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`.A14
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`1887
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`1996 Future Car
`Challenge
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`SP-1234
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`GLOBAL MOBILITY OATABI\SE
`
`All SAE papers, standards, and selected
`books are abstracted and indexed in the
`Global Mobility Database.
`
`Published by:
`Society of Automotive Engineers, Inc.
`400 Commonwealth Drive
`Warrendale, PA 15096-0001
`USA
`Phone: ( 412) 776-4841
`Fax: (412) 776-5760
`February 1997
`
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`TL 240 .A141887
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`1998 Future Car Challenge
`
`Permission to photocopy for internal or personal use, or the internal or personal use of specific
`clients, is granted by SAE for libraries and other users registered with the Copyright Clearance
`Center (CCC), provided that the base fee of $7.00 per article is paid directly to CCC, 222 Rosewood
`Drive, Danvers, MA 01923. Special requests should be addressed to the SAE Publications Group.
`1-56091-946-9/97$7.00.
`
`Any part of this publication authored solely by one
`or more U.S. Government employees in the course
`of their employment is considered to be in the
`public domain, and is not subject to this copyright.
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`No part of this publication may be reproduced in any form, in an electronic retrieval system or
`otherwise, without the prior written permission of the publisher.
`
`ISBN 1-56091-946-9
`SAE/SP-97 /1234
`Library of Congress Catalog Card Number: 96-71843
`Copyright 1997 Society of Automotive Engineers, Inc.
`
`Positions and opinions advanced in this pa(cid:173)
`per are those of the author(s) and not neces(cid:173)
`sarily those of SAE. The author is solely
`responsible for the content of the paper. A
`process is available by which discussions will
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`this paper in full or in part, contact the SAE
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`,.t'.•
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`Persons wishing to submit papers to be con(cid:173)
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`
`Printed in USA
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`PREFACE
`
`The papers in this Special Publication were originally written to fulfill competition requirements
`of the 1996 FutureCar Challenge. These papers document the design, construction, performance,
`and planned improvements of 12 high-efficiency vehicle designs, which represent the results of
`the first of two years of this competition. A paper describing the competition's individual events,
`results, and successful designs has also been included.
`
`The 1996 FutureCar Challenge was held at Ford Motor Company's Dearborn Proving Grounds
`and at the Environmental Protection Agency's National Fuels and Emissions Laboratory in Ann
`Arbor, Michigan during June of 1996. The 1996 FutureCar Challenge was jointly sponsored by
`the U.S. Department of Energy and the U.S. Council for Automotive Research. The mission of
`the Challenge was to develop and demonstrate advanced fuel-efficient vehicles that parallel the
`technology development path of the Partnership for a New Generation of Vehicles (PNGV)
`program. The PNGV development path culminates in a mid-size car having up to three times the
`fuel efficiency while maintaining the performance, safety, and affordability oftoday's production
`vehicles. At the same time as contributing to achieving the objectives of the Partnership, the
`FutureCar Challenge was to help improve engineering education and foster practical learning
`through the development of solutions to real-world engineering problems.
`
`The FutureCar Challenge is a goal-oriented competition. With the exception of specific
`performance and safety standards, the teams were left to solve the problems of producing a
`highly efficient vehicle themselves. This resulted in a wide variety of technologies with the
`potential for solving some of the technical problems associated with radically increasing the fuel
`efficiency oftoday's vehicles. While most of the teams chose to convert their donated Luminas,
`Intrepids, and Tauruses to hybrid electric vehicles, some chose other directions. Some vehicles
`were fueled with alternative fuels, while some used reformulated gasoline or low-sulfur diesel
`fuel.
`
`The dedication of the students and faculty in constructing these highly efficient vehicle
`prototypes cannot be fully conveyed within the scope of these papers. On behalf of all of the
`participants and organizers of the FutureCar Challenge, we extend many thanks to the
`participants and to those companies without whose support, whether through financial
`contributions or in-kind, the 1996 FutureCar Challenge could not have been brought to such a
`successful culmination.
