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Ireneusz Pielecha, Jakub Czajka, Przemysaw Borowski,
Krzysztof Wisocki
Poznan University of Technology
OPERATIONAL PARAMETERS OF HYBRID DRIVE
SYSTEM OF TOYOTA YARIS IN URBAN TRAFFIC
CONDITIONS
The manuscript delivered: April 2013
Abstract: In the paper are presented and discussed results of on-road tests of a hybrid drive system
operating in diversified urban traffic conditions. The data on operation of the combustion engine and electric motors was acquired by utilizing diagnostic connector of the vehicle. Operation of both types of drives was assessed in diversified urban traffic conditions (different traffic intensity during the drive along a particular route). The conditions of the combustion engine and electric motors utilization were analyzed. The fields of the most frequently utilized operating ranges were presented in form of histograms and subsequently they were correlated with the test routes. The energy flow in the system was assessed and the conditions for energy recuperation in the vehicle were presented. The operational ranges which most fully operated advantages of the hybrid drive system were indicated. It was pointed out that the hybrid drive system subjected to tests utilized the electric motor and the battery energy in higher degree than the combustion engine did. Also the quantitative values of operation of driving motors in diversified urban traffic were presented.
Keywords: hybrid drive system, combustion engine, recovery energy
1. INTRODUCTION
The urge to reduce fuel consumption and exhaust gas emissions imposes the need for searching new vehicle drive solutions. Introduction of the hybrid drive systems in automotive vehicles allows for significant reduction of exhaust gas emission and, simultaneously, for partial reduction of fuel consumption. The fuel consumption depends on the type of the hybrid drive system. Currently the two most frequently used solutions are mild and full hybrid. The first – much cheaper, utilizes predominantly a low-power electric motor to assist operation of the combustion engine. The full hybrid drive system allows for driving the vehicle independently by the electric motor or combustion engine (or both of them).
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The knowledge of the real conditions of the vehicles’ movement makes it possible to assess their level of emissions and fuel consumption [2, 4, 5]. At the same time such tests enable critical verification of values obtained in research and type-approval tests [6].
Currently conducted tests of the drive systems in hybrid vehicles take into consideration the aspect of calibrating the cooperation of the combustion engine with electric motors [1] and different types of batteries [7]. Proper choice of settings influences a particular way of controlling energy flow in such a system. The analysis of hybrid drive control systems is reflected in measurements of exhaust gas emissions from such combustion engines [3]. Concurrently, tests associated with hybrid drive systems include also assessment of their power indices. Due to recuperation of energy in such a drive systems, the research from the point of view of their power seems to be essential. Such research also enables assessing in a measurable way the possibility of reducing fuel consumption in diversified driving conditions.
2. THE AIM AND METHODOLOGY OF TESTS
The aim of the conducted tests was to assess the possibilities of utilization of the hybrid drive system in diversified urban traffic conditions. The tests enabled answering the question whether variable conditions of urban traffic have a significant effect on the change of hybrid drive system performance. In the tests Toyota Yaris with hybrid drive system was used. The specifications of the vehicle and its power transmission system are presented in Fig. 1 and Table 1. With the use of the OBD connector and diagnostic information readers, the data associated with operation of the hybrid drive system was obtained and subsequently used for assessment of the drive system performance in urban traffic.
The tests were conducted within the city of Poznan. For this purpose a specified route was used (Fig. 2) in different conditions of urban traffic. The test runs were conducted on the same day, but because of different times of the test runs, the traffic intensity in the city center was different. The parameters of individual test runs are presented in Fig. 2.
