EVS24 Punch Hybrid Powertrain PatrickDebal, Grzegorz Płuciennik, Mechanika Samochodowa, Hybrydowy Napęd
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EVS24
Stavanger, Norway, May 13-16, 2009
Development of a Post
-
Transmission Hybrid Powertrain
Patrick Debal
1
, Saphir Faid
1
, Steven Bervoets
1
, Laurent Tricoche
1
and Brecht Pauwels
2
1
Punch Powertrain, Schurhovenveld 4 125, BE-3800 Sint-Truiden, Belgium, patrick.debal@punchpowertrain.com
2
PsiControl mechatronics
Abstract
Late 2006 Punch Powertrain started the development of a hybrid powertrain. To meet the next generation
of hybrids head on Punch
Powertrain defined ambitious targets with respect to fuel saving, total cost and
vehicle implications. To supply hybrid powertrains to OEMs a minimal impact on the vehicle side is
required.
This paper focuses on the chosen parallel topology, the general system optimisation strategy, the
technology and components selection and the control system development. Simulations for different target
vehicles are performed with detailed component maps. The fuel consumption target is well within reach.
Actual hardware tests are planned for 2009.
Keywords: parallel HEV, powertrain, transmission, switching reluctance motor, lithium battery
Used Abbreviations
BCU
powertrains for small and medium passenger cars.
The company was renamed Punch Powertrain. The
newly developed hybrid powertrain would have to
be competitive with the products from competitors
at the time of introduction and maintain a
competitive level for several years. To assure the
hybrid powertrain meets head on these hybrids
from the competitors Punch defined ambitious
targets.
This paper focuses on the chosen topology, the
system optimisation strategy, the technology and
components selection and the control system
development. Simulations for different target
vehicles are performed with detailed component
maps. The fuel consumption target is well within
reach. Actual hardware tests are planned for 2009.
Brake control unit
CO
2
Carbon dioxide
CVT
Continuous variable transmission
DoE
Design of experiments
ECU
Engine control unit
EMG
Electric motor/generator
EV
Electric vehicle
HCU
Hybrid control unit
LiFePO
4
Lithium iron phosphate
ICE
Internal combustion engine
MCU
Motor control unit
NEDC
New European drive cycle
NiMH
Nickel metal hydride
OEM
Original equipment manufacturer
SoC
State of charge
SR
Switched reluctance
TCU
Transmission control unit
2
Strategic View
The strategic view of Punch Powertrain is to
develop a next generation hybrid powertrain. This
powertrain will needs to lower the barriers for
OEMs to offer hybrid versions of their vehicles.
Ambitious targets were set to fulfil the strategy.
1
Introduction
In 2006 Punch International took over the
Belgian CVT transmission plant from ZF with a
clear
goal:
the
development
of
hybrid
EVS24 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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2.1
Fuel Saving
The main target is a fuel saving of minimum
25%/15% on the NEDC
drive cycle with
gasoline/diesel cars while achieving similar
savings in real world drive cycles. These savings
need to be realised by the powertrain only.
Especially for the gasoline hybrid powertrain the
target is high compared to the theoretically
maximum saving of nearly 40% that can be
attained [1]. Additional measures at the vehicle
level like engine efficiency improvement, mass
reduction and streamlining allow realising further
fuel consumption reduction. The similar savings
of greenhouse gases can help to meet the CO
2
emission target of 130 g/km set forward by the
European Commission.
Figure 1: Hybrid Powertrain by Punch
2.2
EV-Range
An EV-range of at least 13 km at city traffic
speeds fits into policies of some major European
cities to reduce harmful emissions in cities. It
allows emission free driving into and out of most
city centres. When benefits from incentives can
be gained or taxes (e.g. the congestion tax in
London) can be avoided the cost premium for the
hybrid powertrain can be partially or totally
compensated.
3
Hybrid Strategy Development
To meet the fuel saving target as well as the EV-
range only a full parallel hybrid configuration is
within the scope. Because Punch Powertrain
intended to develop a dedicated hybrid
transmission, two configurations were possible.
3.1
Hybrid Configuration
When developing a hybrid powertrain various
system architectures are possible, each with
advantages and disadvantages. The selection of the
optimal system architecture is a compromise
between cost, performance (efficiency) and vehicle
packaging constraints.
2.3
Compatibility
As Punch Powertrain intends to supply the
hybrid powertrain to OEM’s which will integrate
it in vehicles that are also marketed with
conventional powertrains, the hybrid powertrain
should be compatible with a conventional vehicle
architecture. Moreover, the total impact of the
hybridisation on vehicle packaging, functionality
and user comfort should be minimal.
