Sustainable Vehicle Technologies. Driving the Green Agenda

223 Pages·2013·31.26 MB·English

by  Institution of Mechanical Engineers (IMechE) (Auth.)

Sustainable Vehicle Technologies:
Driving the Green Agenda
Automobile Division Organising Committee
Richard Folkson (Chairman) Consultant
Lisa Bingley MIRA
Chris Brace University of Bath
George Haritos University of Hertfordshire
Jon Hilton Flybrid Systems
James Marco Cranfield University
Mike Richardson Jaguar Land Rover
Mark Stanton Jaguar Land Rover
Chris Wheelans
Sustainable Vehicle Technologies:
Driving the Green Agenda
14–15 NOVEMBER 2012
GAYDON, WARWICKSHIRE
Oxford Cambridge Philadelphia New Delhi
Published by Woodhead Publishing Limited
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First published 2012, Woodhead Publishing Limited
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Energy demand assessment of electrified
drivetrains in material extraction and
system manufacturing

C-S Ernst, M Hans, L Eckstein
Institute for Automotive Engineering (ika), RWTH Aachen University, Germany

ABSTRACT

The increasing electrification of the drivetrain implicates the demand for an holistic
evaluation of their primary energy consumption. While numerous studies already
address the use phase of vehicles, this study focuses on the raw material extraction
as well as on the manufacturing processes of all drivetrain components. The key
outcome of this study is a detailed overview of the material composition and the
corresponding energy demand for the material extraction and production phase of
electrified drivetrains. In addition, strategic opportunities to reduce the future
energy demand are discussed by focussing on the identified key parameters.

1 INTRODUCTION

The megatrends emissions, urbanization and peak oil increase the pressure on the
automotive industry to develop innovative and sustainable solutions. The European
Commission has formulated the target to reduce CO -emissions drastically in
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industry and traffic, as formulated in the white paper “Roadmap for moving to a
competitive low-carbon economy in 2050” (1). The electrification of the vehicle’s
drivetrain is one approach to reduce the energy consumption during a vehicle’s
lifetime. Consequently new components like electric machines, power electronics
and batteries have to be integrated into the vehicle. Thus, it is necessary to
develop an integral life cycle analysis to compare the energy demand of different
drivetrain configurations using an holistic approach.

Current surveys of electric mobility and its benefits have a strong focus on the use
phase of the vehicle lifecycle. The prior production phases are widely neglected.
Therefore, this study is focusing on the phases of material extraction as well as
component manufacturing. It deals with the primary energy consumption in these
two phases and compares them for different types of drivetrains with varying
degrees of electrification.

Apart from an internal combustion engine and a battery-powered electric drivetrain,
three hybrid drivetrains have been chosen and included in the analysis. The Mild
Hybrid architecture is currently the most widely spread hybrid drivetrain. It
represents the lowest grade of electrification in the analysis. A Powersplit Full
Hybrid is the next evolutionary step towards electric mobility and is characterized
by the capability of purely electric driving over small distances. Plug-In Hybrids with
external charging capabilities and small range extender engines allow a purely
electric coverage of longer distances and are currently viewed as the most
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© The author(s) and/or their employer(s), 2012
important drivetrains for the near future. In order to compare these different
drivetrains, an identical system power level of 100 kW was chosen. The power was
partitioned between the electrical and conventional drivetrain depending on the
vehicle type. In total, eight different vehicles are included in the analysis.

2 METHODOLOGICAL APPROACH

In order to allow a detailed analysis, a five-step approach is used. Based on an
analysis of the current state of technology for the electrical and hybrid components,
eight reference vehicle drivetrain architectures will be defined. The most important
drivetrain components are assessed in terms of their material composition. Because
of their complexity and the large number, these materials are clustered into groups
(e.g. light metals, steel and iron materials and plastics). The material extraction
processes for each of these groups are analyzed and detailed process models
containing the specific energy consumptions are created. This approach allows a
detailed assessment of the materials extraction lifecycle phase for all necessary
drivetrain components. In order to assess the second phase of component
manufacturing, a detailed literature survey is performed. Key outcome of this
literature survey is an assessment for the specific energy consumption of relevant
manufacturing processes such as casting, forging and processes for electronic
equipment. These assessments are paired with manufacturing process distributions
for the different components in order to evaluate the second phase of component
manufacturing. Finally, each step of the analysis is aggregated into an integral
primary energy demand assessment. The corresponding V-model approach is
pictured in figure 1.

