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Optimizing the University of Wisconsin'sParallel Hybrid-Electric Aluminum Intensive

Vehicle

J. Bayer, M. Koplin, J. Butcher, K. Friedrich, T. Roebke, H. Wiegman, G. R. BowerUniversity of Wisconsin–Madison

Copyright © 1999 Society of Automotive Engineers, Inc.

ABSTRACT

The University of Wisconsin – Madison FutureCar Teamhas designed and built a lightweight, charge sustaining,parallel hybrid-electric vehicle for entry into the 1999FutureCar Challenge. The base vehicle is a 1994Mercury Sable Aluminum Intensive Vehicle (AIV),nicknamed the “Aluminum Cow,” weighing 1275 kg. Thevehicle utilizes a high efficiency, Ford 1.8 liter, turbo-charged, direct-injection compression ignition engine.The goal is to achieve a combined FTP cycle fueleconomy of 23.9 km/L (56 mpg) with California ULEVemissions levels while maintaining the fullpassenger/cargo room, appearance, and feel of a full-size car. Strategies to reduce the overall vehicle weightare discussed in detail. Dynamometer and experimentaltesting is used to verify performance gains.

INTRODUCTION

The FutureCar Challenge (FCC) is a student competitionthat has adopted the goals of the Partnership for a NewGeneration Vehicle (PNGV) program. Those goals areto build a mid-sized car that maintains current standardsof safety, performance, comfort and price, while at thesame time achieving 80 miles per gallon with CaliforniaULEV emission levels. Thirteen universities from NorthAmerica annually compete in the FCC which issponsored by the US Department of Energy and the USConsortium of Automotive Research (USCAR).

Table 1. UW FutureCar 1999 Performance Goals.

Parameter 1999 Goals Combined FTP Fuel Economy 23.9 km/L (56 mpg)

Emissions ULEVAcceleration: 0–100 kph <10 seconds

Range 970 km (600 mi)Vehicle Weight 1275 kg (2805 lbs)

The University of Wisconsin has designed a chargesustaining, parallel hybrid-electric vehicle for the 1999FutureCar challenge (Figure 1). After extensively testingour 1998 FFC vehicle [1] on a chassis dynamometer,areas for improving the vehicle were obvious andextensive changes have been made to the AluminumCow over the past year. The vehicle performance goalsfor this year are listed in Table 1. With a goal of 1275kg, a large emphasis was placed on weight reduction ofeach component in the vehicle.

12kW

Motor

FuelTank39L

8.0 A-hr286V Nom

Ni-CadBattery

50

Figure 1. The University of Wisconsin’s 1999 parallel-assist hybrid electric vehicle layout.

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VEHICLE ENERGY CONSUMPTION MODELING

The road power demand equation represents the energyconsumption of a vehicle over a period of time. Thisequation defines how power is used in a vehicle as ittravels down the road [2]. This equation is the basis forboth the vehicle simulation developed by Wisconsin andalso for all the components and modifications integratedinto the vehicle. The equation to calculate road powerdemand for a given driving condition is shown inEquations 1-6. (Symbol list at end of paper.)

Proad = Proll + Phill + Paero + Paccel + Paux (1)

Proll = m g V Crr cos θ (2)

Phill = m g V sin θ (3)

Paero = 0.5 ρ A V3 Cd (4)

Paccel = d Ekinetic / dt = m V dV / dt (5)

Paux = f(alternator, power steering, etc.) (6)

The road power demand Equation (1) identifies thevehicle design aspects that could be changed to improvethe overall energy efficiency. Using reported efficienciesfor vehicle components and modeling this equation for avehicle driving on the FTP 75 driving cycle, a fueleconomy modeling study was completed. The relativeimportance of reducing each of the equation parameterscan be seen in Figure 2. [3]

0 10 20 30 40 501.0

1.1

1.2

1.3 Mass Aero Tires Accessories

EP

A C

ombi

ned

Fue

l Eco

nom

y M

ag.

Parameter Reduction (%)

Figure 2. Fuel Economy gain vs. parameter reduction.

In order to increase the fuel efficiency of the vehicle, theroad power demand must be decreased. With vehiclemass affecting 3 of the 5 terms in Equation 1, it is clearlythe dominant factor in vehicle energy consumption (seeFigure 2). Therefore, the design focus was on weightreduction in an effort to take advantage of theindisputable efficiency gains that come with lightervehicles.

1998 FUTURECAR CHALLENGE RESULTS

As part of the 1998 FutureCar Challenge, each vehiclewas evaluated on the FTP 75 driving cycle at the EPAlaboratory in Ann Arbor, Michigan. The fuel economyresults are shown in Table 2. These fuel economynumbers were very encouraging because the hybridmode was not operating during the FTP-75dynamometer cycle (EPA City).

Table 2. 1998 FutureCar Challenge Fuel Economy.

Fuel Mileage Test 1998 Fuel Economy(RFG equivalent)

EPA City 34.7

EPA Highway 51.9

Chrysler’s Test Track 75.0

Emissions levels measured at FCC98 are presented inTable 3. In this case, the limiting emission was NMHC,and the emission bracket would be Federal Bracket 13.The engine used was a prototype from Europe and theEngine Gas Recirculation (EGR) system was notoperating. The EGR would drastically reduce the NOx

emissions while also increasing the engine’s thermalefficiency. (Appendix B)

Table 3. Emissions from 1998 FutureCar Challenge.

RegulatedEmissions

EmissionLevels

(g / mile)

FederalEmissionsBracket

NOx 1.836 15CO 1.468 35

NMHC 0.551 13PM10 0.125 21

Reviewing the emission data of Table 3, one would notexpect a compression ignition engine to have high non-methane-hydrocarbon (NMHC) emissions. Thisprototype engine had not yet been optimized. Theengineers responsible for the development of this engineindicated that the combustion bowl and fuel injectorshave since been modified for their production engine.The mixing of the fuel and air in the combustion chamberwas inefficient and thus created incomplete combustion.Replacing the prototype engine with a production versionwill decrease particulate, NMHC and CO emissions.

