| The virtual development between tire and vehicle has increasingly become an important means to improve product performance and shorten product development cycle.More and more vehicle companies need tire model for early virtual development of vehicle dynamics.The semi-empirical tire model is widely used for virtual development because of the high precision expression ability.However,the identification of model parameters relies on a large number of test data.In the process of vehicle development,there is a need for tire modeling with multiple rounds and multiple design schemes.On the one hand,it has brought great pressure on tire force and moment testing,resulting in a long delivery cycle of tire models with high testing costs,which has caused great difficulties for vehicle virtual development,and on the other hand the tire virtual submission based on finite element method has gradually become a new development direction.Whereas the current tire finite element simulation efficiency is relatively low,there is also the problem of modeling efficiency.The research on tire model or prediction method with predictive ability becomes the key to solve the above problems.Scholars have carried out a lot of research on predictive tire model and prediction method.But there are still problems with low accuracy of normalized prediction method due to the incomplete friction separation method and lack of prediction method for dynamic friction and longitudinal slip stiffness,as well as the limitations in the theoretical assumptions of resultant shear force direction.The prediction results of steady-state characteristics have significant deviations,which cannot be used for high-precision tire modeling.Thus,the development of predictive tire model or method with high precision prediction has great benefits in improving the efficiency of tire model submission and reducing costs,and also plays an important role in promoting the development of tire dynamics theory and automobile industry of China.The main contributions of this dissertation are listed as follows.(1)The index of tire stiffness anisotropy is proposed,revealing the rule that tires with similar nominal stiffness anisotropy coefficients have approximately same resultant shear force direction.By studying the tire forces in the adhesion and sliding regions under combined driving/braking and cornering conditions,a theoretical model considering belt/carcass deformation is established,and the index to express tire stiffness anisotropy between longitudinal and lateral direction is introduced.The relationship of tire stiffness anisotropy coefficient between slip angle and slip ratio is analyzed by the theoretical model simulation.It’s shown that tire stiffness anisotropy is the most significant under the small slip angle and small slip ratio conditions.Based on the established theoretical model,the definition of resultant shear force direction is given,and the variation law of the shear force direction in the whole tire footprint under combined slip conditions is deduced.According to the most significant condition of tire stiffness anisotropy,an approximate expression of the resultant shear force direction is derived and a nominal stiffness anisotropy coefficient is defined.Furthermore,a hypothesis about the resultant shear force direction is proposed and fully verified by experiments,which providing a basis for the prediction and correction of the resultant shear force direction and the establishment of reference tire criteria.(2)A prediction method of tire force and moment under pure slip conditions based on dynamic friction and slip stiffness is proposed,and a prediction method for pure longitudinal characteristic from pure lateral characteristic is established.According to the cornering and driving/braking theoretical model,the separation of dynamic friction coefficient from sliding region is presented,then a normalized theoretical model for tire longitudinal force,lateral force and aligning moment under pure slip conditions is deduced.This model reveals that the normalization curves of different tires under similar load are highly coincident.Therefore,the tire force and moment prediction method under pure slip condition is proposed from reference tire,which realizing the high precision prediction of pure cornering and pure driving/braking characteristics based on dynamic friction and slip stiffness.An example of the prediction of tire longitudinal force,lateral force and aligning moment is given,and the result shows that the method in this paper can bring less error and better predicted precision compared with other methods.Furthermore,a method for predicting the longitudinal dynamic friction coefficient from lateral dynamic friction is proposed,as well as a method for predicting the tire longitudinal slip stiffness from static footprint.The experimental verification is carried out in tire development activity,and the results show that the predicted data is in excellent agreement with experimental data.Thus,the purpose of predicting pure longitudinal characteristics from pure characteristics is achieved.(3)A method for predicting and correcting the resultant shear force direction is proposed,then a high-precision prediction method for tire longitudinal force,lateral force,and aligning moment under combined cornering and driving/braking conditions from pure slip test data is established.According to the established combined slip theoretical model and the unified expression characteristics of the Uni Tire model,a prediction method for resultant shear force direction is derived,and it’s proposed to use reference tire test data to correct the resultant shear force direction.The results show that both the resultant shear force and the direction have high prediction accuracy,so the longitudinal and lateral forces have reliable prediction results.By analyzing the generation mechanism of the aligning moment under combined slip condition,the acquisition method of aligning moment caused by the side slip,the carcass translation and the initial aligning moment are put forward,then the aligning moment prediction method of combined slip condition is given out.Through the comparison with test data,it is concluded that the alignment moment prediction results have a good expression and accuracy.In addition,the lateral force and longitudinal force predicted by the method in this paper are compared with the three kinds of prediction methods in the literature.The results show that the prediction accuracy of the proposed method is better than the state stiffness method,Combinator and Similarity.In addition,the double-peak phenomenon of lateral force under the combined slip condition is studied through theory analysis and experimental research,which revealing the mechanism of the double-peak phenomenon and the reason for the prediction model leads to abnormal double-peak phenomenon.(4)The predicted tire force and moment under cornering,driving/braking and combined slip conditions through the presented method are used for parameters identification of PAC2002 tire model.The expression accuracy is compared with the model by test data.And the two tire models are applied to the vehicle dynamics simulation.The results show that these two tire models have approximate mechanical expression accuracy,and the vehicle simulation results have good consistency within the range of vehicle longitudinal acceleration more than-0.6g and lateral acceleration less than 0.8g.As thus,it has been proved that the proposed prediction method in this paper has good reliability and engineering application prospects. |
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