19

Optimizing the University of Wisconsin's Parallel Hybrid-Electric Aluminum Intensive Vehicle J. Bayer, M. Koplin, J. Butcher, K. Friedrich, T. Roebke, H. Wiegman, G. R. Bower

University of Wisconsin–Madison

Copyright © 1999 Society of Automotive Engineers, Inc.

Table 1. UW FutureCar 1999 Performance Goals.

ABSTRACT The University of Wisconsin – Madison FutureCar Team has designed and built a lightweight, charge sustaining, parallel hybrid-electric vehicle for entry into the 1999 FutureCar Challenge. The base vehicle is a 1994 Mercury Sable Aluminum Intensive Vehicle (AIV), nicknamed the “Aluminum Cow,” weighing 1275 kg. The vehicle utilizes a high efficiency, Ford 1.8 liter, turbocharged, direct-injection compression ignition engine. The goal is to achieve a combined FTP cycle fuel economy of 23.9 km/L (56 mpg) with California ULEV emissions levels while maintaining the full passenger/cargo room, appearance, and feel of a fullsize car. Strategies to reduce the overall vehicle weight are discussed in detail. Dynamometer and experimental testing is used to verify performance gains.

Parameter Combined FTP Fuel Economy Emissions Acceleration: 0–100 kph Range Vehicle Weight

1999 Goals 23.9 km/L (56 mpg) ULEV 90% efficiency). Its gear ratios are shown in Table 6. These gear ratios were designed for use in 1300 kg vehicle similar to the Aluminum Cow.

Figure 9. Stress plot from ANSYS analysis of hybrid gearbox. Figure 7. The modified transmission case for the Ford MTX-75 FWD transmission. Table 6. Gear ratios for Ford MTX-75 transmission. Gear 1st 2nd 3rd 4th 5th Differential

Ratio 3.666 2.047 1.258 0.864 0.674 4.060

A custom designed gearbox was develop to couple the electric motor to the engine/road. This was accomplished by modifying the secondary transmission shaft (see Figure 7), which then makes the transmission a durable and efficient torque splitter. This gearbox is a second generation design. The new gear box was fabricated on a Milltronics fix-bed CNC mill from 6061-T6 aluminum billet. The gear box, seen in Figure 8, was originally drawn in AutoCAD which supplied the geometric traces to the CNC controller. Subsequently, the gearbox was solid modeled in ProE so that it could be analyzed using ANSYS (see Figure 9). Before manufacturing the gear box, extensive stress analysis were performed to ensure design’s reliability.

Figure 8. gearbox.

Computer numerically controlled machined

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The transmission placement in the Wisconsin FutureCar is displayed in the packaging diagram (Figure 4). The gear selector and clutch are typical of those found in conventional vehicles. In addition the complete hybrid drivetrain (engine, transmission, and electric motor) was designed to be pre-assembled on the engine cradle subframe and subsequently placed into the vehicle as a unit. Fuel – The 1999 Wisconsin FutureCar has adopted Fischer-Troups fuel for compression ignition engines. Fischer-Troups is considered an alternate fuel as it is derived from natural gas or coal. Similar to synthetic oils, Fischer-Troups contains no impurities. This produces a predominantly straight-chained, clear, clean fuel. Typically it has a cetane number of 70 while containing no sulfur or aromatics. The elimination of sulfur will extend catalyst life while reducing particulate emissions.

ELECTRIC DRIVE SYSTEM Motor/Inverter - The 1999 UW FutureCar uses a 12 kW induction electric motor with a peak power of 30 kW (battery limited). The motor can supply a maximum torque of 100 N-m and a maximum speed of 12,000 rpm. The motor weighs 32 Kg, and delivers 94% peak efficiency. The motor is part of Solectria's prepackaged electric drive system which includes a microprocessor vector control unit, the UMOC 340. The 98% efficient control unit is rated for input voltages ranging from 200350 V and has a 210 Arms limit. The AC induction motor and controller were selected in place of the permanent magnet motor and controller used in last year for numerous reasons. As discussed earlier, the permanent magnet motor adds unnecessary drag to the driveline when not in use and therefore is not desirable in a parallel-assist hybrid vehicle where electric motor utilization is low during steady state driving. These drag losses are converted to heat and require an additional radiator/pump/coolant system in the vehicle. Switching to a lower power AC induction motor the drag loss were eliminated while realizing a 32 kg weight savings.

