| With the development of modern military technology,the wheeled operationallymaneuvering platform requires high mobility,stability and pass ability.To shorten the R&D cycle,reduce the development cost,and quickly find the source of the problem,establishing a high-precision vehicle virtual prototype model for pre-virtual adjustment and load extraction has gradually become the mainstream of vehicle development.As the only part of the vehicle in contact with the road,tires are the key factor for determining the vehicle performance simulation and the accuracy of load extraction.A high-precision dynamic load unsteady tire model for all operation conditions is established,which is suitable for the use scenarios of military vehicles.It has important research significance and practical value for improving the accuracy of load extraction for wave roads and twisted roads and laying a foundation for virtual analysis of off-road road performance.Referring to the current research state,the most classic tire models,i.e.,Uni Tire model and Magic Formula model,have carried out a lot of research on the tire unsteady-state characteristics.However,in order to meet the needs of virtual development of military vehicles,there are still two core problems that need to be solved urgently:(1)The tire unsteady model mainly includes force and moment models.In previous studies,the nonlinear relaxation force model has achieved good simulation results,however,there are still some problems in the study of the aligning moment model.The theoretical mechanism is not clear enough,and the expression accuracy of practical semi-physical model needs to be improved;(2)In the research of unsteady dynamic load characteristics,it mainly focuses on the analyze and verification of side slip and longitudinal slip conditions,however,no in-depth research and verification have been carried out for the combined slip unsteady condition.Aiming at the above problems,this paper establishes an unsteady discrete theoretical model suitable for dynamic load simulation and a simplified nonlinear unsteady analytical model for mechanism analysis.Then,based on the above analysis results,a practical nonsteady nonlinear dynamic load combined slip semi-physical model is developed.Finally,the model was connected to the vehicle dynamics simulation software,and the vehicle application research was carried out.The main research contents and conclusions of this paper are as follows:1.Mechanism analysis of tire unsteady dynamic load combined slip condition.First,the finite element analysis method is used to obtain the response process of the tire force and moment during the dynamic operation of the tire,as well as the change process of the stress distribution in the footprint,under nonlinear slip angle step and dynamic load side slip conditions.A preliminary study on the mechanism of the establishment of unsteady forces and moments of side slip is carried out.Then,in order to further improve the simulation efficiency and clearly analyze the stress distribution law of unsteady working conditions,a discrete theoretical model suitable for dynamic load combined slip conditions was developed.Through discrete simulation analysis of nonlinear side slip angle step,dynamic load side slip,combined slip sweep and dynamic load combined slip conditions,the change process of lateral,longitudinal and vertical stress in the footprint under each condition is output.The establishment process of the aligning moment(Pneumatic trail)under complex conditions of the tire is revealed,which provides a theoretical basis for the development of the semiphysical model.At the same time,a complete set of virtual verification data is also provided to make up for the working conditions that cannot be completed by some bench tests.2.Development of the tire aligning moment model for dynamic load side slip conditions is carried out.Firstly,the analytical theoretical model of the tire unsteady nonlinear lateral force and aligning moment considering the complex deformation of the carcass is deduced,and the frequency response characteristics of the unsteady force and moment under different slip angles are analyzed.Based on the analytical expression of the frequency response of force and moment,the frequency response expression of the pneumatic trail is obtained by further solving,which is the key theoretical basis for establishing the semi-physical model of the unsteady aligning moment.Then,the nonlinear relaxation expression of the lateral force is obtained by simplifying the analytical model,and the analytical expression of the pneumatic trail is decomposed and expressed as a general expression of a second-order system with zero point.The theoretical analysis and semi-empirical expression of the parameters of two poles and one zero point are carried out,and a complete practical semiphysical model of nonlinear unsteady side slip force and moment is constructed.Finally,on the MTS tire testing machine,the tire steady-state and unsteady-state dynamic load side slip tests were carried out,and the newly developed model was used for parameter identification and comparison with the test results.The comparison results between simulation and experiment show that the improved semi-physical model of the non-steady-state back-tonormal force arm has a good expression effect in the nonlinear slip angle step and dynamic load side slip conditions.3.Development of the tire unsteady model for dynamic load combined slip condition is carried out.Firstly,the nonlinear unsteady longitudinal force and lateral force frequency response functions are deduced under the combined slip condition considering the lateral and longitudinal deformation of the carcass,and the analytical expression of the aligning moment relative to the center of the footprint after the deformation of the carcass is obtained.Based on the above,the frequency response characteristics of tire longitudinal force,lateral force and aligning moment under different comprehensive slip levels are analyzed,which provides a complete theoretical framework and theoretical basis for modeling the unsteady semiphysical model of combined slip conditions.Then,develop the unsteady practical semiphysical model of tire combined slip,analogize the pneumatic trail model under the pure side slip condition,and the combined slip input is equivalent to the side slip input to model the unsteady pneumatic trail.Based on the above,the aligning moment formed by lateral force,longitudinal force and longitudinal and lateral offset of the carcass is superimposed,and a complete aligning moment model under combined slip conditions is constructed together.Finally,the tire steady and unsteady combined slip conditions are tested,and the newly developed combined slip unsteady semi-physical model is used for parameter identification and comparison with the test results.The results show that the newly developed unsteady semi-physical model can accurately simulate the force and moment characteristics of dynamic load and unsteady combined slip conditions.4.Research on tire model application and analysis of dynamic load and response performance of military vehicles in typical scenarios.Firstly,the vehicle multi-body dynamics model of an 8×8 wheeled armored vehicle is established,and based on the improved unsteady tire model under combined slip conditions,a special tire model interface under the use environment of the vehicle simulation software is developed.Then,the vehicle dynamics simulation analysis under typical dynamic load conditions is carried out including the constant speed driving condition on the twist road,the braking condition on the twist road and the steady-state steering condition of the whole vehicle under the condition of the sine wave road surface.The wheel dynamic load spectrum and vehicle response are extracted respectively.By analyzing the simulation results of the whole vehicle under dynamic load road conditions,it can be clearly seen that the use of the improved model has a significant impact on the wheel dynamic load and vehicle handling characteristics.In this paper,the mechanism of the force and moment frequency response of the tire combined slip unsteady condition is revealed.For the first time,the nonlinear unsteady frequency response characteristics of combined slip conditions were systematically deduced analytically,and the frequency response expressions of longitudinal force,lateral force and aligning moment(center position after the deformation of the carcass)were obtained.Based on the theoretical model framework,a complete practical semi-physical model of nonlinear unsteady longitudinal force,lateral force and aligning moment under dynamic load combined slip conditions is constructed.The research results will help to improve the simulation ability of the wheel dynamic force and moment characteristics of military vehicles under typical wave road and twisted road conditions.And it is of great significance to the virtual development of military vehicle performance under undulating off-road road conditions and to promote the performance development of wheeled armored vehicles. |