`
`C. Scott Sluder
`Robert P. Larsen
`Center for Transportation Research
`Argonne National Laboratory
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`TABLE OF CONTENTS
`
`Evaluation of High-Energy-Efficiency Powertrain Approaches:
`The 1996 Future Car Challenge ........................................................................................ 1
`
`1996 Future Car Challenge
`
`Concordia University ................................................................................. 9
`
`Lawrence Technological University ....................................................... 23
`
`Michigan Technological University ........................................................ 31
`
`The Ohio State University ........................................................................ 39
`
`University of California, Davis ................................................................ 53
`
`University of Maryland ............................................................................. 65
`
`University of Michigan ............................................................................. 77
`
`University of Wisconsin- Madison ......................................................... 87
`
`Virginia Polytechnic Institute and State University ............................ 101
`
`West Virginia University ........................................................................ 113
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`Design and Development of Hyades, a Parallel Hybrid
`Electric Vehicle for the 1996 FutureCar Challenge
`The Lawrence Technological University FutureCar Team including:
`James Swan, Ivan Menjak
`
`Advisors: Prof. Nicholas Brancik, Dr. Gregory Davis,
`Dr. Richard Johnston, Prof. Charles Schwartz
`
`Lawrence Technological Univ.
`
`is consumed. While the State of Charge (S.O.C.) of the energy
`storage system may be rising or falling instantaneously during
`this type of operation, not enough on-board charging occurs
`during the driving to prevent the S.O.C. from progressively
`depleting when measured over a sufficiently long series of
`repeated driving cycles. As a result, a hybrid vehicle that is
`charge-depleting on a given driving schedule can be treated as
`operating on both 'fuels' (off-board charged) electricity and a
`consumable fuel simultaneously.
`
`INTRODUCTION
`The challenge faced by the twelve universities in the
`FutureCar Challenge was to modify an existing production
`vehicle, without changing the structure of the vehicle, to achieve
`a fuel economy of 34 km per liter and a range of 400 kilometers.
`Space for five passengers and 100 liters of luggage storage
`space was to be provided. At every design stage, effort was
`made to reduce the weight of each component through the use of
`lightweight, high strength materials. Efficiency of each vehicle
`component was considered so that overall system efficiency is
`improved. Improvements in the vehicle's aerodynamics were
`made through the addition of prismatic mirrors, wheelskirts and
`an aerodynamic foil. Through the use of sound engineering
`design, the team feels that the combination of these components
`and their use in a parallel hybrid system offer the most potential
`for meeting the PNGV goals in the near term. Computer studies
`led the team to select the parallel hybrid as the most feasible
`short term option at the lowest cost, using existing engines,
`transmissions, batteries, motors, and electronic components.
`
`ABSTRACT
`Lawrence Technological University is one of twelve
`universities selected to compete in the 1996/1997 FutureCar
`Challenge. The FutureCar Challenge is the premiere, inter(cid:173)
`collegiate engineering design competition to date and is
`sponsored by the U.S. Department of Energy (DOE) and the
`United States Council for Automotive Research (USCAR).
`Twelve competing universities each received either a 1996
`Chevrolet Lumina, a 1995 Dodge Intrepid, or a 1996 Ford
`Taurus. The vehicle was modified to meet the goals of the
`Partnership for a New Generation of Vehicles (PNGV)
`program, to develop enabling technologies leading to the
`production of mid-sized vehicles achieving three times the
`current average fuel economy while maintaining the
`performance, utility, and affordability oftoday's sedans.
`Lawrence Tech will try to meet these goals by implementing a
`parallel diesel-electric hybrid powertrain in a 1996 Ford Taurus.
`
`HEY DEFINED
`As stated in the 1996 FutureCar Challenge Rules and
`Regulations, a Hybrid Electric Vehicle is defined as a vehicle
`that can draw propulsion power from both of the following
`sources of energy: ( 1) consumable fuel and (2) an energy
`storage system (e.g., batteries) that is capable of being charged
`by an on-board generator or an off-board source. The systems
`may be combined in any configuration (e.g., series or parallel).
