EVS8 KINTEX, Korea, May 3-6, 015 Investigation of energy efficiency of hybrid bimodal vehicle Emil Król 1, Jakub Bernatt 1 Institute of Electrical Drives and Machines KOMEL Al. Roździeńskiego 188, PL-40-03 Katowice Email:e.krol@komel.katowice.pl, dyrekcja@komel.katowice.pl Abstract Van with bimodal hybrid drive has been presented in the paper. Its energy efficiency has been determined experimentally for urban and extra - urban traffic conditions using electric drive only with regenerative braking and without. The cost of electric energy of bimodal car has been compared to fuel cost of ICE car driving over the same route with identical load. The bimodal drive is characterized by the fact that IC engine and electric motor can operate individually only they cannot drive the vehicle working together at the same time. However when IC engine operates the electric motor may work in generator mode charging on - board battery and it may also recuperate kinetic energy during braking. In bimodal hybrid drive we may distinguish three different drive modes: - vehicle driven with ICE, electric motor does not work, this is normal mode of operation for extra - urban driving; - vehicle driven with electric motor IC engine does not work, this is usually used in urban driving electric motor is utilized for recuperative braking as well; - vehicle driven with ICE and electric motor operates as generator charging battery or it brakes the vehicle recuperating power into the battery. Tests of energy efficiency of bimodal hybrid vehicle were conducted during driving with recuperative braking. The recuperative braking in hybrid bimodal vehicle may be divided into two phases in " electric " and diesel mode both. The experiments were divided into two stages and carried out in the following way: - during first stage the vehicle rolled downhill for as long distance as possible and it was braked by electric motor with energy recuperation; - during second stage the loaded vehicle was driven over Silesian agglomeration (urban traffic) using electric drive with active procedures of braking energy recuperation. Keywords: van, hybrid bimodal drive, regenerative braking, energy efficiency of the vehicle EVS8 International Electric Vehicle Symposium and Exhibition 1
1 Introduction Hybrid drive is a combination of two drive types. In vehicles hybrid drive is usually a mix of IC engine and electric motor. Hybrid bimodal drive system of a mechanical vehicle, standard make, consists of traditional ICE drive and electric motor assembled into transmission shaft. The motor is supplied from battery via bidirectional power electronics converter [3]. The bimodal drive is characterized by the fact that IC engine and electric motor can operate individually only [], they cannot drive the vehicle working together at the same time. However, when IC engine operates, the electric motor may work in generator mode charging on-board battery and it may also recuperate kinetic energy during braking. In bimodal hybrid drive we may distinguish three different drive modes: - vehicle driven with ICE, electric motor does not work, even though its rotor rotates; this is normal mode of operation for extra-urban driving; - vehicle driven with electric motor, IC engine does not work (it is stopped), this is usually used in urban driving; electric motor is utilized for recuperative braking as well; - vehicle driven with ICE and electric motor operates as generator charging battery or it brakes the vehicle recuperating power into the battery. In each mode of operation, the driver is able to switch off recuperative braking in case when this type of braking might cause the slip of rear wheels upon slippery road surface. The particular mode of operation when battery is charged using IC engine is treated as redundant, since it is economically ineffective. It is much cheaper to charge battery using the power network than to use IC engine for driving and simultaneous charging of on-board battery. There are several advantages of hybrid bimodal drive: long driving range, possibility of recovering braking energy, low driving cost, reduction of exhaust gases emission and dust from braking system - this is felt most strongly in urban traffic, same as noise reduction, which of course improves life comfort in agglomerations. The drawbacks of hybrid drive are: higher price, higher weight and greater fuel consumption in extra-urban driving (due to increased vehicle weight). Bimodal hybrid drive vehicle has been built basing on commercially manufactured Honker Cargo van (previously DZT Pasagon). This car has been used in research