Theoretical Analysis on The Performance of A Traction System

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1 Theoretical Analysis on The Performance of A Traction System Dr. MUKHTAR M.A. MURAD Dep. of automotive & Marine Engineering Technology College of Technological Studies - PAAET KUWAIT murad20001@hotmail.com Dr. JASEM M. ALRAJHI Dep. of automotive & Marine Engineering Technology College of Technological Studies - PAAET KUWAIT Jm.alrajhi@paaet.edu.kw Abstract-This paper describes the construction of a test rig with a view to achieving a purely mechanical, purely electrical and a hybrid mode of operation. The rig comprised of a conventional petrol engine coupled to a gear box, planetary gear drive to have continuously variable transmission, a hydraulic dynamometer, an alternator/motor (torquer) assembly and battery units. Also, the theoretical performance characteristics of the planetary gear, the torque-power relationship, the traction characteristics under different road conditions and the torquer performance relationships have been presented. Keywords: Traction, Dynamometer, power, engine, performance I. INTRODUCTION The internal combustion engines have been in constant use eversince their advent for the automotive vehicles as one of the major traction systems. There have been many innovations and developments in the design and manufacture of such systems. Researchers and planners have however recently shifted towards alternative energy resources for the transport area because of apparent problems faced by internal combustion engine powered vehicles such as pollution, traffic noise, parking problems and threatening shortage of fuel etc. (1). Purely electrical vehicles have been used as automobiles (2,3). Improvements in batteries (4) weight reduction might be attractive for widespread acceptance but pure electric vehicles are still not a practical proposition because of constraints for reasonable performance such as a limited operating range due to limited amount of stored energy and comparable efficiency with other types. The concept of hybrid vehicles, that is a possible combination of two or more sources of power and to combine them in such a manner in the same vehicle that the characteristics/performance of the resultant machine are better for the same specific application, appears to be one of the most promising possibilities particularly for urban use (5,6). A combination of good fuel economy, low emission and good performance can be achieved by hybrid vehicles. Under urban conditions, these can run on purely electrical mode while on long range motorways, internal combustion engine power output may be utilized. The range limitation of the pure electrical vehicles can thus be overcome as hybrid drive. Such hybrid drives are thus also intended to make a contribution towards conserving liquid fuel and to alleviate the pollution problem in cities. Such hybrid system and other alternative systems have been researched by other researchers (7, 8). The present work was aimed to construct a comparatively cheap test rig to test a hybrid traction system and to evaluate the performance of such a system. Such a technology avoids the costly field tests while providing useful guide rules for the optimum use of both sources of energy on-board the system and the plug-in electricity. The constructions of the test rig and its theoretical performance analysis have been presented in this work. II. TEST RIG 2.1 MECHANICAL EQUIPMENT The test rig layout is given in Fig. (1). The engine is a Toyota Type 12R, internal combustion engine having specifications give in Appendix (1). The engine, is coupled to a step-up manual gear box having 4 forward speed ratios (3.31, 2.246, 1.51, 1) and one reverse gear ratio of 3.4. In the planetary gear train the sun gear is driven from the engine, and the planetary carrier is coupled to the alternator. The annular gear of the planetary train is coupled to the hydraulic dynamometer, and another automotive gearbox, having same speed ratios as mentioned before. On its opposite side, from the planetary gear drive fig. (2) the hydraulic dynamometer is coupled to the D.C. machine, across the step-down automotive gearbox, having same speed ratios as for other gear boxes. The D.C machine, may be used as a motor in case it is used to carry the total load (pure electrical mode) or share in this load (hybrid drive). The D.C machine may also be applied as a generator in case it is driven from the engine across the planetary gear drive and the dynamometer rotor. The planetary gear drive was used to feed the engine power to the hydraulic dynamometer and the alternator (speeder). 13

It utilized a planetary gear train of an automotive transmission. The relevant train was modified to suit the particular drive shows details of the drive. Fig. (2) Planetary gear drive Fig.