`An HEY is considered to be charge depleting (SAE Draft
`J 1711) if during vehicle operation over a given driving schedule,
`electrical energy originally supplied from an off-board source is
`depleted during the same time that the on-board consumable fuel
`
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`POWER TRAIN
`The team modified its 1996 Ford Taurus, to create a
`charge depleting, parallel Hybrid Electric Vehicle (HEY) with
`four modes of operation: Normal (Parallel HEY), Motor (Zero
`Emission Vehicle, ZEV), diesel Engine only, and an automatic
`Recharge mode. As shown in Figure 1, the parallel powertrain
`couples a small67 KW turbocharged direct injection diesel
`engine via an aluminum bridge assembly to a 32 KW phase(cid:173)
`advanced brushless DC electric traction motor. The
`combination provides tractive energy to the front wheels via an
`automatic transmission. Despite the complexity of the parallel
`system, it offers greater reliability than a series system due to the
`availability of a limp home mode using either the engine or the
`motor. Series systems generally require a heavier, higher
`powered motor, a separate generator, a smaller internal
`combustion engine, and a battery pack. Energy conversion
`losses in the series system impair its ability to achieve as high a
`fuel economy as the parallel system.
`The overriding goals in the design of the powertrain
`were to maximize energy efficiency and to minimize emissions
`while providing acceptable driveability characteristics. The
`challenge was to fmd the level of motor assist during typical
`driving situations which allows the engine to operate at or near
`peak efficiency and still maintain acceptable performance.
`Since this is a charge depleting HEY, the overall electrical
`efficiency must account for electric utility power production
`losses. The average efficiency of the offboard electric power
`production required to provide charging is estimated to be
`32.1% The nominal efficiency of the electric drivetrain is 80%;
`therefore the combined electric efficiency is 25%. The 38%
`efficiency of the diesel engine can then be can be compared to
`the 25% efficiency of the traction motor system. This
`comparison on the use of energy led to the decision to power the
`vehicle with only the diesel engine at highway speeds. At
`highway speeds the efficiency of the diesel is greater than that of
`the electric traction system and batteries.
`
`Energy Consumption
`To determine the best possible control strategy,
`computer programs were developed to analyze both the city and
`highway cycles of the Federal Test Procedure {FTP). The
`analysis focused on instantaneous energy used by the vehicle
`power plant. Vehicle speed and acceleration were tabulated in
`one second intervals. These two knowns, coupled with vehicle
`weight and drag, were used to calculate the tractive force,
`revolutions per minute at the wheels and energy consumption in
`kwh per km. Additional analyses focused on maximizing the
`overall drivetrain efficiency by experimenting with various
`operating scenarios. For example, during the city cycle, the
`vehicle is at rest approximately 420 seconds out of 1878
`seconds. The decision to shut the diesel engine down during idle
`periods resulted in a reduction of fuel consumption by about
`20%.
`
`Computer simulations predicted the amount of
`electrical assist necessary to provide acceptable performance
`during the FTP City and Highway Cycles. The power assist
`from the electric traction motor was defmed as the percent of
`total power needed to accelerate the car during the driving cycle.
`The amount of electrical assistance is continuously modulated to
`obtain the best possible engine efficiency based on the power
`output, engine revolutions per minute, and accelerator pedal
`
`Figure 1: Hyades Powertrain Layout (plan view)
`
`position. A computer simulation indicated that on average,
`15%-20% electrical assist during the FTP City Cycle, 5%-7%
`electrical assist during the FTP Highway Cycle, no electrical
`assist at idle, and no electrical assist above 70 kph would yield
`the best efficiency and driveability.
`By combining the efficiencies of individual powertrain
`components, the efficiencies of different driving modes were
`determined. This was used to fmd the optimal transmission
`ratio. The most energy efficient operation is at steady state
`speed above 70 kph with the diesel engine operating near peak
`efficiency.
`
`Vehicle Control Strategy
`Control over the vehicle powertrain is accomplished
`using a high-noise-immunity Programmable Logic Controller
`(PLC). The PLC controls the 'on again/off again' operating
`system for the diesel engine; if the accelerator pedal has been
`released for more than 1.5 seconds the diesel engine is shut off
`and declutched automatically. The engine is then restarted
`automatically by the PLC during the next acceleration or, if the
`vehicle stops, when the vehicle accelerates from a stop using the
`electric traction motor alone. This strategy improves FTP fuel
`economy by 10% and reduces emissions by nearly 22%.
