A Mid Sized Sedan Designed for High Fuel Economy and

A Mid-Sized Sedan Designed for High Fuel Economy and Low Emissions: The 1999 UC Davis FutureCar Mark Alexander, Brian Johnston, David Funston, Brian Huff, Richard Carlson, Nathaniel Meyr, Brian Moran, Bruce Momsen and faculty advisors Dr. Andrew Frank and Dr. Andrew Burke University of California, Davis College of Engineering ABSTRACT The University of California, Davis FutureCar Team redesigned a 1994 Mercury Sable Aluminum Intensive Vehicle as a hybrid electric vehicle (HEV) to meet the following goals: triple the fuel economy, achieve California Super Ultra Low Emissions Vehicle level, and qualify for partial zero emissions vehicle credits in California. Coulomb approaches these goals with an efficient powertrain, low vehicle weight, and an advanced control system. The UC Davis charge depletion control strategy maximizes energy economy and provides substantial all-electric operating capabilities. Coulomb’s powertrain couples a smalldisplacement 32 kW Subaru gasoline engine and a 75 kW Unique Mobility brushless DC motor to a modified Nissan continuously variable transmission. This in-line parallel powertrain is simple, compact, and reliable. The motor is powered by a high-power 19 kWh Ovonic nickel metal hydride battery pack. Simulation results predict this vehicle will achieve 4.8L/100 km on the Federal Urban Driving Schedule and 4.2L/100 km on the Federal Highway Driving Schedule. INTRODUCTION The University of California, Davis FutureCar Team participated in the 1999 FutureCar Challenge, which was sponsored by the U.S. Department of Energy and the U.S. Council for Automotive Research. Mirroring the goals of the Partnership for a New Generation of Vehicles, the competition challenged engineering student teams to redesign a mid-size sedan to triple its current fuel economy without sacrificing performance, utility, or cost. Supplementing these goals, UC Davis focused on qualifying for 80% partial zero emissions vehicle (ZEV) credit under the California Low Emissions Vehicle II amendments. UC Davis competed in the 1999 competition with Coulomb, a 1994 Mercury Sable Aluminum Intensive Vehicle (AIV) converted into a hybrid electric vehicle. 1 Joule, the team's previous Challenge entry, doubled its stock 1996 Ford Taurus fuel economy by achieving 4.7L/100 km (49.9 mpg) for combined city/highway driving. Further efficiency increases with Joule would be limited without extensive weight reduction, controls optimization, and powertrain redesign. Coulomb represents these changes. The aluminum frame reduces vehicle mass and a continuously variable transmission (CVT) facilitates optimization of the control strategy. The powertrain combines custom components that have been designed in conjunction with manufacturers to increase efficiency, reliability, and driveability. The following table lists team's design goals. Table 1. UC Davis FutureCar design goals. Coulomb '99 Equivalent energy efficiency California emissions ZEV range FUDS and FHDS range Highway range 0 to 100 kph acceleration drag: Cd Aerodynamic Curb weight 3.9L/100km (60 mpg) ULEV 130 km 400 km HEV 900 km HEV 11 sec HEV 0.29 1300 kg Long Term 2.9L/100km (80 mpg) SULEV 130 km 400 km HEV 900 km HEV 10 sec HEV 0.27 1225 kg VEHICLE CONFIGURATION CHOICE Electric vehicles (EVs) and internal combustion engine vehicles (ICEVs) each have performance advantages, but it would be difficult to meet the team's goals with the range limitations of an EV or the efficiency limitations of an ICEV. Both vehicle types could meet the goals with sufficient development, but studies at UC Davis show the goals can only be met practically with a combination of electric technology and auxiliary power in 1 a hybrid arrangement. HYBRID CONFIGURATION - A hybrid powertrain combines an electric motor with an auxiliary power unit (APU). These components can be combined in three primary configurations: series, parallel, or dual. Each arrangement has advantages and disadvantages that must be considered during the design of a hybrid. Series Hybrid - In a series arrangement, the APU generates electricity, which is distributed to either the motor or the batteries depending on driving conditions. A series configuration decouples the APU from the road load, allowing the use of almost any power generating device. Furthermore, the APU can be operated at a constant speed and load, optimizing engine fuel efficiency and emissions. However, due to the accumulated inefficiencies of multiple energy transfer steps, the distribution efficiency from the fuel to the wheels is relatively low. Additionally, electricity production often requires a generator coupled to the APU and a separate electric motor to drive the vehicle. Parallel Hybrid - In a parallel arrangement, the APU and electric motor can each provide power directly to the wheels. Direct connection of the APU to the driveline leads to very high transmission efficiency, but limits practical APU choices to internal combustion engines that operate over a range of torques and speeds. The engine provides some of the instantaneous power demand, decreasing the use of the batteries. The powertrain requires only an engine and a motor/generator, but power management of the motor/engine combination can be difficult. Dual Hybrid - A dual hybrid uses a powertrain design that combines series and parallel operation. Toyota’s Prius is an example of a dual hybrid; it uses a motor, an engine, and a generator combined through a planetary power-split device. The engine and generator are connected to two inputs of a planetary gear set, and the motor and final drive are connected to the third input. The generator is controlled to set the speed relationship between the motor/final drive and engine, creating an effective CVT for the engine. Some engine power is transmitted from the generator through the motor to the wheels. This splits the power output of the engine between the mechanical gear path (parallel operation) and the electrical generator/motor path (series operation). This system reduces mechanical complexity by eliminating the conventional planetary clutching systems of an automatic transmission and increases efficiency by continuously varying the effective gear ratio. However, it incurs running losses by constantly circulating some power through the electric path. 2 Configuration Selection - UC Davis chose to use a parallel hybrid arrangement because of its potential to achieve high efficiency. The parallel arrangement also provides an opportunity to significantly reduce vehicle emissions through the use of high-efficiency exhaust after-treatment technology and a well-designed powertrain control strategy. UC Davis has over six years of experience in designing and manufacturing successful parallel powertrains. POWERTRAIN DEVELOPMENT Based on the configuration choice, a powertrain was designed to meet the stated goals for Coulomb. Simulations conducted using Advisor, a publicly available hybrid vehicle simulation program, determined the power and energy requirements for the motor, engine, and battery pack. The simulation results are shown in Table 2. Table 2. Powertrain design requirements. Performance Parameter 65 kph cruising power 100 kph cruising power 65 kph cruising power, 6% grade 100 kph cruising power, 6% grade EV power for 0-100 kph in 11.5 sec Battery capacity for 95 km ZEV range on FUDS Battery capacity for 125 km ZEV range on FUDS Energy/Power Required 4.2 kW 11.7 kW 18.9 kW 34.1 kW 75.3 kW 13.2 kWh 18.1 kWh Practical considerations learned from Joule helped to specify a powertrain with good performance, energy economy, and utility. Joule's powertrain was highly efficient, but suffered driveability problems that would make it unacceptable to a consumer. It used a manual transmission and a slightly under-powered electric motor. The motor and discrete gear transmission limited the energy recovered during regenerative braking and differed from the powerful automatic powertrain expected of vehicles in this class. It was determined that only a continuously variable transmission could meet