2 The sun gear of the planetary train was fed from the engine across a step-up gearbox. The planetary gear carrier transmits power to the speeder, while the annular gear feeds power to the dynamometer across a step-up gearbox. The planetary gear drive was locally constructed. It utilized a planetary gear train of an automotive transmission. The relevant train was modified to suit the particular drive shows details of the drive. Fig. (2) Planetary gear drive Fig. (1) Test Rig layout 2.2 ELECTRICAL EQUIPMENT Figure (3) shows a circuit diagram for the electrical equipment applied in the preset testing to fulfill the experiments of the pure electrical and hybrid modes. The D.C. series motor (torquer) is a 4 pole motor which produces 15 kw at a terminal voltage of 220 Volts D.C. and at a speed of 3500 R.P.M. This motor has a field resistance, R f, of Ohms and an armature resistance, R a, of 0.2 Ohms. The torquer is fed from a 220 volt A.C. supply across the switch S 1, the variable potentiometer, the bridge-connected rectifiers D 1, D 2, D 3, D 4 and the change over switch S 2. 14

3 The variable potentiometer is applied to change the line voltage feeding the torquer while the rectifiers, D 1, D 2, D 3 & D 4 are used to rectify the current fed to the torquer. The torquer can also be fed from the battery bank across the change over switch, S 2. The line voltage feeding the torquer from the batteries can be varied by means of the switches S 3, S 4 & S 5. The battery bank can be charged by means of the external battery charger, C, across the change over switch, S6. The torquer speed can be varied by means of the external resistance R 1, R 2, R 3 connected in parallel with the torquer field winding across switches, S8, S9 & S10. The battery bank can also be charged from the speeder across the change over switch, S6. The speeder is a 3 phase alternator producing 22 kva at full load and fed its output across the 6 diodes D 5, D 6, D 7, D 8, D 9 & D 10 in order to be rectified by one battery charging. The alternator field is fed from the battery bank across the switch S 7 and the voltage regulator. The regulator resistance R f is included in the field circuit when the regulator contacts N open to test the speeder III. THEORETICAL PERFORMANCE ANALYSIS 3.1 TRACTION CHARACTERISTICS For the purpose of theoretical analysis of traction characteristics, a typical vehicle has been selected having specifications given in Appendix 1. The characteristics are composed of two sets of curves giving the maximum available tractive effort at different gear ratios with full engine throttle, and tractive resistances at different speeds at level road or at different gradeabilities. So, the maximum possible speed under these conditions can also be ascertained. The method adopted for these computations is given as follows; The values of brake power at different engine speeds are obtained from the engine performance curves for the engine being used in the present study. The values of speed for different gear ratios and engine speeds are obtained as: The values so calculated are presented in Fig. (4) giving the values of tractive effort against the vehicle speed for different gear ratios and gradeabilities. Figure (5) gives the variation of the values of these tractive efforts with vehicle speeds together with the corresponding engine speeds. The tractive resistance, F R, is obtained as: independently of the engine. The speeder is run by the torquer. The output of the alternator is then fed to the external resistances R 4, R 5 & R 6. Fig. (3) Circuit diagram for the electrical equipment for pure electrical and hybrid modes The values of f r, C d and A can be obtained from References (15, 16). The second set of curves are computed in a similar manner for average speeds varying between km-h and for road gradeabilities changing form 0 (level road) to 47%. The corresponding curves are presented in Fig. (4). This figure shows that the car is unable to climb a gradient of 10% on direct drive but it is able to climb a gradient of 45% on the first gear. The car is also able to climb a gradient of 15% on the second gear with a max. speed of 80km/h. Figure (5) gives the variation of the 15

4 rolling resistance, F r, and the tractive resistance, F R, (i.e. combined F r & F a ) with the car running on the level road. Fig. (5) Tractive effort against engine speed and gear ratios Fig. (4) Tractive effort against car speed for different grade-abilities 3.2 TORQUER PERFORMANCE RELATIONSHIPS The torquer is a D.C. series motor as shown in Fig. (6). The back E.M.F. (E b ) is given as: Equation (10) indicates that the motor speed is increased by reducing its excitation. Since at average loads, excitation is proportional to the torque then the motor speed is reduced with increased torque. 16