Ni-Cad batteries are utilized in the hand-held battery power tool industry. Huge gains in NiCad power density and reliability have been accomplished through the developments of companies such as Milwaukee Tool and Sanyo Inc. The battery system was adjusted slightly in order to obtain high power capability and processing efficiency. A battery performance improvement summary for the 1999 vehicle is shown in Table 8. Table 8. NiCad battery performance improvement.

Figure 10. System efficiency map for the Solectria Acgtx20 motor using a UMOC 340 controller operating from 270Vdc. The motor is coupled to the secondary transmission shaft of the 2WD transmission via a custom gear box. The gear box supports the electric motor and includes a 2.30:1 gear ratio (9.34 overall to axle) to decrease the motor speed. This allows the motor to spin in its optimum range of 3000-6000 rpm (37-75kph) (see Figure 10). Battery – The 1998 energy storage system used in the UW-Madison FutureCar was based on high power density Nickel Cadmium C-cells. The technology was capable of delivering 400W/kg (10 sec, 20% voltage variation), thus providing a lightweight system which was near optimal for the charge-sustaining, parallel assist hybrid design. To improve upon the design, and to move to a more optimal overall vehicle efficiency, the energy storage system was re-evaluated for the 1999 competition. Three battery technologies were tested and compared. PNGV style power pulse testing was applied in order to objectively evaluate the relative electrical performances.[9,10] The three chemistries tested were; Thin-Metal Film Lead Acid (TMF Pb), Nickel Cadmium (NiCad), and Nickel Metal Hydride (NiMH). A overview of the technologies are compared in Table 7.

Battery Characteristics Total Cell Mass [kg] Bat. Box Mass [kg] Voltage [V] Capacity [A-h] Energy [kW-h] Power [kW] # Cycle Efficiency [-] *

1998 49 6 272 7.5 2.0 +/- 22 0.87

1999 53 6 286 8.0 2.3 +/- 24 0.89

# - 10 seconds, +/- 20% voltage variation * - at +/- 4kW rate, 30 seconds, 50% SOC

The PNGV style power pulse testing revealed the maximum power capability and efficiency characteristic of the battery. Sample testing was instrumental in improving the battery system design for the 1999 effort. Figure 11. shows the 30 second capabilities of the 1999 battery system. The 10 second power capability is higher due to a lack of diffusion effect during the short duration pulses, hence it was not used as a realistic test of the batteries. The efficiency characteristic as shown in Figure 11 revealed a relatively flat and broad operating range vs. SOC, showing the flexibility of the high power density cell design.

Power Capability and Efficiency vs. SOC 6

Power [pu]

4 Pdis = solid Pchrg = dash

2

30 sec discharge and charge 0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Table 7. Battery performance improvement summary Feature Disadvntg.

Advantage

TMF Pb cost, sulfation

Highest power dens.

NiCad Envirnmnt. Impact

Proven technology

NiMH Only moderate power dens. Promising Technolog y

The final battery selection was based upon probability of success, low cost, and electrical performance. Today, Page 6 of 14

1 0.95 Eff. [pu]

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

0.85 0.8 0

0.1

0.2

0.3

0.4

0.5 0.6 SOC [pu]