the efficiency goals while providing the automatic operation demanded by buyers of modern family sedans. The CVT allows the engine and electric motor to operate at their highest efficiencies for each power required. This is possible since wheel speed and powertrain speed are decoupled by the infinite selection of gear ratios between a minimum and a maximum. The CVT also increases regenerative braking efficiency. Joule also had problems with two of the major power transmission components. The rubber drive belt that coupled the motor to the transmission generated high levels of noise. The electromagnetic clutch that coupled the engine to the transmission caused a slight disruption to the vehicle when engaged. These problems were solved by coupling the motor directly to the transmission and by using an electronically controlled automotive friction clutch to engage the engine. Coulomb uses an in-line, parallel hybrid powertrain which integrates the latest technologies in internal combustion engines, transmissions, and electric motors. A small displacement engine and permanent magnet brushless DC motor are directly coupled to a CVT. A diagram of the powertrain is shown in Figure 1. All conventional engine accessories (starter motor, alternator, cooling fan, power steering pump, and air conditioning compressor) and the mechanical reversing system have been removed and replaced with electric systems. This powertrain design focuses on simplicity, reliability, and manufacturability. Components are either production items or were custom designed with a manufacturer. Modifications use standard materials, tolerances, and design practices. Flywheel and Clutch IC Engine CVT Electric Motor addition of an electric motor mount, and replacement of the mechanical-hydraulic pressure control system with a computer controlled electro-hydraulic pressure control system. Figure 2 shows the high pressure pump, shifting valve body, and reversing components removed from the Nissan CVT and the equivalent replacements added by UC Davis. Nissan Components Final Drive UC Davis Components Figure 2. Internal CVT mechanical simplification. HARDWARE IMPLEMENTATION - Mechanical changes to the CVT were made with the goal of removing unnecessary components while retaining as many stock components as possible. The bi-directional rotation of the electric motor allowed removal of the reversing gear set and all of its related clutch components. The electric motor's high torque at low speed and the lack of engine idle in the control strategy eliminated the need for a torque converter. These modifications reduce the mechanical complexity of the CVT and the operating losses caused by these systems. To couple the electric motor to the transmission, an internal spline was machined into the back end of the input pulley shaft. A custom bracket was manufactured to mount the motor to the case. The stock hydraulic pump and electro-mechanical control system were replaced with computer controlled servo hydraulic pumps to improve system efficiency. The stock hydraulic pump was designed to supply the flow rate required for shifting, lubrication, and maximum belt clamping pressure at low engine speeds. As engine speed increases, the flow rate from this positive displacement pump increases. Since clamping pressure depends only on torque demand instead of engine speed, pressure in the stock system is maintained by increasing fluid bleed-off. Therefore, system losses increase with engine speed. To improve system efficiency, the stock hydraulic pump and electro-mechanical control system were replaced with computer controlled servo hydraulic pumps. This system decouples flow rate from engine speed, and provides the necessary flow rate and clamping pressure on a demand basis, with no bleed-off. 3 Drive Shafts Figure 1. In-line Powertrain Schematic. The powertrain components will be discussed individually in the following sections. CONTINUOUSLY VARIABLE TRANSMISSION CVT SELECTION - The selection of a CVT was limited by available production CVTs capable of meeting the design goals. Transmissions produced by Honda, Volvo, and Nissan were investigated for use in this powertrain. Table 3 shows the maximum allowable torque of each transmission, which indicates its acceleration potential. Table 3. Torque capacities of production CVT's. Class 1.6 L 1.8 L 2.0 L Maximum Allowable Torque 140 Nm 145 Nm 290 Nm Honda Volvo Nissan The Nissan CVT was chosen because of its high maximum allowable torque. A metal push belt transmits torque between two pulleys, which can open and close to change the effective radii. The transmission was modified to improve efficiency and mechanical simplicity. The major changes made to the system include: removal of the reversing planetary gear set and torque converter, Initial bench testing has shown an order of magnitude reduction in parasitic hydraulic losses. The hydraulic circuit including pumps, pressure regulators, and pressure transducers is shown in Figure 3. Output Pulley To maintain pressure in the secondary pulley, a digital controller operates the pressure maintenance pump. The controller uses a proportional-integral (PI) feedback algorithm with pressure command feed forward and ratio shifting disturbance feed forward to command the torque output of the pressure maintenance motor. Controller design was performed using MATLAB simulations and the control gains were hand tuned. The control loop runs at 200 Hz. Figure 5 shows a block diagram of the secondary pressure control system. Shift cmd Ksff Shift Pump Kff P Clamping Input Pulley Pump Sump Figure 3. CVT hydraulic system schematic. CONTROLS IMPLEMENTATION - UC Davis designed the control system for the servo-hydraulic pumps used to regulate secondary pulley pressure and gear ratio. Secondary Pulley Pressure Control - The amount of torque that the CVT can transmit is a function of its gear ratio and the pressure in the secondary pulley, as shown in Figure 4. If the torque input exceeds the CVT torque capacity, the CVT belt slips resulting in possible failure of the belt and scoring of the pulleys. The powertrain control module (PCM) uses the accelerator and brake pedal positions to determine how much torque the driver desires to use, and it sets the secondary pulley pressure accordingly. However, there is a slight delay between the pressure command and the pulley pressure response, so the PCM also limits the torque output of the powertrain to a level that the instantaneous pressure in the secondary pulley can transmit. Pressure cmd CVT I satu satu Figure 5. Pressure control block diagram. CVT Ratio Control - The pump in the circuit between the primary and secondary pulleys of the CVT is the ratio shifting pump. A second digital controller independently operates the ratio shifting pump to move fluid back and forth between the primary pulley and secondary pulley. This controller uses proportional feedback of the ratio and ratio time derivative to command the torque output of the ratio shifting motor. It also feeds the shift motor command to the secondary pulley pressure controller for shift disturbance compensation. This controller was designed with the aid of MATLAB simulations and runs its control loop at 50 Hz. Figure 6 is a block diagram of the CVT ratio control system. To pressure system Rcmd re rdcmd Kr rde rdot Krdd Krdot CVT 1/s R 3.5 MPa 300N-M Input Torque on Primary Pulley Figure 6. Shift control block diagram. The development of the ratio control loop took a very interesting turn in mid-development. It was first thought that a velocity controlled shift motor was necessary to maintain proper shift control. This method proved very difficult to implement. In general, the desired rate of change of ratio is very slow, so low speed and zero speed commands are common. This operating range is difficult for velocity controlled servo systems, which will consume significant power to actively maintain zero speed. CVT seal leakage in the primary pulley also must be compensated for with flow through the shift pump. When using a velocity controlled motor, precise information on the flow