5 At extremely heavy loads, the iron losses becomes saturated & is constant in which case Ta Ia Fig. (7) Motor power stages Motor Power Stages Fig. (6) D.C. series motor as a torquer Figure (7) shows three power stages for the motor. 3.3 TORQUE-SPEED CHARACTERISTICS OF MOTOR In order to be able to cover the full working range of torque-speed variation during urban pure electrical mode, in addition to urban and suburban hybrid mode, the motor torque speed should be changed within a wider range than the present machine allows. This is obtained by means of suitable resistances, R1, R2, R3...etc. connected in shunt with the field winding as shown in Fig. (6). 3.4 PLANETARY GEAR PERFORMANCE Speed Relationships The speeds of the 3 components of the epicyclic gear train are correlated by Willi's Equation (16) and are given by: Also Ta = T + Tf where: T = Shaft torque & Tf = lost torque, torque lost in iron, friction and windage losses. Also (stage 1- stage 2) Ia Rt (14) = Motor copper losses, the copper losses are mainly dependent upon the motor load. While (stage 2 - stage 3) = Iron, friction and windage losses, these losses are primarily dependent upon the motor load. where Ns, Nr & NA are the relative speeds of the sun gear (R.P.M), planetary carrier and the annular gear respectively, Clockwise rotative speeds are given a positive sign while anticlockwise speeds are denoted by a negative sign. where d = pitch diameter of gear & T = No. of teeth of gear. The epicyclic gear may have all the three components of the train running or it may have two components only running and the third component braked. If two of the three components of the train have equal speeds, then the third component of the train must have the same speed. This can be justified from Equation (19). In such a case the train is locked and all of the three components of the train rotate bodily with the same speed. In the epicyclic gear train, applied in the present analysis, the sungear is attached to the engine, the planetary carrier is fitted to the speeder while the annular gear is connected to the dynamometer. The epicyclic train is used with three different configurations which are described below: 17

6 A. Hybrid Drive In this case the three components of the train are running, the sun gear and planetary carrier rotate clockwise while the annular gear rotates anticolockwise (Fige. 8). The speeds of the three components of the train are correlated by Willi's E q. (Eq.19). N s & N r have positive values while N A has a negative value. Power is fed from the engine both to the speeder and dynamometer (driving wheels). Where T represents the torque applied on the sun gear, planetary carrier and annular gear. Considering the equilibrium of the planetary gear, Fig. (8), the force Fs, acting rightwards is transferred from the sun gear to the planetary gears. The same force Fs acting leftwards, is transferred from the planetary gears to the annular gear. Considering the equilibrium of forces acting on the planetary gears, the force applied on the planetary gears pins on which the planetary gears pins on which the planetary gears rotate freely, is equal to 2 F s and is acting rightwards while the reaction force acting on the planetary gears has the same value but is acting leftwards. The analysis of forces results in: Fig. (8) Sun gear, planetary carrier and annular gears rotating in hybrid mode. The equilibrium of forces is also shown B. Pure Mechanical Mode In this case all the engine power is fed to the dynamometer. The planetary carrier is braked and the alternator is stationary. Hence N r = 0 and E q. (19) now reduces to: Equation (24) shows that the power fed to the planetary carrier (alternator) & annular gear (dynamometer) is proportional to their respective rotating speeds. Similar analysis results in: C. During Alternator Testing In this case the alternator is driven by the torquer while the sun gear is braked. Thus Ns = 0 and Eq. (19) now reduces to: TORQUE & POWER RELATIONSHIPS (HYBRID OPERATION) The sungear (engine) drives both the planetary carrier (Alternator) and annular gear (Dynamometer). The power transferred by the sungear P s, the planetary carrier P r and annular gear P A can be found from: IV. CONCLUSIONS A test rig that is representative of a hybrid vehicle has been constructed. All the components were either available locally or fabricated by using the available facilities. The theoretical performance of such a system has been evaluated. Subsequent experimental analysis, which will be the subject of another research paper, is expected to provide useful data for the interpretation of the optimum performance of a hybrid vehicle including the selection of optimum gear ratios between the power source and traction wheels. Also, the control field tests on a n expensive hybrid vehicle could thus be avoided. The traction characteristics of the system have also been computed theoretically and presented graphically. Maximum available tractive effort at different gear ratios and with full throttle openings (i.e. maximum power) has been obtained. 18

