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31 3 Technologies for Improving the Fuel Economy of Passenger Cars and Light-Duty Trucks This chapter examines a variety of technologies that could be applied to improve the fuel economy of future passenger vehicles. It assesses their fuel economy potential, recogniz- ing the constraints imposed by vehicle performance, func- tionality, safety, cost, and exhaust emissions regulations. The committee reviewed many sources of information related to fuel economy-improving technologies and their associated costs, including presentations at public meet- ings and available studies and reports. It also met with au- tomotive manufacturers and suppliers and used consultants to provide additional technical and cost information (EEA, 2001; Sierra Research, 2001). Within the time constraints of this study, the committee used its expertise and engi- neering judgment, supplemented by the sources of infor- mation identified above, to derive its own estimates of the potential for fuel economy improvement and the associ- ated range of costs. In addition, after the prepublication copy of the report was released in July 2001, the committee reexamined its technical analysis. Representatives of industry and other groups involved in fuel efficiency analysis were invited to critique the committeeâs methodology and results. Several minor errors discovered during this reexamination have been corrected in this chapter, and the discussion of the methodol- ogy and results has been clarified. The reexamination is pre- sented in Appendix F. FUEL ECONOMY OVERVIEW To understand how the fuel economy of passenger ve- hicles can be increased, one must consider the vehicle as a system. High fuel economy is only one of many vehicle attributes that may be desirable to consumers. Vehicle per- formance, handling, safety, comfort, reliability, passenger- and load-carrying capacity, size, styling, quietness, and costs are also important features. Governmental regulations require vehicles to meet increasingly stringent require- ments, such as reduced exhaust emissions and enhanced safety features. Ultimately these requirements influence final vehicle design, technology content, andâthe subject of this reportâfuel economy. Manufacturers must assess trade-offs among these sometimes-conflicting characteris- tics to produce vehicles that consumers find appealing and affordable. Engines that burn gasoline or diesel fuel propel almost all passenger cars and light-duty trucks. About two-thirds of the available energy in the fuel is rejected as heat in the exhaust and coolant or frictional losses.1 The remainder is transformed into mechanical energy, or work. Some of the work is used to overcome frictional losses in the transmission and other parts of the drive train and to operate the vehicle accessories (air conditioning, alternator/generator, and so on). In addition, standby losses occur to overcome engine friction and cooling when the engine is idling or the vehicle is decelerating. As a result, only about 12 to 20 percent of the original energy contained in the fuel is actually used to propel the vehicle. This propulsion energy overcomes (1) inertia (weight) when accelerating or climbing hills, (2) the resis- tance of the air to the vehicle motion (aerodynamic drag), and (3) the rolling resistance of the tires on the road. Con- sequently, there are two general ways to reduce vehicle fuel consumption: (1) increase the overall efficiency of the powertrain (engine, transmission, final drive) in order to deliver more work from the fuel consumed or (2) reduce the required work (weight, aerodynamics, rolling resis- 1Theoretically gasoline or diesel engines (and fuel cells) can convert all of the fuel energy into useful work. In practice, because of heat transfer, friction, type of load control, accessories required for engine operation, passenger comfort, etc., the fraction used to propel the vehicle varies from as low as zero (at idling) to as high as 40 to 50 percent for an efficient diesel engine (gasoline engines are less efficient). Further losses occur in the drive train. As a result, the average fraction of the fuel converted to work to propel the vehicle over typical varying-load operation is about 20 percent of the fuel energy.