rate to the primary pulley is necessary to ensure that the motor 4 Pressure P cmd P ct 50N-M 0.7 MPa 0.434 Overdrive Ratio 2.326 Reduction Figure 4. CVT torque capacity map. rotates at the correct rate. This information is not available, making this type of control very difficult. For these reasons a current controlled motor setup was chosen, with an additional compensation loop in the control software. INTERNAL COMBUSTION ENGINE The first step in selecting an engine that meets the requirements for space, power output, efficiency, and emissions was choosing a fuel. FUEL SELECTION - The fuel used has to be capable of achieving both low emissions and high fuel economy while maintaining vehicle practicality. The main fuel options were compressed natural gas (CNG), diesel, methanol, ethanol, and reformulated gasoline (RFG). Compressed natural gas has high potential for emissions reduction and good potential for vehicle efficiency due to its high compression ratio. However, there are currently some practical problems in a passenger car application. Even when stored at pressures as high as 20 MPa, the volumetric energy density (kWh/L) is low, requiring large tanks to meet range goals. Additionally, CNG is not yet widely available at the pressure and purity required for vehicle operation. Diesel fuel is already used in the transportation industry, so it is widely available, inexpensive, and practical. Diesel engines generally have high thermodynamic efficiency due to the lean-burn properties of diesel combustion. Unfortunately, the long hydrocarbon chains tend to cause particulate formation, and the lean-burn cycle tends to cause high nitrogen oxide emissions. The development of effective aftertreatment devices for diesel engines is in the initial stages. With current technologies, the use of diesel fuel would make it difficult to achieve the emissions targets. Methanol and ethanol have been suggested for use in reducing vehicle emissions, but thus far many other fuel types, including RFG, have shown the ability to 2 match them. The production of methanol and ethanol is currently inefficient and uneconomical. The total energy expended on production of these fuels is higher than 3 most other conventional fuels. Both fuels have potential for vehicle use, but they do not represent a significant advantage over RFG. Reformulated gasoline was introduced in California to replace conventional gasoline. It can be burned in an engine designed for normal gasoline operation, but its formulation reduces heavy aromatics, light olefins, benzene, and sulfur levels. This contributes to lower hydrocarbon, carbon monoxide, nitrogen oxide, and 4 particulate emissions. After-treatment technology for gasoline engines is well developed and is continually improving. RFG also benefits from an established and efficient fuel processing and distribution infrastructure. The UC Davis team chose RFG due to its ability to provide efficiency increases and its potential for decreasing emissions with a widespread fuel infrastructure and consumer familiarity. ENGINE CHOICE - The gasoline engine was selected to meet the driving requirements of the vehicle. The most important considerations were the required power and total length. The engine must also have low fuel consumption and emissions and be lightweight and compact. Simulation results and real-world testing with Joule established that 30 kW would be required for hill climbing and acceleration requirements. Additionally, the engine must operate very efficiently at 12 kW, the expected power requirement at a highway cruise of 105 kph. These power requirements eliminated many small industrial engines. The entire in-line powertrain had to be less than 945 mm in length to fit into the powertrain bay without chassis modification. The motor and transmission lengths were fixed, leaving 450 mm for the engine. This limitation eliminated most of the engines available, and necessitated a worldwide engine search. Practical considerations were used to further narrow the engine choices. The engine must rotate clockwise to match the direction of the CVT. It needed to be water-cooled, lightweight, and easily adaptable to the transmission. This final consideration eliminated most motorcycle engines, which integrate the transmission case into the engine block casting. The engines that met these criteria are summarized in Table 4. The Orbital engine has gone through a limited pilot production, while the Subaru and Toyota engines are currently in mass production. The Subaru engine powers a small Japanese car called the Vivio and the Toyota engine is found in the Prius hybrid. Table 4. Engine choices. Engine Options Orbital Toyota Prius Subaru Vivio Min. BSFC Power Length Displace(g/kWh) (kW/rpm) (mm) ment (cc) 270 230 260 40/6000 43/4000 32/6000 290 445 360 800 1497 658 The two-stroke engine from Orbital Engine Company achieves low fuel consumption and emissions due to its direct injection and oil metering systems. The engine meets the power and length requirements. It is the lightest and smallest of the engine options, but could not be obtained prior to the 1999 Challenge. The Toyota Prius engine is designed specifically for use in a HEV. The high-expansion-ratio engine matches the low fuel consumption of small automotive direct injection diesel engines. This is accomplished by setting the mechanical compression ratio at 13.5:1, but operating the engine with an effective compression ratio of 4.8:1 to 9.3:1 by using variable valve timing. Engine displacement and a low maximum speed allows reduced frictional losses. The lowest effective compression ratio is used to counter engine vibration during starting. The engine operates at a stoichiometric air-fuel ratio over its entire range and uses a close-coupled three-way 5 catalyst to produce very low emissions. This engine is ideally suited for use in Coulomb and was the team’s 5 primary choice, but it was unavailable due to limited production quantities and proprietary concerns. The Subaru Vivio four-cylinder engine was selected based on its power, size, efficiency, and availability. It uses a sequential closed-loop fuel injection system to operate at a stoichiometric air-fuel ratio, which minimizes fuel consumption and emissions. The engine operates smoothly and quietly and protects itself from system failures. Spare parts, diagnostic equipment, and technical support are readily available since it is currently mass-produced. INTEGRATION - Integrating the engine required the manufacture of a transmission mounting plate and the installation of a custom cooling system. The most significant integration challenge was developing a coupling system that allowed reliable, efficient, and smooth on-off engine operation. Engine Coupling System - In order to allow allelectric operation, the coupling clutch between the engine and transmission must completely engage and disengage the engine. It should lock in the open and closed positions without consuming power and should return to the closed state upon failure of the actuating system. The stock engine friction clutch will meet all of these requirements with the addition of an automatic actuating system that locks the clutch open. A small industrial linear actuator with a normally closed holding brake was selected to move a stock Chevrolet Geo clutch fork. When the engine is being engaged, it is started from a stop by slipping the clutch. Position feedback from the linear actuator is used by a microcontroller to regulate the rate of clutch engagement. This, along with added torque from the electric motor and up-shifting the CVT, diminishes the severity of the negative torque spike on the powertrain during engagement. EMISSIONS CONTROL SYSTEM - The goal of meeting very low emissions is difficult to achieve with a powertrain control strategy that requires on-off engine operation. An emissions system using mostly stock components was used for the competition, but the development of a more advanced system is part of an ongoing research program. Testing for this research will involve an evaluation of an electric heater for