30 sec, Pow = 2 pu 0.7

0.8

0.9

1

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

Control Strategy - The Wisconsin team has developed a hybrid control strategy that is state of voltage (SOV) regulating. A SOV regulating strategy will monitor the battery voltage and maintain that voltage within a prescribed range, resulting in a battery which avoids full and empty regions.[12] Transient emissions caused by changes in the engine load are reduced by using the motor to meet rapid increases in road power demands. The engine power output is then gradually increased while the motor power output is simultaneously decreased. Buffering the engine from the road in this manner also increases the vehicle fuel economy. The UW control strategy has only one mode of operation. This results in a FutureCar that operates similarly to a conventional automobile. There are no added modes, switches, pedals, or dials with which the driver might be concerned. The control strategy is designed as a state machine with three states. By developing the control strategy as a finite state machine, the software is restricted to run in only one state at a time. Since the current vehicle state can always be determined, each state can be tested, debugged, and tuned separately. Each of the states are reviewed in the following sections. State 1: Engine Only – The first state is engine only. In this state, the vehicle operates as if the electrical system were not present. This state is used at low speeds, when the clutch is in, when the car is in neutral, or when the battery is so low that attempting to use it could cause damage. In this state, the accelerator input goes directly to the engine, with the motor providing no torque. State 2: Regenerative Braking – The second state is the regenerative braking state. Regenerative braking (regen) is the act of using the mechanical energy from the wheels to drive the motor, generating electricity for storage in the battery. This process recharges the battery while decreasing the vehicle speed. The vehicle goes into the regenerative braking state only if the brake pedal is depressed and the battery pack is not fully charged. The brake pedal travel is split into two portions as seen in Figure 12. The first 2 cm (0.75in) of Page 7 of 14

travel only enables regenerative braking. After 2 cm, regenerative braking is saturated and the stock hydraulic brakes engage to help slow the vehicle. This allows a conservative driver to regenerate large amounts of energy during anticipated breaking, but retains the ability to break hard when needed. For previous competitions, the Wisconsin FutureCar used a rotary potentiometer attached to the brake pedal to produce an analog signal based on the first small amount of brake pedal travel; however, no resistance was incorporated for this regen travel distance. As a result, the first few centimeters, the regen portion, was traversed through quickly until resistance was felt in the form of hydraulic fluid actuating the friction brakes. The speed with which the regen portion was traveled through reduced the effectiveness of the regenerative braking capability. In order to improve its effectiveness, a new sensor with hydraulic resistance was designed. Braking System Capacity Applied (%)

Computer – The Wisconsin FutureCar team has been successful in past competitions partly due to the flexibility of the control system. The control strategy is run on a custom-built computer system consisting of a Computer Dynamics single-board pentium machine with a touch-screen user interface. The computer's Micro Industries data acquisition boards are connected to a custom-designed board that collects input signals from sensors throughout the car and distributes control signals to actuators and controllers. The data acquisition boards have a maximum capability of 48 digital inputs and outputs, 16 analog inputs, and 16 analog outputs. By using a computer, the team can program in common languages (C/C++) and remain flexible in the hardware and software designs.

100 90 Brake Switch Activated

80 70 60 50 40

Regenerative Braking System Conventional Braking System

30 Master Cylinder Reservoir Closes

20 10 0 0

10

20

30

40

50

60

Brake Pedal Depression (mm)

Figure 12. Depiction of the application of the regenerative and conventional braking systems in the vehicle. An instrumented hydraulic piston is attached to the end of the existing master cylinder. As the brake pedal is depressed, the brake fluid forces this hydraulic piston to compress a resistive spring. Initially, a brake line pressure of 100 kPa (14.5 psi) is needed to initiate the movement of the piston while a mechanical stop is used to limit the piston’s stroke at a pressure of 350 kPa (see Figure 12). A position sensor attached to the piston is used by the control computer to adjust the amount of regenerative braking. After the piston contacts the stop, the disc braking system operates normally. The 350 kPa preload causes a very smooth transition between the regenerative and conventional braking systems. State 3: HEV – HEV state is the third and most common state in the control strategy. This state contains the SOC regulator control code which manages the battery voltage as previously described. To optimally control the vehicle systems in the HEV state, the control laws for this state will involve fuzzy logic.

The hybrid diesel-electric propulsion state uses fuzzy logic to synthesize accelerator pedal, battery state-ofcharge and vehicle speed sensor inputs into commands to the diesel engine and electric motor. Using a small number of rules, the basic relationships between inputs and desired outputs will be described using fuzzy sets. For example, an increased accelerator pedal measurement will result in an increased command to the motor to increase available torque while the engine command is increased slowly to control soot emissions. Safety is insured by range checking all inputs and outputs. If a value entering or leaving the computer is too low or too high the computer will adjust the value to the closest bound, or shutdown.

supply up to 100 amps of current to the 12 V system which contains the Bolder battery for starting current demands. The Bolder battery is capable of supplying 500 cranking amps for approximately 10 seconds and it can be recharged from the high voltage battery pack in under 60 seconds. Table 9. Aluminum Cow Component Summary. Component