32 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS tance, and accessory load) to propel the vehicle. These con- cepts are illustrated in Figures 3-1 and 3-2. Regenerative braking and shutting the engine off during idling also save energy, as discussed in the section on hybrid electric ve- hicles, below. Vehicle fuel economy currently is determined according to procedures established by the Environmental Protection Agency (EPA). Vehicles are driven on a dynamometer in a controlled laboratory (in order to eliminate weather and road variables.)2 Both city and highway driving are simulated. The city test is a 7.5-mile trip lasting 23 minutes with 18 stops, at an average speed of about 20 miles per hour (mph). About 4 minutes are spent idling (as at a traffic light), and a short freeway segment is included. The vehicle begins the test after being parked overnight at about 72Â°F (22Â°C) (cold soak). The highway test is a 10-mile trip with an average speed of about 48 mph. The test is initiated with a warmed- up vehicle (following the city test) and is conducted with no stops and very little idling. The basis for compliance with CAFE (and comparison of the technologies below) is the current EPA Federal Test Procedure (FTP-75) with city, highway, and combined (55 percent city/45 percent high- way) ratings in miles per gallon (mpg) (CFR, 2000). During city driving, conditions such as acceleration, en- gine loading, and time spent braking or at idle are continu- ally changing across a wide range of conditions. These varia- tions result in wide swings in fuel consumption. Inertial loads and rolling resistance (both directly related to weight) com- bined account for over 80 percent of the work required to move the vehicle over the city cycle, but less for the high- way cycle. A reduction in vehicle weight (mass) therefore has a very significant effect on fuel consumption in city driv- ing. This strong dependence on total vehicle weight explains why fuel consumption for the new vehicle fleet correlates linearly with vehicle curb weight, as shown in Attachment 3A. Weight reduction provides an effective method to reduce fuel consumption of cars and trucks and is an important goal for the government-industry program Partnership for a New Generation of Vehicles (PNGV). Reducing the required pro- pulsion work reduces the load required from the engine, al- lowing the use of a smaller engine for the same performance. In the search for lightweight materials, PNGV has focused on materials substantially lighter than the steel used in most current vehicles. Components and body structure fabricated from aluminum, glass-fiber-reinforced polymer composites (GFRP), and carbon-fiber-reinforced polymer composites (CFRP), including hybrid structures, are being investigated (NRC, 2000a). Reducing vehicle weight without reducing practical space for passengers and cargo involves three strategies: (1) sub- stitution of lighter-weight materials without compromising 2Aerodynamic drag is accounted for in the results by incorporating coast- down data from other tests. Nevertheless, there are significant differences between the mileage tests and real-life driving. For example, the dynamom- eter is connected to only one pair of tires, but on the road, all tires are rolling. Most drivers experience lower fuel economy than suggested by EPAâs results. It should be noted that the test driving cycles were derived from traffic pattern observations made many years ago, which may not be representative now. A review of the validity of the test cycles for todayâs traffic patterns would seem appropriate. ENGINE ACCESSORIES TRANSMISSION INERTIA (WEIGHT) ROLLING RESISTANCE AERODYNAMIC DRAG SYSTEM EFFICIENCY ROAD LOAD FINAL DRIVE FUEL CONSUMPTION FIGURE 3-1 Energy use in vehicles. SOURCE: Adapted from Riley (1994).
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 33 structural strength (e.g., aluminum or plastic for steel); (2) improvement of packaging efficiency, that is, redesign of the drive train or interior space to eliminate wasted space; and (3) technological change that eliminates equipment or reduces its size. Design efficiency and effectiveness can also result in lighter vehicles using the same materials and the same space for passengers and cargo. Automotive manufacturers must optimize the vehicle and its powertrain to meet the sometimes-conflicting demands of customer-desired performance, fuel economy goals, emis- sions standards, safety requirements, and vehicle cost within the broad range of operating conditions under which the ve- hicle will be used. This necessitates a vehicle systems analy- sis. Vehicle designs trade off styling features, passenger value, trunk space (or exterior cargo space for pickups), and utility. These trade-offs will likewise influence vehicle weight, frontal area, drag coefficients, and power train pack- aging, for example. These features, together with engine per- formance, torque curve, transmission characteristics, control system calibration, noise control measures, suspension char- acteristics, and many other factors, will define the drivability, customer acceptance, and marketability of the vehicle. Technology changes modify the system and hence have complex effects that are difficult to capture and analyze. It is usually possible, however, to estimate the impacts of spe- cific technologies in terms of a percentage savings in fuel consumption for a typical vehicle without a full examination of all the