Hybrid Electric Cars, Combustion Engine driven cars and their Impact on Environment Essay

Fig. 1. Estimated grows of Planet Earth Population But the expected grow of automobiles will grow much rapidly. The growth will be caused mainly with inevitable living standard improving in many countries like Africa, South Asia and South America together with enlarging of population in these regions. The estimated grows of automobiles over whole Earth is shown in Fig. 2. From comparison of both figures results that the population may grow between years 2000 to 2050 from 6 to 10 milliards that means 1. 7 times, but the expected vehicle number will grow from 0. 7 to 2. 5 milliards that is 3. 6 times. This work was supported by Research Center of Combustion Engines and Automobile Technology. 40 35 30 25 20 15 10 5 0 1980 Rada1 1990 2000 2010 2020 2030 years Fig. 3. Total world production of CO2 These problems are so serious that they became very important theme of international discussions. Results of these discussions were settled in the Kyoto Protocol. Kyoto Protocol is an agreement made under the United Nations Framework Convention on Climate Change (UNFCCC) Automobiles produce approximately a half of the total world production of CO2. Let us imagine that a good new car produces approximately 160 g of CO2 pro each km. There are many possibilities how to diminish this terrible amount. Electric hybrid cars are produced in enlarging numbers and they reach enlarging popularity between customers. They bring a new possibility how to diminish the world CO2 production. II. ELECTRIC HYBRID CAR SYSTEMS Hybrid electric vehicles combine electric and internal combustion engine drive. Hybrid electric vehicles combine the zero pollution benefits of electric motors with the high fuel energy density benefits of the thermal engine. Hybrid electric drives adjust the combustion engine load and revolutions into the point of best motor efficiency and lowest motor emissions. [1], [4], [6], [7]. A. Basic Drive Configurations Series hybrid drive in Fig. 4 presents a combination of different energy sources. In the picture the energy sources are the combustion engine and the battery. The internal combustion engine ICE propels a generator. Total power in form of the generator electric power and the battery electric power are summed in the traction motor. There is no mechanical connection between ICE and wheels. internal combustion engine generator ICE gear box GB battery traction motor TM BAT ICE Fig. 5 Parallel hybrid drive G battery Combined switched hybrid drive in Fig. 6 is based on series hybrid drive with mechanical coupling using a clutch between generator and traction motor. It is series hybrid drive when the clutch is off. BAT traction motor internal combustion engine ICE TM generator G battery BAT coupling Fig. 4. Series hybrid drive Battery acts as energy buffer. Advantage of series hybrid drive is the possibility to operate the thermal engine ICE in optimal revolutions quite free from the car velocity. That results in low specific fuel consumption and in low gas emission for any traction load and car velocity. Efficiency of energy conversions in the system must be taken in account. Parallel hybrid drive in Fig. 5 is a combination of ICE and electric traction motor on the same shaft. Traction motor is supplied by battery and its output is separated from the ICE output. Final traction torque is sum of both motors torque. Power transmission is more effective than in series hybrid drive because the mechanical ICE output is not transformed in electrical output. But the ICE cannot work in optimal load regime because its speed is not free from the car velocity. traction motor internal combustion engine TM Fig. 6. Combined switched hybrid drive The generator supplies the electric energy to the traction motor. When the car speed and ICE speed and power are high but the difference between ICE speed and car speed is small, it is better to operate the scheme as parallel hybrid drive and the clutch is on in such a case. On this regime the ICE power and speed are high and the ICE can operate with small output changes. The difference between desired traction output and ICE optimal output is stored in or discharged from the accumulator. The drive is depicted in Fig. 9. It consists with gasoline engine, double rotor DC generator, and traction motor. traction motor Combined hybrid with planetary gear in Fig. 7 is a topology where mechanical power splitting is used. The splitting is performed in the planetary gear. In this scheme the generator rotates with speed, which is difference between the ICE and car speed. This solution allows