This document discusses a study on developing a hybrid powertrain for a mid-size vehicle using a 48V mild hybrid system. The goal is to achieve lower CO2 emissions than a diesel vehicle while maintaining driving performance. A turbocharged gasoline engine would be paired with an electric motor and electric supercharger. Simulation results showed the hybrid concept could meet the 95g CO2/km target and provide better acceleration than a turbocharger alone, due to the electric supercharger improving torque at low engine speeds. The hybrid was also found to have lower total ownership costs than gasoline or diesel variants over 5 years.

1. 48V Hybridization Of A Mid Size Vehicle Using Electric Motor And Electric Assisted Supercharger
Abstract
In a context of growing demand for sustainable transportation worldwide, different technical solutions for hybrid
vehicles are nowadays investigated as effective ways to improve efficiency of the driveline and thus to reduce CO2
emissions. As a matter of fact, the CO2 emission targets set by EU (95 g/km in 2020 and 75 g/km in 2025) are
extremely demanding.
In order to reach the 2020 CO2 emission target with a spark ignition engine, solutions needs to be developed
(hybridization) or reinforced (downsizing). At the same time, no compromise should be done between fuel
consumption and fun-to-drive. While turbocharged engines exhibit poor transient performance (“turbo lag”), an
electric supercharger allows improving fuel consumption, turbo lag and increasing engine torque at low speed.
The subject of this study is to present a cost effective solution package for a gasoline engine, achieving lower CO2
emissions compared to a state of the art Diesel engine without compromising fun to drive.
Target
• Baseline: Golf VII 1.6L TDI, a state-of-the-art conventional diesel vehicle.
• Target those kind of CO2 figures with a mild-hybrid vehicle (48 Volt) powered by a turbocharged gasoline engine
and equipped with a manual transmission.
• Provide better driving performance (fun-to-drive) by adopting an electric-assisted supercharger (eSC).
Hybrid Architecture Selection
Benchmark (C-segment)
Results
Conclusion
• Through Mild Hybridization (48V) it has been possible to achieve considerable CO2 benefit regarding conventional
gasoline and meet the 95 gCO2/km target.
• Thanks to the E-Machine (15kW) and electric supercharger (4kW) (especially at low and mid load) the fuel
improvement is not at the expense of the fun-to-drive.
Acknowledgement
Special thanks go to Mr Sebastien Potteau from Valeo and Mr Prakash Dewangan from IFP School for their
continuous support and availability.
Curb
Weight
(kg)
Power
(hp)
Torque
(Nm)
Maximum
speed
(km/h)
80-120
km/h (s)
30-60
km/h (s)
NEDC FC
(L/100km)
CO2
(g/km)
1295 105 250 192 11,6 6,7 3,9 99
M
M
T
D
M
T
DM
M
M
T
D
M
T
D
M
e-Supercharger Implementation
Gear Selection Optimization
Pros: Limited extra-weight.
Cons: No regenerative braking when clutch disengaged,
Undergoes engine resistive torque when running Full
Electric or regenerating during braking.
Pros: E-Machine can be totally decoupled from engine.
Cons: Additional clutch (limited space for transverse
engine).
Pros: Double shaft suitable with transverse engine,
Regenerative braking with engine totally decoupled.
Cons: Additional transmission ratio (weight).
P1
P2
P3 P4
0
1
2
3
4
5
6
5,38 5,09
(-5,4%)
4,03
(-25,1%) 3,52
(-34,6%)
4,13
(-23,2%) 3,90
(-27,5%)
FuelConsumption(L/100km)
FUEL CONSUMPTION (L/100KM)
As the C-segment cars usually adopt a
transverse engine the P3 architecture
has been preferred with a gear ratio of
3 to ensure the CO2 target.
Assumptions: Imposed gear shifting, ideal Stop &
Start, E-Machine (15 kW) not used for cranking and all
the braking torque can be recovered by the E-
Machine.
Assumptions: Stop & Start disabled during the first
150s to warm up the engine.
Gear Shifting Strategy (Manual Transmission) :
• When vehicle speed is constant or increase a gear
has to be engaged (safety).
• When decelerating shift to neutral to recover the
max energy.
• E-machine (15kW) ensures take off.
• A fuel penalty is added to a gear shifting.