system-level effects. Such a comparative approach is used in this chapter.3 Although CAFE standards and EPA fuel economy rat- ings are defined in the now-familiar term miles per gallon (mpg), additional assessment parameters have been identi- fied to assist in the evaluation process, including fuel con- sumption in gallons per 100 miles; load-specific fuel consumption (LSFC) in gallons per ton (of cargo plus pas- sengers) per 100 miles; and weight-specific fuel consump- tion (WSFC) in gallons per vehicle weight per 100 miles. Attachment 3A further explains why these parameters are meaningful engineering relationships by which to judge fuel economy and the efficiency of moving the vehicle and its intended payload over the EPA cycle. Figure 3-3 shows the actual energy efficiency of vehicles of different weights. For both city and highway cycles, the fuel consumed per ton of weight and per 100 miles is plotted against the weight of the vehicle. Normalizing the fuel con- sumption (dividing by weight) yields an efficiency factor (in an engineering sense), which is particularly useful in com- paring fuel savings opportunities. It is also useful that the weight-adjusted or normalized values can be reasonably ap- proximated by a horizontal line. Points above the line repre- sent vehicles with lower-than-average efficiency, which re- quire more than the average amount of fuel to move a vehicle of a given weight over the EPA certification cycle. In prin- ciple, given sufficient lead time and business incentives (eco- nomic or regulatory), the vehicles above the line could be improved to the level of those below the line, within the limits of customer-desired performance and vehicle utility features. As an example, a 4,000-lb vehicle, in principle, could drop from 2 gallons per ton-100 miles (25 mpg) on the highway cycle to 1.4 (35.7 mpg) using technologies dis- cussed later in this chapter. However, although larger, heavier vehicles have greater fuel consumption than smaller, lighter vehicles, their energy efficiencies in moving the ve- hicle mass (weight) are very similar. These data also suggest that the potential exists to improve fuel consumption in fu- ture vehicles. However, changing conditions such as safety FIGURE 3-2 Where the energy in the fuel goes (proportions vary with vehicle design, type of engine, and operating conditions). SOURCE: NRC (1992). 3Further explanation of the methodology is provided in Appendix F.
34 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS regulations, exhaust emission standards, consumer prefer- ences, and consumer-acceptable costs must be traded off. The remainder of this chapter attempts to outline this com- plex relationship. Future Exhaust Emission and Fuel Composition Standards New environmental regulations will have a significant impact on certain technologies that have demonstrated the potential for significantly improving fuel economy. In par- ticular, the possible introduction of diesel engines and lean- burn, direct-injection gasoline engines will be affected. Ox- ides of nitrogen (NOx) and particulate matter (PM) standards are particularly stringent (NRC, 2000b) compared, for in- stance, with current and future standards in Europe, where diesel and lean-burn gasoline have significant market pen- etration. The Clean Air Act Amendments of 1990 imposed new federal regulations on automotive emissions and authorized EPA to determine the need for and cost and feasibility of additional standards. EPA made this determination and will initiate so-called Tier 2 regulations, phasing them in over model years 2004 to 2009. The Tier 2 standards are very complex and will not be addressed here in detail. However, certain key features will be mentioned as they impact poten- tial fuel economy gains. Unlike current emission standards, Tier 2 standards will vary depending on vehicle type rather than weight class. Interim phase-in schedules and durability requirements (the life expectancy that must be demonstrated for emission control systems) also vary by weight. Emissions from large sport utility vehicles (SUVs) and passenger vans weighing between 8,500 and 10,000 lb gross vehicle weight (GVW), which are currently exempt under Tier 1, will be regulated under Tier 2 standards. However, pickup trucks in this same weight range (NRC, 2000b) will not. EPA has also promulgated regulations to reduce sulfur in gasoline to 30 parts per million (ppm) (EPA, 1999) and in diesel fuel to 15 ppm (EPA, 2000b). Tier 2 includes a âbinâ system that allows manufacturers to average emissions across the fleet of vehicles they sell each year, unlike the current system that requires each ve- hicle to meet the same emissions standard. Vehicles certified in a particular bin must meet all of the individual emission standards (NOx, nonmethane organic gases, CO, formalde- hyde, PM) for that bin. In addition, the average NOx emis- sions level of the entire fleet sold by a manufacturer will have to meet the standard of 0.07 g/mile. During the phase- in period, 10 bins will be allowed, but after 2009, the 2 most lenient bins will be dropped. EPA has communicated its belief that the combination of bins, averaging, and a phase-in period could allow the intro- duction of new diesel and other high-efficiency engine tech- nology. However, the high development and production costs for such engines, combined with the high uncertainty of meeting the ultimately very low NOx and PM standards, even with the reduced sulfur level in diesel fuel (15 ppm) 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 6800 G al lo ns /T on o f V eh ic le W ei gh tâ 10 0 M ile s Highway Test Average = 1.68 Weight, lb FIGURE 3-3 EPA data for fuel economy for MY 2000 and 2001 cars and light trucks. SOURCE: EPA, available online at <http:// www.epa.gov/otaq/mpg.htm>.