sign in sign up
<<
Home , Actuator, Automatic transmission, Torque converter, Transmission (mechanics)

Review Paper

doi:10.5937/jaes13-7727 Paper number: 13(2015)1, 313, 51 - 59 MODERN DESIGN AND CONTROL OF AUTOMATIC AND THE PROSPECTS OF DEVELOPMENT Dejan Matijević The School of Electrical and Computer of Applied Studies, Belgrade, Serbia Ivan Ivanković* University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia Dr Vladimir Popović University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia

The paper provides an overview of modern technical solutions of automatic transmissions in auto- motive industry with their influence on sustainable development. The objective of the first section is a structural view of specific and control systems of presently used automatic transmis- sions, with emphasis on implementation. The second section is based on perspectives of development, by integrating some branches of soft computing, such as fuzzy logic and artificial neural networks in order to create an optimal control algorithm for obtaining a contribution to fuel economy, exhaust emission, comfort and performance. Key words: , Mechatronics, , Soft Computing

INTRODUCTION which is depended by coefficient of friction and normal load on the drive . Lower limitation Almost all automobiles in use today are driven by is defined by maximal speed that vehicle can internal combustion , which are charac- reach. Shaded areas between traction forces terized by many advantages, such as relatively through are losses. To decrease good efficiency, relatively compact stor- power losses and to be as closely as possible age and high power – to – weight ratio [07]. to the ideal traction hyperbola, the gearbox with But, fundamental disadvantages are: enough ratios is needed. • Incapability to produce from rest (zero speed) and relatively low torque at small engine rpm ; • an internal combustion engine only produces maximum power at a certain engine speed; • fuel consumption is strongly dependent on the operating point in the engine’s perfor- mance map; It is not hard to conclude that speed charac- teristic of internal combustion engine is not the most appropriate for the vehicle movement with Figure 1: Traction diagram for a vehicle with for four speed gearbox [06] a high efficiency. The desired characteristic is “ideal traction hyperbola” which can be obtained Besides characteristics of drivability, which should only by maximum available engine power Pmax be satisfied by certain type of transmission for through all vehicle speeds [07]. specified vehicle, there are also requirements re- The area below the ideal traction hyperbola in lated to the fuel consumption, installation space, the traction diagram, shown on Figure 1 for vehi- comfort, convenience and product costs. It is not cle with a four speed gearbox, could be used for easy to fulfill all these demands, but because of vehicle movement. Upper limitation is related to high competition, great efforts have been made in maximum traction force between and road, the field of research and development.

* University of Belgrade, Faculty of mechanical engineering, Kraljice Marije 16, Belgrade, Serbia.; 51 [email protected] Dejan Matijević- Modern design and control of automatic transmission and the prospects of development

It was reflected on automatic transmissions too, But even today, when benefits of control systems because from the beginning of series vehicle and mechatronics utilization are clearly evident, production, it has been tended to processes au- many people especially in (where percent tomatization. Gear changing automatization has of sold passenger with AT is only 15 to 20 crucial impact on traffic safety, because driver percent, while in and this gets much less tired than with manual transmis- percentage goes up to 80 to 90 [02]) believe that sion, where is demanded constant changing of automatic transmission are too much expensive gear ratio according to the road conditions and for maintenance and that are less reliable be- traffic situations. This is especially important for cause of their complexity and connections with city . other electronic systems in the vehicle, without Despite higher complexity, there are less nega- deep understanding of their advantages. But, tive effects on gearbox sustainability and reliabil- automatic transmission utilization differs through ity caused by driver’s unprofessional handling vehicle segments, and it is shown on Figure 2. with automatic over . Of course, the highest percentage of their appli- Utilization of planetary gear sets enabled much cation is in Luxury segment. Small and seg- greater number of gear ratios than it is possible to ments are economically unsuitable for installa- obtain with manual transmission (for commercial tion of automatic transmissions. It is important to up to 18). Continuously variable trans- notice a positive grade in automatic transmission missions have theoretically an infinite number of usage in Sports segment in the last few years gear ratios, what leads to maximal approxima- and the reasons for that are decreasing of gear tion of ideal traction hyperbola. shifting time (especially with DCT transmissions) and better utilization of engine performance.