DYNAMOMETER RESULTS

In the fall of 1998, the Aluminum Cow was tested on achassis dynamometer on two different occasions. Bothtests were completed with a fully functioning hybridvehicle. City fuel economy results are listed in Table 4.

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TABLE 4. Dynamometer FTP 75 City Fuel EconomyResults using the 1998 Hybrid Design.

Vehicle Testing Mode(94 Sable-AIV)

FTP-75 Fuel Economy(RFG Equivalent)

No Hybrid Mode - FCC 98(Electric Motor Removed)

34.7

No Hybrid Mode - Fall 98(Unique Motor Spinning)

29.0

Hybrid Mode - Fall 98 35.8Load Leveling - Fall 98 35.6

The FTP 75 city cycle was used to compare theeffectiveness of the hybrid drivetrain as the highwaycycle rarely uses the hybrid mode. The inclusion of anuncontrolled permanent magnet electric motor into thedrivetrain of the Aluminum Cow produced a 16.4%decrease in fuel economy. After experimenting with twodifferent control strategies, the best hybridized strategyhad a 3.2% fuel economy advantage over the samevehicle with no electric motor.

0

500

1000

1500

2000

2500

79675749444239363228241916129641

Vehicle Speed (MPH)

Lo

ss (

W)

Measured DataUQM Prediction

Figure 3. Drag force generated by the Unique Mobilitypermanent magnet electric motor.

The permanent magnet free-spinning drag losses (seeFigure 3) add to the drivetrain’s resistance and isanalogous to a 20% increase in the dynamometer’saero drag setting. The higher efficiency of thepermanent magnet motor offsets its drag during non-utilized periods during the city cycle, but the drag grosslyexceeds the benefits during the FTP 75 highway cyclecausing similar reductions in fuel economy.

The dynamometer testing results from the fall of 1998were closely scrutinized and were the dominant factor indeciding to modify the hybrid drivetrain for this year. Thepermanent magnet motor was replaced with acomparable induction motor - following is the reasoningand documentation of the 1999 Aluminum Cow.

COMPONENT SELECTION

Once the vehicle drag requirements are minimized, andpast performance data is reviewed, drivetraincomponents must be appropriately selected to processthe power flow in the hybrid as efficiently as possible.The selected drivetrain components could potentiallyachieve an overall fuel efficiency in excess of our 23.9km/L (56 mpg) [4] fuel economy goal.

Because components that exactly match theoreticalspecifications are rarely obtainable, componentavailability had to be considered while the teamsearched for a desirable combination of engine,transmission, and electric drive system.

When searching for components, Americanmanufacturers were considered first. This was done toboth minimize component lead times and also toincrease the feasibility of manufacturing the FutureCarlocally.

A packaging diagram of the Wisconsin FutureCar isshown in Figure 4. Throughout the selection process,appropriately sized components were chosen tomaximize energy efficiency and minimize weight.

ModifiedFuelTank

HighVoltageBatteryPack

Ford TDIEngine

SolectriaElectricMotor

Ford FWDTransmission

Figure 4. UW vehicle packaging diagram.

Engine - Depending on the size of the electric drivetrain,the engine in a power-assist parallel hybrid vehicleshould have a power capability in the range of 50-80 kW(70-110 hp). This is based on the power required toaccelerate the vehicle from 0-100 kph (0-60 mph) in 12seconds and sustained hill climbing requirements. A 5-passenger vehicle that weighs 1500 kg (3300 lbs)requires 75 kW (100 hp) to accomplish this performance,while it requires 35 kW (50 hp) to maintain 100 kph on a6% grade [3].

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1000 1500 2000 2500 3000 3500 4000 45000

10

20

30

40

50

60

70

Engine Speed (rpm)

Pow

er (

kW)

200

210

220

230

240

250

260

270

280

290

Figure 5. Characteristics for the Ford 1.8L TDIcompression ignition engine - LYNX 90PS [5].

A search of economically viable engines revealed twoengine alternatives – spark-ignited (SI) or compressionignited (CI). A recent study by Thomas et al. [4],concluded that natural gas hybrid and diesel hybridvehicles produce the lowest overall greenhouse (CO2)gas emissions – even lower than hydrogen fuel cellvehicles. It also concluded that among these twopowertrains, a diesel hybrid was 14% more fuel efficientthan a natural gas hybrid. The diesel hybrid is the mostfuel efficient piston powered option considered by thisstudy. For the aforementioned reasons, the Wisconsinteam chose a direct-injection compression ignition (CIDI)engine for its 1999 FutureCar. After a lengthy search,Ford Motor Company agreed to donate a 66 kW (88 hp),1.8 liter, 4-cylinder, turbo-charged, direct-injectioncompression ignition engine (see Figure 5 and Table 5)with a maximum thermal efficiency of 42%.

TABLE 5. Engine Build Details for the Ford 1.8L TurboCIDI LYNX 90 PS Engine [5].

Engine Component SpecificationRated Power 66 kW at 4000 rpm

Maximum Torque 200 Nm @ 2000 rpmSpeed Range 800 - 4800 rpm

Bore 82.5 mmStroke 82.0 mm

Displacement 1753 ccCompression Ratio 19.34 : 1

Swirl Ratio 2.4Fuel Injection Pump Bosch VP30EGR valve diameter 16 mm

Turbocharger Garrett T15Control System EEC V

After-Treatment - Historically, exhaust after-treatmenthas been developed for SI engines. These enginesused closed-loop controls to keep the air/fuel ratiostoichiometric, where the 3-way catalyst operates

effectively. If the engine were operated lean, the NOx

conversion efficiency would drop drastically while richcombustion would cause excessive CO and HCemissions. In the case of CI engines, the engine isalways operated lean, and 3-way catalyst technology isnot applicable.

The LYNX 90PS engine is equipped with a platinumloaded catalyst. The catalyst is mainly designed toreduce hydrocarbon (HC) and carbon monoxide (CO)emissions but it also slightly reduces particulate andnitric oxide (NO) emissions as shown in Figure 6. Fromthe four different catalyst tested, Ford chose aproduction catalyst loading of 40 g / ft3.