fast warmup and phase-change material for heat retention. ELECTRIC MOTOR The in-line powertrain requires a compact motor with high torque capacity and a speed range that matches the transmission and engine. Joule used a Unique Mobility (UQM) brushless DC motor designed for electric vehicles with performance characteristics very similar to those required. For Coulomb, the UC Davis team contacted UQM to design an electric motor optimized for use in a parallel HEV. UC Davis established the required physical and performance characteristics of the new motor, designated SR218SSH. The CVT maximum allowable torque input is 290 Nm and maximum engine output is 6 50 Nm, so maximum motor torque was chosen to be 240 Nm. Maximum power was selected to be 75 kW to meet the acceleration goal. Motor length was limited to 130 mm by the transmission and frame rail. The diameter was constrained to 280 mm for proper drive shaft clearance. Table 5 lists the specifications of the SR218H EV motor and the SR218SSH hybrid motor. Table 5. Electric motor specifications. Parameter SR218H (EV) SR218SSH (HEV) Maximum torque 226 Nm 240 Nm Continuous torque 150 Nm 100 Nm Maximum power 53 kW 75 kW Continuous power 32 kW 30 kW Maximum speed 8000 RPM 6000 RPM Maximum efficiency 94% 92% Length 216 mm 127 mm Diameter 280 mm 280 mm Mass 47.6 kg 28.6 kg UQM manufactured the SR218SSH motor and met all of UC Davis's requirements for hybrid use. Its peak power is two and a half times greater than its continuous power and its size and weight are much less than the similar SR218H EV motor. This is possible because the engine provides some motive power, so the motor's duty cycle is reduced. The only drawback is a slight reduction in peak efficiency. Figure 7 shows the most efficient range of the motor to be around 4000 RPM. At 2500 RPM, which corresponds to the engine's peak efficiency region, motor efficiency is also good at low power. This results in a high combined efficiency when the engine and electric motor are both providing power. Figure 7. SR218SSH motor efficiency map. The UC Davis Team worked with UQM to design the motor output shaft and mounting interface with the CVT. The output shaft is a floating quill shaft that transmits torque through splines at each end. This design allows a slight misalignment between the motor and CVT. Otherwise, almost perfect alignment would be required for long life. The shaft was manufactured from heat-treated 8620 steel and designed to have a life exceeding 1000 hours with a misalignment of .25 mm. The conical shape of the transmission allowed UQM to extend the internal components of the motor beyond the 127-mm length to meet the design requirements. The motor mounting interface seals the concave face of the motor to the CVT with an O-ring, which allows transmission fluid to lubricate the splines. The mount is made from 6061 aluminum and has a centering register to assure proper alignment of the motor during assembly. Figure 8 shows an exploded view of the final motor design and cross-section of the CVT. 100 Engine Turn-On Speed (kph) Engine and Motor Motor Only 0 100% (0 km) 50% (100 km) 10% (400 km) State of Charge (Distance Traveled) Figure 9. Engine control strategy. Coulomb's control strategy can displace gasoline usage with electrical energy usage. Figure 10 shows the gasoline usage for Coulomb and for a CAFE vehicle (Corporate Average Fleet Economy). Coulomb uses electrical energy to satisfy initial vehicle travel. Single Vehicle Vehicle Liters of Gasoline Consumption 40 35 30 25 20 15 10 5 0 0 100 200 300 400 Figure 8. SR218SSH motor and CVT cross section. VEHICLE CONTROL STRATEGY Coulomb uses a charge depletion control strategy in combination with an ideal operating line CVT shifting strategy. In a charge depletion (CD) system, the batteries are charged by an off-board charger and regenerative braking. Over a typical driving schedule, the state of charge (SOC) of the battery pack decreases. This differs from the charge-sustaining strategy often used in HEVs, where the APU is used to maintain the battery SOC. The CD strategy avoids the inherent energy conversion losses in an ICE/alternator combination and the battery charge/discharge losses. CHARGE DEPLETION - Coulomb uses the charge depletion control strategy illustrated in Figure 9. At the engine turn-on speed, the powertrain transitions from allelectric operation to assisted-engine operation. During city driving at a high state of battery charge, Coulomb operates as an EV. At highway speeds or at a low state of charge, the vehicle uses the engine to decrease the rate of battery depletion. Lowering the engine turn-on speed increases the proportion of time that the engine is on, allowing more range per unit of electrical energy used. The strategy biases initial vehicle operation to electricity, but allows the range to be maintained by increasing gasoline usage as battery charge depletes. A city cycle driving range of 400 km is possible before recharging the battery pack. Typical highway driving occurs at speeds in the assisted-engine regime, so range is limited by fuel storage capacity instead of the energy stored in the battery pack. CAFE Vehicle Charge Depletion Vehicle Distance Traveled (km) Figure 10. Single vehicle fuel economy. The total gasoline displacement is especially effective when the American daily driving distribution is considered. Figure 11 shows that about 75% of drivers 6 could travel on Coulomb's ZEV range alone. Figure 12 shows gasoline consumption weighted with the population distribution. This distribution demonstrates that a fleet of CD vehicles like Coulomb can displace significantly more gasoline than single vehicle performance would indicate. A fleet of vehicles like Coulomb uses approximately 8% of the gasoline of a fleet of conventional vehicles. A study using similar data found that a charge depletion vehicle can operate for approximately 73% of 7 its annual travel using stored electricity. The California Air Resources Board (CARB) has recognized this gasoline displacement and revised the LEVII requirements based on NPTS Vehicle Miles Traveled 8 data. CARB will give partial Zero Emissions Vehicle credits to vehicles which meet a new Super Ultra Low Emissions Vehicle standard at 250,000 km and have zero evaporative and refueling emissions. Partial ZEV credit is calculated using fuel-cycle emissions, all-electric range, off-vehicle charging capability, and use of advanced batteries. Coulomb is eligible for up to 80% partial ZEV credit under these regulations. 7 1 Fraction of Drivers Satisfied 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 25 50 75 100 125 150 1 7 5 200 225 2 5 0 275 300 325 350 375 400 engine operation, the IC engine IOL is used to set the transmission gear ratio. This strategy maximizes steady state energy economy. During transient operation, the control system allows deviations from the IOL to improve driveability. DRIVEABILITY AND PERFORMANCE - Use of the CVT and the IOL control strategy requires a drive-by wire-control system, so the IC and electric motor output commands are not directly connected to the accelerator pedal. The powertrain controller sets the throttle and torque command based on accelerator and brake pedal positions and powertrain speed. During transient operation, the powertrain cannot instantly obtain the IOL speed for the power output commanded by the driver. To maintain driveability, the powertrain controller uses the electric motor to instantaneously provide requested power and shifts the transmission towards the ideal operating point for that power. Figure 13 illustrates this process. Constant Power Line 400 Distance (km) Figure 11. Cumulative daily travel. Vehicle Liters of Gasoline 8.0 Consumption (x10 ) -8 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 CAFE Fleet Charge Depletion Fleet 100 200 300 Power km Traveled Figure 12. Daily gasoline usage of a representative fleet. A study using similar data found that a charge depletion vehicle can operate for approximately 73% of 9 its annual travel using stored electricity. The California Air Resources Board (CARB) has recognized this gasoline displacement and revised the LEVII requirements based on NPTS Vehicle Miles Traveled 10 data. CARB will give partial Zero Emissions Vehicle credits to vehicles which meet a new Super Ultra Low Emissions Vehicle standard at 250,000 km and have zero evaporative and refueling emissions. Partial ZEV credit is calculated using fuel-cycle emissions, all-electric range, off-vehicle charging capability, and use of advanced batteries. Coulomb is eligible for up to 80% partial ZEV credit under these regulations. IDEAL OPERATING LINE - The IC engine efficiency varies dramatically over its operating range. For each possible power output there is an output speed which allows optimum fuel efficiency. The collection of these points for every power output is called an Ideal Operating Line (IOL). Like the IC engine, the electric motor has its own IOL. These IOLs are used to optimize energy efficiency. Coulomb's CVT can achieve any gear ratio between low gear and overdrive. For a given output speed, the transmission can accommodate a wide range of input speeds whereas discrete gear manual and automatic transmissions typically only allow 3 to 5 input speeds. This allows a CVT vehicle to keep the electric motor or the gasoline engine operating on their IOLs for steady state operation. During all-electric operation, the CVT ratio is set to operate the electric motor on its IOL. During assisted8 Increase in Power Command. Motor IOL Speed Figure 13. Engine IOL operation example. During IC operation, the powertrain controller uses the IC to provide as much power as possible to the wheels while staying on its IOL. In most cases, the IC operates at wide open throttle while the CVT shifts to change the IC power output. The powertrain controller uses the electric motor to provide the power needed to satisfy the driver's instantaneous demands. Power Control & Torque Control - The IOL control algorithm requires a power request to perform its throttle and CVT ratio calculations. At low speeds, most power commands translate into very large torque commands that are unattainable. An implementation of power control alone would make the response to the pedals so sensitive that the vehicle would be undriveable. The solution to this problem is to divide the interpretation of the accelerator and brake pedals into two different regimes. One regime is a torque command area for control at low speeds, and the other is a power command at medium and high speeds. Under torque command, the accelerator position is proportional to the torque demanded from the wheels. The CVT gear ratio is maintained at the lowest gear, and the IOL’s of the electric motor and IC are ignored. By using this type of control at low speeds, vehicle driveability is maintained. The powertrain transitions from torque control to power control at 20 kph. At this vehicle speed, the powertrain speed is high enough to maintain the IOL shifting algorithm for the CVT. In the power control mode, the powertrain controller interprets the pedal positions as power demands for input to the IOL shifting algorithm. CONTROL HARDWARE - The powertrain control module is a Z-World BL1700 microcontroller. This 16 bit processor has similar capabilities to the Motorola 6800 series microcontrollers currently used in automotive controlers, so implementation of the vehicle control software in current automotive microprocessors would require minimal effort and cost. The BL1700’s main advantage over other controllers is its remote programming ability, which aids program development and testing. An additional feature of the BL1700 is a watchdog timer, which automatically resets the controller if the controller crashes. This feature allows the PCM to recover from unforeseen software errors and hardware glitches. The PCM monitors accelerator pedal position, brake pedal position, vehicle speed, powertrain speed, CVT gear ratio, CVT pulley pressures, battery pack state of charge, and transmission selector position to determine how to operate the car. It controls the electric motor torque, regenerative braking, electric motor direction, the IC clutch, the IC ECU relay, the CVT secondary pressure setting and the CVT ratio setting. A key feature of the UC Davis powertrain control module is a graphical user interface (GUI) running on a laptop personal computer. This interface allows an engineer to record data from the PCM, adjust control parameters in real time, and override normal control outputs. The driver does not need to use the GUI to operate Coulomb. TRACTION BATTERY BATTERY SELECTION - The choice of battery is important for maximizing the efficiency and emissions benefits of the charge depletion control strategy. The battery needs high specific energy to provide sufficient energy storage for a long all-electric range. High specific power or low internal resistance permits maximum recovery of regenerative braking energy and allows fullpower accelerations to low states of charge. High energy density minimizes packaging requirements, which is important when converting an ICEV into a HEV. The battery should also have a high cycle life and be maintenance free to be consumer acceptable. The choice of battery for Coulomb began during the development of Joule. Joule used a nickel metal hydride (NiMH) battery pack from Ovonic Battery Company since it met all of the requirements necessary to successfully implement the charge depletion control strategy. This battery pack consisted of 90 Ah cells designed for electric vehicles. Specific energy was high at 70 Wh/kg, but specific power was only adequate at 220 W/kg. Since that time, Ovonic has developed a high-power 9 NiMH battery with high specific energy that is intended for use in HEVs. UC Davis worked with Ovonic to develop a battery pack that is ideally suited to the operating characteristics of a charge depleting HEV. This battery has been optimized for both pulse power and EV use by changing the cell chemistry to achieve high energy density, high power density, and long cycle life. Table 6 lists the physical characteristics and performance information of a 28 Ah module and a 60 Ah module. Table 7 shows the properties of a 316 V nominal battery pack constructed from each module. This voltage matches the nominal input voltage of the electric motor system. Table 6. High-power HEV NiMH battery specifications. Battery Specifications Nominal voltage Nominal capacity Mass Specific energy Energy density Specific power (50% DOD) Power density (50% DOD) OBC 7-HEV-28 7.2 V 28 Ah 4.3 kg 48 Wh/kg 102 Wh/L 550 W/kg 1200 W/L OBC 14-HEV-60 14.4 V 60 Ah 13.3 kg 70 Wh/kg 190 Wh/L 500 W/kg 1300 W/L Table 7. 316 V nominal battery pack properties. Pack Properties Nominal voltage Nominal energy Peak power (50% DOD) Mass Number of modules OBC 7-HEV-28 316.8 V 8.9 kWh 104 kW 189 kg 44 OBC 14-HEV-60 316.8 V 19.0 kWh 146 kW 293 kg 22 Vehicle simulations were used to determine the trade-offs between weight, energy economy, and allelectric range for each battery pack. The charge depletion control strategy was set to maximize allelectric range and to have a city driving range of 400 km. Table 8 lists the simulation results. A vehicle with the 60 Ah pack has five times the initial all-electric range with only a 3.3% reduction in energy economy. For this reason, the 60 Ah battery pack was chosen for Coulomb to maximize partial ZEV credit without compromising efficiency or performance. Table 8. Vehicle simulation results for 28 Ah and 60 Ah battery packs. Vehicle Performance FUDS energy economy FHDS energy economy Initial all-electric range Total all-electric range 0-100 kph acceleration OBC 7-HEV-28 4.6 L/100 km 4.1 L/100 km 19 km 64 km 10.5 sec OBC 14-HEV-60 4.8 L/100 km 4.2 L/100 km 101 km 145 km 10.75 sec BATTERY BOX INTEGRATION - The batteries were placed in two long boxes between the center tunnel of the vehicle and the side frame rails. Each box extends from the firewall to the rear passenger foot well. The location of the pack required removing the floor and tunnel, which were replaced with the structure shown in Figure 14. The battery box was