Manufacturer

Rating

Engine

Ford 1.8 L TDI

66 kW @ 4000 rpm 200 N-m @ 2000 210 g/kW-hr @ 2000

Transmission

Ford MTX-75

5-speed w/ Reverse 4.06 Diff. Ratio

Motor

Solectria AC gtx 20

12 kW continuous ≤100 N-m ≤12,000 rpm

Inverter

Solectria UMOC 340

56 kW ≤ 210 Arms 200 - 350 Vdc

Battery

Sanyo Sealed NiCad

+/- 24 kW 2.3 kWh

AUXILIARY SYSTEMS For the 1999 Wisconsin FutureCar a number of the parasitic loads were removed from the engine including the air conditioning, power steering and alternator. Selfcontained units that run independently of the engine replaced these systems. Systems which are electrically driven can be easily controlled to match demand periods and are easily controlled. The implementation of the new systems also allowed for optimization of these systems. Air Conditioning - The air conditioner compressor is Matsushita LRA 71. 115 Vac, single phase self contained rotary compressor. The system is capable of removing 16000 BTU/hr. The compressor is run off of a 1.5 hp adjustable speed motor controller, Reliance model SP200. With the removal of its dependence upon the engine speed the new air conditioner can run at required speeds and can even be throttled back. This prevents the air conditioner from having to blend warm outside air to achieve an intermediate temperature improving the efficiency of the system.

WEIGHT REDUCTION In and effort to reduce the weight of the vehicle many components were reconstructed of Aluminum. A more complete description of the benefits and uses of aluminum is discussed in Appendix A. Battery Box – The physical size of the battery box is comparable to the volume of the spare tire well. For this reason, the spare tire well was removed so the battery box could be suspended from the trunk floor without sacrificing any trunk space.

Power Steering - The LYNX 90PS power steering pump was replaced by a DELPHI Electro-Hydrolic (EH) steering module. The EH module contains a 12 volt motor which is directly coupled to a hydraulic pump. The module also contains a controller which adjusts the current to the electric motor proportional to the pumps output pressure. The EH module uses 15 watts during standby compared to 150 watts for the LYNX 90 PS pump. At peak load, it requires 750 watts. The new steering system reduces power draw by up to 80% [11]. 12 Volt System - The 12 Volt system was totally redesigned with the objective of removing redundant systems and excess component weight. The conventional 12 V alternator (9 kg) was removed from the vehicle and replace with two 600 Watt Vicor DC to DC converters (1 kg). In addition, the traditional automotive SLI battery (18 kg) was replaced with a small Bolder thin-metal film lead acid battery (1 kg). The DCDC converters use the high voltage battery pack to Page 8 of 14

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

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 clamped together around the modules. Each battery module is held in the center and at both ends by these sets of acetyl strips, which also serve as excellent insulators. Additional electrical insulation is provided by the shrinktube which covers each of the 56 modules. This design requires a minimum amount of support material while completely restraining the cells. Aluminum structural angle beams 5 cm (2 in) on each side and 3.2 mm (.125 in) thick are used to anchor the acetyl strips together and to mount the entire pack to the vehicle.

rims weighing only 8.2 kg (18 lb.) each. This exchange results in a savings of nearly 9.2 kg (20 lb.) total. Engine Cradle - In a joined effort with Tower Automotive the Wisconsin FutureCar team replaced the stock steel engine cradle with a prototype Aluminum cradle. The original steel engine cradle weighed 22.7 kg (50 lbs) and was replaced by a all Aluminum engine cradle that weighed in at a little over 9kg (20lbs).

