The Validation And Improvement Of Non-steady State UniTire Model’s Precision

A car can’t be always traveling on the good road straightly in a constant speed, it generally turns, experiences the uneven road surface, sometimes drives through the different roads, such as dry pavement, the road with water, ice and snow road. The tire always rolls in a non-steady state, in that case, the lateral velocity of the tire, the road surface conditions(like friction coefficient), and the vertical force between the tire and road surface are always changing, and all of these factors affect the lateral mechanical properties of the tire, also directly affect the handling and stability characteristics of the car, so the lateral non-steady state mechanical properties of the tire are very important, and establishing a precisely non-steady state tire model that could expresses tire mechanical properties under some complicated working conditions has important practical significance.This paper mainly studied the non-steady state mechanical properties of the tire under the cornering conditions, and improved the existing Uni Tire semi-empirical non-steady state model by means of designing and implementing a large number of transient tests and applying the finite element model, and finally the Uni Tire model was compared with the PAC2012 model and experimental data in order to verify its expressing ability and precision.Firstly this paper accomplished some steady state tests under the pure cornering condition, the lateral stiffness tests, and kinds of transient tests, such as side-slip angle step tests, changing the road surface friction coefficient tests, changing the vertical force tests and so on. The purpose is to analyze the tire lateral mechanical characteristics under the complex conditions; what’s more, it provided important evidences to validate the precision of the tire model. It is concretely represented from the following several aspects: the significance of tire mechanical characteristics, the test equipment, test plan’s formulation and implementation, the output curves of the test results, and the analysis of the experimental phenomena.Secondly the modeling mechanism of the PAC2012 model was introduced and analyzed, The PAC2012 model has been recognized by the industry and widely used in various kinds of vehicle dynamics softwares, so the PAC2012 model has been introduced as a reference in this paper. This paper introduced the development history of the PAC2012 model briefly, analyzed the steady state characteristics of modelling, and studied the non-steady state modelling process in detail. Combining with the tire mechanical characteristics of the tests in the previous chapter, validated the precision of the PAC2012 tire model.Then this paper introduced the Uni Tire semi-empirical model knowledges of steady state modeling from tire coordinate system, inputs and outputs, the central formulas and parameters. And proposed a new method to establish Uni Tire non-steady state tire model. This method equals tire tread to tread damper, tire body to spring and damper. Establishing the unified force and moment balanced equations at any moment, finally through the analysis of the theoretical solution,non-steady state tire model is obtained. According to the test and FE simulation, make Uni Tire non-steady state semi-empirical model perfect.Finally the main work is comparing the precision and expression ability of the Uni Tire semi-empirical non-steady model and the PAC2012 model with the test data.