Mobility and Vehicle Mechanics

7-21

Authors: Dragoljub Radonjić

Analysis and comparison of the comparative cycles is of great importance in assessing the effectiveness and efficiency of actual cycles of internal combustion engines. In conventional combustion engines are used the three main comparative cycles: otto, diesel and dual. The development of internal combustion engines, by applications: the new system of mixture formation (GDI, HCCI), variable valve timing, overboost system and aftertreatment of exhaust gases, bring to modification of the real working cycle, but also the need to introduce new comparative cycle such as Atkinson, Miller, Gruden and HEHC cycles. Previous methods of analysis and comparison of the ideal cycle is reduced to the determination of the expression of specific work and thermal efficiency of each cycle as a function of the characteristic parameters, adopting the criteria of comparison and finally, comparison of the specific work and efficiency of the given cycle at different values of the selected parameter. This paper presents a new method of comparison based on the application of the general thermodynamic cycle (GTC), introduced by the author. From the general thermodynamic cycle, in particular procedures can be carried out, all possible cycles for converting heat into work (total: 130), and by determining the expression of specific work and efficiency of this cycle and placing them in appropriate conditions can obtain expressions for the specific work and efficiency of each cycle. On the basis of these procedures has been developed a software package that provides graphical views of the following characteristics of the selected cycle: P-v and T-s diagrams, changes the specific work and thermal efficiency as a function of the desired dimensionless parameter, as well as the comparison of two or more cycles according to proposed criteria.

37-54

Authors: Zoran Nikolić, Zlatomir Živanović

First Electric Vehicle (EV) has been made in in 1837. This type of motor vehicles has dominated throughout the whole 19th century. In the early 20th century the faster and more robust vehicles with Internal Combustion Engine (ICE) overcame them until late 20th century, when ecological and economic problems of further application of these vehicles have emerged. The interest in EV has risen sharply. Researches are working in several directions in order to reduce the need for oil derivatives considering that the EV's are weak primarily due to inferior "reservoir of energy" to fully meet the current driving habits. Savings can be achieved in two ways, by making more economic motor vehicles or by the use of alternative fuels. Combining an electric propulsion and IC engine drives a hybrid vehicle is obtained, with a greater amount of batteries and "plug in" that is to some extent possible to reduce fossil fuel consumption and exhaust emissions. Intensive research work on exploring new battery is still to come. Today promising results with Li - air batteries, fuel cells and super capacitors, as well as the efforts of major car manufacturers indicate that the EV could soon appear massive in the streets of cities. This paper deals with the development of EV, following the development of powertrain and can conclude the fact that in the near future this type of drive could return.

63-77

Authors: Dobrivoje Ćatić, Jasna Glišović, Sandra Veličković, Jasmina Blagojević, Marko Delić

Weibull distribution is one of the most frequently used theoretical models for approximation of empirical distributions of random variables with continuous variation. Procedures for graphical, grapho-analytical and analytical determination of Weibull distribution parameters are described in detail in this paper. Based on the graphical method for determining the position parameters of three-parameter Weibull distribution, the analytical procedure is developed, which is based on the application of the method of least squares. The set of points is approximating with the square parabola, and based on the sign of the second derivative, the information for further proceedings is obtained. For the defined procedure, an algorithm of the computer program for determination of the Weibull distribution parameters is presented in paper. By using the program, based on data from the exploitation related to the operation time until failure, the reliability modelling of wheel’s drum in braking system of light commercial vehicles was performed. The graphical and non-parametric tests were used to test the theoretical model of distribution.