on efficiency of braking energy recuperation. Introduction. Honker Cargo van with hybrid bimodal drive The Model of bimodal hybrid drive car has been built in Institute of Drives and Electrical Machines Komel [1]. Commercially available Honker Cargo van has been additionally equipped with electric drive consisting of electrical motor, bidirectional power electronics converter and battery set []. Electrical substitutes of brake assist and steer assist pumps have also been installed as well as electrical heating for periods of driving in electric mode [3]. Honker Cargo is a rear drive car. Electrical motor has been assembled on the drive transmission shaft between IC bloc (ICE + gearbox) and differential. Photo of the car is shown in Fig.1 and layout of electric drive elements is shown in Fig.. Parameters of electric drive system: - maximum power of electric motor - 70 kw; - maximum torque of electric motor - 50 Nm; - capacity of traction battery - 1kWh; - weight of electric drive system - 440 kg. Electric motor is excited with permanent magnets placed inside the rotor and supplied from power electronics converter generating sinusoidal current waveform (motor control unit), the converter is fed from Li-Ion battery set. Electric drive system operates without gearbox, the gear lever is blocked in neutral position [5]. Traction parameters of vehicle using electric drive: - maximum driving range - 100 km; - maximum speed - 70 km/h; - battery charging time - c. 3 hours (for 3-phase charger). Bimodal hybrid drive can operate in two independent modes (hence its name). In the first mode of operation, which might be called "diesel mode", the car is driven exclusively by standard IC engine (diesel engine in vans). The diesel mode is used for long distance extra- urban driving. In diesel mode the car is driven by IC engine with a standard gearbox; its range and speeds at different gears are comparable to those of car equipped with IC engine only. The dynamic characteristics of the vehicle are slightly worsened, since battery and electric motor increase vehicle weight. In diesel mode the electric motor operates only as generator charging battery during braking or accessing road crossings and during battery charging using IC engine. If IC engine is used to drive the vehicle, the electric motor may operate as generator up to EVS8 International Electric Vehicle Symposium and Exhibition
vehicle speed equal to 85 km/h; if this speed is exceeded, the electric motor is disconnected from the inverter and it is switched on again when vehicle speed drops down to less than 30 km/h. Switching motor-inverter connection on and off occurs automatically, without driver's participation. Figure 1: Honker Cargo van with bimodal hybrid drive Figure : Layout of hybrid bimodal drive elements In "electric mode" the car is driven by electric motor only. This electric mode is used in agglomerations and built-up areas. In electric mode the maximum speed of the vehicle over flat terrain is 70 km/h, in case of loaded car driving downhill its maximum speed has been limited to 75 km/h. When this speed is exceeded, electrical braking is switched on automatically independently of whether driver presses brake pedal or continues to press down acceleration pedal. Since only electric motor is used, the "electric mode" of drive operation is characterized by high ecological qualities. The emission of harmful exhaustion gases and carbon dioxide is eliminated, the dustiness due to abrasion of brake shoes and lining is reduced, there is also a significant reduction of noise generated by operating IC engine. It assumed that IC engine will be used for long-distance driving, in extra-urban areas or outside built-up areas. In urban traffic and built-up areas the electric motor will be used as main drive. However, if possible, the electric drive may also be used outside urban areas. Urban traffic is characterized by frequent braking, stops due to traffic jams, crossings and start-ups. This type of work is unfavourable and ineffective for ICE drive, since torque-speed curve of IC engine is characterized by the fact, that optimum working point is reached at higher motor speeds. During start-up the IC engines emit particularly large amounts of harmful atmosphere pollutants and produce substantial noise. The use of electric drive in passenger cars and vans in urban areas should cause significant reduction of air pollution and noise. 