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 35 that will be available in 2006 (EPA, 2000b), has delayed production decisions. In general, the committee believes that the Tier 2 NOx and PM standards will inhibit, or possibly preclude, the introduction of diesels into vehicles under 8,500 lb unless cost-effective, reliable, and regulatory-com- pliant exhaust gas aftertreatment technology develops rap- idly. A key challenge is the development of emission control systems that can be certified for a 120,000-mile lifetime. In theory, the bin system will allow diesels to penetrate the light-duty vehicle market, but manufacturers must still meet the stringent fleet average standard. For example, for every vehicle in bin 8 (0.2 g/mile NOx), approximately seven vehicles in bin 3 (0.03 g/mile) would have to be sold in order to meet the 0.07 g/mile fleet-average NOx standard. These same factors have caused the committee to con- clude that major market penetration of gasoline direct-injec- tion engines that operate under lean-burn combustion, which is another emerging technology for improving fuel economy, is unlikely without major emissions-control advancements. Californiaâs exhaust emission requirementsâsuper ultralow emission vehicle (SULEV) and partial zero emis- sion vehicle (PZEV)âare also extremely challenging for the introduction of diesel engines. In particular, the California Air Resources Board (CARB) has classified PM emissions from diesel-fueled engines as a toxic air contaminant (CARB, 1998). (Substances classified as toxic are required to be controlled.) TECHNOLOGIES FOR BETTER FUEL ECONOMY The 1992 NRC report outlined various automotive tech- nologies that were either entering production at the time or were considered as emerging, based on their potential and production intent (NRC, 1992). Since then, many regulatory and economic conditions have changed. In addition, auto- motive technology has continued to advance, especially in microelectronics, mechatronics, sensors, control systems, and manufacturing processes. Many of the technologies identified in the 1992 report as proven or emerging have already entered production. The committee conducted an updated assessment of various technologies that have potential for improving fuel economy in light-duty vehicles. This assessment takes into account not only the benefits and costs of applying the technologies, but also changes in the economic and regula- tory conditions, anticipated exhaust emission regulations, predicted trends in fuel prices, and reported customer preferences. The technologies reviewed here are already in use in some vehicles or are likely to be introduced in European and Japanese vehicles within 15 years. They are discussed below under three general headings: engine technologies, transmis- sion technologies, and vehicle technologies. They are listed in general order of ease of implementation or maturity of the technology (characterized as âproduction intentâ or âemerg- ingâ). The committee concludes its assessment of potential technologies with some detailed discussion of the current and future generations of hybrid vehicles and fuel- cell power sources. For each technology assessed, the committee estimated not only the incremental percentage improvement in fuel consumption (which can be converted to fuel economy in miles per gallon [mpg] to allow comparison with current EPA mileage ratings) but also the incremental cost that ap- plying the technology would add to the retail price of a ve- hicle. The next subsection of this chapter, âTechnologies Assessed,â reviews the technologies and their general ben- efits and challenges. After that, the section âEstimating Potential Fuel Econ- omy Gains and Costsâ presents estimates of the fuel con- sumption benefits and associated retail costs of applying combinations of these technologies in 10 classes of produc- tion vehicles. For each class of vehicle, the committee hypothesizes three exemplary technology paths (technology scenarios leading to successively greater improvements in fuel consumption and greater cost). Technologies Assessed The engine, transmission, and vehicle technologies dis- cussed in this section are all considered likely to be available within the next 15 years. Some (called âproduction intentâ in this discussion) are already available, are well known to manufacturers and their suppliers, and could be incorporated in vehicles once a decision is reached to use them. Others (called âemergingâ in this discussion) are generally beyond the research phase and are under development. They are suf- ficiently well understood that they should be available within 10 to 15 years. Engine Technologies The engine technologies discussed here improve the energy efficiency of engines by reducing friction and other mechanical losses or by improving the processing and com- bustion of fuel and air. Production-Intent Engine Technologies The engine tech- nologies discussed here could be readily applied to produc- tion vehicles once a decision is made to proceed, although various constraints may limit the rate at which they penetrate the new vehicle fleet: â¢ Engine friction and other mechanical/hydrodynamic loss reduction. Continued improvement in engine component and system design, development, and com- puter-aided engineering (CAE) tools offers the poten- tial for continued reductions of component weight and thermal management and hydrodynamic systems that improve overall brake-specific efficiency. An im-