Figure 2: Market share of vehicles with automatic transmissions (in %) through years

ELECTRONIC TRANSMISSION CONTROL CAN communication as it is shown on Figure 3. It leads to reduction of costs and complexity while Electronic control of automatic transmissions increasing diagnostic functions and reliability. represents an integration of electrics, electronics Basic automatic transmission control systems and . The basic functions are achieved are: by use of sensors, and appropriate • Automated manual transmission (AMT); software in the transmission control unit (TCU). • Hydrodynamic mechanical transmission Advanced functions include networking of the (HMT); control units into one global system, what en- • Continuously variable transmission (CVT); ables information exchange between them, by • Dual transmission (DCT); 52 Journal of Applied Engineering Science 13(2015)1, 313 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development

Figure 3: Communication between electronic control units by CAN protocol [06]

AUTOMATED MANUAL TRANSMISSION process, but it also enables faster gear shifting. (AMT) It is achieved because the clutch torque is only marginally above the engine torque. The regula- The automated manual transmission combines tion process enables dropping the clutch torque the advantages of manual transmissions with at the moment when the driver takes his foot off function of automatic transmission [01]. The the accelerator pedal, Figure 5. greatest advantage of this transmission is high efficiency which is characterized for manual transmissions. Their automatization leads to low- a. ECM er specific fuel consumption over manual trans- b. AST mission controlled by average driver. It enables lower level of CO2 emission, which is one of the 1. Available signals most important global issues. Also, by avoiding 2. Clutch with an installation of the clutch pedal, the increasing integrated ECM ECU safety with operating comfort and convenience 3. Gear recognition are achieved. 4. Shift-intention Two basic types of this kind of transmission are: recognition on shift lever • Electric-motor clutch management (ECM); 5. Clutch actuator with • Automated shift transmission (AST); integrated AST ECU The basic difference between these two types of 6. Transmission actuator transmissions is higher level of automatization of 7. Selector lever the AST because there is no mechanical connec- tion between the selector lever and the transmis- sion, as it is shown on the Figure 4. Examples of application ECM systems are: Mercedes A – Class, Figure 4: Review of ECM and AST systems [01] Fiat Seicento and Hyundai Atoz. Examples of ap- plication AST systems are: VW Lupo, MCC Smart and Corsa [01]. In conventional systems of manual transmissions, the maximal clutch torque must be 50% to 150% higher than defined maximal engine torque. The reasons for that are strong fluctuations of the torque on the flywheel, especially with modern diesel engines, and the requirement that the clutch must trans- fer engine torque under all extreme conditions. To decrease these negative effects, function of torque correction during gear shifting is imple- mented in the control system of AST. This meth- od not only that achieves smoother control of the Figure 5: Review of clutch and engine torque control Journal of Applied Engineering Science 13(2015)1, 313 during gear shifting 53 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development

HYDRODYNAMIC MECHANICAL The most important basic functions of Hydrody- TRANSMISSION (HMT) namic mechanical transmission control are the shift point control, the lockup converter clutch The main component of hydrodynamic mechani- control and engine torque control during shifting cal transmission is a . The torque [02]. The basic shift point control, which is related converter is a power take-up element, which also for other transmission control types, uses works as an additional gear in the start-up range shift maps which are stored in the unit memory. and also serves to damp vibrations [01]. Torque The shift point limitations are defined by minimal converter is connected to the of the and maximal engine speed. To avoid frequent engine by flex drive plate. The flex drive plate shifting between two gears under certain engine also has a function to decrease torsion rigidity of load and vehicle speed, the hysteresis between the transmission and with massive torque con- the upshift and the downshift characteristic is verter, filled with automatic transmission fluid, embedded. To improve this basic function and there is no need for heavy and expensive dual to obtain higher hysteresis between upshift and mass flywheel to smooth stresses and vibrations downshift characteristics, an adaptive func- coming from the engine. Function of multiplying tion is incorporated. It can be achieved only by engine torque is achieved by stator assembly, software changes with use of already existing located between the and the as- components in the system. The simplest trans- sembly in the torque converter. Characteristic of mission control takes into account just three pa- the torque converter is shown on the Figure 6. rameters. These are vehicle speed (determined by the transmission output speed), the position as indicator of engine load and the ac- celerator pedal position as driver command. The adaptive function uses vehicle acceleration, as additional parameter, which is calculated from transmission output speed over time. Calculated or actual vehicle acceleration is compared with set value which is determined from traction re- sistance characteristic and depends from actual vehicle speed and engine load. Basic principle of adaptive shift point control is shown of Figure 7.