3 Testing of energy efficiency of bimodal hybrid vehicle Tests of energy efficiency of bimodal hybrid vehicle were conducted during driving with recuperative braking. The recuperative braking in hybrid bimodal vehicle may be divided into two phases, in "electric" and diesel mode both. In the first phase recuperative braking is activated, when driver does not use acceleration pedal; this corresponds to engine braking in ICE vehicle. The second phase is activated when driver presses down brake pedal; this pedal is equipped with sensors and information on pedal movement is transmitted to vehicle s electronic control unit (ECU). ECU controls electric braking force in relation to brake pedal displacement. ECU is programmed in such a way, that maximum energy is recovered during the braking period, when friction brakes do not yet operate with full efficiency. The experiments were divided into two stages and carried out in the following way: - during first stage the vehicle rolled downhill for as long distance as possible and it was braked by electric motor with energy recuperation; - during second stage the loaded vehicle was driven over Silesian agglomeration (urban traffic) EVS8 International Electric Vehicle Symposium and Exhibition 3
using electric drive with active procedures of braking energy recuperation. For first stage we have chosen the roads between Salmopol Creek and Wisła Malinka village; the road goes downhill and its parameters were identified as: - length of route l = 5.8 km, difference in heights h = 360 m. The roadmap is shown in Fig.3; - the weight of vehicle including load and driver was determined to be equal to m b = 3175 kg; - the drive was monitored by recording value of recovered energy: E e = 1.9 kwh. driven over Silesian agglomeration (urban traffic), using electric drive only with active braking energy recuperation procedure. Total driving time was 53 minutes, average speed was equal to 9.4 km/h, total distance covered was 6 km. During driving electrical parameters of the drive as well as vehicle speed and elevation above sea level were recorded. Results of the experiments were used to determine energy efficiency of Honker Cargo van with bimodal drive in urban driving. Figure 3: Roadmap for test stage #1 of bimodal hybrid vehicle Energy balance of drive: - difference in car's potential energy between upper and lower section of route Figure 4: Total electric energy supplied by the battery during driving The diagram of energy output by the battery during driving in Sosnowiec and its environs is shown in Fig.4. On the basis of recorded current waveforms (Fig.5) and main battery voltage waveform it was possible to calculate energy needed by the vehicle for driving 6 km. This energy was equal to E hbp = 9. kwh, where recovered energy was E hbpo = 0.8 kwh and energy supplied by main battery was E hbpp = 8.38 kwh Em = msgh 3.6 6 = 3. 11 kwh (1) - mechanical energy dissipated in resistance to motion and energy transformation circuit (motor and inverter): Er = Em Ee = 3.11 1.9= 1. 1 kwh () The percentage distribution of recovered energy E e% =61% and dissipated energy E =39 r% % During second stage of tests the hybrid bimodal vehicle with 800 kg load was Figure 5: Battery current waveform recorded during driving EVS8 International Electric Vehicle Symposium and Exhibition 4
Figure 6: Part of battery current waveform recorded during driving Fragment of current waveform recorded for current drawn from and input back into the battery during recuperative braking is shown in Fig.6. Negative current denotes current drawn during driving, positive current is current recuperated during braking or decelerating for bimodal hybrid drive. When recuperative current course is analyzed, we may clearly perceive two phases of recuperative braking; current peaks are seen for a short time when brake pedal is pressed and longer periods of constant current braking imitate braking with IC engine. Figure 8: Total energy recuperated during braking Figure 9: Total energy recuperated during braking Figure 7: Electric power output and input into the main battery Figure 10: Road elevation above sea level during test EVS8 International Electric Vehicle Symposium and Exhibition 5