Punch Powertrain aims at a segment of front wheel
driven vehicles, where the conventional layout
consists of a transverse positioned four cylinder
engine directly connected to a transmission which
incorporates a differential.
When developing a CVT based hybrid, there are
basically two options within the system
architecture. The first option is to link the electric
motor/generator with the powertrain before the
CVT variator. Although the motor/generator can
be located elsewhere a configuration similar to
some other hybrid powertrains with a flywheel
motor/generator is quite common. At Punch
Powertrain this is called the “PRE” configuration.
The other configuration, hence called the “POST”
configuration, links the electric motor/generator
behind the variator.
For both configurations a physical simulation
model of the powertrain including system
optimisation strategy was developed. A first step in
2.4
Target Segments
Punch Powertrain targets the most popular
vehicle segments of small and medium passenger
cars and small vans in Europe. Both Toyota and
Honda have proven that in these segments a
considerable number of hybrid vehicles can be
sold [2].
2.5
Cost Target
Punch Powertrain has set strict cost targets to
lower the barrier for OEMs and their customers
to buy vehicles with this powertrain. Buyers in
these target segments are very cost sensitive.
Therefore the cost premium for the hybrid must
clearly allow a high return on investment.
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this strategy development is to create a holistic
view on the optimisation principles. To reach the
ambitious fuel reduction targets a system
optimisation rather than a component
optimisation [3] is required. The optimisation
principles were cast into newly developed
mathematical models to derive the operating
areas for the different hybrid modes.
Efficiency Engine + CVT - 1000 cc 3 cyl - 3300 rpm
35%
30%
EV
mode
25%
20%
Generate
mode
Conventional
mode
Assist
mode
15%
10%
5%
The key advantage of the POST configuration is
a higher system efficiency. Additionally, the
higher efficiency of the POST configuration
allows a substantially increased EV-range
compared to the PRE-configuration when using
the same battery capacity.
An advantage of the PRE-configuration is the
fact that the electric motor/generator with lower
torque specification can be used due to the torque
multiplication through the CVT transmission.
0%
0
25
50
75
100
125
150
175
200
225
Torque [Nm]
Figure 3: Use of the Hybrid Modes depending on
Torque Levels at a Given Speed
The calculation scheme allowed comparing both
the PRE and POST configuration. Overall the
POST configuration resulted in higher fuel savings
on both type approval drive cycles and real world
drive cycles. The PRE configuration demonstrated
a higher launch acceleration from stand still due
the torque multiplication by the variator. Due the
higher fuel saving potential Punch Powertrain
opted for the POST configuration although this
requires a more powerful electric motor/generator.
3.2
Basic Simulations
3.3
High-end, Dynamic Simulations
In parallel with the calculation scheme, a highly
detailed and dynamic hybrid powertrain simulation
was developed in Matlab®/Simulink® by using
the SimDriveLine® toolbox. The POST
configuration strategy was carried over from the
calculation scheme and further refined. The
powertrain simulation tool uses a forward
approach, i.e. driver action causes vehicle
acceleration. Furthermore, the inertia of all
powertrain components as well as highly detailed
component models are included. This allows fully
simulating the transient behaviour inside the
powertrain and adopting the strategy to obtain a
good driveability (low jerk level).
Tritec 1000 3 cylinder + CVT - MOL cycle
Figure 2: Combined Efficiency of Engine with CVT
Initially, a backwards [4] calculation scheme in
spreadsheet was used to implement and refine the
strategies. This scheme was first based on simple
component characteristics as a first validation of
the optimisation principles. The required torque
at the wheels is calculated backwards to engine
and motor torque. Gradually, the calculation
scheme was extended with more complex
component maps. This required a migration from
a spreadsheet based tool to a Matlab® based
application. Eventually, the calculation scheme
contained very detailed component maps and
yielded realistic fuel consumption results for
non-hybrid vehicles.
200
Max
31%
30%
29%
28%
27%
25%
23%
20%
15%
10%
5%
BYD
HEV
180
160
140
120
100
80
60
40
20
0
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
Secondary Speed [rpm]
EVS24 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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Because the simulations could easily be run
overnight, all possible configurations were
simulated. Figure 5 shows the main results. The
size of the electric motor has the highest impact on
the fuel saving, especially for the larger vehicle.
Also the effect with a real traffic cycle is
substantially larger.
