Study On Tire Longitudinal-Slip Properties Considering Transient Vertical Load And Transient Slip Ratio

In this thesis the development of the tire model for the dynamic longitudinal characteristics will be discussed. The objectives of this thesis are the development and implementation of a mathematical model of a pneumatic tire that is well suited for vehicle simulations. The requirements for the model development are: A compact relatively fast tire model, as it has to be used for vehicle dynamic simulations. Accurate representation of measured slip characteristics. The theoretical boundary conditions satisfied. Low frequency range, so the inertial forces are considered small and will be neglected.Rather than modeling the complex tire structure in all its details, the most important dynamic properties of the tire will be taken into account in a mathematical model of the tire. The model developed in this thesis is considered to be a general model for the longitudinal tire behavior. It is expected that the basic structure of this parametric mathematical model will not have to be changed to represent different types of types of tires and that a type of tire will be represented by a set of parameters under the model. Such an approach will lead to a relatively compact tire model.On the basis of the theoretical study on the longitudinal slip characteristics, a non-steady non-linear handling tire model is established, and then validated by experimental investigations. The outline of this thesis is presented as follows.Chapter 2 presents the basic concepts which are needed for the model development such as the Contact Process coordinate system, slip ratio, longitudinal relaxation length. The force generation of a rolling tire is also presented.Chapter 3 presents the theoretical model of the longitudinal slip properties. First, the shear force generated by tires under steady-state conditions is discussed as this is one of the most important aspects affecting the low frequency vehicle response. The brush model is introduced as it is sufficiently simple that an analytical solution can be given although it is physically based. This solution has a qualitatively reasonable correspondence with experimentally found tire characteristics. Secondly, the transient tire behavior is studied where the brush model is considered again. It is well known that the force response of the tire to various external inputs is delayed. This phenomenon is typically characterized by the relaxation length of the tire. One way to model the variation of slip or vertical load is to consider the tread as a finite number of elements. However, for linear modeling where no sliding occurs and where the variations in the input quantities are small, an analytical approach is preferable. The analytically obtained Frequency Response Functions (FRFs) of the brush model and the theoretical model considering carcass compliance are presented. Thirdly, a simulation model for large variations of slip or vertical load is presented, in which the tread elements are modeled as individual elements that may slide or adhere to the road surface.Chapter 4 presents the experimental investigations of the longitudinal slip properties.Chapter 5 presents the pragmatic semi-empirical model of the longitudinal slip properties which satisfies the boundary conditions of theoretical model. This model is based on matching transient tire responses with a set of first order differential equations rather than extensively modeling of physical tire properties, and thus the computations are much easier and faster, and measured slip characteristics can easily be incorporated. So, the typical structure of the...