Study On The Force Direction Based On The Tire Brush Model Of Variable Parameter

The establishment of car dynamic model is inseparable from tire dynamics model, which directly affects the simulation and the precision of vehicle dynamics modeling. Therefore, it has a very important role and far-reaching significance of the study on the tire mechanical properties. The tire is a complex viscoelastic structure with obvious nonlinear characteristics. Whether it is the empirical model or physical model, there are two important questions need to be resolved in the process of modeling:(1) the problem about modeling the force direction in complex conditions.(2) The problem about dynamic friction characteristics.Around the above problems, this paper will carry out the following research work on the basis of the tire brush model:Firstly, analyzing simplified theoretical model in the complex conditions which includes longitudinal slip and concerning, the simplified model can qualitatively reflect the tire mechanical properties and the expression is simple, the deduced formula is not complicated and making the provision for the force direction and angle range. There are several limitations of the simplified model:the force direction is different in the attachment region and slip the area because it is anisotropic, while in the model assumptions, the force direction is consistent with direction in the attachment area; the friction coefficient will be gradually decreasing with the increase of slip velocity. However, during the simulation, it is assumed that the friction coefficient is constant and unchanging; the carcass is elastic and makes the longitudinal stiffness and cornering stiffness inconsistent which has an effect on the tire mechanical properties.Secondly, considering the complex deformation of carcass and explaining its effect on the longitudinal and cornering characteristics is to obtain that the tire longitudinal sliding stiffness is not affected by the lateral force and carcass deformation, but the cornering stiffness、aligning stiffness and the initial the aligning arm of force will be affected by lateral force and carcass deformation. Further the tire brush model of variable parameter is put forward on basis of analyzing the variation of lateral stiffness at the small sliding, medium sliding and the big sliding. Defining the nominal cornering stiffness is compatible to the boundary conditions. Compared with the deviation which is caused by the assumption that the direction of shear stress in the slip area is the same as that in adhesion area, the modified model is complied with the fact that the force direction is consistent with slip velocity direction under the conditions of composite slip.Then, by the simulation of experimental data under the conditions of longitudinal slip cornering composite on the basis of the theoretical model which verified the force direction based on tire brush model of variable parameters, we can get the following conclusions longitudinal slip stiffness increases with increasing vertical load; lateral stiffness is not increased with the increase of vertical load, but the increase of lateral stiffness increased is gradually slowed down, or even declined in the increasing. Test data under the composite condition shows that the force direction is different from the attachment orientation and slip direction which is obtained by the longitudinal slip stiffness and lateral stiffness. It is consistent with the attachment direction in small slip ratio and consistent with the slip direction in big slip ratio which is consistent with the previous analysis.Finally, the model is verified through a large number of experimental data by considering the influence of camber to discuss the tire mechanics characteristics. Camber has a lot of influence on the lateral force, especially in the large camber angle. This paper will use the definition of the unified tire model proposed by Professor Guo Konghui that the camber is equivalent to the equivalent lateral slip rate so as to calculate the force direction angle. Camber angle has a small influence on lateral stiffness and longitudinal force. Curves of longitudinal force are basic coincidence with different camber angle. It has a great influence on lateral force because it will cause the original action point offset center point force in tire contact patch, the aligning torque which is caused by carcass elasticity leads to produce certain torsion angle that lead to change the lateral force. The force direction based on tire brush model of variable parameter including the influence of camber can exactly express the force direction under composite condition. It not only controls the error in a certain range, but also obviously has less parameters and the calculation is more concise.