Assist
Assist
EV
EV
Conv
Conv
Generate
Generate
Figure 4: Operating Points and Actual Modes during a
Real World Cycle
Figure 4 shows the results for a certain C-
segment vehicle. The upper graph shows the non-
hybrid (magenta) as well as the hybrid operating
points of engine+transmission. This allows
dividing the complete speed-torque maps into
different areas with different operating modes of
the hybrid powertrain as shown in the lower
graph of Figure 4.
Secondary Speed
Secondary Speed
Figure 5: DoE results Ranked from Low to High Impact
The DoE was also used to investigate the
robustness of the hybrid strategy. The optimal
configuration derived from the DoE yields fuel
savings above target. The savings are realised for
representative vehicles in both segments and for
both cycles (NEDC and real world).
3.4
Optimisation
by
Design-of-
Experiments
The simulation tool was used to perform a DoE
to find the optimal components sizing. For the
electric motor and the battery system three levels
of components were used. Two engines were
used, one was the standard engine and the other
one was largely downsized. To assess the
robustness of the strategy the simulations were
performed for two vehicle types and on two
cycles.
4
Component
and
Subsystem
Selection
The selection of the batteries and the electric
motor/generator are two important cornerstones in
how the hybrid strategy can achieve the fuel saving
target. While maximising the efficiency gains on
the engine side, and keeping the system within cost
and mass constraints, the electrical losses must be
minimized to maintain the total efficiency gain in
the system.
Table 1: DoE Variables and Levels
Electric motors
SR157
SR210
SR246
(number is
lamination diameter)
4.1
Electric Motor/Generator Drive
The combination of the electric motor/generator
and its power electronics must have a high
efficiency over a wide speed and torque range. At
the same time the drive should provide a high
power density and a low cost. An investigation of
available technologies, products and suppliers
resulted in the choice for a switched reluctance
(SR) motor/generator. This type of electric
motor/generator is the best match to the above
requirements.
Battery systems
CAEC 9.5 Ah
K2 10.0Ah
K2 12.5Ah
Engines
1.6l – 4 cylinder
1.0l – 3 cylinder
Vehicles B-segment
C-segment
Cycles NEDC
MOL (real world)
For all different configurations the full impact of
the components (e.g. a larger, more efficient
motor/generator or battery pack also implied
increased vehicle mass) was included.
Punch Powertrain decided to partner with
PsiControl mechatronics to develop and produce
the SR motor/generator. PsiControl mechatronics
has more than 10 years experience in industrial SR
drives.
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Figure 7: Prototype Battery System
An evaluation of different suppliers of a
combination of LiFePO
4
cells and battery
management systems yielded a preliminary short
list of possible battery system suppliers. The list is
considered as preliminary because LiFePO
4
technology is still immature and important players
are still expected to emerge.
5
Transmission Design
The design of the CVT transmission for the hybrid
powertrain was based on the existing CVT
transmission from Punch Powertrain. The new
development should maintain a maximal level of
compatibility to the current production CVT, to
reduce manufacturing cost.
Some mechanical features of the transmission
could be completely eliminated, such as the
conventional reverse drive system (replaced by
electric reverse function of the traction motor) and
the engine driven oil pump (replaced by a separate
electric powered oil pump).
A new feature that was added to the transmission
is the connection of electric motor to the secondary
variator shaft of the CVT. This was achieved by
use of a high volute chain which combines high
efficiency (> 98 %), durability and low acoustic
noise. This chain connection causes minimal
changes to the rest of the transmission and allows a
fairly long electric motor/generator. Consequently
a large number of parts is carried over from the
conventional CVT.
Figure 6: SR Motor - Sample Stator and Rotor
PsiControl mechatronics needed to develop a
new approach. In contrast with industrial
applications with nominal speed and torque, the
motor/generator loading in an automotive hybrid
powertrain is very diverse. Different design tools
like the thermal modelling needed adaptations to
cope with the varying load.
The result is a compact but powerful electric
drive. Tests show that the motor is matching its
predicted performance. Currently it is tested
using the HCU to control the motor output and
the prototype battery pack to investigate their
combined performance.
4.2
Battery System
The efficiency and the EV-range target rule out
the use of NiMH batteries. Classic Lithium
chemistries as currently used for laptops and cell
phones pose a serious safety risk especially when
these cells are scaled to capacities as required for
hybrid vehicles. Therefore Punch Powertrain opts
for the LiFePO
4
chemistry. This emerging
chemistry combines high efficiency, usable SoC
range, sufficient power and energy density,
excellent cycle life and safety.
Figure 8: Hybrid Transmission with Electric
Motor/Generator. New parts in exploded view
By meeting the tight sizing constraints the hybrid
powertrain will fit in nearly any engine bay that
EVS24 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium
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