Toolkit for Tomorrow`s Car - Southwest Research Institute

by Scott T. McBroom
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help meet performance, emissions and fuel economy goals for
the 21st century, engineers in the
SwRI Engine and Vehicle Research Division are developing comp uter software
tools that simulate advanced vehicle powertrains. This effort is part of the Partnership for a New Generation of Vehicles, or
PNGV (see box on this page).
i1 0
The PNGV Challenge
A major goal of the PNGV program,
and the targeted use of the software being
developed at SwRI, is development by
2004 of a production prototype mid-size
family sedan with a fuel economy of up to
80 miles per gallon. That is three times the
fuel efficiency of today's comparable class
of vehicles such as the Ford Taurus,
Chrysler Concorde, and Chevrolet
Lumina. The goal further challenges engineers to maintain or improve current levels of performance, size, utility, and cost
of ownership, and the new vehicle m ust
meet or exceed federal safety and emissions requirements.
While there are many ways to
achieve 80 mpg, the hybrid electric vehicle is seen as one of the more promising
alternatives. A hybrid vehicle is on e in
which two sources of energy are converted to power the vehicle (see sidebar
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on p age 13). Hybrid vehicles offer a number of advantages: they can recover
energy normally dissipated by the
brakes, reduce gaseous emissions by
virtue of their smaller heat engines, and
improve fuel economy with more efficient electric drives.
Another alternative, the conventional powertrain consisting of a reciprocating internal combustion engine and
transmission, averages only 27 mpg in
today's mid-size sedans. Though fuel
efficiency gains have been made over the
last two decades, just 15 percent of the
energy from the gasoline in the tank is
u sed to move the vehicle. Considerable
improvements in en gine efficiency and
significant vehicle weight reduction
would be required for a conventionally
powered sedan to meet the up to 80-mpg
goal. Many are confident, however, that
such improvements can be made.
The breadth of existing and conceptual technologies being considered and
the anticipated cost of research and development to build prototype cars of the
future require that a comprehensive analytical capability be designed to select and
integrate the most appropriate technologies. The United States Council for Automotive Research (USCAR) hopes to meet
this ch allenge with the PNGV Systems
Analysis Toolkit.
The Partnership for a New Generation of
Vehicles is a cooperative research and
development initiative made up of the
United States Council for Automotive
Research - a consortium of the Ford
Motor Company, General Motors Corporation , and Chrysler Corporation - and
the U.S. government. President Clinton
called for formation of the partnership
September 29, 1993, with the goal of
developing a prototype family-size sedan
comparable in price, safety, performance, comfort, and range to today's
six-passenger sedans, but with reduced
emissions and a fuel economy three
times that now possible in such vehicles.
The PN GV Toolkit
The PNGV Systems Analysis Toolkit
will be used to evaluate p owertrain configurations and components such as
advanced heat engines and energy storage devices in conventional and hybrid
electric vehicles, two options determined
by PNGV participants to be among the
most capable of satisfying program goals.
It provides an opportunity for component
exp erts to see how their technologies
interact in the context of whole and varied vehicle systems.
The Toolkit allows analysts to conduct
trade-off studies for performance considerations such as 0-60 mph acceleration, fuel
Technology Today· Spring/Summer 1997
economy, and emissions, as well as for
nonperformance considerations such as
cost and reliability. The immediate results
of the trade-off studies include projection
of component power and energy requirements, identification of areas where energy
is being lost, and management of power
and energy, all of which will aid in determining which components and systems
can help the car of the future achieve up to
80mpg.
The first phase of Toolkit development was completed in December 1996.
" '·:"~-
o•••
The next phase is
scheduled for completion in
August 1997, with planned enhancements
beyond 1997 to include porting the Windows™-based program to client workstations or networks, allowing users to
simultaneously perform virtual design
prototyping, vehicle simulation, and visualization on a single platform; permitting
the addition of custom component models and data so as to perform a wider
range of simulations; and upgrading the
program to provide for high-fidelity,
dynamic analyses.
Three sections make up the Toolkit
architecture. The graphical user interface
allows vehicle definition, results reporting, and static modeling, including cost
and reliability analyses. Vehicle power-
train models developed
with the MATLAB/SimulinkT M
programming language are used to
assess performance, emissions, and fuel
economy through a program developed
at SwRI called APACETM (see following
section). Finally, a software database is
provided for storage of a component
library, vehicle configurations, and simulation results.