The large void in the battery box is used to enclose the entire high voltage switch gear and DC-DC converters. By combining all the HV components and removing redundant systems, a modular HV unit was created. A clear polycarbonate box, for protection, will enclose the battery. The total weight of the battery box is 59 kg (130 lbs). Brakes/Suspension – To reduce the weight and brake drag, CNC 4-piston aluminum brake calipers were installed in place of the Sable stock brake calipers. Typical brake calipers employ a single piston. The brake pads slide on pins when the brakes are released in order to retract the brake pads. Over time, the pin/caliper interface becomes corroded, preventing sliding. When this occurs, the calipers do not fully disengage resulting in a disk drag force which decreases overall efficiency. The 4 piston calipers do not rely on this sliding and actively minimize the residual drag force on the disk. In addition, at 1.1 kg (2.5 lbs) each, they save 3.2 kg (7 lbs) per side over the standard brakes. The AIV was supplied with DurAlcan metal matrix composite aluminum rotors each weighing 2.3 kg (5 lbs) less than the stock steel rotors. In order to adjust for a lighter chassis and modified weight distribution, the team installed Koni coil-over struts on all 4 corners. The struts allow for the adjustment of ride height, camber, caster, toe, and rebound damping. Not only have they allowed us to optimize the handling of the FutureCar, but they will also save about 0.9 kg (2 lbs) per wheel since they have aluminum strut bodies. To fit the newer engine cradle design, the front steel spindles were upgraded to cast aluminum spindles which save 1.4 kg (3 lbs) per front wheel. In addition, the new spindles facilitated the mounting of the new calipers. Through the use of all these aluminum components, the overall vehicle weight will be reduced by 23 kg (50 lbs). Aluminum Wheels – Another opportunity for weight reduction appeared in the wheel rims. The original aluminum alloy rims weighing 10.5 kg (23 lb.) each were replaced with lighter, American Racing aluminum alloy

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Figure 14. Finite element analysis displacement results for a Ford Taurus aluminum engine cradle with a 6 kN load. When replacing stamped steel with aluminum, the strength of the steel can be matched by heat treating the 6061aluminum component to a T6 state. However, the deflection of the aluminum is still approximately 3 times greater than its steel counter-part. Figure 14 illustrates the predicted displacement on the engine cradle for a 6 kN load applied to the bottom of the engine cradle. This load simulates the vehicle cornering with a lateral acceleration of 10 m/s2. Because the static support of the engine is directly onto the uni-body frame in the Aluminum Cow, the maximum stress strain and displacement of the aluminum engine cradle are well within acceptable limits. A-Arms - The A-arms were also replaced with lighter, stiffer aluminum counterparts. Tubular aluminum with a 31.8 mm diameter and 6.4 mm wall were bent and welded in a triangular pattern. In this instance, the volume of material was almost doubled in an effort to create a stiffer yet lighter replacement. Figure 15 shows the completed arms. The steel A-arms weighed 3.7 kg, the Aluminum A-arms weighed only 2.2 kg.

assembled (see Figure 17). The first vehicle was left in its stock configuration. An underbody panel was installed on the second model; this model also included smaller rear view mirrors and a round-corner trunk lid. The second and third models were identical with the front underbody panel being replaced with a air dam on the third model. A slippery smooth finish was applied to each model by spraying them with a lacquer enamel finish.

Figure 15. Aluminum A arms constructed from thick wall aluminum tubing. Engine Mounts- The engine mounts were another item with the possibility for improvement in design. The engine mounts were redesigned out of aluminum and were also examined under finite element analysis to make certain there was not a potential for failure. Figure 16 shows the results of a finite element analysis.

A wind tunnel at the University of Wisconsin was used to perform the study. It was capable of producing wind speeds up to 45 meters per second (100 mph). The cross-sectional area of the tunnel's measurement section was approximately 900 cm2. A plate was installed parallel to the air flow to simulate ground effects. An instrumented arm extended into the bottom of test section to measure both drag and lift on the vehicle. An airfoil shrouded the arm to ensure accurate drag measurements.

Figure 17. A still frame image of a 1/25 scale Ford Taurus during wind tunnel testing. A pitot tube was used to measure the air velocity in the test section. During the experiment, the pitot tube pressure was randomly varied from 2 inches of water to 5 inches of water in 0.25 inch increments and 20 data points were collected for each vehicle test. 8 different test sets were collected to ensure repeatability in the experiment.

Figure 16. Engine Mount finite element stress analysis.