10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

100

Production Catalyst Loading

HydrocarbonsCarbon Monoxide

Particulates

Nitric Oxide

Con

vers

ion

Effi

cien

cy (

%)

Catalyst Loading (g / ft3)

Figure 6. Platinum loading levels versus conversionefficiency for exhaust constituents for the LYNX 90PScatalyst.

In addition to the production catalyst, Deguzzi, thesupplier for the LYNX 90PS catalyst, will be furnishing alean NO catalyst with an estimated efficiency of 40% inaddition to a NO trap. The trap actual cause the NO toadhere to the surface of the catalyst. Once the catalystsurface is loaded with NO, a small injection of fuel intothe exhaust stream (2-3 % fuel economy penalty)causes a slightly fuel rich exhaust gas stream. In theabsence of oxygen, the NO converts to diatomic nitrogenand oxygen and the NO trap is ‘regenerated’.Regeneration is usually done every 30-60 secondsduring normal operation in order to keep the catalystefficiency above 75%.

Transmission - A transmission that would couple theengine to the road efficiently had to be selected as well.To perform this coupling, a Ford MTX-75, manual front-wheel drive transmission manufactured for use with aLYNX 90 PS engine was selected. A manualtransmission was selected for its low throughput losses(> 90% efficiency). Its gear ratios are shown in Table 6.These gear ratios were designed for use in 1300 kgvehicle similar to the Aluminum Cow.

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Figure 7. The modified transmission case for the FordMTX-75 FWD transmission.

Table 6. Gear ratios for Ford MTX-75 transmission.

Gear Ratio1st 3.6662nd 2.0473rd 1.2584th 0.8645th 0.674

Differential 4.060

A custom designed gearbox was develop to couple theelectric motor to the engine/road. This wasaccomplished by modifying the secondary transmissionshaft (see Figure 7), which then makes the transmissiona durable and efficient torque splitter. This gearbox is asecond generation design. The new gear box wasfabricated on a Milltronics fix-bed CNC mill from 6061-T6aluminum billet. The gear box, seen in Figure 8, wasoriginally drawn in AutoCAD which supplied thegeometric traces to the CNC controller. Subsequently,the gearbox was solid modeled in ProE so that it couldbe analyzed using ANSYS (see Figure 9). Beforemanufacturing the gear box, extensive stress analysiswere performed to ensure design’s reliability.

Figure 8. Computer numerically controlled machinedgearbox.

Figure 9. Stress plot from ANSYS analysis of hybridgearbox.

The transmission placement in the Wisconsin FutureCaris displayed in the packaging diagram (Figure 4). Thegear selector and clutch are typical of those found inconventional vehicles. In addition the complete hybriddrivetrain (engine, transmission, and electric motor) wasdesigned to be pre-assembled on the engine cradle sub-frame and subsequently placed into the vehicle as a unit.

Fuel – The 1999 Wisconsin FutureCar has adoptedFischer-Troups fuel for compression ignition engines.Fischer-Troups is considered an alternate fuel as it isderived from natural gas or coal. Similar to syntheticoils, Fischer-Troups contains no impurities. Thisproduces a predominantly straight-chained, clear, cleanfuel. Typically it has a cetane number of 70 whilecontaining no sulfur or aromatics. The elimination ofsulfur will extend catalyst life while reducing particulateemissions.

ELECTRIC DRIVE SYSTEM

Motor/Inverter - The 1999 UW FutureCar uses a 12 kWinduction electric motor with a peak power of 30 kW(battery limited). The motor can supply a maximumtorque of 100 N-m and a maximum speed of 12,000 rpm.The motor weighs 32 Kg, and delivers 94% peakefficiency. The motor is part of Solectria's prepackagedelectric drive system which includes a microprocessorvector control unit, the UMOC 340. The 98% efficientcontrol unit is rated for input voltages ranging from 200-350 V and has a 210 Arms limit.

The AC induction motor and controller were selected inplace of the permanent magnet motor and controllerused in last year for numerous reasons. As discussedearlier, the permanent magnet motor adds unnecessarydrag to the driveline when not in use and therefore is notdesirable in a parallel-assist hybrid vehicle where electricmotor utilization is low during steady state driving.These drag losses are converted to heat and require anadditional radiator/pump/coolant system in the vehicle.Switching to a lower power AC induction motor the dragloss were eliminated while realizing a 32 kg weightsavings.

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Figure 10. System efficiency map for the SolectriaAcgtx20 motor using a UMOC 340 controller operatingfrom 270Vdc.

The motor is coupled to the secondary transmissionshaft of the 2WD transmission via a custom gear box.The gear box supports the electric motor and includes a2.30:1 gear ratio (9.34 overall to axle) to decrease themotor speed. This allows the motor to spin in itsoptimum range of 3000-6000 rpm (37-75kph) (seeFigure 10).

Battery – The 1998 energy storage system used in theUW-Madison FutureCar was based on high powerdensity Nickel Cadmium C-cells. The technology wascapable of delivering 400W/kg (10 sec, 20% voltagevariation), thus providing a lightweight system which wasnear optimal for the charge-sustaining, parallel assisthybrid design.

To improve upon the design, and to move to a moreoptimal overall vehicle efficiency, the energy storagesystem was re-evaluated for the 1999 competition.Three battery technologies were tested and compared.PNGV style power pulse testing was applied in order toobjectively evaluate the relative electricalperformances.[9,10] The three chemistries tested were;Thin-Metal Film Lead Acid (TMF Pb), Nickel Cadmium(NiCad), and Nickel Metal Hydride (NiMH). A overviewof the technologies are compared in Table 7.

Table 7. Battery performance improvement summary

Feature TMF Pb NiCad NiMHDisadvntg. cost,

sulfationEnvirnmnt.

ImpactOnly

moderatepowerdens.

Advantage Highestpower dens.

Proventechnology

PromisingTechnolog

y

The final battery selection was based upon probability ofsuccess, low cost, and electrical performance. Today,

Ni-Cad batteries are utilized in the hand-held batterypower tool industry. Huge gains in NiCad power densityand reliability have been accomplished through thedevelopments of companies such as Milwaukee Tooland Sanyo Inc.