Fig. 1. The object of the tests and the schema of the hybrid drive system of Toyota Yaris HSD (MG1 – motor/generator 1, MG2 – motor/generator 2) MG2 MG1 Hybrid drive system Inverter Reducingplanetary gear Battery Combustion engine Power splitdevice
Table 1 Parameters of power transmission systems of Toyota Yaris HSD [8]
COMBUSTION ENGINE
Type and configuration of cylinders Spark ignition engine, R4, 16-valve
Engine capacity 1497 cm3
Maximum power 55 kW/74 KM/4800 rpm
Maximum torque 111 N·m/3600 rpm
Transmission Automatic E-CVT
Complete vehicle kerb weight 1160 kg
CO2 emissions 79 g/km
ELECTRIC MOTOR
Maximum voltage 520 V
Maximum power 45 kW/62 KM/6000 rpm
Maximum torque 169 N·m
Total power of combustion engine/electric motor 74 kW/100 KM BATTERY
Type Nickel-metal hydride battery (NiMH)
Number of cells 20
Capacity 6.5 A·h
Test Run
no. Route 1 Route 2 Route 3 Route length S [m] 10035 10009 9981 Drive time t [s] 1552 1902 2194 Maximum velocity Vmax [km/h] 69 63 67 Average velocity vr [km/h] 23.28 20.03 17.04
Fig. 2. The plan of the route in the centre of Poznan (route length S = 10 km) with parameters for first three test runs
3. RESULTS OF THE TESTS OF THE HYBRID DRIVE
SYSTEM
In order to determine operation conditions of the hybrid drive system, the analysis of the combustion engine was conducted. The three routes indicate that in this type of drive engine the range of the combustion engine operation is strictly determined (Fig. 3). Operation of the
RONDO EGRZE MALTA START/ KONIEC CENTRUM POZNANIA
combustion engine (excluding idle speed) in the hybrid drive system takes place within the range from 1000 to 3500 rpm utilizing about 80 to 90% of the maximum torque. Within the range from 1000 to 2000 rpm there utilized either insignificant values of the torque (about 20 to 30 N·m) or significant torque (from 90 to 100 N·m). Considerable share of the engine operation within this range is visible in the analysis of the run time of the combustion engine on so called time density map of the engine operation (Fig. 3). The share of the engine operation at idle speed is minimal. The share of the combustion engine operation below 1000 rpm without the load occurs as a result of combustion engine being started or stopped. Also the share of operation at idle speed is insignificant (the low engine speed are the result of starting the engine). It is characteristic, however, that starting of the combustion engine involved its operation at a higher torque of about 1000 rpm and at low load (20 N·m).
Fig. 3. Characteristics of operation of the combustion engine during the three test runs along the urban route (Mo-ICE – combustion engine torque)
0 20 40 60 80 100 120 0 1000 2000 3000 4000 5000 6000 Mo [ N m ] n [rpm] Mo-ICE Mo-max 0 20 40 60 80 100 0.00 0.03 0.06 0.09 0.12 0.15 200 1000 1800 2600 3400 4200 Mo [Nm] Sh ar e U i [-] n [rpm] 0 20 40 60 80 100 120 0 1000 2000 3000 4000 5000 6000 Mo [ N m ] n [rpm] Mo-ICE Mo-max 0 20 40 60 80 100 0.00 0.05 0.10 0.15 200 1000 1800 2600 3400 4200 Mo [Nm] Sh a re U i [-] n [rpm] 0 20 40 60 80 100 120 0 1000 2000 3000 4000 5000 6000 Mo [ N m ] n [rpm] Mo-ICE Mo-max 0 20 40 60 80 100 0.00 0.03 0.06 0.09 0.12 0.15 200 1000 1800 2600 3400 4200 Mo [Nm] Shar e U i [-] n [rpm] Route 3 Route 2 Route 1
Selected parameters characterizing operation of the power transmission system for the Route 2 are presented below. The variable driving speed indicates frequent acceleration and braking of the vehicle, which results in frequent actuation of the combustion engine (Fig. 4). The number of actuations is significant. Such conditions should promote the hybrid drive system, as the combustion engine speed is often equal to zero. Frequent decelerations create conditions in which the drive system can recuperate the kinetic energy of the vehicle. The periods of energy recuperation are not long (Fig. 5), however the braking torques are significant (reaching up to 200 N·m). As a result, during one braking process the system is able to recuperate about 1500 W·s which is 0.4 W·h.
