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Why hybrid vehicles?
Ivan Mahalec, 2006.03.
1. Oil
CO2
Earth temperature
Figure 1. Left: The world’s production of oil and gas and the projection of availability of reserves calculated on
the basis of consumption in 2005 (Gboe = Giga billion barrels oil equivalent). Right: The increase of CO2
concentration in the atmosphere and the mean earth temperature.
Fossil fuels have two disadvantages:
their reserves are final
by extracting the carbon on the surface of the earth and by its combustion the amount of CO2 in the
atmosphere is increasing by which the greenhouse effect is amplified and that contributes to the global
warming.
The Association of Constructors of European Automobiles ACEA, motivated by Kyoto protocol, has set the
goal that by the year 2008 the CO2 emission of entire fleet of passenger cars should not be larger than 140 g/km.
As a consequence of using relatively high power engines this goal could not be achieved even if all vehicles
would be powered by diesel engines. But hybrid vehicles easily achive this emission level and therefore in the
forthcoming years they will receive more and more attention.
Figure 2. Left: goal of ACEA group: to lower the CO2 emission of the entire fleet of European constructor’s
passenger cars to 140 g/km by the year 2008. Right: the expected future increase of alternative vehicle drives.
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2. Hybrid drive systems
Hybrid drive systems can, on the basis of the link between mechanical and electrical part, be divided in three
groups:
series,
paralel and
series – paralel hybrid.
On the other hand, on the basis of electrical drive autonomy, hybrids are divided into:
mild hybrid and
full hybrid.
Series
Bat
Parallel
Bat
Wheels
Inv
Wheels
Inv
ICE
Inv
Seriesparallel
Bat
Gen
ICE
Gen
EM
EM
Inv
Mechanical energy path
ICE
PSD
EM
Electrical energy path
Figure 3. Schematics of hybrid drives. Marks: Bat - battery; EM –electric motor; Gen –generator; Inv –
inverter; ICE – internal combustion engine; PSD – power splitting device; published in [5.].
η = max
HYBRID
120
Engine torque Me , (Nm)
100
240
246
80
250
60
vmax
EG
EG - for electric generator drive
260
40
V
- for driving
300
20
Drive resistances
v = konst., climb = 0
400
800 g/kWh
1000
2000
∞
V
3000
4000
Engine speed, min-1
5000
6000
Figure 4. The comparison of internal combustion engine operation at conventional and hybrid vehicle in
engine fuel consumption map.
In the hybrid vehicle the internal combustion engine operates in the region of minimum specific fuel
consumption, and the excess power, that is a result of difference between generated power and power needed
for drive, is transferred to generator that charges the battery. In Prius the generator also supplies energy for
electric motor that helps the IC engine
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3. Fuel consumption and harmful emission
Figure 5. Fuel consumption (l/100km) of three Prius hybrid generations and of similar conventional automobile.
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l/100km 13
12
11
10
9
8
7
6
1975
290
g CO2/km (petrol)
250
g CO2/km (diesel)
g CO2/km
210
170
Fuel consumption
1980
1985
1990
1995
2000
130
2005
Figure 6. The fuel consumption of the German vehicle fleet driven with new European drive cycle, according
to the VDA data, and on the basis of this consumption the calculated emission of CO2.
Figure 7. The efficiency of the Prius and its rivals based on Well-to-Wheel analysis.
Figure 8. The harmful emission of the Prius.
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4. Toyota Prius – the world’s no 1
Prius THS II
Battery
Power
regulator
Generator
IC Engine
Power
splitting
device
High voltage
part
Inverter
Electric
motor
Wheels
Transmission
Mechanical energy
Electrical energy
Figure 9. The schematics of drive system of hybrid vehicle Toyota Prius THS II. Characteristics: IC engine:
1.5 dm3, process 4-cycle Otto/Atkinson, reduced engine friction, PICE,max = 57 kW at 500 min-1, 115 NM at
4200 min-1, ge,min = 225 g/kWh (ηe,max = 37 %); electric motor: PEM,max = 50 kW; maximum total vehicle power
82 kW above 85 km/h (Pmax = PICE,max + 50 % (PEM,max)); 1300 kg; 0-100 km/h for 10,9 s; 170 km/h; 104 g
CO2/km.
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Figure 10. The Schematics of a drive system and of a power transmission system.
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Figure 11. Toyota Prius: action schemes.
Slika 12. Down - left: when braking Prius’s electric motor becomes generator.
Figure 13. The characteristics of the IC engine (left) and of the electric motor (right).
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Figure 14. Common action of IC engine and electric motor.
Figure 15. Left: common action of IC engine and electric motor.
Right: comparison of acceleration of Prius and of classic vehicle with petrol engine of 2.4 dm3.
Figure 16. Comparison of acceleration of Prius and of classic vehicle with an equally strong diesel engine.
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Figure 17. The electric drive system and the power transmission system.
Figure 18. Ni-MH battery: 28 serially connected packages with 7,2 V = 202 V; 6,5 Ah; 30 kg; durability
300.000 km.
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