0
50
100
150
0
1
2
3
4
5
0 200 400 600 800 1000
Vehiclespeed(km/h)
Gears
Time (s)
Gear Shifting
Optimal Gear Shifting Fixed Gear Shifting Vehicle speed
0
20
40
60
80
100
120
0 1000 2000 3000
Vehiclespeed(km/h)
Time (s)
Cycles
NEDC RDE
Real Driving Emissions in Paris
110
79
4,6
3,3
0
1
2
3
4
5
6
0
20
40
60
80
100
120
140
FuelConsumption(L/100km)
CO2(g/km)
RDE Cycle
-28,2%
Fuel Consumption NEDC: 3,72L/100km
(2,8% Fuel Saving)
0
50
100
150
200
250
500 1500 2500 3500
Torque(Nm)
Engine RPM
Engine operating point evolution of 60-
100km/h acceleration
e-Supercharger
Turbocharger
Max Torque [Nm]
• Electric-assisted supercharger is able to considerably reduce the time to torque, thus
increases the fun-to-drive of a vehicle. Improvement could reach more than 10%.
• This improvement is especially interesting when the engine is running at low RPM.
• E-motor is another good enabler of better acceleration performance, but requires
rapid depletion of the battery capacity.
Cost Calculation Gas Hybrid Diesel
Tax (€/year) 1000 1475
Maintenance (€/year) 900 1000
Fuel consumption (€/year) 605 560
Total cost (€/5years) 12525 15175
(2650€/5years Savings)
129
99 89
5,4
3,8 3,7
0
1
2
3
4
5
6
0
20
40
60
80
100
120
140
FuelConsumption(L/100km)
CO2(g/km)
NEDC Cycle
-31,0%
Conventional
Gasoline
Diesel Golf VII
14,01
13,42
14,05
13,46
12,42 12,70
9,82
8,88
5,97
9,46
8,30
5,52
5,0
6,0
7,0
8,0
9,0
10,0
11,0
12,0
13,0
14,0
15,0
80-120km/h 60-100km/h 30-60km/h
Duration(s)
Range Of Roll-on Acceleration On 5th Gear
Roll-on performance of vehicles with/without
an e-supercharger (4kW)
TC w/o EM eSC w/o EM TC w/i EM eSC w/i EM
Final
Architecture
Conventional
Gasoline
Final
Architecture
Team Members: Thomas REDLINGER, Shixiong ZHAO, Aggelos ZOUFIOS, Stanish GUNASEKARAN
0
1
2
3
4
5
6
DIESEL GASOLINE HYBRID
FuelConsumption(L/100km)
Fuel Consumption and CO2 Emissions
3,9 4,0 4,8 5,0 5,43,2 3,8 3,4 4,4
99
84
104
110 114
124
84
88
101
Diesel Gasoline Hybrid
A
Golf VII
1.6 TDI
Peugeot 308 II
1.2 THP
Toyota Auris
136h
B
Peugeot 308
Blue HDI 120
Ford Focus III 1.0
Ecoboost
Peugeot
3008
Hybrid4
C
Alpha Romeo
Giullietta 1.6
JTDM-2 105
Renault Mégane
Energy TCe 130
Honda
Insight II
-10,1%
A C A B CB A B C
Assumptions Gas Hybrid Diesel
Mean distance in France (km/year) 12 700 12 700
Ownership duration (year) 5 5
Fuel rate (€/L) (Super 98) 1.28 1.17
Fuel consumption (L/100km) 3.72 3.9
Additional components：
• E-Supercharger (4kW)
• E-motor (15 kW)
• Battery pack (48V)
• DC/DC converter
• Cables
Comparison: Proposed Hybrid vs. Conventional Gasoline vs. State of Art Diesel (Golf VI 1.6TSI)
Weight Increase + 43 kg + 3 kg
Additional Cost + 1285 € (*) + 285 € (*)
CO2 Benefit 40 g/km 10 g/km
CO2 Reduction Cost 32,1 €/gCO2/km 28.5 €/gCO2/km
Cycle Definition
Fuel Consumption & CO2 Emission
System Overview
Total Cost of Ownership Estimation
Additional Weight and Cost Estimation
(*) : Indicative Market Price for 2020 for mass production (> 200 000 pieces / year)
Engine Selection & Optimization
IC Engine
1,6L 4 cylinders
Turbocharged
Max Torque
[Nm/L]
170,9
Max Power
[KW/L]
67,3
Specific Torque
Engine Downsized
to 1,2L
 Improving Fuel
Consumption
 Heat losses proportional
to the available surface
area
𝑸 = 𝒉 ∗ 𝑨 ∗ (𝑻𝒈 − 𝑻𝒘𝒂𝒍𝒍)
3 cylinders
implementation
3-cyclinders Implementation
Assumptions:
 S/B ratio for conventional
gasoline engines = 0,8
 Exhaust gas losses = 30 % of
the fuel energy
 Constant mean wall
temperature and BMEP
9,15 % reduction in heat
transfer area
 2,75% gain in fuel
consumption
Diesel Golf VII