`Continuously starting and stopping the diesel engine will not
`significantly effect emissions because high catalytic convertor
`temperatures are maintained longer when the large quantities of
`air, normally encountered in a diesel engine idle operation, are
`no longer being pumped through the engine and catalyst.
`The Normal Mode of operation for the vehicle is
`parallel HEY. The diesel engine and electric motor are ·
`simultaneously able to provide motive power. The maximum
`combined peak power is 96 kw @ 4000 rpm and peak torque of
`663 Nm @ 2000 rpm. Computer projections predict that the
`vehicle will travel a 1/5 of a kilometer in under 14 seconds, a
`diesel fuel consumption of 17 Liters and 16 KWH of electrical
`energy extrapolated over 400 km based on the combined FTP
`city and highway cycle (Reference 1 ). The advantages of this
`mode include the maximum power provided by the two sources,
`a single electric motor controller, and some weight and cost
`savings compared to other concepts. The diesel engine operates
`at near peak efficiency while additional loads are handled by the
`traction motor.
`The Motor Mode of operation for the vehicle is pure
`
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`electric. To meet zero emission requirements the diesel engine
`is declutched from the transaxle and shut down. All power
`to the wheels is now derived from the traction motor. The
`traction motor system features include a high efficency, liquid
`cooled design, 18 pole permanent magnet neodymium iron
`boron magnets, 4 quadrant operation, and a microprocessor
`based controller with closed loop torque control. This mode is
`selected when the driver elects to eliminate the consumption of
`diesel fuel and thereby, reduce on-board vehicle emissions. The
`advantages of using the traction motor as the sole power source
`are smoothness, reduced noise and no emissions output. The
`disadvantages of this mode are modest acceleration due to the
`weight of the vehicle in relation to the power of the traction
`motor and a limited range of approximately II 0 km.
`In Engine Mode of operation for the vehicle the diesel
`engine is the only source of motive power. This mode will only
`be used in an emergency situation as in the event of an electrical
`system failure or low State Of Charge (S.O.C.) in the main
`battery pack that could not be remedied by emergency on-board
`recharging.
`Regeneration is the ability to use the kinetic energy of
`the vehicle to capture energy in the form of electricity which
`would normally be lost as heat by friction brakes. The electrical
`traction system is used as an alternator for the main battery pack.
`Regeneration is invoked whenever the accelerator pedal is
`released for more than 1.5 seconds (i.e. coastdown) or when the
`brake pedal is depressed. Normal engine braking during
`coastdown in a conventional vehicle is simulated by regeneration
`during deceleration. Upon application of the brake pedal,
`regeneration content approaches I 00 Amperes to recover a high
`percentage of the kinetic energy; in many instances use of the
`service brakes will not be required to stop the vehicle. Only
`about 12-20% of the available energy will be recovered. To
`maximize the amount of energy recovered the PLC sends a
`signal to the transmission to downshift. By downshifting the
`transmission, higher motor speeds are maintained. Recharging
`the batteries by regeneration thereby extends the range of the
`pack while minimizing the weight, size, and cost of the pack.
`Finally, the PLC utilizes regenerative braking during all modes
`except Engine Mode.
`If the main battery pack is at a dangerously low S.O.C.,
`the PLC will activate the Recharge Mode, an emergency charge
`algorithm. The driver is informed of the condition through
`audible/visual warning signals. At what would normally be an
`idle period the transmission is automatically shifted to neutral
`and the diesel engine speed is raised to approximately 2000 rpm
`(which is in the range of peak thermal efficiency) to continue
`recharging at a high rate. When the accelerator pedal is
`depressed, the PLC disengages the clutch, returns the engine to
`800 rpm (idle speed), and electronically shifts the transmission
`back into drive.