Vehicle systems analysis begins by
creating computer models that simulate
the major effects of desired powertrain
components. The program can, for example, calculate how much energy is left in
the battery given a number of different
driving scenarios. The analysis also allows
integration of components into appropriate configurations and produces results
related to key vehicle characteristics. In
addition to increased fuel efficiency, key
desired characteristics for the PNGV prototype vehicle include acceleration of 0-60
mph in 12 seconds, continuous driving on
Senior Research Engineer Scott McBroom of SwRI's Engine and Vehicle
Research Division manages the PNGV Systems Analysis Toolkit program.
At the Institute since 1988, he specializes in hybrid and electric vehicle systems analysis and integration. He also has experience in active suspension
and hydraulic system design, integration, and analysis.
Technology Today. Spring/ Summer 1997
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The PNGV Systems Analysis
Toolkit includes a handling module designed to show the effects
of changing vehicle weight distribution, which is likely when
hybrid propulsion subsystems
are added. The module calculates understeer coefficient and
characteristic speeds, assuming
typical vehicle structural and
suspension parameters.
Baseline: 166%
I
Front
\!Ieight:
Revised:
167%
Q!J
134%
Understeer
Coefficient:
Rear
\!Ieight:
@]
133%
I
I
I
Yaw Velocity Gain (dey/sec/dey)
Front ---\!Ieight Distribution - - - Rear
a 6.0-percent grade at 55 mph, and a
range of 380 miles.
It is anticipated that the Toolkit
will be used by PNGV participants to
determine the direction and magnitude of research programs necessary to
remain on schedule while meeting
technical requirements. Before delivering a prototype in 2004, participants
must produce a concept vehicle by the
year 2000. To accomplish this task, the
most promising technologies will be
identified with the aid of an Institutedeveloped program that assesses vehicle and component performance.
APACETM
As a means to narrow the broad
field of candidate technologies, Institute engineers have created a new simulation program known as Advanced
Understeer
Acceptable
-1.5
Oversteer
Static Understeer Coefficient
w •
Powertrain Assessment, Comparison, and
Evaluation, or APACETM, for integration
into the PNGV Toolkit. APACETM models
the emissions, performance, and fuel efficiency of conventional and hybrid electric vehicles and their components.
Component models are programmed in
MATLAB/Simulink™. Components completed to date include:
• Direct Injected Spark Ignited Engine
• Direct Injected Compression Ignited
Engine
SwRI Group Leader of Powertrain Controls Joe Grogan (from left) and Research Engineer Dr. Jayant Sarlashkar, both of the Engine and Vehicle Research Division, provided
design and implementation of transmission, engine, and control models for APACpM.
Research Analyst Don Mowbray contributed configuration management as well as software technical and architecture support, and Research Engineer David Buntin designed
and implemented energy storage, electric machines, and control strategies. Mowbray
and Buntin work in the Automation and Data Systems Division.
12
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m
~
Speed (mph)
Technology Today. Spring/Summer 1997
~
W
~
1ft!)
~
• Turbo-Alternator (turbine engine integrated with high-speed alternator)
• Permanent Magnet Motor and
Generator
• AC Induction Motor
• AC Synchronous Generator
• Advanced Batteries
• Lead Acid Battery
• Electromechanical Flywheel Battery
• Ultra-Capacitor
• Manual Transmission
• Automatic Transmission
• Continuously Variable Transmission
• System Controls
To implement the models, APACETM
relies on time-based integration for performance prediction. This "forward-looking" approach simulates the behavior of
actual control systems and enlists control
loops to set and correct the behavior of
the system. For example, in a conventional vehicle model, when the software
element simulating the driver wishes to
achieve a desired speed from rest, an
acceleration command is produced. The
command is received by the power controller, which then issues a throttle command to the engine. If by the next
simulation time step the vehicle has not
achieved the desired speed, the acceleration command is increased. MATLAB/
Simulink™ uses a variable time step
integrator that decreases the time step
until the difference between desired and
actual vehicle state falls within a specified tolerance.