Figure 6: Characteristic of the torque converter [01]

It can be noticed from the diagram on the Fig- ure 6, that there is a converter area v<85 % with maximum efficiency up to 90 %, and the clutch area v>85 % when a one-way clutch is activated in order to obtain mechanical connection be- tween pump and turbine assembly. This leads to increased efficiency up to 97 %, because fluid slip is eliminated, but there is no torque conver- sion. In order to accomplish enough gear ratios, for this type of transmission in luxury vehicles usually seven or eight speeds are available, Figure 7: Basic principle of adaptive shift planetary gear sets are used. Different gear ra- point control [07] tios are achieved by certain elements of planetary gear sets by bands and . By this way, the shift point correction is obtained They are regulated by electro hydraulic actua- what leads to better control of the process and tors, controlled by electronic transmission con- possibility for implementation of different shift trol unit. maps into the database of the transmission con- 54 Journal of Applied Engineering Science 13(2015)1, 313 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development trol unit (TCU). For example, one shift map can Generally, during downshift process a short in- be adopted for low fuel consumption, which has terruption of the tractive power transfer should shift points in the range of best efficiency of the occur to minimize undesired vibrations incurred engine, and the other one should enable highest by higher revolving energy. During upshift pro- engine output power. The selection of appropri- cess a torque reduction should be obtained in ate shift map can be done by the driver, with a order to decrease power losses. selector push button or a switch. CONTINUOUSLY VARIABLE Function of lockup torque converter clutch is TRANSMISSION (CVT) important for reducing power losses caused by converter slip. For increasing the efficiency it is Principle of operation of continuously variable necessary to close the clutch as often as pos- transmission is based on infinite number of gear sible. But beside function of increasing torque, ratios and because of that its theoretical efficien- the torque converter is an important component cy is higher than other transmission systems. to prevent vibrations coming from the engine. It Because transfer and transformation of power can be concluded that the clutch activation is a parameters are accomplished by friction ele- compromise between low fuel consumption and ment, which is crucial for CVT operation, due to driving comfort. Situations in which the clutch is slipping, power losses are higher as higher pow- certainly open are, driving in the first gear, during er transfer is requested. shifting process and under high torque demand The largest number of CVT units is made with a with low engine speeds. Reasons for it are ob- as wrap element. Figure 8 shows the struc- taining torque increase for improved accelera- ture of the most common based CVT sys- tion and reduction the level of vibrations under tems. If two cones of the pulley fall apart, the non stationary conditions. In other driving situa- diameter of the pulley becomes small; while they tions which are mainly defined by constant load, are close, the diameter of the pulley is large. Be- the clutch should be closed. Torque converter cause the length of the driving belt is fixed, when clutch is controlled by on/off , the diameter of the drive pulley becomes small, regulator or a PWM solenoid. the diameter of the driven pulley must become Like with automated manual transmission, a large by closing two cones of the pulley together, function of engine torque control during shifting and vice versa [13]. must be incorporated to the process regulation. For obtaining that function, a communication with engine management system is crucial. Depend- ing of engine type and system of mixture forma- tion different methods of engine torque control are possible. For gasoline engines the fastest regulation process is achieved with an ignition angle. It is also used for idle speed regulation. The advantage over throttle position regu- lation, which is characterized by its inertia and need for parallel correction of injection time for obtaining defined lambda factor of the mixture, is shorter response time of the system. Injection quantity correction is applied for diesel engines and beside variation of injection time it also in- cludes injection pressure correction (Common Figure 8: Pulley based CVT [04] Rail - CR, Unit Pump System-UPS, Unit Injec- tor System - UIS). The parameters of engine Rubber belts have tendency for straining and torque regulation are defined by calibration data slipping, what is the reason for reducing its ef- for each combination of the engine, gearbox and ficiency. Entering of new materials makes CVT the vehicle, so regulation process is controlled transmission more efficient and reliable. One of by transmission input speed in order to obtain design improvements is metal belt, which com- synchronization during gear shifting process. prises two steel strips connected with thin highly resistant metal. Metal belts are not slipping and

Journal of Applied Engineering Science 13(2015)1, 313 55 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development with them CVT transmission can transfer higher contact pressure. Depending of the chosen fric- loads. Also they produce less noise than rubber tion elements there are different types of varia- belt. For greater demands, steel chain could be tor’s principles which could be in use. Example used as wrap element. It is also flexible, but much of mechatronic unit for CVT transmission with more strength than any other element. System both controlled pulleys and the torque converter with steel chain is implemented with sensor of is shown on Figure 9, and its operating principle torque for ensuring enough tension with optimal on Figure 10.

