friction between leaf springs.According to the mechanism of hysteresis,a dynamic equivalent mechanical model of leaf spring for vehicle dynamics simulation is proposed,and the influence of leaf spring hysteresis on ride comfort is further discussed by using twodegree-freedom vehicle model.It is pointed out that both the shock absorber and the leaf spring hysteresis can reduce the vehicle vibration,howerver the coexistence of the above two factors may increase the vehicle vibration.It is suggested to reduce the leaf spring hysteresis while installing the shock absorber,or to increase the leaf spring hysteresis in the case of no shock absorber.In order to match the powertrain mounts reasonably to reduce the vehicle idle vibration,a new mounting optimization method is proposed under the consideration of reduced vehicle flexible body as a supporting frame.Numerical results show that the response of the coupled model is consistent with that of Adams vehicle model,but it has higher solving efficiency.The coupling model contains more modal frequencies than the traditional six-degree-of-freedom model.Meanwhile,the mounting scheme optimized by the six degree of freedom model performs poorly in the vehicle coupling model,and the vibration of the frame rises instead of falling,which does not comply with the expectation.Finally,with the help of the coupling model and optimization algorithm,the optimization for powertrain mounts is carried out to minimize the frameend vibration,so that the vibration level of the frame is reduced.Based on the above work,the vibration dynamic equation of commercial vehicle is derived by coupling nonlinear leaf spring,main structure reduction model and suspension system.The drop test and bump test are constructed,and the corresponding simulation results are compared.The results show that the time domain response trend of the whole vehicle model is consistent with that of the real vehicle,and the frequency domain response can reflect the main characteristics.As a result of this,the model construction method has practical application value.In the face of the practical dilemma that the load for vibration response and vibration fatigue calculation is difficult to be measured directly,model reduction and time-domain iterative reverse engineering is combined.By using the reduced model,the multi segment sinusoidal and broken line excitations with 5% response noise are inversely solved.Finally,it is verified that the proposed method is insensitive to the regularization parameters and has good reverse precision.Finally,taking the vehicle response signal of actual road test as the target,the load reverse calculation is carried out on a model.After several iterations,good excitation result can be obtained.