Mobility and Vehicle Mechanics

15-26

Authors: Dejanu Marcel, Dascalu Traian, Popa Dinel, Pârlac Sebastian, Salamu Gabriela

The experimental bench has in its composure a laser equipment, a high speed recording video equipment, a measuring system for recording pressure variations and a static enclosure in which experiments are conducted. The recording of images was done using the shadow graph technique, a source of light with xenon and a 3000 frames/s high speed camera with a resolution of 512x512 pixels. There were recorded and analyzed the next phenomenon: the variation of the flame front depending on the initial pressure, the variation of the pressure from inside the chamber depending on the initial pressure and also the shape and the way of how the flame front is propagated. The results are presented under the form of images and diagrams.

35-50

Authors: Adrian Clenci, Adrian Biziiac, Pierre Podevin, Rodica Niculescu

Reducing fuel consumption is a prime objective in the automotive industry in order to meet legal and customer demands due to the increasing price of oil. Variable valve actuation offers many opportunities for improving the spark ignition engine’s performance in areas such as fuel economy and pollutant emissions. This study presents a variable intake valve lift (ViVL) mechanism, used to enhance fuel economy in the area of idle operation and low part loads, which are the ones most frequently encountered in a vehicle’s operation time. Currently, this mechanism is self-regulated thanks to a hydro-mechanical system and allows a continuous intake valve lift variation during engine operation. Our studies revealed that the ability to control valve lift does indeed offer the ability to control intake air mass but also has the added benefit that it improves the fuel-air mixing process and controls air motion. This is particularly important at idle and low part loads when low lifts are to be used for improving the fuel economy or for achieving the required power. The paper focuses on the experimental results obtained when approaching idle operation with different configurations of the intake valve timing system. Results indicating the potential of the ViVL system for fuel economy improvement, as well as results regarding the in-cylinder pressure evolution are presented in this paper. Last but not least, the paper also presents a so-called Sleep&Start strategy, which can be seen as an alternative to the Stop&Start micro-hybridization solution. In other words, once a ViVL system has been installed on an engine, it should be used in every possible way in order to obtain a high benefits/cost ratio.

19-29

Authors: ejanu Marcel , Popa Dinel, Dascălu Traian, Tabacu Ion, Pârlac Sebastian

The experimental bench has in its composure a laser equipment, a high speed recording video equipment, a measuring system for recording pressure variations and a static enclosure in which experiments are conducted. The recording of images was done using the shadowgraph technique, a source of light with xenon and a 3000 frames/s high speed camera with a resolution of 512x512 pixels. There were recorded and analyzed the next phenomenon: the variation of the flame front depending on the initial pressure, the variation of the pressure from inside the chamber depending on the initial pressure and also the shape and the way of how the flame front is propagated. The results are presented under the form of images and diagrams.

43-63

Authors: Dobrivoje Ninković, Dragan Taranović, Saša Milojević, Radivoje Pešić

Thermodynamic performance (delivery rate and power intake) and reliability of reciprocating compressors are dependent upon the valves. Since the valves open and close automatically, there is a high degree of coupling between the gas flow through the valve and the sealing element dynamics; a mismatch between the two leads inevitably to degradation of the compressor performance and/or short valve life. The latter is due to impact forces between the sealing element and other parts of the valve assembly. Therefore, matching the valves to the compressor application at hand is a complex task that calls for the use of the corresponding simulation models. Surveyed in the paper are mathematical models for the prediction of the valve performance, consisting of the sub models describing compressible gas flow through the valves, sealing element dynamics, and the interaction of the latter with the flow. Flow models based on the discharge coefficient are intrinsically not able to predict the critical flow regime with sufficient accuracy, requiring thus experimental data that are not always available. It is also suggested that other loss calculation approaches, such as the stagnation pressure loss model, should be investigated as possible alternatives to the discharge coefficient concept.

27-40

Authors: Saeed Abu Alyazeed Albatlan

In particular, a commercial vehicle may meet critical braking conditions when the vehicle is partially or fully loaded, and when the road is wet or slippery. Under these conditions, the vehicle can spin out, the tractor can jackknife or the trailer can swing out. The air brake system has many design variables; there must be intense research on a method on how to prevent dynamic instability and how to maximize vehicle deceleration. So; some of the commercial vehicles are provided with the combination valve. The behavior of this valve is important to improve the braking performance. In this study, mathematical models and a computer simulation program is used to evaluate the valve and vehicle braking performance characteristics. The measurements performed on the valve using the test rig concord with mathematical model.

69-89

Authors: Miroslav Demić, Jovanka Lukić, Živorad Milić

Investigations of a human body behavior exposed to whole body vibration of vehicles are important in design phase of vehicles. Results make possible to model human vehicle oscillatory system and vehicle parameter optimization from ride comfort aspects. Experimental results of investigations of motor vehicles users vibratory loads (passengers and duty) depending on operational conditions (road surface, vehicle speed). Obtained results were base for further investigation of human body behavior exposed to whole body vibrations in laboratory conditions.

25-38

Authors: Saeed Abu Alyazeed Albatlan

Some of hydraulic brake systems for passenger cars and light trucks are provided with load sensing proportioning valve. The behavior of this valve is important to improve the braking performance. This study presents the development and validation of a mathematical model of the change of valve design parameters on its performance according to application requirements. Experiments have been performed to measure the behavior of line pressure before and after the valve. The model results have good agreement with the experimental results.

51-46

Authors: Boris Rakić, Lozica Ivanović, Danica Josifović, Blaža Stojanović, Andreja Ilić

In this paper, the analysis of the influence of variation in position of output shaft to load on the Cardan joint cross shaft in power transmitters is shown. Cardan shafts are the systems that provide alterations of angles between axes of the shafts, which are involved in the power transmission, so as theirs relative translations. Those properties make Cardan shafts very suitable for using in power transmitters, especially at motor vehicles. The kinematic of power transmitters with Cardan joints is highly specific in relation to variation in position of the axis of the output and input shafts. Those variations in positions cause the alterations of the maximal stresses at the branches of the Cardan joint cross shaft and, also, at its bases. The analysis of the motions at this power transmitter is presented in the first part of the paper and also, the diagrams of relations between the specific kinematic values are given. The analytical calculation of the stresses at the cross shaft of the Cardan joint, as function of the angular position of the shaft is done. The second part of the paper deals with forming of the analytic, so as with numeric calculation of stresses in the critical section of the cross shaft. The results obtained by numeric and analytic method are evaluated and the conclusions about stress concentration and stress distribution for different positions of Cardan joints are done.