The battery system was adjusted slightly in order toobtain high power capability and processing efficiency. Abattery performance improvement summary for the 1999vehicle is shown in Table 8.

Table 8. NiCad battery performance improvement.

Battery Characteristics 1998 1999 Total Cell Mass [kg] 49 53 Bat. Box Mass [kg] 6 6

Voltage [V] 272 286 Capacity [A-h] 7.5 8.0 Energy [kW-h] 2.0 2.3 Power [kW] # +/- 22 +/- 24

Cycle Efficiency [-] * 0.87 0.89# - 10 seconds, +/- 20% voltage variation* - at +/- 4kW rate, 30 seconds, 50% SOC

The PNGV style power pulse testing revealed themaximum power capability and efficiency characteristicof the battery. Sample testing was instrumental inimproving the battery system design for the 1999 effort.Figure 11. shows the 30 second capabilities of the 1999battery system. The 10 second power capability is higherdue to a lack of diffusion effect during the short durationpulses, hence it was not used as a realistic test of thebatteries. The efficiency characteristic as shown inFigure 11 revealed a relatively flat and broad operatingrange vs. SOC, showing the flexibility of the high powerdensity cell design.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

2

4

6

Power Capability and Efficiency vs. SOC

Power[pu]

30 sec discharge and charge

Pdis = solid Pchrg = dash

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.8

0.85

0.9

0.95

1

Eff.[pu]

SOC [pu]

30 sec, Pow = 2 pu

Eff.dis = solid Eff.chrg = dash Eff.cycle = da-dot

Figure 11. Per-unit power and efficiency vs. SOC for theNiCad battery system under 30 second pulse testing.(Pbase=2.3kW, Efficiency rated at 2 per unit power)

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Computer – The Wisconsin FutureCar team has beensuccessful in past competitions partly due to theflexibility of the control system. The control strategy isrun on a custom-built computer system consisting of aComputer Dynamics single-board pentium machine witha touch-screen user interface. The computer's MicroIndustries data acquisition boards are connected to acustom-designed board that collects input signals fromsensors throughout the car and distributes controlsignals to actuators and controllers. The dataacquisition boards have a maximum capability of 48digital inputs and outputs, 16 analog inputs, and 16analog outputs. By using a computer, the team canprogram in common languages (C/C++) and remainflexible in the hardware and software designs.

Control Strategy - The Wisconsin team has developeda hybrid control strategy that is state of voltage (SOV)regulating. A SOV regulating strategy will monitor thebattery voltage and maintain that voltage within aprescribed range, resulting in a battery which avoids fulland empty regions.[12] Transient emissions caused bychanges in the engine load are reduced by using themotor to meet rapid increases in road power demands.The engine power output is then gradually increasedwhile the motor power output is simultaneouslydecreased. Buffering the engine from the road in thismanner also increases the vehicle fuel economy.

The UW control strategy has only one mode ofoperation. This results in a FutureCar that operatessimilarly to a conventional automobile. There are noadded modes, switches, pedals, or dials with which thedriver might be concerned.

The control strategy is designed as a state machine withthree states. By developing the control strategy as afinite state machine, the software is restricted to run inonly one state at a time. Since the current vehicle statecan always be determined, each state can be tested,debugged, and tuned separately. Each of the states arereviewed in the following sections.

State 1: Engine Only – The first state is engine only. Inthis state, the vehicle operates as if the electrical systemwere not present. This state is used at low speeds, whenthe clutch is in, when the car is in neutral, or when thebattery is so low that attempting to use it could causedamage. In this state, the accelerator input goes directlyto the engine, with the motor providing no torque.

State 2: Regenerative Braking – The second state isthe regenerative braking state. Regenerative braking(regen) is the act of using the mechanical energy fromthe wheels to drive the motor, generating electricity forstorage in the battery. This process recharges thebattery while decreasing the vehicle speed.

The vehicle goes into the regenerative braking state onlyif the brake pedal is depressed and the battery pack isnot fully charged. The brake pedal travel is split into twoportions as seen in Figure 12. The first 2 cm (0.75in) of

travel only enables regenerative braking. After 2 cm,regenerative braking is saturated and the stock hydraulicbrakes engage to help slow the vehicle. This allows aconservative driver to regenerate large amounts ofenergy during anticipated breaking, but retains the abilityto break hard when needed.

For previous competitions, the Wisconsin FutureCarused a rotary potentiometer attached to the brake pedalto produce an analog signal based on the first smallamount of brake pedal travel; however, no resistancewas incorporated for this regen travel distance. As aresult, the first few centimeters, the regen portion, wastraversed through quickly until resistance was felt in theform of hydraulic fluid actuating the friction brakes. Thespeed with which the regen portion was traveled throughreduced the effectiveness of the regenerative brakingcapability. In order to improve its effectiveness, a newsensor with hydraulic resistance was designed.

0 10 20 30 40 50 600

10

20

30

40

50

60

70

80

90

100

Master CylinderReservoir Closes

Brake SwitchActivated

Regenerative Braking System

Conventional Braking System

Bra

king

Sys

tem

Cap

acity

App

lied

(%)

Brake Pedal Depression (mm)

Figure 12. Depiction of the application of theregenerative and conventional braking systems in thevehicle.

An instrumented hydraulic piston is attached to the endof the existing master cylinder. As the brake pedal isdepressed, the brake fluid forces this hydraulic piston tocompress a resistive spring. Initially, a brake linepressure of 100 kPa (14.5 psi) is needed to initiate themovement of the piston while a mechanical stop is usedto limit the piston’s stroke at a pressure of 350 kPa (seeFigure 12). A position sensor attached to the piston isused by the control computer to adjust the amount ofregenerative braking. After the piston contacts the stop,the disc braking system operates normally. The 350 kPapreload causes a very smooth transition between theregenerative and conventional braking systems.

State 3: HEV – HEV state is the third and mostcommon state in the control strategy. This state containsthe SOC regulator control code which manages thebattery voltage as previously described. To optimallycontrol the vehicle systems in the HEV state, the controllaws for this state will involve fuzzy logic.