`
`Transmission Modifications
`The stock Taurus AX4S automatic transmission has
`been extensively modified, including the elimination of the
`torque convertor. An opening in the transmission housing was
`provided to allow the motor drive belt to connect to the input
`shaft of the transmission. The diesel engine is coupled to the
`transmission with a single dry plate clutch that is engaged and
`disengaged with a hydraulic servo mechanism automatically
`controlled by the PLC. To reduce the amount of flow required
`
`25
`
`through the transmission, high performance seals have been
`incorporated to reduce internal leakage. The Transmission
`Control Module (TCM) controls a variable force solenoid (VFS)
`which is an input to the main regulator valve. This valve
`controls the pump bore ring which has been modified to act as a
`pressure regulator. The hydraulic and electric circuitry has been
`modified to allow the PLC to select neutral without driver
`intervention. When the throttle is opened the solenoid will be
`energized to re-engage the forward clutch. The shift points were
`determined by selecting the gear which has the highest torque
`output at any point in time while minimizing absolute fuel
`consumption. This system improves overall drivetrain
`efficiency while maintaining the ease of operation of a stock
`automatic transmission.
`The Final Drive Ratio (FDR) was changed to achieve
`maximum powertrain efficiency. Final drive ratios below 3.37
`were excluded because of the noise, vibration, and harshness
`(NVH) expected when the transmission is coupled with the
`diesel engine. A ratio of 3 .3 7 was selected for use which
`represents a very modest decrease in acceleration compared to
`the stock FDR of3.77. With the new FDR a 5% increase in fuel
`economy is obtained. The vehicle is capable of climbing a 33
`percent grade even though the electric traction motor is the
`initial motive power source until the vehicle reaches a speed of
`12 kph.
`
`PROGRAMMABLE LOGIC CONTROLLER
`The PLC, with inputs from the stock Enhanced Electronic
`Engine Control Module (EEEC V) and the Electronic Diesel
`Control module (EDC), is responsible for real-time processing
`of all input comands and updating system outputs. The system
`power requirement is 24 VDC, supplied from the traction
`battery pack via DC-DC converters. All input, output cards are
`grounded to the vehicle common. The PLC hardware is
`described further in the appendix.
`
`Operator Interface
`The Operator Interface unit is a graphic, user-interface panel,
`inputs to which consist of a numeric keypad, system function
`keys, and user-defmed function keys. The panel output is a
`back-lit liquid crystal display. All screens are interlaced through
`manipulation of global function control (Fl is return to previous
`screen). The Interface Panel has memory storage independent
`from the PLC. File execution allows user input to the PLC via a
`serial data stream. The unit is powered by the same 24 VDC
`supply as the PLC. Vehicle drivers will be able to select the
`mode of vehicle operation as well as monitor vital vehicle signs
`through the operator interface.
`
`Programming Strategy
`All Hyades' control programs are written in ladder logic because
`of the graphic user interface on-line programming features. The
`unique design of the CPU architecture dictates the use of block
`programming. This programming style allows the programmer
`to create a small main line program to run a continual
`housekeeping and update routine. All other function 'blocks' are
`called into the main line program as certain criteria are met.
`The ladder program consists of a main routine program and
`eight subroutines. The main program is a series of calls to the
`function subroutines. A conditional return to the mainline
`program is contained in each function subroutine which was
`
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`Operating Map Characteristics
`
`5.00
`
`4.50
`
`4.00
`
`3.00
`
`2.50
`
`2.00
`
`1.50
`
`1.00
`
`0.50
`
`,-....
`Cll
`..::::
`0 >
`Cll ·-Cll
`'-"
`......
`Cll <
`'""'
`0
`......
`0
`::E
`
`Accelerator Position (volts)
`
`5
`
`Vehicle Speed (mph)
`
`Figure 2: Operating map indicating loads of motor assist (0-5 volts) as a function of accelerator position and vehicle speed.
`
`created for each mode of operation such as normal drive,
`regeneration braking, initial start-up, etc.
`
`Operating Map
`Although the diesel engine is capable of operating at
`42% indicated peak thermal efficiency at maximum torque of
`663 Nm @ 1900 rpm, the engine rarely operates in this range
`during normal driving. The most critical element ofthe control
`strategy has been the development of the 'operating map'
`designed to modulate motor assist to maintain engine operation
`at highest possible efficiency at all times. This optimum range
`occurs at approximately 2000 rpm at a load near 30 kw. At this
`point the bsfc is at a low 0.111 kg/kwh. The operating map
`dictates the percent of power assist supplied by the motor and is
`dependent on accelerator pedal position and vehicle speed.