The forward-looking technique
allows development of realistic control
(Untitled) Parallel Hybrid
[8J Comparison
••••••••
lb-----~~.....-
Driving Cycle
Not Met
5101 Engine
5-speed Manual
PM Mtr
Li-Ion Baltery
(N 0 Peaking)
(N 0 Gener ator)
Power Electronics
35.2kW
BO.2kW
23.5kW
73.4 kW 1.0 kW
..........lLf
..
List Price
algorithms that can be used in hardwarein-the-loop analyses, in which the computer model (software) controls a vehicle
component (hardware) operating on a
test stand. This reduces experimental
proto typing by permitting evaluation of
component performance as part of a simulated system.
Conclusions
Though the PNGV Toolkit has the
immediate task of supporting development of an up to 80-mpg production prototype by the year 2004, its future use
may be much broader. Using the Toolkit,
it may one day be possible for automotive
engineers to design a variety of new vehicles entirely by computer - selecting a
powertrain, sizing components, and evaluating performance, cost, and reliability
through a user-friendly interface that
automates the process. With automakers
targeting a 28-month concept-to-production turnaround time, digital prototyping
and simulation will save time and
resources by reducing the many stages
of hardware development and testing .•:.
Acknowledgments
Collaborating with Southwest Research
Institute on PNGV Toolkit development is
TASC, Inc., with assistance from Reality
Graphics, Oakland University in
Rochester, Michigan, and the University of
Michigan in Ann Arbor. The first phase of
this effort was supported by NASA; current work is sponsored by the U.S. Army
National Automotive Center. USCAR provides technical direction, and technical
• ~ • Handling
~~~--~~~---,
510 1Engine
77 kW
Reliability I~
A~
ut~
o~
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an~s~_-f7,-,-7-,-,kW
-"--+-_ _1
Operating Cost 1~(N~o~M:!.':o:!.':
to:'.L
r) -,--_+-_-+_ _1
(No Baltery)
(N 0 Peaking)
~
73.4 kW
Max Accel
~
Performance results for hybrid
and conventional powertrains
will be plotted for comparison by
the PNGV Toolkit. First, vehicle
definitions will be fed into the
SwRI-developed APACpM performance analysis program,
which calculates how each vehicle will perform under simulated
conditions_ The results will be
displayed in a fashion similar to
what is seen in this representational illustration.
1~(N~o~G~e~
ne~ra~to~r)~+-_-+_ _1
(No Power
support is provided by the Ford Motor
Company, General Motors Corporation,
Chrysler Corporation, National Renewable
Energy Laboratory, Idaho National Engineering Laboratory, Argonne National Laboratory, and Lawrence Livermore National
Laboratory.
Development of the APACETM program would not have been possible without the contributions of several SwRI staff
members, among them Joseph Baumgartner, John Bishop, David Buntin, Joseph
Grogan, Don Mowbray, Cherian Olikara,
Jayant Sarlashkar, and Dr. Robert Thring.
Series and Parallel Hybrid Vehicles
A series hybrid electric vehicle has one prime mover, an electric motor,
powered by a battery and/ or an engine turning an electric generator. The
motor converts electrical power to mechanical power for propulsion . Electric
power for the motor is available from an electrical energy storage device
and/ or a hybrid power unit (HPU) . The HPU consists of an internal combustion engine and a generator. The engine converts the heat energy potential of a hydrocarbon fuel into mechanical power. The mechanical power of
the engine is converted to electrical power in the generator, and the electrical
power of the generator is then used by the drive motor to move the vehicle.
The electric power created by the generator can also be used to recharge the
electrical energy storage device.
In a parallel hybrid electric vehicle, there are two prime movers - an
internal combustion engine and an electric motor. The engine converts the
heat energy potential of a hydrocarbon fuel into mechanical power. The sum
of the engine power and motor power is available at the wheels. A controller
determines the load share of each device depending on the total required
power, the operating efficiency, and the limitations of each device. Control
can be optimized for fuel economy, performance, emissions, and range.
In both series and parallel configurations, the vehicle is capable of capturing some of the energy normally lost to friction heat in the brakes during
deceleration. To do this, the electric motor used for propulsion can be
switched to operate as a generator. The electricity generating process provides a braking torque, and the electricity produced is stored in the batteries.
Technology Today · Spring/ Summer 1997
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