Comparison of
Drivetrain
System level drivetrains and
configurations
implications
Component Analysis of
level drivetrains
Analysis of Analysis of
Individual part
material extraction manufacturing
level
processes processes

Figure 1 - Methodological approach of this study

3 STATE OF THE ART OF ELECTRIC AND HYBRID VEHICLES

When assessing the current state of technology in electric and hybrid drivetrains it
becomes apparent that new components like the electric motor and the vehicle´s
battery need to be analyzed in detail.

For the electric motor, there are different technological options to be considered.
The main categories that are used in order to evaluate the different existing options
are the motors´ overall efficiency, its costs as well as its weight and volume in
relation to its power capabilities.

The permanent-magnet synchronous motor (PSM) is the leading technology
solution regarding the shown criteria and is therefore chosen as the electric motor
for both hybrid and electric drivetrains. However, the biggest advantage is also the
biggest disadvantage. The NdFeB-magnets used in PSMs allow for a very high
efficiency and low noise. But they are critical from a non-technical, strategic
perspective. More than 90 % of rare earth mining capabilities are located in China,
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which results in strong dependencies on single material sources especially for
companies without production capabilities in the country. Also, high-strength rare
earth magnets gain importance since they are being used in almost all electronic
devices such as cell phones or hard disks, which could further exacerbate the
supply situation in future. These challenges concerning rare earth magnets have
lead to strong research activities focusing on electric motors for hybrid and electric
vehicles that do not use rare earth magnets but still offer high efficiency. Other
options without high-strength natural magnet materials will most likely start being
used in future generations of electric vehicles.

Table 1 - Comparison of electric machines for use in xEV (2), (3)
Technical Factors
Asynchronous Direct Permanent- Switched Transverse
machine Current magnet Reluctance Flux Machine
Machine
- Machine - synchronus Machine - -
ASM DCM motor -PSM SRM TFM
Torque density 0 - ++ + ++
Efficiency 0 - ++ 0 +
Mass + - ++ + ++
Noiselevel + + ++ - --
Developmentstatus ++ ++ + 0 --
Economical factors
Machine ASM DCM PSM SRM TFM
Inverter costs + ++ 0 - --
Motorcosts 0 -- 0 + -
System costs 0 0 0 - -
Manufacturing costs + - 0 ++ --
Hybrid and electric vehicle usage
Ranking 2 5 1 3 4

As for the vehicle battery, the research activities are even further spread-out
between different options. Currently, the main focus in series development is on
the Lithium-Ion / Lithium-Polymer battery technology. Within this class of batteries,
there are different material options that are currently being researched or already
being put to use in current hybrid and electric vehicles. Two of the most promising
ones are Lithium-Manganese Oxide Spinel (LMO) and Lithium-Iron Phosphate (LFP).
Figure 2 shows a comparison between different available Lithium-Ion technologies
in the key categories of energy density, power density, safety, eco-friendliness and
durability.

While Mild Hybrid as well as Plug-In Hybrid and Electric Vehicles today mostly use
the Lithium-Ion class of batteries, Full Hybrid vehicles such as the Toyota Prius or
the BMW X6 ActiveHybrid are only starting to replace Nickel-Metalhydrid technology
in the current or upcoming generations. However, it seems clear that a shift
towards Lithium-Ion batteries will occur, so that the Nickel-Metalhydrid technology
will gradually phase out of hybrid vehicles as well.