`These two elements provide an indication of road load power for
`a diesel engine. Accelerator position is measured by the
`accelerator position sensor that is mounted in the engine
`compartment. Utilizing these two inputs, the PLC will
`recognize a high load situation such as passing or hill climbing
`and will call for full motor assist by sending a high voltage
`signal to the motor controller. Under low load conditions such
`as highway cruising, the accelerator voltage signal is low and the
`vehicle speed is high. In this scenario, the PLC sends a zero
`
`voltage to the motor controller indicating no assistance is
`required. At speeds above 70 kph on level roads, the motor will
`only provide assist if more torque is required, such as in a
`passing situation. The operating map, shown in Figure 2, has
`been defined as a three dimensional surface plot with the vehicle
`speed on the x-axis, the accelerator position on they-axis, and
`the output voltage to the motor controller on the z-axis.
`
`CHASSIS
`Modifications to the stock chassis were made to
`provide packaging space for batteries, electrical components,
`fuel storage, and I 00 liters ofluggage storage. In addition, the
`suspension, brakes, and power steering were modified.
`
`Brake System
`The entire stock braking system was replaced with a
`four wheel aluminum disc brake system. An electric vacuum
`pump provides the vacuum necessary to operate the power
`assisted brakes. This system reduces the weight of the
`production braking system by 18 kg without sacrificing stopping
`ability.
`
`Fuel System
`The fuel system was easily converted from a gasoline
`
`26
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`
`system to diesel. The stock fuel tank was modified in order to
`use the existing filler neck, fuel lines, fuel pump, fuel level
`sending unit and mounting position. The capacity of the tank is
`now approximately 34 liters. No evaporative emission system is
`required with diesel fuel.
`
`Power Steering
`The stock power steering system was dependent on
`continuous engine operation. The vehicle control strategy
`allows for several modes of operation that do not always include
`the engine. There was an additional desire to reduce the amount
`of energy the power steering system consumed. The preliminary
`engineering targets were II Nm of steering wheel torque and
`1.1 kw for a dry park. To meet these targets, an Electrically
`Powered Hydraulic Steering System (EPHS) replaced the engine
`driven pump and uses the production rack. The gravity fed
`pump provides pressure to the rack and returns fluid to the
`reservoir, passing through a stock power steering fluid filter.
`The total weight of the system is 19 kg, one kg more than the
`stock system. System efficiency is increased by 59%, requiring
`only 0.85 kw for a dry park.
`
`Battery Containment
`Electrical energy is stored in 13 Nickel Metal Hydride
`battery modules. Each module has a nominal voltage of 13.2
`VDC and the capacity to store 1.25 KWH. The Battery
`Containment System was designed to safely store and thermally
`manage the 13 NiMH batteries. The containment unit is divided
`into two parts (Figure 3 and 4), one in the trunk, and a smaller
`one in the console area. Separating the battery pack into two
`compartments provides better front to rear weight distribution as
`well as meeting the passenger and luggage space requirements.
`The weight distribution of Hyades, from front to rear is 56/44.
`The battery containment system was designed for high strength
`and minimum weight. Aluminum honeycomb sandwich
`material was used to construct the walls. The sections of wall
`were attached to each other via aluminum members that are
`adhesively bonded and mechanically joined to prevent failure
`due to de-lamination. The thermal management system is
`designed so that a module temperature will not exceed 40°C.
`Cooling fans provide 15 cfm to 20 cfm of airflow per module.
`These fans maintain negative battery compartment pressure to
`ensure that any leakage will flow into the battery compartment to
`be exhausted. Proper thermal management is achieved through
`controlled airflow between modules.
`
`Su&pension
`To compensate for the change in weight distribution
`and overall vehicle weight. Several different production air
`suspension system components were adapted for use on the
`Hyades. The advantages of the air suspension system over the
`stock suspension system are a two position ride height,
`improved handling characteristics, and an adjustable ride
`quality. The function of this semi-active ride control is to read
`the road surface every ten milliseconds (every 280 mm@ 95
`kph). Each damper force is automatically and independently
`adjusted between soft and hard to optimize ride quality. The
`road surface is read via height sensors at each comer of the
`vehicle. The necessity for higher damping forces is primarily
`driven by low frequency motion of the body with respect to the
`wheels. With no low frequency inputs, or the presence of high
`
`:- .;: u.:·
`
`il.v:'.}• .-cere:."!!
