Chapter 1 – INTRODUCTION
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Chapter 1
INTRODUCTION
1.1. Problem statement
The purpose of this Master thesis is to examine the steady-state turning of a real vehicle and analyze its directional behaviour.
Simple equations describing the behaviour of such a vehicle will be developed and their significance illustrated using the handling diagram theory.
A single-track model is employed for the analysis: even if such scheme refers to a very simple vehicle model, it has been largely used by many authors [1], [2], [3] to understand and develop the lateral vehicle dynamics. In particular, considering a vehicle negotiating a curve, it is possible to observe a difference between the wheel’s longitudinal axis and the wheel speed vector. Such a difference is the so called “tyre side slip angle α”: it is responsible of the development of the tyre transversal forces,
which are significant parameters in the analysis of the vehicle dynamics. However, the measurement of tyre sideslip angle might be too expensive in the case of an ordinary test vehicle, and the results obtained unsatisfactory. For all these reasons is preferable to estimate it.
An evaluation of sideslip angle may be developed using a simple equation, known as “handling equation”, proposed by Pacejka in [4]: it does not allow direct measurement of such quantity, but the difference between front and rear tire sideslip angle.
Thanks to this approach, it is possible to plot the handling diagram, one of the most popular tools for the analysis of the steady-state directional behaviour of vehicles. This Master thesis shows the influence that tyre pressure has on the modification of the handling diagram, and its influence on the understeering-oversteering vehicle’s behaviour.
The inflation pressure of tires results to be one of the vehicle parameters that can be more easily modified by users of a vehicle; it represents also one of the
Chapter 1 – INTRODUCTION
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parameters which mainly can affect the tyre characteristics and therefore may influence the generation of horizontal forces between tread and road.
To achieve all these results the commercial software CarMaker® was used. Through it, a complete car model was created and validated. Two different tyre models were introduced, considering also different pressures. Subsequently, all the manoeuvres tested in the proving ground were simulated in this software and compared to the experimental data.
All these analysis were afterwards situated in a more general theory, developed by [5], [6], [7], where the handling surface concept is introduced and the handling diagram is considered as just a special case of it.
1.2. Outline of the thesis
The Master thesis is structured as follows.
In the second chapter the vehicle model used, the analysis of the steady-state directional behaviour of a rear wheel drive vehicle and the handling diagram concept are briefly presented.
The third chapter describes the most important part of the thesis. Here, the test car used is presented. Afterwards, all the different manoeuvres tested in the proving ground are described: performances obtained through experimentation are introduced, using the handling diagrams.
In the fourth chapter the CarMaker® simulation model is deeply analyzed. After a short presentation of the software characteristics, the design of the test car model is here described. Its validation, together with a comparison with the results obtained from experimental data is discussed.
Chapter five provides the description of the handling surface theory and how is possible to extract this from simulation data.
Finally, in chapter six the conclusions of this work and further developments are presented.