Figure 9: Mechatronic unit for CVT Transmission [06]

Figure 10: Scheme of control CVT Transmission [06]

The main component of this mechatronic unit is via pulley ratio linkage controlled by stepper is line pressure solenoid valve, which regulates motor. For this mechatronic circuit, stepper mo- the pressure from a pump in a range 5 - 60 bar. tor is the least reliable part of the system. But At idle the pressure is 15 bars. Reason for such enables more precise control, be- high is demand for high transmis- cause its proper activation is a condition for gear sion efficiency, which could be achieved only by ratio changing. All CVT units have a planetary strong clamping force of the belt, to decrease gear set for reverse operation and two clutch belt slippage as much as possible. For achiev- packs for forward and reverse motion. If there is ing sufficient clamping force on the belt, second- a torque converter, there are for lock ary pressure solenoid is responsible. Also, there up clutch regulation. Because torque converter is a solenoid for the primary pulley, but before offers good starting response, pulleys transmis- the pressurized fluid comes into that solenoid, sion ratios could be beneficial to over drive range it must pass through ratio control valve, which so large ratio span could be covered. In order

56 Journal of Applied Engineering Science 13(2015)1, 313 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development to achieve better efficiency TCC PWM Solenoid ing to neutral first in order to adjust the spinning regulates the pressure of the fluid in a range 0 speed of the input shaft, and just after to shift - 10 bars, and there is a TCC Lock-Up On/Off to the next gear. The mechatronics of DCT are regulator for activating torque converter clutch housed in the gearbox, surrounded by oil. They lock up as soon as possible. comprise an and an elec- tro-hydraulic control unit. The mechatronics form DUAL CLUTCH TRANSMISSION (DCT) the central control unit in the gearbox. All sensor Dual clutch transmission (DCT) presents the fur- signals and all signals from other control units ther development of the automated shift trans- come together at this point and all actions are mission (AST), designed and developed by initiated and monitored from here. By hydraulic and , with first application in 1992 means, it controls and regulates gear actuators in motor racing . This type of transmission via pressure modulation and selector has a high efficiency because power transfer is valves, but it also controls the pressure and flow achieved by clutches instead of . of cooling oil for both clutches. The Mechatron- of DCT is similar as manual trans- ics assembly can adapt to learn the positions of mission, with application of collar, synchroniz- the clutches, the positions of the gear actuators er and gear set in order to perform gear shift. for each specific gear and the main transmission Biggest advantage of DCT is fast gear shifting, fluid pressure. Example of electro-hydraulic con- without interruption of the , what trol unit is shown on Figure 12 [11]. enables relatively low fuel consumption. [01,13] Dual clutch transmission is characterized by two main shafts and associated clutches in its structure, one for odd (1st, 3rd,5th) and the other for even gears (2nd, 4th, 6th), as it is shown on Figure 11.

Figure 12: Electro-hydraulic control unit for DCT [11] DEVELOPMENT OF THE TRANSMISSION CONTROL ALGORITHMS In 2013. Rolls – Royce engineers designed Sat- ellite Aided Transmission, new control system where the transmission control unit is connected to Global Position System (GPS) receiver [09]. With this kind of communication, vehicle control system can determinate road profile in front of the vehicle, so gear shift prediction could be achieved. Therefore vehicle performance and fuel economy could be improved, with higher comfort, because problems of inadequate gear shifting on a slope Figure 11: Basic construction of dual shift or in a curve could be avoided. But entering navi- transmission [13] gation systems has even more sense for com- As soon as computer detects that the spinning plex control systems of automatic transmission, speed of the input shaft is too high, for example which include adaptive functions of self learning. in the first gear, it prepares the next speed, by One of the crucial steps in developing of soft- engaging 2nd gear’s collar to the 2nd gear. Only ware is calibration process. Because transmis- after that, the clutch for the odd gears should sion control is nearly connected to the engine disengage, and the 2nd gear’s input shaft should management and many other systems, fulfilment engage. For smoother application, despite short of many opposite requirements which should be gear shifting time, it is possible to perform “dou- meet in the best manner for every system in ev- ble clutching” what could be obtained by shift- ery driving situation, is practically impossible to