DRAG REDUCTION As shown in Equation 4 of the Vehicle Energy Consumption section, some power loss of a vehicle can be attributed to aerodynamic drag. This loss is dependent on several factors, of which only the frontal area profile and drag coefficient can be changed. The following steps were taken to reduce the Wisconsin FutureCar's frontal area profile, drag coefficient, and coefficient of rolling resistance. Wind Tunnel Testing – An aerodynamic study of the vehicle was performed via wind tunnel testing. Three different Ertel 1/25-scale Ford Taurus models were Page 10 of 14

After post-processing, results were plotted as drag coefficient versus wind tunnel velocity. The results from the 5th data set are plotted in Figure 18. It was observed that at slow speed, the models have the same relative drag coefficient. As the velocity increases, the model with the underbody panel measured the lowest drag coefficient. Compared to the stock model, the underbody panel provided a 6% lower drag coefficient while 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 test are an order of magnitude lower than for the real vehicle, similar or exaggerated relations are expected for overthe-road Reynolds numbers. From the wind tunnel results, the Wisconsin FutureCar Team concluded that the greatest reduction in aerodynamic drag would be realized by streamlining the underbody of the AIV Sable.

Stock

0.73

Air Dam

Drag Coefficient (Cd)

0.75

0.71

Belly

0.69

Linear

the edge of the trunk. The addition of the spoiler creates small-scale turbulence which causes the streamline to recollect sooner behind the vehicle. This decreases the dead zone behind the vehicle and reduces drag. Based on simulation results the spoiler should reduce the overall drag of the vehicle by about 8%. Tires – Equation 2 shows that vehicle power loss is directly related to the tire’s rolling resistance. The UW FutureCar Team has opted to use Goodyear’s experimental low rolling resistance tires. This particular tire has the best available coefficient of rolling resistance - less than 0.00625.

0.67

0.65

0.63

0.61

0.59 15

20

25

30

35

40

45

50

Wind Tunnel Speed (m / s)

ALTERNATIVE ENERGIES

Figure 18. Wind tunnel test data indicates that the use of an underbody panel will reduce the drag coefficient whereas the use of a spoiler will increase it. Aerodynamic Simulation - In an effort to find a way to reduce the drag force of the 1999 FutureCar a 2-D profile of the car was modeled and tested in a finite element program, Fluent 5.0. Different locations and designs of spoilers were simulated to determine which designs were worth pursuing in physical testing.

Solar Array- The 1999 FFC will have two solar arrays, both mounted upon the roof. Each panel is made up of 36 Kyocera 4" square polycrystalline silicon cells connected in series to produce 12Vdc. The two panels are connected in parallel to the cars 12V system. Each panel should be able to supply 50 Watts. This is sufficient to supply the diesel engine's electronics as well as the touch screen computer and other steady state driving loads. During long periods of storage the solar cells will be able to maintain the vehicle's batteries.

INTENDED MARKET Producing a hybrid vehicle that has a high level of consumer acceptability was a high priority for the University of Wisconsin FutureCar Team. Accordingly, the team entered the FutureCar Challenge committed to maintaining full passenger and cargo room in the vehicle, to producing a seamless appearance similar to the original, and to retaining the driving feel of a stock Mercury Sable. The 1999 Wisconsin FutureCar accomplishes all of these goals. The intended market for this car includes drivers looking for a mid–size sedan with the following characteristics: • Figure 19. Fluent analysis of car profile at 30 [m/s]. Figure 19 shows the results of a simulation on the base car profile. The spoiler designs with the smallest drag force were used for physical testing. Underbody Panel – Since approximately 10% of all vehicle drag comes from underneath the car, the Wisconsin team has made a panel that shelters the underbelly. Reinforced, 24 gauge aluminum sheet metal provides a smooth underbody surface which decreases the drag coefficient. Spoiler - From the simulations a trunk mounted spoiler was designed in an effort to reduce the pressure drag of the vehicle. The spoiler is made of Aluminum and is designed as a reversed airfoil, 4 inches long and .5 inches tall. The spoiler will be mounted 5 inches above Page 11 of 14

• •

Enhanced performance 0-100 kph in < 10 seconds 145 kph (90 mph) maximum speed 970 km (600 mi) range Impressive fuel economy 23.9 km/L (56 mpg) 1.1 cents/km (1.8 cents/mi) travel cost Creature comforts Turn-key start up Air conditioning Cruise control Power windows AM/FM radio & cassette player Touch screen computer interface Televisions in both headrests

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

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

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

The design of this vehicle makes it simple to operate, with a conventional turn–key start. No extra switches or buttons are required to start or drive the vehicle. The advanced control strategy allows an operator to achieve the 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 travel another 970 km.