split into a two-part structure, with replacement beams used as the top half of the enclosure. Shallow tubs containing the batteries were bolted to the bottom of the structure to complete the lower half of the box. This design allows easy removal of the batteries and allows the addition of corner supports and crossbeams across the top of the batteries to increase the car's torsional stiffness and ensure secure seat mounting. THERMAL MANAGEMENT - A cross-flow cooling system was designed to minimize the battery box height. This allows the ride height to be maintained without intruding into the passenger compartment. The air is taken from the passenger compartment to ensure that the ambient temperature does not reach extremes. At temperatures below 5°C and above 35°C the capacity of the batteries is significantly reduced. The comfort level of the passengers ensures that the inlet temperature is maintained in this range. The eleven 12-cell modules are arranged laterally in the enclosures with gaps between them for airflow. The large centrifugal blowers mounted near the rear wheel well draw air in through the tunnel, diagonally between the batteries and out under the frame rails. This flow pattern is shown in Figure 16. The large volume of the exhaust plenum ensures that the pressure drop along its length is negligible. Figure 14. Battery box structure. BATTERY BOX FABRICATION - The battery boxes were designed and fabricated to be strong, lightweight, compact, and safe. The exterior of the box was constructed using 1.6 mm 5052 sheet aluminum, which has good strength, weld-ability, and ductility. The floor of the box consists of a layer of carbon fiber, a 6 mm layer of foam, and three layers of fiberglass for electrical insulation as shown in Figure 15. The batteries are spaced apart by strips of ABS plastic laminated to the floor. Lengths of T-section aluminum insulated by ABS and rubber secure the batteries to the floor of the tub. An aluminum angle frame was riveted to the edge of the aluminum tub to increase strength and provide a mounting bracket. The frame rails and the top of the box were insulated with two layers of fiberglass. Figure 16. Battery box air flow. The airflow through the battery box is controlled by a thermal management system located in the front portion of the box. Temperature sensors monitor the temperature of six locations inside each box. A microcontroller processes these temperatures, determines the required flow rate and sends pulse width modulated power to the corresponding fan. If the temperature continues to increase with the fans at full duty cycle, a signal is sent to the HVAC controller to turn on the compressor and duct air to the inlet plenum. If the temperature is still increasing, a signal is sent to the powertrain control module, which limits the power draw by the electric motor. BATTERY CHARGING – The 60 Ah battery pack charges from 10% to 100% SOC in 6.5 hrs using the standard charging profile for NiMH batteries (20 A constant current, 390 V constant voltage, 5 A constant current equalization). The pack is charged using a standard inductive charging system, commonly found in every major metropolitan area throughout California and Arizona. Fiberglass Foam Carbon Fiber Aluminum Figure 15. Battery box material construction. 10 LOAD SENSITIVITY ANALYSIS A sensitivity analysis was performed on Coulomb to determine the importance of various road and accessory load reductions. Figure 17 shows the results of this sensitivity analysis centered around estimated parameters for the stock Mercury Sable AIV. C o u l o m b Electric Drive Efficiency Sensitivity Federal Urban Driving Schedule 200 190 Figure 18. Body design for CD reduction. BODY REDESIGN - Research based on test data suggested that a CD reduction to 0.29 would require slight modifications to the front end, extensive modifications to the rear end, and the addition of belly 11,12 pans, rear wheel fairings, and rocker panels. All redesigned body panels were manufactured from carbon fiber composites with plastic and aluminum fixtures added to aid in manufacturing and mounting. Carbon fiber was chosen for its high strength to weight ratio, stiffness, and its ability to easily form complex curves. Actual production versions of these panels would likely use aluminum or glass-mat thermoplastics. Front End - The front bumper was modified to smooth out the airflow and promote attached laminar 13 flow over the front portion of the car. Other configurations could have reduced the CD further, but were impractical due to packaging restrictions such as radiator placement and battery charging interface. The changes to the front end are illustrated in Figure 19. Vehicle Watt-hours per Mile 180 170 160 Vehicle Frontal Area (Af), Drag Coefficient (Cd) Vehicle Mass Coefficient of Rolling Resistance, Crr Electrical Accessory Load -20% -10% 0% 10% 20% 30% 150 140 -30% Percent Change in Parameter Figure 17. Sensitivity analysis. The mass sensitivity curve has the steepest slope, so energy economy is most sensitive to reductions in vehicle mass. For this reason, UC Davis chose the AIV, which is 325 kg lighter than the stock steel vehicle. This represents a 21% reduction in mass, which translates to a 12% increase in fuel economy. Low weight was stressed for all modifications and additions to the AIV. Rolling resistance had the second largest effect on energy economy. Replacement of the stock tires ( Crr = 0.008) with Goodyear low rolling resistance tires (Crr = 0.0055) was an easily implemented fuel economy improvement. Any further decrease in rolling resistance could only come from a more advanced tire technology. Aerodynamic drag and accessory loads are the only loads left for reduction. To reduce these, UC Davis focused on refining aerodynamics and reducing the accessory loads of the climate control and power steering systems. AERODYNAMICS AND BODY DESIGN A reduction in vehicle drag coefficient (CD ) will substantially decrease the power required to drive the car, especially at highway speeds. Body modifications were limited by the competition rules and the dimensions of the original 1994 Mercury Sable frame. Tuft tests were performed to help visualize the airflow over the vehicle and locate critical areas. Three main trouble areas were identified: the base of the windshield, the base of the rear window, and the entire rear portion of the vehicle. The windscreen orientations were fixed by the competition rules and the complexity of the work required. However, drag could be reduced through body modifications to the front, rear, and bottom of the car. Figure 18 shows the estimated airflow improvements. 11 Figure 19. Original vs. new front end design. Rear End - The back end of the vehicle was divided into two main areas, the trunk lid and the bumper. The rear bumper was reshaped to blend with the back belly pan and wheel fairings. The aluminum trunk lid was retained because of its low mass, but a carbon fiber addition to the end creates a sharper deck edge and integrates the lid into the rest of the rear end. Small sections were added to each side of the rear end to continue the new deck edge. The changes to the rear end are illustrated in Figure 20. Belly Pans - Five belly pans were added to smooth 14 the airflow under the car. The front belly pan guides the air under the vehicle. This flow continues across the center section, which is constructed out of three separate panels. Two of the belly pans double as skid plates for the battery boxes, and the third panel covers the center section between the battery boxes. The rear belly pan covers the rear section of the vehicle and smoothes airflow to the back bumper. Figure 21 illustrates these changes and shows the estimated C d reductions. weight. Despite the drop in vehicle thermal loads, peak system loading is unaffected since the hot soak temperature for a stationary vehicle remains the same. SYSTEM DESIGN - Research concluded that a heat pump was the least complex and most energy 17 efficient temperature control system available. As a result, integration of this technology using