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Lithium-Nickel-Cobalt-Aluminium Lithium-Nickel-Cobalt-Manganese
(NCA) (NCM)
Energy Density Energy Density
Eco-Friendliness Power Density Eco-Friendliness Power Density
Costs Safety Costs Safety
Stability and Life Stability and Life
Expectancy Expectancy
Lithium-Manganese-Spinel Lithium-Iron-Phosphate
(LMO) (LFP)
Energy Density Energy Density
Eco-Friendliness Power Density Eco-Friendliness Power Density
Costs Safety Costs Safety
Stability and Life Stability and Life
Expectancy Expectancy
Figure 2 - Comparison of different Lithium-Ion technologies
(4, 5, 6, 7, 8, 9)

For this study, PSMs are used as the motors in all hybrid and electric vehicles, while
the Lithium-Ion technology is used to model the vehicles batteries. As for the
specific material combination, the LMO battery based on Lithium and Manganese is
chosen since it has successfully been tested and is sold in the current GM Plug-In
platform vehicles. The LFP technology, which might be able to gain market share in
the next couple of years, is not used due to a lack of data concerning the exact
material composition of battery cells.

4 ANALYSIS OF THE MATERIAL COMPOSITION

The focus of this study is on the core components of the electrified drivetrains. All
components, which differ from an xEV to an ICE vehicle, are regarded in a delta
analysis. They are divided into three categories: motor with necessary auxiliaries
(power electronics, exhaust system), transmission systems and energy storage
systems. For the further research, eight reference vehicle configurations are
defined as shown below.

The data on the material composition for each of the individual components is
gathered from product catalogues, prior research activities and available company
information. If there is no data available, the material composition is estimated
using best judgment and proxy values. In this paper, only exemplary data can be
presented to give an insight into the research. The most influencing components
are described in the following, as there are the vehicle’s internal combustion engine
and the traction battery. All research data is integrated in a scalable calculation
model to cover all possible drivetrain configurations.
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Table 2 - Reference vehicle drivetrain architectures
Conventional Powersplit Serial Hybrid Battery
Mild Hybrid
(ICE) Hybrid (HEV) (PHEV) Electric (BEV)
2.0l Nat. Asp. 1.4 l Turbocharged 1.2 l Nat. Asp. 1.0 l Nat. Asp. None
Engine
(100 kW) (85kW) (70 kW) (50 kW)
Transmission Manual Manual Powersplit Direct Direct
Exhaust System
Yes Yes Yes Yes None
and Fuel Tank
Electric Motor* None 15 kW PSM 50 kW PSM 100 kW PSM 100 kWPSM
Generator* None None 50 kW PSM 50kW PSM None
Power DC/DCand small DC/DC and medium DC/DCand large DC/DCand large
None
Electronics AC/DC Converter AC/DC Converter AC/DC Converter AC/DC Converter
High voltage 3 m, 35 mm2 3 m, 35 mm2 3 m, 50 mm2 3 m,50 mm2
None
cable Cross section Cross section Cross section Cross section
ElectricDriving
0 km 0 km 5 km 36, 40, 60, 80 km 100 km
Range
Battery** None 0.7 kWh 1.6kWh 7.6 / 8.5 / 12.8 / 21.3 kWh
17.1 kWh
Key:
*: Specific power 0.56 kg/kW
**: Energy Density (Cell) 175 Wh/kg (PHEV, BEV), 120 Wh/kg (Powersplit), 95 Wh/kg (Mild Hybrid)
Power Density (Cell) 2,300 W/kg (PHEV, BEV), 2,500 W/kg (Powersplit), 3,200 W/kg (Mild Hybrid)
Min. State-of-Charge 25 % (PHEV, BEV), 50 % (Powersplit), 65 % (Mild Hybrid)

4.1 Internal combustion engine (ICE)
The internal combustion engine (ICE) is one of the most heavy-weight systems in
every modern drivetrain and therefore has a large influence on the material bill of
the vehicle. The results of the material composition breakdown of eight ICEs are
shown in Figure 3. One main result is the low dependency of the material
composition on key engine variables, such as the number of cylinders and fuel type
used. Thus, it seems reasonable to use the average material composition found in
the analyzed engines in the model.