A compact design not only aids in manufacturing but also minimizes the number of serviceable parts. If needed, threaded fasteners are conveniently located so that disassembly is quick and easy.

•

COST ANALYSIS The estimated total cost of the 1999 UW FutureCar at high volume production is $28,000. This cost estimate is based upon a Mercury Sable list price of $21,000, an additional cost of $11,000 for new engineering, and a $4000 savings from replacing the conventional drivetrain. In order to estimate these costs, several assumptions were made. • • • • • •

Just as any prototype vehicle must be modified before it is put into production, the following features of the Wisconsin FutureCar would be changed in preparation for mass production.

The cost of manufacturing the aluminum unibody and enclosure panels is 1.4 times that of manufacturing steel [5]. Components that are not “off the shelf” can be mass produced at a cost of 20-30% of the price that the Wisconsin team paid. All other vehicle components are the same as those 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 to be $54,000. This estimate assumes that the cost of a prototype AIV is $31,000. The remainder of the cost is obtained from the special order prices of the hybrid components.

MANUFACTURING POTENTIAL The Wisconsin FutureCar component selection and packaging has been chosen for ease of procurement, access, and maintenance. This design inherently favors obtaining components and assembling the vehicle in mass production. The current trend in automotive manufacturing is to use common platforms – the use of common components on multiple vehicles (i.e. engines, transmissions, and frames). Adapting to the methods of Ford, GM and Chrysler, the Wisconsin FutureCar team adopted this methodology in 1998. This vehicle could be easily integrated into a conventional vehicle production line and would need supplemental tooling only for installation of the battery pack. The electric motor would simply bolt onto a standard transmission fitted with a special secondary shaft. Additional components would be Page 12 of 14

•

Replace the Pentium control computer with an embedded computer. Design the battery pack to fit behind the rear seat back.

Combining these modifications with the existing design before incorporating the FutureCar into the assembly line would significantly reduce the time and cost of production.

SUMMARY The Wisconsin FutureCar Team has successfully converted a prototype 1994 Mercury Sable AIV into a, power assist, charge sustaining parallel hybrid-electric vehicle. The UW FutureCar was designed to exceed the stock Sable fuel economy and emissions standards without sacrificing performance or consumer acceptability. This was accomplished by using advanced technologies as well as existing automotive science. The team used traditional hybrid-electric components; including an AC induction electric motor with matched inverter; a high power density Ni-Cad battery pack; and a compression ignition internal combustion engine in an attempt to reach the FutureCar Competition fuel economy goal of 80 miles per gallon. In addition, the Wisconsin team incorporated several advanced technologies into its 1999 FutureCar. The use of computer simulation to optimize control software coupled with an aggressive fuzzy logic control strategy helped realize team goals. Finite element analysis such as Fluent and ANSYS were used to minimize vehicle testing time while verifying the integrity of using aluminum and polycarbonate to reduce the vehicle weight. All while keeping the vehicle design cost effective and modular so that it could be implemented into an automotive production line.

9.

ACKNOWLEDGMENTS The outstanding contributions of Advisor Dr. Glenn Bower regarding sound engineering, student education, and professional conduct have been invaluable to the UW FutureCar Team. His dedication, along with the financial support and enthusiasm of the UW College of Engineering, has given team members the ability to flourish with new opportunities and experiences. The patient work of the FutureCar organizers to create and facilitate the Challenge is also greatly appreciated by the members of the Wisconsin team. The funding for such organization, as well as the availability of competition facilities, seed money, and platform vehicles, is made possible by the generous contributions of USCAR, USDOE, USEPA, ANL, Chrysler Corp., Ford Motors, and General Motors. We would especially like to thank Ford with whom we have maintained a close working contact, and from whom we have received much knowledge and help dating back to the initial designs of the 1998 FutureCar. We would like to extend our thanks to all of these organizations who have been instrumental to the FutureCar Challenge and the promotion of energy efficient vehicles.