36 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS provement in fuel consumption of 1 to 5 percent is considered possible, depending on the state of the baseline engine. â¢ Application of advanced, low-friction lubricants. The use of low-friction, multiviscosity engine oils and transmission fluids has demonstrated the potential to reduce fuel consumption by about 1 percent, compared with conventional lubricants. â¢ Multivalve, overhead camshaft valve trains. The ap- plication of single and double overhead cam designs, with two, three, or four valves per cylinder, offers the potential for reduced frictional losses (reduced mass and roller followers), higher specific power (hp/liter), engine downsizing, somewhat increased compression ratios, and reduced pumping losses. Depending on the particular application and the trade-offs between valve number, cost, and cam configuration (single overhead cam [SOHC] or double overhead cam [DOHC]), im- provements in fuel consumption of 2 to 5 percent are possible, at constant performance, including engine downsizing (Chon and Heywood, 2000). However, market trends have many times shown the use of these concepts to gain performance at constant displace- ment, so that overall improvements in fuel consump- tion may be less. â¢ Variable valve timing (VVT). Variation in the cam phasing of intake valves has gained increasing market penetration, with an associated reduction in produc- tion cost. Earlier opening under low-load conditions reduces pumping work. Under high-load, high-speed conditions, variations in cam phasing can improve volumetric efficiency (breathing) and help control re- sidual gases, for improved power. Improvements in fuel consumption of 2 to 3 percent are possible through this technology (Chon and Heywood, 2000; Leone et al., 1996). â¢ Variable valve lift and timing (VVLT). Additional ben- efits in air/fuel mixing, reduction in pumping losses, and further increases in volumetric efficiency can be gained through varying timing and valve lift (staged or continuous). Depending upon the type of timing and lift control, additional reductions in fuel consumption of 1 to 2 percent, above cam phasing only, are possible (Pierik and Burkhanrd, 2000), or about 5 to 10 percent compared to two-valve engines (including downsizing with constant performance). â¢ Cylinder deactivation. An additional feature that can be added to variable valve lift mechanisms is to allow the valves of selected cylinders to remain closed, with the port fuel injection interrupted. Currently, this tech- nology is applied to rather large engines (>4.0 liter) in V8 and V12 configurations. This approach, which is sometimes referred to as a variable displacement en- gine, creates an âair springâ within the cylinder. Al- though both frictional and thermodynamic losses oc- cur, they are more than offset by the increased load and reduced specific fuel consumption of the remain- ing cylinders. However, engine transient performance, idle quality, noise, and vibration can limit efficiency gains and must be addressed. Improvements in fuel consumption in the range of 3 to 6 percent are pos- sible, even given that reductions in throttling losses associated with higher load factors over the operating cycle cannot be double counted. â¢ Engine accessory improvement. As engine load and speed ranges continue to advance, many engine acces- sories such as lubrication and cooling systems and power steering pumps are being optimized for reduc- tions in energy consumption and improved matching of functionality over the operating range. The evolu- tion of higher-voltage (i.e., 42 V) powertrain and ve- hicle electrical systems will facilitate the cost-efficient applications of such components and systems. Im- provements in fuel consumption of about 1 to 2 per- cent are possible with such technologies. â¢ Engine downsizing and supercharging. Additional im- provements in fuel consumption can be gained by re- ducing engine displacement and increasing specific power (while maintaining equal performance) by boosting the engine (turbocharger or mechanical su- percharger). Degraded transient performance (turbo- lag) typically associated with turbochargers can be sig- nificantly offset by incorporating variable geometry turbines or mechanical (positive displacement) super- chargers. Additional modifications for transmission matching, aftertreatment system warm-up, and other factors that can degrade exhaust emissions control must also be considered. Improvements in fuel con- sumption of 5 to 7 percent are considered possible with this approach, at equivalent vehicle performance (Ecker, 2000). However, when this concept is com- bined with multivalve technology, total improvements of about 10 percent are possible compared with a two- valve engine baseline. Emerging Engine Technologies The following engine tech- nologies are considered emerging for passenger car and light- duty truck applications. Significant market penetration in the United States is likely to take 5 to 10 years. Some of them are already in production elsewhere (in Japan or Europe), where they may benefit from high fuel taxes, government incentives for particular engine types or displacements, and more lenient exhaust emission or vehicle safety standards. The discussion that follows outlines not only the benefits but also the technical challenges or economic hurdles for each technology. â¢ Intake valve throttling (IVT). Advances in micropro- cessor technology, feedback control, electromechani- cal actuation, sensor technology, and materials con-