Footers are to be provided, with a horizontal line 1pt thick at 3 mm from the bottom of the page. The tests started and ended at the same elevation above sea level, which eliminated impact of potential energy on test results. During test drive c. 8.9% of energy consumed during driving was recuperated; for passenger cars with electric drive this quantity is usually twice as high [4]; this is due, among other factors, to significantly smaller rolling resistance and higher speeds. Theoretical comparison of energy consumed by commercially manufactured car and bimodal drive car during urban drive has also been conducted. Assumptions: - weight of commercial vehicle is 160 kg, load is equal to 800 kg plus driver weight 75 kg, total weight is m s = 3035 kg; - weight of bimodal hybrid drive is 600 kg, load is equal to 800 kg plus driver weight 75 kg, total weight is m s = 3475 kg; - vehicles drive around in urban environment for 8 hours a day, bimodal vehicle is driven by electric motor and energy is recuperated during braking; - vehicles brake 10 times per hour from 50 km/h speed to 0 km/h ( v = 13,89 m/s), during 8 hours number of braking cycles is equal to n = 80. Energy lost in the brakes by commercial vehicle during braking: ms 1 v Esh = n= 6. 5 kwh (3) Energy lost by bimodal drive vehicle during braking: mbv Ebh = n= 7. 45 kwh (4) It is assumed that 61% of this energy will be recuperated via electrical motor and directed into the battery, and 39% will be lost to motion resistance and in energy transformation circuit. Recuperated braking energy transmitted into the battery: Eo = 0.61 Ebh = 4. 54 kwh (5) If average speed in urban traffic is assumed to be 5 km/h, then during 8 hours the vehicle may cover distance of 00 km. During this time the bimodal hybrid vehicle will recover energy equal to 4.54 kwh, which will allow for extra driving distance of c. 14. km (load equal to 800 kg). In case of ICE vehicle this energy would be dissipated and lost completely. Additional advantages for the driver may be defined as longer life of braking system, since frictional elements of the braking system will wear more slowly; the environmental gains are lack of exhaust gases and dust emanating from abraded brake elements. The specific energy consumption by loaded bimodal vehicle is e b = 0.3 kwh/km. 4 Conclusion The use of hybrid bimodal drive in van which operates mostly in urban areas reduces operational costs of the vehicle and the car does not burden the environment. The cost of oil used for 100 km distance in extra-urban driving for van equipped with Diesel engine is equal to c. 60 zł. In urban traffic, due to low driving speed and frequent stops and acceleration periods this cost is equal to c. 80 zł. The cost of charging the batteries needed to cover 100 km in urban area by a vehicle driven by electric motor is equal to c. 1 zł. So, for users of transport vehicles fitted with electric motors, e.g. supply companies and messenger services, it is possible to reduce operational costs quite considerably. Substantial economical saving due to use of electric drive guarantees return of financial outlay needed to install this drive in vehicles. International transport companies also demonstrate interest in vehicles with electric or hybrid drives, since paying attention to natural environment issues is favourably looked upon by the customers. Electric and hybrid drive vehicles will be seen more and more often on our roads. Nowadays this technology is still very expensive, this is predominantly due to battery cost. However, the market is fast developing and prices of electric and hybrid vehicles will continuously decrease. should be positioned preferably on the top or the bottom of the page. References [1] Hybrydowy, bimodalny napęd spalinowoelektryczny dla samochodów transportu osobowego i towarowego o masie całkowitej do 3.5t. Projekt finansowany przez Narodowe Centrum Badań i Rozwoju nr N R01-0085-10.. [] Król E, Białas A: Koncepcja napędu hybrydowego przeznaczonego do samochodu dostawczego. Zeszyty Problemowe - Maszyny Elektryczne. Nr 1/01. [3] P.Dukalski, A.Białas,W.Radwański, B.Będkowski, A. Fręchowicz: Koncepcja napędu z silnikiem BLDC o przełączalnej liczbie zwojów w napędzie samochodu elektrycznego. - Przegląd Elektrotechniczny 10.013. EVS8 International Electric Vehicle Symposium and Exhibition 6
[4] R.Rossa, Badania eksploatacyjne samochodu osobowego zelektryfikowanego zestawem e-kit, - Zeszyty Problemowe Maszyny Elektryczne. Nr /014 (10) [5] Elektromagnetyczna blokada skrzyni biegów pojazdu hybrydowego. Patent: P401916 BOBRME Komel. Authors Emil Król was born in Zamość in the Poland, on July 3, 1977. He graduated from the Silesian Technical University in 00. Since 004 working in the Institute of Electrical Drives and Machines KOMEL, where he is designing and making laboratory test of various types of electric machines and devices. Jakub Bernatt, prof, PhD, CEO of Electrical Drives and Machines Institute KOMEL, Poland. Graduated from Silesian University of Technology. Main areas of interest : permanent magnet drives and motors for eletromobility EVS8 International Electric Vehicle Symposium and Exhibition 7