`~: •. :.::- ~~..~
`
`Figure 3: Front Battery Containment Box
`
`~ FLAiFICY. F~~ 121
`I
`1
`
`'--"··"'''··"']''
`. ... ,. .. " ,. ""
`1"'·1
`s...--s: 4L 1~r~t--~ -"'o
`'I 0'
`e:AcKm
`
`0
`
`, I
`J
`
`~ C'l ~ 0
`
`AL'.MI\t'~ ,:~t.:'fCYS
`SA\~(::.; vc:~l~~
`
`Figure 4: Rear Battery Containment Box
`
`frequency inputs, the control module will command the dampers
`to the soft setting to maximize comfort. Minor modifications to
`the chassis were necessary to adapt the system to the vehicle.
`The penalty in implementing the new system was an addition of
`6.5 kg of weight over the stock suspension. The air suspension
`system has an increased load carrying capacity as well as the
`capability ofload-leveling and will reduce the drag coefficient
`(Cd) of the vehicle at highway speeds by approximately 7% by
`lowering the ride height of the car by 60 mm (Reference 2). The
`computer controlled system will combine the traditional smooth
`ride of a luxury car with the sure-footed control more commonly
`found in sports sedans.
`
`BODY
`
`The initial engineering targets were to reduce the body
`weight of the vehicle by 113 kg. and improve aerodynamic drag
`by 10%.
`
`Prismatic Mirrors
`A prismatic mirror system was installed to reduce
`aerodynamic drag. The prismatic mirror design places most of
`the rear-view m,irror system inside of the passenger
`compartment and yet provides the same field of view as a
`conventional mirror. By replacing the conventional mirrors with
`prismatic mirrors the drag coefficient (CJ is reduced by
`approximately 0.0 13. The optics of the prismatic mirror consist
`of a Fresnel lens attached to a prism and a reflective surface in
`conjunction with an ocular prism. An adjuster fitted to the
`ocular prism allows for optimal viewing by the driver. Light
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`rays enter through the Fresnel lens, which bends the light. The
`refracted light rays go through the prism and are reflected from
`the mirror to the driver (See Figure 5). The prisms are used to
`avoid light diffraction that may cause a rainbow effect.
`Contributions to the loss of light in the prismatic mirror design
`include 20% for the geometric sloping face and 16% through the
`conventional mirror. This results in a typical light loss of
`approximately 35% which is less than conventional mirrors
`when the image is seen through tinted glass.
`
`Body Panels
`To further smooth the flow of air over the vehicle, rear
`wheel skirts have been fabricated. A new hood and the rear
`wheel skirts are fabricated of carbon fiber composite which has
`a weight comparable to that of aluminum. The stock front steel
`fenders were replaced with fenders fabricated of aluminum at
`about half the weight.
`
`Window Replacement
`To achieve a reduction in the weight of the windows,
`formable polycarbonate plastic was used to replace the tempered
`glass that was installed in the four doors and rear window of the
`vehicle. A total weight savings of 14 lbs. was achieved through
`the replacement of the glass windows.
`
`Aerodynamic Foil
`A small air foil was installed on the rear deck lid to
`reduce aerodynamic drag. References 3 and 4 provide graphs
`and ratio formulas that were used in the design of the
`Aerodynamic Foil. The optimum height of the Aero Foil had
`been experimentally determined to be a specific ratio of the
`wing height to the roof height. The reduction in the overall
`vehicle coefficient of drag was optimized to 0 .I 0 by utilizing the
`experimentally determined curves and setting the ratio of foil
`width to overall width to 0.45. The foil acts to reduce the drag
`coefficient by smoothing out the vortices created by airflow as it
`rakes down the vehicle's backlight and the deck surface.
`
`Seat Replacement
`The front and rear seats were replaced with seats
`constructed of6005-T6 (extruded aluminum tracks) and 606