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 37 tinue to accelerate. As a result, electromechanical IVT is advancing to the point where BMW has an- nounced the introduction of its so-called Valvetronic concept. When multipoint fuel injection is used, both the lift and timing of the intake valves can be con- trolled to maintain the correct air/fuel ratio without a throttle plate. This has the potential to essentially eliminate the pumping losses across the normal but- terfly throttle valve. Also important is the potential to use conventional three-way-catalyst (TWC) after- treatment technology and incorporate cylinder deac- tivation. However, significant cost and complexity in actuation, electronic control, and system calibration are to be expected. Improvements in fuel consump- tion of an additional 3 to 6 percent above VVLT are possible with this technology. Compared with two- valve engines, total system improvements may ap- proach 6 to 12 percent. â¢ Camless valve actuation (CVA). A further evolution of fast-acting, completely variable valve timing (not limited by the lift curve of a camshaft) is represented by electromechanical solenoid-controlled, spring- mass valve (EMV) systems (Siemens, BMW, FEV) and high-pressure hydraulic-actuated valves with high-speed, digital control valve technology (Ford, Navistar). In addition to reducing pumping losses, this technology facilitates intake port and cylinder deactivation and allows the use of conventional TWC aftertreatment. Technical challenges in the past for EMV have been to minimize energy con- sumption and achieve a soft landing of the valve against the seat during idle and low-speed, low-load operation, for acceptable noise levels. These issues appear to be solved through advances in sensor and electromagnetic technologies. EMV systems are ex- pected to see limited production within 5 to 7 years. Improvements in fuel consumption of 5 to 10 per- cent relative to VVTL are possible with this tech- nology. Compared with fixed-timing, four-valve engines, total system improvements of 15 percent or more have been demonstrated (Pischinger et al., 2000). â¢ Variable compression ratio (VCR) engines. Current production engines are typically limited in compres- sion ratio (CR) to about 10:1 to 10.5:1 with the use of high-octane fuel, owing to knocking under high load. However, significant improvements in fuel consump- tion could be gained with higher CR under normal driving cycles. Many different VCR approaches that allow improved efficiency under low load with high CR (13-14:1) and sufficient knock tolerance under full load with lower CR (~8:1) are under development. Saab appears to have the most advanced VCR proto- types. Automakers, suppliers, and R&D organizations are currently exploring many other approaches that are applicable to both inline and Vee engine configura- tions. Several of these are expected to enter production within 10 years. Compared with a conventional four- valve VVT engine, improvements in fuel consumption of 2 to 6 percent are possible (Wirbeleit et al., 1990). The combination of VCR with a supercharged, downsized engine is likely to be effective, giving the maximum advantage of both systems and reducing total fuel consumption, at constant performance, by 10 to 15 percent. However, the potential complexity of the hardware, system durability, control system development, and cost must be traded off for produc- tion applications. Many additional engine technologies with good potential for improved fuel consumption are the subject of R&D. Others are currently offered in markets with higher fuel prices (due to higher taxes) or exhaust emission standards more lenient than the upcoming federal Tier 2 emission stan- dards (or Californiaâs SULEV standards, set to begin in model year 2004). A brief summary of these technologies is presented below, including reference to the areas of uncer- tainty and the need for further development. â¢ Direct-injection (DI) gasoline engines. Stratified- charge gasoline engines burning in a lean mode (when more air is present than required to burn the fuel) offer improved thermodynamic efficiency. However, the technology faces potential problems in controlling par- ticulate emissions and NOx. Trade-offs between the maximum operating range under lean conditions ver- sus stoichiometric operation (when the exact amount of air needed to burn the fuel is present) with early injection must be developed. Although lean-burn DI engines of the type offered in Europe could improve fuel consumption by more than 10 percent, NOx-con- trol requirements that necessitate stoichiometric op- eration and the use of TWCs limit the potential fuel consumption improvement to between 4 and 6 percent (Zhao and Lai, 1997). â¢ Direct-injection diesel engines. The application of small (1.7- to 4.0-liter), high-speed (4,500-rpm), tur- bocharged, direct-injection diesel engines has seen tre- mendous expansion in passenger cars and light-duty trucks in Europe. Increasing power densities (>70 hp/ liter), achieved through the application of advanced, high-pressure, common-rail fuel injection systems; variable geometry turbochargers; and advances in noise, vibration, and harshness (NVH) control tech- nologies, combined with high-efficiency, lean-burn combustion systems and practically smokeless and odorless emissions, have greatly improved customer acceptance in Europe. The high low-speed torque and relatively flat torque curve also offer significant drivability improvements. Fuel consumption improve-