Fig. 4. Parameters of the vehicle movement and of the combustion engine
Fig. 5. Parameters of energy recuperation in the hybrid drive system
Conditions of combustion engine operation influence operation of the electric drive system causing significant changes of the speed of the MG1 motor (generator) and MG2 (electric motor). In the system a planetary reduction gear was utilized, resulting during the tests in the speed of MG2 motor not exceeding about 4000 rpm and generating the torque of about 100 N·m (the torque of such value is generated at lower speeds, which is
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 S [m] V -ve h [ k m /h] 0 40 80 n-IC E [ rp m ] 0 2000 4000 En gi n e s to p [ -] 0.0 0.5 1.0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 S [m] R ec. br a cki n g t o rq ue [N m ] -200 -100 0 Ti m e o f e n e rgy re c . [s ] 0.0 0.1 0.2 Rec . e n er gy [W s] -2000 -1000 0
associated with the characteristics of the operation field of the electric motor). The MG1 generator achieves much higher speeds, at the same time obtaining much lower values of the torque (about 40 Nm).
Considerable number of braking of the vehicle gives the opportunity to recuperate the vehicle kinetic energy. The analysis of the instantaneous energy recuperated during braking indicates recuperation of about 200 Wh during the test run in urban conditions. The hybrid drive system in Toyota Yaris enables, to a considerable degree, utilization of the electric motor to drive the vehicle, at the same time diminishing the share of the combustion engine operation. Significant number of engine disconnections (about 80), caused that during the test run along Route 2 the combustion engine drive system was disconnected for about 1400 sec. It allows for significant reduction of fuel consumption.
Due to the fact that the vehicle with hybrid drive system is able to recuperate kinetic energy, the battery state of charge (SOC) does not have to be at its maximum. It means that during driving, despite utilizing the energy accumulated in the battery, its state of charge is variable. As it is apparent in Fig. 6, driving in urban conditions induces constant discharging and recharging of the battery. The SOC values were compared with the time and the value of the torque during the energy recuperation phase. It shows that insignificant braking periods allow for constant recharging of the battery. For this reasons the urban conditions are those preferred for the hybrid drive system.
Fig. 6. Changes of the state of charge of the battery during the test run along Route 2 Particular routes have been compared with consideration given to the driving speed during the three test runs (Fig. 7). Characteristic are the points indicating the necessity to stop the vehicle (speed is equal to 0). At the initial phase of the third route (S = 800 – 1500 m) might be observed a considerable limitation of the vehicle movement due to the huge traffic intensity at low speed (traffic jams). Despite this, it should pointed out that the opportunities for energy recuperation occur precisely in the same points of the route, independent of the traffic intensity. It is associated with necessary stops of the vehicle (so called ‘green wave’ in case of urban traffic in the city center does not fulfill its function). Independent of the route, the maximum values of the braking torque (regenerative) are on similar level (about 20 Nm).
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 S [m] T im e of e n e rgy r e c .[ s ] 0,00 0,08 0,16 0,24 SO C [ % ] 54 60 66 Mo -r ec [N m ] -200 -100 0
Independent of the traffic conditions, the number of the vehicle stops is similar and amounts to about 80 (Table 2). The accumulated distance, during which the engine was disconnected, also achieves similar level and amounts to about 4500 m, which constitutes less than 50% of the whole distance covered. As the drive time was variable, it was necessary to determine a time-dependant index of engine stops. It amounts to about 70% of the drive time. Considering variable drive time, the periods of energy recuperation are very different. However, the total energy recuperated is similar (Table 2). The share of operation at idle speed is insignificant in urban conditions. The share of the engine operation at idle speed is less than 4%, while the share of the distance covered in such conditions is a bit higher and amounts to about 5%.
Fig. 7. Comparison of the driving speeds in subsequent routes (a) and values of braking torque on energy generators (MG1) during tests in urban conditions (b)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 S [m] V -ve h [ k m /h] 0 0 30 60 90 V-v e h [km/ h ] 0 30 60 90 V-v e h [km/ h ] 0 30 60 90 Route 1 Route 2 Route 3 a) 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 S [m] M o -r ec [Nm ] c -200 -100 0 M o -r ec [Nm ] 0 -200 -100 0 Mo -r ec [Nm ] -200 -100 0 Route 1 Route 2 Route 3 b)
Different states of battery charge were observed indicating considerable opportunities for energy recuperation and battery charging (particularly during the test run on Route 3, where the batteries were significantly discharged).