Journal of Applied Engineering Science 13(2015)1, 313 57 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development describe with defined mathematical model. Mod- downhill driving, because of decreasing throttle ern software development processes demand valve angle, the control unit upshift what di- very little human interference, or even their com- rectly reduces the engine effect. Desired plete absence in calibration process. Therefore, flexible shift control, besides basic input param- fuzzy logic as a branch of logic that uses the de- eters, also observes factors such as, road grade, gree of participation of some element in the sys- angle, vehicle acceleration and vehicle tem, more than just strictly true or false definition mass, toward to achieve better performance, of its membership, will be very used in modern fuel and emission characteristics, so unneces- control systems. Introduction of fuzzy logic is sary gear shifting could be avoided. further encouraged by increasing the number of CONCLUSION variables which should be calibrated. With fuzzy logic as basis, artificial neural network could be Automatic transmissions for vehicles with inter- designed. The main advantage of this approach nal combustion engines could be broadly divid- is online training using real-time vehicle data ed, according to their principle of operation, into and adaptive calibration on control capability. four described concepts (AMT, HMT, CVT and [08] The block diagram of described algorithm is DCT). All four concepts are widely used today, shown on the Figure 13. but in different share according to the market demands.The most used are of course HMTs because of the long history of usage and devel- opment. People in Europe generally more prefer manual transmission, so even development of automatic transmission was determined by au- tomatization of that well known operating prin- ciple. Thus was created AMT system. Also, ro- botization of the manual transmission designed DCT, characterized by high efficiency, high bear- ing forces, no interruption of the tractive force and fast gear shifting. As already mentioned, in Japan and USA there are much more vehicles with automatic transmissions than in Europe. Especially in Japan, the most popular solution Figure 13: Block Diagram of the Gear Shift Algorithm is CVT because of its features such as, optimal with adaptive control [10] fuel consumption in entire engine map, high ra- tio span, high comfort and improved driveabil- The inputs of the controller are signals from sen- ity. There is a growing interest of usage of CVT sors and GPS system and according to them concept all around the world, but it refers only for controller determinants appropriate gear ratio, lower vehicle segments, caused by power trans- but it also has a feedback from driver interven- fer limitations, related to the slipping of the friction tion, to update the membership functions in the element. Its greater application is also related to real time so it can accommodate better different common use of CVT concept on hybrid vehicles. driving patterns in the future. The advantages of Hybrid transmissions are specific subset of au- this control will be shown by comparing it with tomatic transmissions. Depending on the con- the simplest (traditional) control, which takes cept of hybrid systems different constructions into account just vehicle speed, throttle valve of hybrid transmissions are in use. In many hy- angle and accelerator pedal position as input brid vehicles is used a constantly variable drive parameters. Problems in traditional control are ratio, without relying on belts and pulleys. This expressed especially during driving on the road can be accomplished by proper regulation of slope. During uphill driving, the driver releases electric motors, whose output characteristics are the gas pedal before entering the curve to re- the most similar to the desired ideal traction hy- duce vehicle speed and in traditional observation perbola over other types of powertrain. It should of just a vehicle speed and throttle valve angle, be mentioned that simpler hybrid vehicles use upshift could be done. But right after the curve, a conventional CVT, or even conventional man- driver presses the accelerator pedal to increase ual or hydrodynamic mechanical transmission. speed, when the downshift must occur. During 58 Journal of Applied Engineering Science 13(2015)1, 313 Dejan Matijević- Modern design and control of automatic transmission and the prospects of development