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Weight Data
(kg) Source
3%
Engine 1 49% 36% 10% 2% 110 (10)
2%
Engine 2 56% 28% 12% 2% 126 (10)
3%
Engine 3* 66% 21% 9% 2% 103 (10)
3%
Engine 4 51% 35% 11% 1% 93 (10)
Engine 5 45% 37% 4% 10% 4% 142 Research
Engine 6 42% 39% 4% 11% 4% 180 Research
Engine 7 46% 33% 6% 12% 3% 143 Research
Engine 8 49% 30% 6% 13% 3% 176 Research
Average 51% 32% 4% 11% 3% *: Gray-Iron CylinderHousing
and Head
Steel and Iron Light Metals Other metals Polymeres Others
Figure 3 - Weight distribution of selected combustion engines (10)

The next step in the analysis scales the model to different performance levels found
in the different drivetrain architectures. While conventional vehicles fully rely on the
combustion engine in every driving situation, hybrid vehicles use their electric
motors to assist smaller, so called downsized, combustion engines. This difference
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needs to be modelled in order to allow a detailed comparison. Therefore, two ratios
are used to scale the vehicle engine model. First, the weight is determined as a
dependent variable on the engine displacement. Regression data over approx. 30
different engines shows an increase in weight of 70 kg for every additional
1,000 cm3 of cylinder capacity. The second ratio used, is that between the engines
power level and its engine displacement. With downsizing being a major trend
across the industry, this ratio increases steadily. However, extra power has to be
generated using either extra engine displacement or substituting it by using
additional measures such as turbochargers or compressors. Looking at engines
currently on the market it is evident that turbocharged engines weigh around 16 kg
more than naturally aspirated engines of the same size. Statistic data suggests that
engines with a specific power level above 60 kW/1.000 cm3 are usually
turbocharged, while engines with a specific power level below that threshold are
most likely naturally aspirated.

4.2 Lithium-Ion Battery system model for PHEV and BEV
The battery system of the Opel Ampera is chosen as reference for the detailed
analysis steps of the material composition. The core component of the battery
system is the battery cell. Coffee-Bag cells with technical specifications like the EIG
PLC C cell (11) are chosen for this model. They may be considered as state of the
art cells, which are actually available on the market today. The material
composition of these cells bases on information from (12). The necessary battery
management system has been modelled scalable, so that it fits the different battery
capacities, using analysis results from (13, 14 and 15).

Copper (10.7 %) LiPF (1.4 %)
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15.2 kg 2.0 kg
(cid:131) Anode (cid:131) Electrolyte salt Aluminium (20.0 %)
(cid:131) Cabling
Carbon (11.2 %) 28.3 kg (cid:131) Cathode
15.8 kg (cid:131) Cooling system
(cid:131) Anode
Ethylene carbonate (11.8 %)
16.7 kg LiMnO (16.6 %)
2 4
(cid:131) Electrolyte fluid 23.6 kg
(cid:131) Cathode material
Plastics (15.5 %)
Steel (12.8 %)
18.1 kg (cid:131) Tray 21.9 kg (cid:131) Housing cover
(cid:131) Separator
(cid:131) Mounting plates
(cid:131) Isolation
(cid:131) Screws, ...
(cid:131) …
Total weight of all components: 142.5 kg

Figure 4 - Material composition of a Lithium-Ion battery system
(17.1 kWh) for a PHEV or BEV with 80 km operating range

To complete the battery system, the additional components like cooling fins,
mounting plates, structural parts and the housing have been added. The size of
these components is as well dependent on the battery capacity. For our analysis a
constant material composition has been defined with 55 % steel and iron, 20 %
aluminium, 20 % plastics and 5 % copper, which corresponds with the analyzed
Opel Ampera battery system. Furthermore a charging module for the battery was
modelled. It weighs approx. 6.2 kg using a material composition from (16).
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