USABC Electric Vehicle Battery Test Procedures Manual, Revision 2, U.S. DOE, Idaho National Engineering Laboratory, DOE/ID-10479, Jan. 1996 10. PNGV Battery Test Manual, U.S. DOE, Idaho National Engineering Laboratory, DOE/ID-10597, Jan. 1997 11. http:\\www.delphiauto.com, 5-3-99 12. Wiegman, H., Vandenput, A., "Battery State Control Techniques for Charge Sustaining Applications," SAE Publ. 981129, SP-1331, 1998, pp 65-75 , and 1999 SAE Transactions

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)

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

REFERENCES 1. 2. 3.

4. 5. 6. 7. 8.

Thiel, M.P., et al., “The Development of the University of Wisconsin’s Parallel Hybrid-Electric Aluminum Intensive Vehicle,” SAE Publications February 1999, SAE . Bower, G.R., et al. , “Design of a Charge Regulating, Parallel Hybrid Electric FutureCar,” SAE Publications February 1998, SAE 980488. Johnston, Brian, et al. , “The Continued Design and Development of the University of California, Davis FutureCar,” SAE Publications February 1998, SAE 980487. Thomas, C.E., et al., “Societal Impacts of Fuel Options for Fuel Cell Vehicles,” SAE Publications October 1998, SAE 982496. "1.8L DI TCI LYNX 90 PS in Focus - Engine and Vehicle Performance Data", Ford of Dunton, England, November 1998. Cuddy, Matthew R. and Wipke, Keith B. "Analysis of the Fuel Economy Benefit of Drivetrain Hybridization," SAE 970289. Mariano, S. and Tuler, F. and Owen, W., "Comparing Steel and Aluminum Auto Structures by Technical Cost Modeling." JOM, 45(6):20-22, 1993. Gallopoilos, N.E., “Environmental Vehicle,” EDS, Dearborn, MI, 1996.

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Note: Appendix follows on next page.

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

APPENDIX

Alloy & Temper

A. ADVANTAGES OF ALUMINUM - Aluminum is a versatile and useful metal with many advantages, including its light weight, resistance to environmental conditions, high elasticity, ease of working and forming, and the high strength of aluminum alloys (up to and exceeding the strength of steel). For an equal volume of material, 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 sectional area 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.

Ultimate Strength (ksi)

Yield Strength (ksi)

Modulus of Elasticity (ksi)

Alum. 2014-T6, T651 Alum. 6061-T6, T651 Alum. 7075-T6, T651

70

60

10.6

42

37

10.0

83

73

10.4

Steel 1020 HR Steel 1018 A

66 49.5

42 32

30 30

Because of the global need for reduced fuel consumption, the automotive industry is interested in exploring the possibility of substituting aluminum for steel in passenger vehicles. For example, the Audi 5000s had an aluminum frame with a 48.6% lower weight (as part of a joint project between Audi and ALCOA). Other examples of aluminum body construction include US Postal mail cars, the US Army HMMWV multi-purpose vehicles, and semi truck trailers such as those produced by Freightliner Corporation. In all these applications, the use of aluminum has saved money by improving fuel mileage through weight reduction. Its strength has improved the overall designs, while its corrosion resistance prolonged the life of the vehicles. (Aluminum forms a protective oxide coating which prevents rust related failures.) Companies such as ALCOA and BMW are developing new manufacturing processes for aluminum. The BMW 500 series axles were hydroformed for higher stiffness and fatigue strength, and then GMA welded together. Aluminum tends to respond well to GMA and GMAimpulse welding. For high-quality joints, TIG welding is also used.

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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) to achieve high thermal efficiency. Unfortunately, high incylinder temperatures promote the formation of NOx during combustion. It has been found that NOx emissions can be reduced by introducing exhaust gas into the intake charge. This practice is known as exhaust gas recirculation (EGR). NOx emissions can further be reduced by cooling this recirculated exhaust gas. The Ford engine was originally equipped with an EGR intercooler. This heat exchanger lowers the temperature of the EGR stream by using the cooling system as its heat sink. This exchange of heat results in two advantages. First, cooling of the exhaust gas produces lower NOx emissions from forming. Second, the coolant that is heated is then pumped directly to the heating system for the vehicle. This will provide heat to the cabin much more quickly and efficiently than the stock heating system