But hybrid transmissions also include devices entifi c-Technological Support to Enhancing the for power splitting between power sources, and Safety of Special Road and Rail Vehicles” and their proper regulation, by hybrid control sys- TR 35040 – “Developed New Methods for Diag- tem is crucial for obtaining desired output per- nosis and Examination Mechanical Structures”). formance in accordance with fuel economy and The authors wish to express their gratitude to all battery state of charge. Regardless of the type persons who helped making this paper better. of automatic transmission and the type of power source it is obvious that in future control strate- REFERENCES gies of ATs will be more and more complicated. 1) Bauer, H. (editor) (2004) Electronic Transmission The issue of gear shifting optimization still repre- Control ETC, Stuttgart, Robert Bosch GmbH. sents a real challenge to scientists and experts 2) Blagojevic, I., Ivanovic, G., Jankovic, S., in the field of motor vehicles, because only op- Popovic, V. (2012) A model for gear shifting timized gear shifting enables the best possible optimization in motor vehicles, Transactions relation between vehicle motion regimes and en- of FAMENA, 36 (2), 51-66. gine working regimes [03,02]. Toward a contribu- 3) Blagojevic, I., Vorotovic, G., Ivanovic, G., tion to gear shift optimization many parameters Jankovic, S., Popovic, V. (2012) Energy ef- will be observed with implementation of adaptive ficiency improvement by gear shifting optimi- functions which will compare actual (measured) zation, Thermal Science, 17(1), 91-105. and set (calculated) value of some signals in or- 4) http://auto.howstuffworks.com/cvt2.htm, der to obtain functionality of the system in de- preuzeto 3.2.2015. fined limits. It will be very apparent further inte- gration of electronic transmission control system 5) http://www.youtube.com/watch?v=pnuuZd9seg, into one global system which will also include preuzeto 3.2.2015. GPS navigation, capable to predict appropriate 6) Jurgen, R.,Denenberg, J. (1999) Automotive Elec- gear ratio according to operating state of the tronics Handbook (2nd ed), New York, McGraw-Hill. vehicle and road conditions, taking into account 7) Naunheimer, H., Bertsche, B., Ryborz, J., desired vehicle performance, fuel economy, ex- Novak, W. (2011) Automotive Transmissions haust emission, traffic safety, comfort and con- – Fundamentals, Selection, Design and Ap- venience, in order to obtain maximal efficiency. plication (2nd ed), Berlin, Springer-Verlag For accomplishing such a complicated goal ap- 8) Poliščuk, J.E. (2004) Ekspertni sistemi, Pod- plication of fuzzy logic is very perspective, espe- gorica, Faculty of Electrical Engineering. cially when control algorithms are upgraded with 9) Stanojevic, D., Spasojevic, V., Stevanovic, I., artificial intelligence. It is quite evident that fur- Nedic, A. (2013) The contemporary automat- ther contribution to automatic transmissions will ic gearboxes - Review of the current state be obtained through more mechatronics usage, and interpretation of advantages and disad- networking and soft computing application. It is vantages of their use with respect to vehicle also well known that maintenance management performance and traffic safety, Journal of Ap- has a delay in relation to technical development plied Engineering Science, 11(2), 89-97. (Management Gap) [12]. In order to compensate 10) Sun, Z., Habbale, K. Challenges and Opportu- this negative fact for the maintenance systems nities in Automotive Transmission Control, In of large fleets of vehicles, probably sophisticated proceedings of American Control Conference, expert systems for problem solving will be devel- June 8-10, 2005, Portland, 3284-3289. oped. A significant influence for maintainability 11) The 02E Direct Shift Gearbox – Design and Func- these complex and networked systems will have tion, Self Study Program, Course Number 851 403 engineers in research and development depart- (2004), Auburn Hills, Volkswagen of America, Inc. ments through integration of proper safety and 12) Vasic, B. (2004) Menadžment i inženjering u diagnosis functions into the control algorithms. održavanju, Beograd, Institut za istrazivanja ACKNOWLEDGEMENTS i projektovanja u privredi. This paper is a result of two important projects 13) Yao, C.-H. (2008) Automotive Transmissions: financed by the Ministry of Education, Science Efficiently Transferring Power from Engine to and Technological Development of the Repub- , ProQuest Discovery Guides. lic of Serbia (project number TR 35045 – “Sci- Paper sent to revision: 13.02.2015. Paper ready for publication: 12.03.2015. Journal of Applied Engineering Science 13(2015)1, 313 59