Detailed data referring to the obtained parameters of the hybrid drive system operation are presented in Table 2 and in Fig. 8, where the substantial share of electric motors operation of Toyota Yaris hybrid drive system was demonstrated. The share of the combustion engine was limited to almost 50% of the route distance. It means that original assumptions of the hybrid drive creators are slowly being achieved. The problem is only achieving fuel consumption reduction by 50%. Toyota Yaris drive system with its parameters of combustion engine and electric motors operation are getting closer to electric motors with Range Extender system, in which a small combustion engine charges batteries required to drive the vehicle.
Table 2 Characteristic parameters referring to the hybrid drive system of Toyota Yaris 1.5 HSD
utilized in urban conditions
Parameter Unit Route 1 Route 2 Route 3
Route distance m 10035 10009 9980.9
Drive time s 1551.6 1901.9 2193.9
Number of combustion engine stops – 77 79 72
Energy recuperated W·h 205.3 192.0 193.9
Period of energy recuperation s 262.7 237.8 196.6
Share of drive period with energy recuperation % 16.9 12.5 9.0 Distance covered by the vehicle at engine idle speed m 479.0 552.2 497.0 Share of distance covered at engine idle speed % 4.8 5.5 5.0
Period of engine operation at idle speed s 44.1 54.1 72.3
Share of engine operation period at idle speed % 2.8 2.9 3.3 Distance covered with combustion engine stopped m 4685.7 4818.2 4196.3 Share of distance with combustion engine stopped % 46.7 48.1 42.0 Period of distance covered at idle speed combustion engine
stop s 1064.1 1401.0 1547.0
Share of combustion engine stop period % 68.6 73.7 70.5
Fig. 8. Share of time of combustion engine operation and energy recuperation of the hybrid vehicle utilized in urban conditions
68.6 73.7 70.5 46.7 48.1 42.0 16.9 12.5 9.0 4.8 2.8 5.5 2.9 5.0 3.3 0 20 40 60 80 100
Route1 Route 2 Route3
Shar e [% ] Shareofcombustionenginestopperiod Shareofdistancewithcombustionenginestopped Shareofdriveperiodwithenergyrecuperation Shareofdistancecoveredatidlespeed Shareofengineoperationperiodatidlespeed
4. CONCLUSIONS
It was demonstrated that the hybrid drive system tested in urban conditions utilizes electric motor and battery energy to a larger degree than the energy of combustion engine. In the investigated cases specific advantages of the use of hybrid drive system in urban conditions are the following:
a) combustion engine operation is limited to keeping constant speed within average load values and operation similar to external characteristics;
b) drive along the distance of about 10 km enables recuperation of energy of about 200 W·h (20 W·h/km);
c) share of time of operation of the drive system in electric mode amounts to about 70%, independent of the test conditions;
d) share of the distance covered in electric mode exceeds 50% of the whole route, independent of the test conditions.
References
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8. www.toyota.pl (dostp z dnia 8.02.2013).
WSKANIKI PRACY NAPDU HYBRYDOWEGO TOYOTY YARIS W WARUNKACH RUCHU MIEJSKIEGO
Streszczenie: W artykule przedstawiono wyniki bada drogowych napdu hybrydowego eksploatowanego
w zró nicowanych warunkach ruchu miejskiego. Wykorzystujc zcze diagnostyczne uzyskano informacje o pracy silnika spalinowego oraz silników elektrycznych. Dokonano analizy wykorzystania silnika spalinowego i silników elektrycznych. Wskazano obszary najczciej wykorzystywanych zakresów pracy w postaci histogramów, a nastpnie zestawiono je z trasami przejazdu. Dokonano oceny przepywu energii w ukadzie oraz przedstawiono warunki odzyskiwania energii w poje dzie. Wskazano obszary pracy pojazdu, które w najwikszym stopniu wykorzystuj zalety napdu hybrydowego. Wykazano, e napd hybrydowy w wikszym stopniu wykorzystuje silnik elektryczny i energi akumulatorów ni silnik spalinowy. Podano ilociowe wartoci wykorzystania silników napdowych w zró nicowanych warunkach miejskich.