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The hybrid diesel-electric propulsion state uses fuzzylogic to synthesize accelerator pedal, battery state-of-charge and vehicle speed sensor inputs into commandsto the diesel engine and electric motor. Using a smallnumber of rules, the basic relationships between inputsand desired outputs will be described using fuzzy sets.For example, an increased accelerator pedalmeasurement will result in an increased command to themotor to increase available torque while the enginecommand is increased slowly to control soot emissions.

Safety is insured by range checking all inputs andoutputs. If a value entering or leaving the computer is toolow or too high the computer will adjust the value to theclosest bound, or shutdown.

AUXILIARY SYSTEMS

For the 1999 Wisconsin FutureCar a number of theparasitic loads were removed from the engine includingthe air conditioning, power steering and alternator. Self-contained units that run independently of the enginereplaced these systems. Systems which are electricallydriven can be easily controlled to match demand periodsand are easily controlled. The implementation of thenew systems also allowed for optimization of thesesystems.

Air Conditioning - The air conditioner compressor isMatsushita LRA 71. 115 Vac, single phase selfcontained rotary compressor. The system is capable ofremoving 16000 BTU/hr. The compressor is run off of a1.5 hp adjustable speed motor controller, Reliancemodel SP200. With the removal of its dependence uponthe engine speed the new air conditioner can run atrequired speeds and can even be throttled back. Thisprevents the air conditioner from having to blend warmoutside air to achieve an intermediate temperatureimproving the efficiency of the system.

Power Steering - The LYNX 90PS power steering pumpwas replaced by a DELPHI Electro-Hydrolic (EH)steering module. The EH module contains a 12 voltmotor which is directly coupled to a hydraulic pump. Themodule also contains a controller which adjusts thecurrent to the electric motor proportional to the pumpsoutput pressure. The EH module uses 15 watts duringstandby compared to 150 watts for the LYNX 90 PSpump. At peak load, it requires 750 watts. The newsteering system reduces power draw by up to 80% [11].

12 Volt System - The 12 Volt system was totallyredesigned with the objective of removing redundantsystems and excess component weight. Theconventional 12 V alternator (9 kg) was removed fromthe vehicle and replace with two 600 Watt Vicor DC toDC converters (1 kg). In addition, the traditionalautomotive SLI battery (18 kg) was replaced with a smallBolder thin-metal film lead acid battery (1 kg). The DC-DC converters use the high voltage battery pack to

supply up to 100 amps of current to the 12 V systemwhich contains the Bolder battery for starting currentdemands. The Bolder battery is capable of supplying500 cranking amps for approximately 10 seconds and itcan be recharged from the high voltage battery pack inunder 60 seconds.

Table 9. Aluminum Cow Component Summary.

Component Manufacturer Rating

EngineFord

1.8 L TDI

66 kW @ 4000 rpm200 N-m @ 2000

210 g/kW-hr @ 2000

TransmissionFord

MTX-755-speed w/ Reverse

4.06 Diff. Ratio

MotorSolectriaAC gtx 20

12 kW continuous≤100 N-m

≤12,000 rpm

InverterSolectria

UMOC 340

56 kW≤ 210 Arms

200 - 350 Vdc

BatterySanyo

Sealed NiCad+/- 24 kW2.3 kWh

WEIGHT REDUCTION

In and effort to reduce the weight of the vehicle manycomponents were reconstructed of Aluminum. A morecomplete description of the benefits and uses ofaluminum is discussed in Appendix A.

Battery Box – The physical size of the battery box iscomparable to the volume of the spare tire well. For thisreason, the spare tire well was removed so the batterybox could be suspended from the trunk floor withoutsacrificing any trunk space.

Figure 13. 2.3kWh NiCad battery with 15 cell strings.

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Figure 13 shows a picture of the high voltage (HV)battery box. In order to hold the 56 modules in place,four sets of machined acetyl strips were clampedtogether around the modules. Each battery module isheld in the center and at both ends by these sets ofacetyl strips, which also serve as excellent insulators.Additional electrical insulation is provided by the shrink-tube which covers each of the 56 modules. This designrequires a minimum amount of support material whilecompletely restraining the cells. Aluminum structuralangle beams 5 cm (2 in) on each side and 3.2 mm (.125in) thick are used to anchor the acetyl strips together andto mount the entire pack to the vehicle.

The large void in the battery box is used to enclose theentire high voltage switch gear and DC-DC converters.By combining all the HV components and removingredundant systems, a modular HV unit was created. Aclear polycarbonate box, for protection, will enclose thebattery. The total weight of the battery box is 59 kg (130lbs).

Brakes/Suspension – To reduce the weight and brakedrag, CNC 4-piston aluminum brake calipers wereinstalled in place of the Sable stock brake calipers.Typical brake calipers employ a single piston. The brakepads slide on pins when the brakes are released in orderto retract the brake pads. Over time, the pin/caliperinterface becomes corroded, preventing sliding. Whenthis occurs, the calipers do not fully disengage resultingin a disk drag force which decreases overall efficiency.The 4 piston calipers do not rely on this sliding andactively minimize the residual drag force on the disk. Inaddition, at 1.1 kg (2.5 lbs) each, they save 3.2 kg (7 lbs)per side over the standard brakes. The AIV wassupplied with DurAlcan metal matrix compositealuminum rotors each weighing 2.3 kg (5 lbs) less thanthe stock steel rotors.

In order to adjust for a lighter chassis and modifiedweight distribution, the team installed Koni coil-overstruts on all 4 corners. The struts allow for theadjustment of ride height, camber, caster, toe, andrebound damping. Not only have they allowed us tooptimize the handling of the FutureCar, but they will alsosave about 0.9 kg (2 lbs) per wheel since they havealuminum strut bodies.

To fit the newer engine cradle design, the front steelspindles were upgraded to cast aluminum spindleswhich save 1.4 kg (3 lbs) per front wheel. In addition, thenew spindles facilitated the mounting of the newcalipers. Through the use of all these aluminumcomponents, the overall vehicle weight will be reducedby 23 kg (50 lbs).