7 Also the values of tractive resistance at different speeds and gradeabilities have been computed. From these values, the maximum possible car speed at a given gear ratio and gradeability could be obtained. These results also determined the capability of the car to climb a certain gradient at a given gear ratio. REFERENCES [1] E.F OBERT, "Internal Combustion Engine", Haper and Bow, New York, [2] G.N.FERSEN, "Bosch Investigates Hybrids", Automotive Industries, pp 43-45, April 15, [3] "Electrical Vehicle Development", Automotive Engineering, vol.84, No.8, pp 38-42, August, [4] Burke, A, Miller, M "Performance Characteristics of Lithium. Ion batteries of various chemistries for plug-in hybrid vehicles, Evs24, Stavanger, Norway May NOTATION (A) Mechanical Notation A = Car frontal area C = coefficient d = Diameter F = Force, Resistance, Effort f = Coefficient i = Gradeability of road, Gear ratio N = Rotative speed P = Power p = Pressure V = Car Speed W = Car Weight µ= Efficiency α = Road inclination ρ = density (m2) (m) (N) (R.P.M) (kw) (Bar, KP/cm2) (m/s, km/h) (kp) (Degree) (kg/m3) [5] G.H. GELB, N.A. RICHARDSON, T.C. WANG, B. BERMAN, "An Electromechanical Transmission for Hybrid Vehicle Power Trains-Design and Dynamometer Testing", SAE paper , [6] A. BOLANDI, C.R. WEBB, "A Hybrid Passenger Car", Proc. I. Mech. E. No. C-205, London, [7] V.F. ROON, "Prototype Development of Small Urban Transit Vehicle", University of Florida, June [8] R.H. GUESS, E.L. LUSTENADER, "Development of a high Performance Lightweight Hybrid electric Vehicle", Fourth International Electric Vehicle Symposium, Dusseldorf, Sep., [9] J. DEGRUNCHY, "Do it Yourself, Electric Car", Electric Review, December, [10] G. LARSON, H. ZUCKERBERG, "Hybrid Heat Engine Propulsion for Urban Buses", Fourth International Symposium on automotive Propulsion System", [11] "hybrid Vehicle Technology: Constraints and Application Study', aerospace Corporation Report, [12] N.H. BEACHLEY, A.A. FRANK, "Electronic-Hybrid Cars Evaluation and Comparison", SAE Paper , [13] A. KALBERLAH, "Electronic and Hybrid Vehicles in Germany", Proc. I. Mech. E. Vol. D3, London, [14] I FORSTER, J.R. BUMBY, "A Hybrid Internal Combustion Engine/Batter Electric Passenger Car for Petroleum Displacement", Proc. I. Mech. E. Vol. 202, No. D1, [15] J. GUMLETON, D.L. FRANK, S.L. GENSLAK, A.G. LUCAS, "Special Purpose Urban Cars", SAE , [16]. BOSSEAUX, "I, AUTOBLLE' Pub. Dunod, Paris, [17] H.D. ARTAMOIVOV, V. A. ILARIONOV, M. M. MORIN, "Motor Vehicles", Pub. Mir, Moscow, [18] Toyota Hybrid System THS11", Toyota Motor Corporation, Tokyo, May [19] R. BERNARDO, F. BRITO AND J. MARTINS, A survey on Electric/hybrid Vehicles SAE Suffices A = Annular gear a = Air resistance e = Engine g = Gradient, Gear box Further Suffices 1, 2, 3, 4 refer to first, second, third and fourth gear, respectively. R = Tractive resistance r = Rolling resistance, Planetary carrier, Required s = Sun gear t = Tractive, Transmission, Tyre (B) Electrical notation A = Ammeter a = Number of parallel paths D = bridge connecting rectifier, Diode E = Electro-motive force e = External battery charger I = Current K = Constant p = Number of pair of Poles R = Resistance S = Switches V = Voltage Z = Total number of conductors Φ = flux (lines per pole) Suffices A = Alternator a = Armature b = Back E.M.F. e = Electrical f = Field L = Line i = Input o = Overall, Output s = Shunt t = Torquer (Volts) (Amps) (Ohms) (Volts) 19

8 PPENDIX 1 VEHICLE AND ENGINE SPECIFICATIONS A) ENGINE Bore 81 mm Stroke 77 mm Number of cylinders 4 Engine displacement 1587 cm3 Compression ratio 9 Max. Power 56kW/5600 R.P.M. (DIN) Max. Engine Torque 123 Nm/4000 R.P.M. (DIN) B) VEHICLE Curb weight Max. Payload Overall length Overall width Overall height Wheel base Tread front/rear Ground Clearance 950 kg 500 kg 4135 mm 1635 mm 1385 mm 2430 mm 1425/1405 mm 160 mm 20

[Mukhtar, 2(9): September, 2013] ISSN: Impact Factor: INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY

[Mukhtar, 2(9): September, 2013] ISSN: Impact Factor: INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Consumpton Comparison of Different Modes of Operation of a Hybrid Vehicle Dr. Mukhtar M. A. Murad *1, Dr. Jasem Alrajhi 2 *1,2