splitting the ICE output into two parts. rotating stator control unit generator ~ ~ generator gasoline engine traction motor ICE planet gear Fig. 7. Combined hybrid with planetary grar The first part is proportional to the difference between the ICE and car speed and the second is proportional to the car speed. The first part is transformed into electric energy in the generator and supplied to the traction motor. The second part is transferred by the output planet shaft directly to car wheels. This scheme allows controlling the engine speed and torque and this is the way how to minimize fuel consumption. Electric power splitting drive using DC machines was used on Czechoslovak express motor cars in the year 1936. The patent document was emitted in Czechoslovakia with Nr 53 735 on 25. February 1936. [1], [2], [3]. DC machines were usual on railway vehicles at that time. The vehicle was called :†Slovenska Strela† and remained in service till the year 1950. It should be reconstructed and modernized later on. But electrification of the main railway connection between Prague-Kosice replaced this very interesting vehicle with express electric locomotives. Fig. 8. Express railway car â€Å"Slovenska Strela† clutch rotor output shaft Fig. 9. Electric power splitting drive of express car â€Å"Slovenska Strela† The ICE drives a DC generator which â€Å"stator† and rotor can rotate separately. The â€Å"stator† is firmly coupled with the ICE shaft. The rotor is coupled with car wheels. On the car shaft is mounted a DC electric traction motor supplied by the voltage induced in the generator. The splitting is performed in the generator. The relative speed between generator â€Å"stator† and rotor is difference between the ICE and car speeds. This solution allows split the ICE output into two parts. The first part is proportional to the difference between the ICE and car speed and the second is proportional to the car speed. The first part is transformed into electric energy in the generator and supplied to the traction motor. The second part is transferred directly by means of electromagnetic torque in the generator air gap to the car wheels. This scheme allows controlling the ICE speed independently from the car speed and this is the way how to minimize fuel consumption. Model of Electric Power Splitting Drive Using AC Machines was implemented in the laboratory of Josef Bozek Research Center of Engine and Automotive Technology at the Technical University in Prague. The physical model of the drive is seen in Fig. 10. It is experimental electric hybrid car drive of a small power. [5], [9], [11], [13], [14], [15]. The output is 7. 5 kW, 0 – 6000 min-1.. Electronic converters and supercapacitor EC are integrated in the circuit between electric power divider SPGM and traction motor TM. The super capacitor as a peak energy storage has 100F, 56V and 400 A. It is able to accept the kinetic energy during braking the vehicle of the mass 1500kg from the velocity 60km/hour and regenerate it during next speeding up. Principle of the system is depicted in Fig. 10. The combustion engine COM ENG drives the electric power divider SGPM. The power divider is a special double rotor synchronous permanent magnet generator. The first rotor is firmly connected with the combustion engine shaft. The second rotor is firmly connected with the traction motor TM and with car wheels. The traction motor is supplied with electric power induced by differential velocity between first and second rotors. Parameters of this electric power (voltage, current and frequency) are changed in electronic converter in EC. Power of the combustion engine is divided into two parts. used for evaluation and comparison of car’s performance, pollution production, efficiencies etc. Simulations were performed on New European Driving Cycle NEDC. The NEDC is shown in Fig. 11. Total distance 10,9km Speed (km/hour) EC ELM CLUTCH COM ENG TM SGPM base Fig. 10. Physical model of Electric Splitting Drive Using AC Machines The incoming power P1=T1* ? 1 is the power of combustion engine producing torque T1 at angular velocity ? 1. Torque T1 is transferred with electromagnetic force to the second rotor, rotating at angular velocity ? 2 which is the same as car velocity. Power transmitted to car wheels by this torque is therefore Pm=T1*? 2. Remaining power is induced by magnetic field into the electric winding arranged on the second rotor. Neglecting losses this power is Pel=P1-Pm=T1*(? 1-? 