Aluminum Wheels – Another opportunity for weightreduction appeared in the wheel rims. The originalaluminum alloy rims weighing 10.5 kg (23 lb.) each werereplaced with lighter, American Racing aluminum alloy

rims weighing only 8.2 kg (18 lb.) each. This exchangeresults in a savings of nearly 9.2 kg (20 lb.) total.

Engine Cradle - In a joined effort with Tower Automotivethe Wisconsin FutureCar team replaced the stock steelengine cradle with a prototype Aluminum cradle. Theoriginal steel engine cradle weighed 22.7 kg (50 lbs)and was replaced by a all Aluminum engine cradle thatweighed in at a little over 9kg (20lbs).

Figure 14. Finite element analysis displacement resultsfor a Ford Taurus aluminum engine cradle with a 6 kNload.

When replacing stamped steel with aluminum, thestrength of the steel can be matched by heat treating the6061aluminum component to a T6 state. However, thedeflection of the aluminum is still approximately 3 timesgreater than its steel counter-part. Figure 14 illustratesthe predicted displacement on the engine cradle for a 6kN load applied to the bottom of the engine cradle. Thisload simulates the vehicle cornering with a lateralacceleration of 10 m/s2. Because the static support ofthe engine is directly onto the uni-body frame in theAluminum Cow, the maximum stress strain anddisplacement of the aluminum engine cradle are wellwithin acceptable limits.

A-Arms - The A-arms were also replaced with lighter,stiffer aluminum counterparts. Tubular aluminum with a31.8 mm diameter and 6.4 mm wall were bent andwelded in a triangular pattern. In this instance, thevolume of material was almost doubled in an effort tocreate a stiffer yet lighter replacement. Figure 15 showsthe completed arms. The steel A-arms weighed 3.7 kg,the Aluminum A-arms weighed only 2.2 kg.

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Figure 15. Aluminum A arms constructed from thickwall aluminum tubing.

Engine Mounts- The engine mounts were another itemwith the possibility for improvement in design. Theengine mounts were redesigned out of aluminum andwere also examined under finite element analysis tomake certain there was not a potential for failure.Figure 16 shows the results of a finite element analysis.

Figure 16. Engine Mount finite element stress analysis.

DRAG REDUCTION

As shown in Equation 4 of the Vehicle EnergyConsumption section, some power loss of a vehicle canbe attributed to aerodynamic drag. This loss isdependent on several factors, of which only the frontalarea profile and drag coefficient can be changed.

The following steps were taken to reduce the WisconsinFutureCar's frontal area profile, drag coefficient, andcoefficient of rolling resistance.

Wind Tunnel Testing – An aerodynamic study of thevehicle was performed via wind tunnel testing. Threedifferent Ertel 1/25-scale Ford Taurus models were

assembled (see Figure 17). The first vehicle was left inits stock configuration. An underbody panel wasinstalled on the second model; this model also includedsmaller rear view mirrors and a round-corner trunk lid.The second and third models were identical with thefront underbody panel being replaced with a air dam onthe third model. A slippery smooth finish was applied toeach model by spraying them with a lacquer enamelfinish.

A wind tunnel at the University of Wisconsin was used toperform the study. It was capable of producing windspeeds up to 45 meters per second (100 mph). Thecross-sectional area of the tunnel's measurementsection was approximately 900 cm2. A plate wasinstalled parallel to the air flow to simulate groundeffects. An instrumented arm extended into the bottomof test section to measure both drag and lift on thevehicle. An airfoil shrouded the arm to ensure accuratedrag measurements.

Figure 17. A still frame image of a 1/25 scale FordTaurus during wind tunnel testing.

A pitot tube was used to measure the air velocity in thetest section. During the experiment, the pitot tubepressure was randomly varied from 2 inches of water to5 inches of water in 0.25 inch increments and 20 datapoints were collected for each vehicle test. 8 differenttest sets were collected to ensure repeatability in theexperiment.

After post-processing, results were plotted as dragcoefficient versus wind tunnel velocity. The results fromthe 5th data set are plotted in Figure 18. It was observedthat at slow speed, the models have the same relativedrag coefficient. As the velocity increases, the modelwith the underbody panel measured the lowest dragcoefficient. Compared to the stock model, theunderbody panel provided a 6% lower drag coefficientwhile the spoiler increased the drag coefficient by 4%.This relationship was observed in all 8 data sets.Although the Reynolds numbers for the wind tunnel testare an order of magnitude lower than for the real vehicle,similar or exaggerated relations are expected for over-the-road Reynolds numbers.

From the wind tunnel results, the Wisconsin FutureCarTeam concluded that the greatest reduction inaerodynamic drag would be realized by streamlining theunderbody of the AIV Sable.

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0.59

0.61

0.63

0.65

0.67

0.69

0.71

0.73

0.75

15 20 25 30 35 40 45 50

Wind Tunnel Speed (m / s)

Dra

g C

oef

fici

ent

(Cd

)

Stock

Air Dam

Belly

Linear

Figure 18. Wind tunnel test data indicates that the useof an underbody panel will reduce the drag coefficientwhereas the use of a spoiler will increase it.

Aerodynamic Simulation - In an effort to find a way toreduce the drag force of the 1999 FutureCar a 2-Dprofile of the car was modeled and tested in a finiteelement program, Fluent 5.0. Different locations anddesigns of spoilers were simulated to determine whichdesigns were worth pursuing in physical testing.

Figure 19. Fluent analysis of car profile at 30 [m/s].

Figure 19 shows the results of a simulation on the basecar profile. The spoiler designs with the smallest dragforce were used for physical testing.

Underbody Panel – Since approximately 10% of allvehicle drag comes from underneath the car, theWisconsin team has made a panel that shelters theunderbelly. Reinforced, 24 gauge aluminum sheet metalprovides a smooth underbody surface which decreasesthe drag coefficient.