advanced components was pursued. Sizing system component capacities for steady state conditions would increase efficiency at the cost of poor peak system performance. In contrast, sizing components for the peak load would offer fast hot-soak "pull-downs" while increasing energy consumption at steady state. The nominal peak design capacity was selected at 4.68 kW (16,000 BTU/hr) based on computer modeling and input from industry experts. The system design was validated and optimized through laboratory bench tests. The piping and instrument diagram is shown in Figure 22. The system uses a Sanden SHS 33 variable-speed, electric scroll compressor. Volumetric output of the compressor can be varied to meet pumping demands, which reduces energy consumption. An additional improvement over the stock automotive system is the replacement of the orifice tube with thermostaticexpansion valves for better flow control over the range of compressor speeds. The refrigerant used in the system is 1.2 kg of HFC 134a. A fin and tube external heat exchanger was chosen to take advantage of the large surface area and depth available. The shape of the heat coil and the multi-flow configuration increases heat rejection and increases 18 performance at very low temperatures. To further reduce energy consumption in cooling mode, a concentric tube heat exchanger (subcooler) was added in series between the external coil (condenser) and the stock cabin coil (evaporator). The liquid refrigerant to the evaporator is subcooled by the air entering the compressor prior to entering the evaporator, increasing the heat absorption capacity. External Coil Cooling Heating 15,16 Figure 20. Original vs. new rear end design. Figure 21. Belly pan design and estimated CD reduction. The front and center sections are flat panels parallel to the road. The back panel are slightly inclined to meet with the back bumper and help direct the airflow. The ratio of the total vehicle length to the length of the inclined section was used to select an angle of 7 which °, reduces drag while meeting ramp angle requirements. Rocker Panels – New rocker panels were added to the sides of the car to visually blend the bottom of battery boxes into the vehicle. These panels act as wheel spats to smooth airflow around the front and rear wheel wells and as ducts for the battery exhaust. Wheel Fairings – Partial wheel fairings were made for the rear wheel wells. These fairings are hinged to the rear bumper and semi-rigidly attached to the top and front of the rear wheel well. This mounting configuration will allow easy access to the rear wheels. CLIMATE CONTROL SYSTEM The passenger heating, cooling, and ventilation system consumes the most energy of any vehicle accessory. In Coulomb, the battery pack powers the climate control system since intermittent operation of the engine prohibits a constant source of engine coolant heat or air conditioning power. To increase real-world driving range, the vehicle thermal loads were reduced and a climate control system was developed using efficient system components. VEHICLE THERMAL LOADS - Coulomb's thermal load response was evaluated to determine the capacity design point of the heating and cooling system. Data obtained from the Ford Climate Control group was used to design the new system. Transparent Southwall Solis window film was used to reduce the amount of solar infrared radiation transmitted into the vehicle by 50% and ultra-violet radiation by 98%. This reduced the continuous cooling loads without adding significant 12 Heating Mode Cooling Mode Suction 4-Way Valve Cooling Heating Comp Discharge Cooling Subcooler Heating Internal Coil Heating NOTE: CABIN FAN REMOVED FOR CLARITY Figure 22. Heat pump piping diagram. The stock air handling case and ductwork were modified to reduce pressure drop. The conventional switched-resistance blower was replaced with an ITT Automotive PWM blower to reduce energy loss. Supplemental heating for very cold climates and rapid "pull-up" of cold soaks is provided by a 2 kW selfregulating positive temperature coefficient (PTC) electric heater, which can be modulated to match the load. System Operation - The system cools using the heat pump, efficiently meeting peak cooling loads and continuous cooling loads. Heating is provided from one of three sources: the stock heater core, the heat pump used in “heat” mode, or the PTC heater. Heating with waste engine heat is preferred when available, but the heat pump can also be used to meet continuous loads. For extreme conditions, the PTC heater can quickly warm the cabin. A microcontroller maintains a requested temperature setting while maximizing efficiency. Depending on loads and available power supplies, the different components of the system will be used. The climate control system in Coulomb successfully combines high performance with high efficiency. The system has a COP of 3 and the compressor draws as little as 500 W at its slowest speed. POWER STEERING A high-voltage power steering pump from the General Motors EV1 electric vehicle was used to allow all-electric and on-off operation. Table 6 shows the close correspondence between the pump flow output and the requirement of the Mercury Sable rack. This pump operates in the correct voltage range and allows duty cycle modulation, which can reduce energy consumption at high speeds. Table 6. Power steering pump characteristics. Max Pressure 10.6 MPa 10.2 MPa Min Flow Rate 3.4 L/min. 3.4 L/min. The prototype system reduced energy use significantly, but suffered from two control problems that prevented its use in Coulomb for the competition. The first problem is noise in the torque sensor. The second problem is the variation in pressure system response as the wheels are loaded and unloaded. Unfortunately, these problems could not be solved in time for the competition, so the EV1 system was used. SUSPENSION AND BRAKING SUSPENSION - The suspension was modified to allow adjustment of the springs and dampers to match the final weight distribution of the vehicle. The stock struts were replaced with adjustable coil over struts allowing easy adjustment of damping and ride height. The front strut mounts were also made adjustable to allow front-end alignment following a change in ride height. BRAKING - An electronically controlled vacuum pump was connected to a vacuum accumulator, the brake booster, and the climate control vacuum servos. The booster is used with the original brakes to provide braking characteristics similar to the original system. The accumulator ensures that vacuum will be maintained during heavy brake use, even if the pump responds slowly. Regenerative braking assists the conventional braking system by using the motor as a generator to recover kinetic energy. Regenerative braking is used as much as possible to recover energy that would otherwise be wasted as brake heat. In Coulomb, regenerative braking is blended with the conventional braking to make the brake response seem normal to the driver. Regenerative braking is used in the initial portion of pedal travel, and conventional braking blends smoothly as the brake pads displace to engage the rotors. The regenerative braking reaches a maximum as the brake pedal is pressed harder, so regenerative braking is used for light braking, and conventional brakes are used for hard stops. MANUFACTURABILITY AND RECYCLABILITY POTENTIAL Coulomb was built using as many off-the-shelf parts as possible to ensure that established manufacturing techniques could be used to construct a production version. Most of Coulomb’s components are already mass produced, including: the engine, the transmission, a similar unibody, the front and rear seats, the front and rear suspension and braking systems, the climate control system, and the power steering system. The inline engine/transmission/motor package is simple and modular, which increases manufacturability. Aluminum and composite components were chosen or manufactured whenever possible. Both of these materials exhibit high potential for manufacturability and recyclability. Aluminum components - Aluminum alloys reduce