2). Power Pel is transferred via electronic converter in EC to the traction motor TM and finally added to power Pm on car wheels. Incoming power P1 from combustion engine is by this technique divided into two parts Pm and Pel. Combustion engine can rotate with angular velocity which does not depend from the car velocity III. SIMULATION OF FUEL CONSUMPTION OF HYBRID ELECTRIC CARS Main advantage of electric hybrid cars is the diminishing of fuel consumption. The production of CO2 depends on the fuel consumption and on the working conditions of the ICE. The working conditions of the ICE are much better in electric hybrid cars than in conventional cars generally. Simulations were done with the mathematical model of Electric Power Splitting Drive Using AC Machines. Measured parameters and features obtained in the laboratory [11], [13], [14] were used for the simulation. The mathematical model of a conventional car and hybrid electric car with electric power divider was established in [15] [16] Comparisons of this art are usualy done on different standard driving cycles. Standard driving cycle represents a driving pattern of a certain geographic region (North America, Europe, Asia-Pacific). These driving cycles are Time (s) Fig. 11 New European Driving Cycle Parameters of compared cars and results of simulation are shown in Tab. 1 TABLE I SIMULATION RESULTS Vehicle type, manufacturer Driving Cycle Total mass (kg) Specific Consumption during total NEDC (l/100km). Total emissions CO2 (g) Specific emissions (g/km) First case Second case NEDC Skoda 1. 2HTP NEDC 1450 1120 5. 1 5. 9 1333 1540 122. 9 142 Model Fabia Two cases are shown. In both of them the New European Driving Cycle was simulated. Case first: Hybrid electric car with electric power divider. The mass of the car respects the additional mass of electric part of the powertrain. Case second: Conventional car Skoda Fabia 1. 2 HTP. The results shown in Tab. 1 allow to make following conclusions: When comparing fuel consumption and CO2 emissions between hybrid car with electric power divider versus conventional car of the same class (that means the same primary ICE engine power and respecting additional mass of the electric powertrain machines), we can conclude that the fuel consumption and CO2 emissions are significantly lower at the hybrid car. Hybridization of such cars brings not only fuel savings but also is much more environmentally friendly. I. CONCLUSION The production of dangerous greenhouse gas emissions and consumption of world energy resources become a serious problem. Especially CO2 emissions can influence the climate stability of Planet Earth. The automobile business contributes to this development a lot. But the automobile technology has space to be improved. The electric and hybrid electric vehicles can contribute to diminishing of fuel consumption and green gases production. The hybrid electric vehicles makes it possible to operate the combustion engine in more suitable regimes with better fuel combustion conditions. Some hybrid systems even enable to operate the combustion engine in best relation between power and revolutions. Systems with power dividers allow the engine to operate in revolutions that are quite independent from the car velocity. Simulations were done with the mathematical model of Electric Power Splitting Drive Using AC Machines. Measured parameters and features obtained in the laboratory were used for the simulation. Simulations were performed on New European Driving Cycle NEDC. Results of one commercial car and one hybrid electric car with electric power divider are published. Fuel consumption of the hybrid car on the new European Driving Cycle was 5,1 l/km. The commercial car consumed 5,9 l/km. The hybrid car consumption is 13. 6% lower then at commercial car. Similar numbers were obtained with respect to CO2 production. The hybrid car produced 1333 g CO2 on the New European Driving Cycle. Commercial car produced 1540 g CO2. Hybrid car with electric power divider produced 13. 5% less CO2 . REFERENCES [1] V. Klima : Electro-mechanic drive DELKA and its comparison with Dieselelectric drive. (Elektro mechanicky pohon DELKA a jeho srovnani s normalnim Diesel-elektrickym pohonem. ) Elektrotechnicky obzor 1949, Nr. 19, Pg. 489-496 [2] J. Sousedik : Patent document Czechoslovakia Nr 53 735 from 25. February 1936. [3] J. Bilek: Electric drive of motor cars â€Å"Slovenska strela† (Elektricka vyzbroj motorovych vozu â€Å"Slovenska strela†). Elektrotechnicky obzor 1937, Nr16, Pg249-253, Nr. 21 Pg. 331-336. [4] J. Mierlo: Simulation software for comparison and design of electric, hybrid electric and internal combustion vehicles with respect to energy, emission and performances. Vrije Universiteit Brussel. [5] Z. Cerovsky, P. Mindl, S. Fligl, Z. Halamka and P. 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