Spoiler - From the simulations a trunk mounted spoilerwas designed in an effort to reduce the pressure drag ofthe vehicle. The spoiler is made of Aluminum and isdesigned as a reversed airfoil, 4 inches long and .5inches tall. The spoiler will be mounted 5 inches above

the edge of the trunk. The addition of the spoiler createssmall-scale turbulence which causes the streamline torecollect sooner behind the vehicle. This decreases thedead zone behind the vehicle and reduces drag. Basedon simulation results the spoiler should reduce theoverall drag of the vehicle by about 8%.

Tires – Equation 2 shows that vehicle power loss isdirectly related to the tire’s rolling resistance. The UWFutureCar Team has opted to use Goodyear’sexperimental low rolling resistance tires. This particulartire has the best available coefficient of rolling resistance- less than 0.00625.

ALTERNATIVE ENERGIES

Solar Array- The 1999 FFC will have two solar arrays,both mounted upon the roof. Each panel is made up of36 Kyocera 4" square polycrystalline silicon cellsconnected in series to produce 12Vdc. The two panelsare connected in parallel to the cars 12V system. Eachpanel should be able to supply 50 Watts. This issufficient to supply the diesel engine's electronics as wellas the touch screen computer and other steady statedriving loads. During long periods of storage the solarcells will be able to maintain the vehicle's batteries.

INTENDED MARKET

Producing a hybrid vehicle that has a high level ofconsumer acceptability was a high priority for theUniversity of Wisconsin FutureCar Team. Accordingly,the team entered the FutureCar Challenge committed tomaintaining full passenger and cargo room in thevehicle, to producing a seamless appearance similar tothe original, and to retaining the driving feel of a stockMercury Sable. The 1999 Wisconsin FutureCaraccomplishes all of these goals. The intended market forthis car includes drivers looking for a mid–size sedanwith the following characteristics:

• Enhanced performance0-100 kph in < 10 seconds145 kph (90 mph) maximum speed970 km (600 mi) range

• Impressive fuel economy23.9 km/L (56 mpg)1.1 cents/km (1.8 cents/mi) travel cost

• Creature comfortsTurn-key start upAir conditioningCruise controlPower windowsAM/FM radio & cassette playerTouch screen computer interfaceTelevisions in both headrests

The UW FutureCar has a clean body and passengercompartment. The interior of the vehicle maintains the

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size, shape and amenities of the original Mercury Sablewith the addition of a touch screen computer console.

The design of this vehicle makes it simple to operate,with a conventional turn–key start. No extra switches orbuttons are required to start or drive the vehicle. Theadvanced control strategy allows an operator to achievethe same performance after traveling 970 km (600 mi)that they experienced at the beginning of the journey,and only a five minute fueling service in order to travelanother 970 km.

COST ANALYSIS

The estimated total cost of the 1999 UW FutureCar athigh volume production is $28,000. This cost estimate isbased upon a Mercury Sable list price of $21,000, anadditional cost of $11,000 for new engineering, and a$4000 savings from replacing the conventionaldrivetrain. In order to estimate these costs, severalassumptions were made.

• The cost of manufacturing the aluminumunibody and enclosure panels is 1.4 times thatof manufacturing steel [5].

• Components that are not “off the shelf” can bemass produced at a cost of 20-30% of the pricethat the Wisconsin team paid.

• All other vehicle components are the same asthose found in a stock Mercury Sable.

• 100,000 vehicles are manufactured each year.• The cost of labor is negligible.• All costs have been assessed in 1999 dollars.

The cost for a single prototype FutureCar is estimated tobe $54,000. This estimate assumes that the cost of aprototype AIV is $31,000. The remainder of the cost isobtained from the special order prices of the hybridcomponents.

MANUFACTURING POTENTIAL

The Wisconsin FutureCar component selection andpackaging has been chosen for ease of procurement,access, and maintenance. This design inherently favorsobtaining components and assembling the vehicle inmass production.

The current trend in automotive manufacturing is to usecommon platforms – the use of common componentson multiple vehicles (i.e. engines, transmissions, andframes). Adapting to the methods of Ford, GM andChrysler, the Wisconsin FutureCar team adopted thismethodology in 1998. This vehicle could be easilyintegrated into a conventional vehicle production line andwould need supplemental tooling only for installation ofthe battery pack. The electric motor would simply boltonto a standard transmission fitted with a specialsecondary shaft. Additional components would be

minimal and could be installed by the regular assemblyline workers onto existing hardware.

A compact design not only aids in manufacturing butalso minimizes the number of serviceable parts. Ifneeded, threaded fasteners are conveniently located sothat disassembly is quick and easy.

Just as any prototype vehicle must be modified before itis put into production, the following features of theWisconsin FutureCar would be changed in preparationfor mass production.

• Replace the Pentium control computer with anembedded computer.

• Design the battery pack to fit behind the rearseat back.

Combining these modifications with the existing designbefore incorporating the FutureCar into the assemblyline would significantly reduce the time and cost ofproduction.

SUMMARY

The Wisconsin FutureCar Team has successfullyconverted a prototype 1994 Mercury Sable AIV into a,power assist, charge sustaining parallel hybrid-electricvehicle. The UW FutureCar was designed to exceed thestock Sable fuel economy and emissions standardswithout sacrificing performance or consumeracceptability. This was accomplished by using advancedtechnologies as well as existing automotive science.

The team used traditional hybrid-electric components;including an AC induction electric motor with matchedinverter; a high power density Ni-Cad battery pack; anda compression ignition internal combustion engine in anattempt to reach the FutureCar Competition fueleconomy goal of 80 miles per gallon.

In addition, the Wisconsin team incorporated severaladvanced technologies into its 1999 FutureCar. The useof computer simulation to optimize control softwarecoupled with an aggressive fuzzy logic control strategyhelped realize team goals. Finite element analysis suchas Fluent and ANSYS were used to minimize vehicletesting time while verifying the integrity of usingaluminum and polycarbonate to reduce the vehicleweight. All while keeping the vehicle design costeffective and modular so that it could be implementedinto an automotive production line.

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ACKNOWLEDGMENTS

The outstanding contributions of Advisor Dr. GlennBower regarding sound engineering, student education,and professional conduct have been invaluable to theUW FutureCar Team. His dedication, along with thefinancial support and enthusiasm of the UW College ofEngineering, has given team members the ability toflourish with new opportunities and experiences.