weight while meeting the manufacturing and recycling 13 Stock Pump EV1 Pump The EV1 pump met the necessary design requirements, but the UC Davis team's work with CVT hydraulics demonstrated that a similar power steering system could be designed to use energy only on demand. A servo-hydraulic system was designed to amplify the torque request of the driver by creating a pressure differential across the steering rack piston. A diagram of the prototype system is shown in Figure 23. Servo Motor Gear Pump Right Fill Controller To Steering Wheel Left Fill Torque Sensor Power Assist Piston Rack and Pinion Gearing Figure 23. Servo hydraulic power steering system. goals. Aluminum has a low density, a high strength-toweight ratio, and excellent corrosion resistance. Aluminum benefits from an existing manufacturing infrastructure in the automotive industry. It is readily bonded, welded, brazed, soldered, or mechanically fastened. There are new technologies to further reduce the cost of making aluminum components, including continuous slab casting, yttrium garnet laser-welding, structural adhesive bonding and high-pressure 19 hydroforming. Aluminum has also shown excellent durability to repairs and is 100% recyclable. Aluminum is able to sustain recycling, meaning that it can be recycled repeatedly with no loss in material performance or quality. About 60 to 70% of aluminum used in vehicles made today is from recycled metal, which saves 95% of 11 the energy required to make new aluminum. Coulomb uses aluminum for the entire body-inwhite and the battery boxes, which would be incorporated into the stamped vehicle structure in a production version. Using aluminum for the body structure can reduce the weight by up to 50% compared to an equivalent steel structure while improving stiffness and crashworthiness. Tests have shown that a spot welded and bonded aluminum box beam will absorb as much energy as a similar steel beam at 55% of steel's 11 weight. Aluminum was used extensively in Coulomb’s powertrain. The entire powertrain casing could be cast in four main parts: the engine block, two transmission cases, and the electric motor case. Composite components - Composites would be used for the non-metallic parts of a mass produced version of this vehicle, due to their formability and extremely high stiffness to weight ratio. Glass-mat thermoplastics ( GMTs) are some of the most cost-effective and environmentally-friendly forms of composites, and were specifically developed for highimpact automotive applications, including bumper 20 beams, knee bolsters, and load floors. GMTs are known for their ability to reduce weight, consolidate parts, and deliver excellent, predictable performance at a systems cost comparable to steel, aluminum, and other 21 plastic systems. Advanced GMT (GMT+), a new composite technology, provides significant improvements in strength and energy management behavior for automotive bumper applications. Compared to standard GMT, GMT+ can reduce the mass of the bumper by 0.45 13 to 1.36 kg at a cost savings of $1 to $4 per part. GMT materials are melt reprocessable since they are thermoplastic. Therefore, parts can be diced and reused in compression or injection-compression molding 13 operations. GMTs will potentially be compatible with post-consumer recycling. GMTs would be used for interior panels, non-structural body panels, belly pans, and ducts. EXPECTED OPERATIONAL USE OF VEHICLE AND INTENDED MARKET Coulomb is intended for national sale since battery pack size and vehicle control strategy can be adapted to 14 regional needs without sacrificing energy economy or performance. In states with stringent emission standards such as California, New York, and Massachusetts, the vehicle would be sold with a large battery pack and the charge depletion control strategy to maximize its emissions reducing potential. In states with less stringent emissions laws, a smaller battery pack could reduce vehicle cost. CONCLUSION The UC Davis FutureCar Team has redesigned a 1994 Aluminum Intensive Mercury Sable as a charge depletion hybrid electric vehicle. Coulomb incorporates a blend of advanced and conventional automotive technologies to produce a vehicle capable of high efficiency and low emissions. This vehicle is designed to qualify for 80% partial ZEV credit under the LEVII revisions to the California ZEV mandate. Coulomb is an extension of the work performed on Joule. Increases in fuel economy were only possible through fundamental changes in the concept implementation. The extensive redesign of the vehicle included a new frame, a continuously variable transmission, an adaptable engine, a custom motor, high-power batteries, and powerful control hardware. These changes increase manufacturability, driveability, consumer acceptance, and energy efficiency. The vehicle achieves high fuel economy with low emissions, and approaches PNGV goals. 1 Reimers, Gregory, "A Comparative Investigation of Nine Optimized Hybrid-Electric Vehicle Powertrains to Determine the Viability of a 2.94V100km (80MPG) Automobile Capable of Reducing Exhaust Emissions," Masters Thesis, University of California, Davis, 1996 2 Sperling, Dan and M. A. DeLuchi. Is Methanol the Transportation Vehicle of the Future?, published in Alternative Transportation Fuels: An Environmental and Energy Solution D. Sperling, ed., Quorum Books, New York, 1989. 3 M. A. DeLuchi, Emissions of Greenhouse Gasses from the Use of Transportation Fuels and Electricity. Volume 1: Main Text, Center for Transportation Research, Energy Systems Division, Argonne National Laboratory, Illinois, 1993. 4 Maxwell, Timothy T. and Jones, Jesse C., Alternative Fuels: Emissions. Economics, and Performance. Society of Automotive Engineers, Inc., Warrendale, PA, 1995. 5 Toshifumi Takaoka, et.al., A High-Expansion-Ratio Gasoline Engine for the TOYOTA Hybrid System, TOYOTA Technical Review Vol. 47 No. 2 April 1998 6 Compiled from National Personal Transportation Survey, Federal Highway Administration, 1995. 7 Ronning, Jeffrey. The Viable Environmental Car: The Right Combination of Electrical and Combustion Energy for Transportation. SAE 971629. 8 Friedman, David, et.al. Partial ZEV Credits: An Analysis of the California Air Resources Board LEV II Proposal to Allow Non-ZEV's to Earn Credit Toward the 10% ZEV Requirement of 2003. Institute of Transportation Studies, Davis, CA. March 1998. 9 Ronning, Jeffrey. The Viable Environmental Car: The Right Combination of Electrical and Combustion Energy for Transportation. SAE 971629. 10 Friedman, David, et.al. Partial ZEV Credits: An Analysis of the California Air Resources Board LEV II Proposal to Allow Non-ZEV's to Earn Credit Toward the 10% ZEV Requirement of 2003. Institute of Transportation Studies, Davis, CA. March 1998. 11 Investigation into Vehicle Aerodynamics, Warrendale, PA, SAE, 1995 12 Wolf-Heinrich Hucho and Syed R. Ahmed, Aerodynamics of Road Vehicles, 4 th ed, Warrendale, PA, 1998 13 M.A. Dorghram and St. Helier Jersy, Impact of Aerodynamics on Vehicle Design, Channel Islands, UK, 1983 14 A.J. Scibor, Road Vehicle Aerodynamics, Rylski, London Pentech Press, 1975 15 Atkinson, Ward J., Occupant Comfort Requirements for Automotive Air Conditioning Systems, SAE 860591. 16 Sullivan, R. and Selkowitz, S., Effects of Glazing and Ventilation Options on Automobile Air Conditioning Size and Performance, SAE 900219. 17 Dieckman, J. and Mallory, D., Study of Long Term Options for Electric Vehicle Air Conditioning. (1991) Arthur D. Little EGG-EP-9831 18 Sugihara A. and Lukas, G., Performance of Parallel Flow Condensers in Vehicular Applications. SAE 900597 19 The Aluminum Association, Aluminum Update: Automotive Aluminum - Your Choice for Value, Jan. 1998 20 Nichols, David, "Glass-mat thermoplastics from structural parts," Advanced Materials and Processes. (Oct. 1994): 29 21 Bassett, Walt and Battino, Gerry. Advanced GMT Technology Boosts Performance of Automotive Bumper Components. SAE 970480 Other Technical References: Johnston, Brian, et.al. The Continued Design and Development of the University of California, Davis FutureCar, SAE 980487 15