The patient work of the FutureCar organizers to createand facilitate the Challenge is also greatly appreciatedby the members of the Wisconsin team. The funding forsuch organization, as well as the availability ofcompetition facilities, seed money, and platformvehicles, is made possible by the generous contributionsof USCAR, USDOE, USEPA, ANL, Chrysler Corp., FordMotors, and General Motors. We would especially like tothank Ford with whom we have maintained a closeworking contact, and from whom we have received muchknowledge and help dating back to the initial designs ofthe 1998 FutureCar. We would like to extend our thanksto all of these organizations who have been instrumentalto the FutureCar Challenge and the promotion of energyefficient vehicles.

Finally, the authors of this report wish to recognize all ofthe members of the Wisconsin FutureCar Team whohave contributed to the success of the “Aluminum Cow”and elevated the engineering standards at the Universityof Wisconsin.

REFERENCES

1. Thiel, M.P., et al., “The Development of the University ofWisconsin’s Parallel Hybrid-Electric Aluminum IntensiveVehicle,” SAE Publications February 1999, SAE .

2. Bower, G.R., et al. , “Design of a Charge Regulating,Parallel Hybrid Electric FutureCar,” SAE PublicationsFebruary 1998, SAE 980488.

3. Johnston, Brian, et al. , “The Continued Design andDevelopment of the University of California, DavisFutureCar,” SAE Publications February 1998, SAE980487.

4. Thomas, C.E., et al., “Societal Impacts of Fuel Options forFuel Cell Vehicles,” SAE Publications October 1998, SAE982496.

5. "1.8L DI TCI LYNX 90 PS in Focus - Engine and VehiclePerformance Data", Ford of Dunton, England, November1998.

6. Cuddy, Matthew R. and Wipke, Keith B. "Analysis of theFuel Economy Benefit of Drivetrain Hybridization," SAE970289.

7. Mariano, S. and Tuler, F. and Owen, W., "ComparingSteel and Aluminum Auto Structures by Technical CostModeling." JOM, 45(6):20-22, 1993.

8. Gallopoilos, N.E., “Environmental Vehicle,” EDS,Dearborn, MI, 1996.

9. USABC Electric Vehicle Battery Test Procedures Manual,Revision 2, U.S. DOE, Idaho National EngineeringLaboratory, DOE/ID-10479, Jan. 1996

10. PNGV Battery Test Manual, U.S. DOE, Idaho NationalEngineering Laboratory, DOE/ID-10597, Jan. 1997

11. http:\\www.delphiauto.com, 5-3-9912. Wiegman, H., Vandenput, A., "Battery State Control

Techniques for Charge Sustaining Applications," SAEPubl. 981129, SP-1331, 1998, pp 65-75 , and 1999 SAETransactions

SYMBOLS

m = mass of vehicle (kg)

g = gravitational acceleration (9.8 m/s^2)

V = velocity (m/s)

θ = inclination of road (rad)

ρ = density of air (~ 1.3 kg/m^3)

A = frontal area of car (~2 m^2)

Cd = drag coefficient (~.30)

Crr = coefficient of rolling resistance (~.008)

Note: Appendix follows on next page.

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APPENDIX

A. ADVANTAGES OF ALUMINUM - Aluminum is aversatile and useful metal with many advantages,including its light weight, resistance to environmentalconditions, high elasticity, ease of working and forming,and the high strength of aluminum alloys (up to andexceeding the strength of steel). For an equal volume ofmaterial, its strength is equivalent to that of mild steel.However, its stiffness is lower by a factor of three,requiring the designer to increase the cross sectionalarea of critical parts or to reevaluate their structure.Aluminum is easily machinable and can be cast as well.The material properties are compared in Table A.1.

Because of the global need for reduced fuelconsumption, the automotive industry is interested inexploring the possibility of substituting aluminum forsteel in passenger vehicles. For example, the Audi5000s had an aluminum frame with a 48.6% lowerweight (as part of a joint project between Audi andALCOA). Other examples of aluminum body constructioninclude US Postal mail cars, the US Army HMMWVmulti-purpose vehicles, and semi truck trailers such asthose produced by Freightliner Corporation. In all theseapplications, the use of aluminum has saved money byimproving fuel mileage through weight reduction. Itsstrength has improved the overall designs, while itscorrosion resistance prolonged the life of the vehicles.(Aluminum forms a protective oxide coating whichprevents rust related failures.)

Companies such as ALCOA and BMW are developingnew manufacturing processes for aluminum. The BMW500 series axles were hydroformed for higher stiffnessand fatigue strength, and then GMA welded together.Aluminum tends to respond well to GMA and GMA-impulse welding. For high-quality joints, TIG welding isalso used.

Table A.1 - Material properties for aluminum and steel.

Alloy & Temper UltimateStrength

(ksi)

YieldStrength

(ksi)

Modulus ofElasticity

(ksi)

Alum. 2014-T6,T651

70 60 10.6

Alum. 6061-T6,T651

42 37 10.0

Alum. 7075-T6,T651

83 73 10.4

Steel 1020 HR 66 42 30Steel 1018 A 49.5 32 30

B. EXHAUST GAS RECIRCULATION

One of the main drawbacks of compression ignition (CI)engines is the high oxides of nitrogen emission levels.CI engines utilize high compression ratios (15-18:1) toachieve high thermal efficiency. Unfortunately, high in-cylinder temperatures promote the formation of NOx

during combustion. It has been found that NOx

emissions can be reduced by introducing exhaust gasinto the intake charge. This practice is known asexhaust gas recirculation (EGR). NOx emissions canfurther be reduced by cooling this recirculated exhaustgas.

The Ford engine was originally equipped with an EGRintercooler. This heat exchanger lowers the temperatureof the EGR stream by using the cooling system as itsheat sink. This exchange of heat results in twoadvantages. First, cooling of the exhaust gas produceslower NOx emissions from forming. Second, the coolantthat is heated is then pumped directly to the heatingsystem for the vehicle. This will provide heat to the cabinmuch more quickly and efficiently than the stock heatingsystem