38 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS ments of 30 to 40 percent or more are possible com- pared with conventional two-valve gasoline engines. The challenges, which inhibit widespread introduction in the United States, include meeting strict NOx and particulate emission standards for Tier 2 and SULEV; much higher engine and vehicle purchase price ($2,000 to $3,000) than conventional gasoline engines; and uncertain U.S. customer acceptance. The creation of NOx and particulate emissions is exacerbated by the stratification present in the fuel/air mixture resulting from in-cylinder injection. R&D activities continue on emission control through advanced combustion and fuel injection concepts, fuel composition (low sulfur), aftertreatment technologies (selective catalytic reduc- tion [SCR], NOx traps, particulate filters), and control of noise and vibration. Although DI diesel engines are offered in some trucks over 8,500 lb and are offered by one manufacturer (VW) for passenger cars under cur- rent Tier 1 emissions standards, wide use in sport util- ity vehicles (SUVs) and light-duty trucks has not occurred, and the ability of this technology to comply with the upcoming Tier 2 and SULEV standards is highly uncertain. Transmission Technologies The second group of technologies assessed by the com- mittee involves improvements in the efficiency with which power is transmitted from the engine to the driveshaft or axle. Production-intent Transmission Technologies Over the past 10 years, transmission technologies have been evolving toward increasing electronic control, adapting torque con- verter lock-up, four- and five-speed automatics (from three- and four-speed), and various versions of all-wheel drive (AWD) or four-wheel drive (4WD) and traction control, ranging from continuous, traction-controlled AWD to auto- matic 2WD-4WD traction control in some SUVs. â¢ Five-speed automatic transmission. A five-speed au- tomatic transmission permits the engine to operate in its most efficient range more of the time than does a four-speed transmission. A fuel consumption improve- ment of 2 to 3 percent is possible, at constant vehicle performance, relative to a four-speed automatic. â¢ Continuously variable transmission (CVT). Several versions of continuously variable transmissions are offered in production in Europe and Japan and a few in the United States (by Honda and Toyota). Historically, these transmission types have used belts or chains of some kind to vary speed ratios across two variable- diameter pulleys. The major production units utilize compression belts (VanDorne) or tension chains. Other approaches are also being pursued for future produc- tion. Depending on the type of CVT and the power/ speed range of the engine, this technology can improve fuel consumption by about 4 to 8 percent. However, production cost, torque limitations, and customer ac- ceptance of the systemâs operational characteristics must be addressed. Emerging Transmission Technologies Automotive manu- facturers continue to seek ways to reduce the mechanical (frictional and hydrodynamic) losses of transmissions and improve their mating with engines. The various types of hy- brid vehicles will also involve changes in conventional trans- missions. These emerging technologies are likely to be avail- able in the latter part of the current decade. â¢ Automatic transmission with aggressive shift logic. Shift schedules, logic, and control of torque transfer can significantly affect perceived shift quality. Ad- vanced work on methods to reduce losses associated with torque converters or torque dropout is being pur- sued. It is estimated that a 1 to 3 percent improvement in fuel consumption can be obtained through such measures. However, these will be highly affected by customer perception in the United States and may re- quire quite some time for significant acceptance. â¢ Six-speed automatic transmission. Advanced six- speed automatic transmissions can approach the per- formance of CVT transmissions without limitations in the ability to transmit torque. An additional improve- ment of 1 to 2 percent in fuel consumption is possible, compared to a five-speed automatic. Based on their higher cost and control complexity, such transmissions will probably see only limited introductionânamely, in high-end luxury or performance vehicles. â¢ Automatic shift/manual transmission (ASM/AMT). In the continuing quest to reduce mechanical losses, manufacturers are developing new generations of au- tomatic transmissions that eliminate the hydraulic torque converter and its associated pump, replacing it with electronically controlled clutch mechanisms. This approach offers two basic possibilities: The torque from different gear sets can be intermittently inter- rupted (as in a conventional manual transmission) through the use of a single electronically controlled clutch; or the torque can be continuously controlled, without dropout, through the use of two electronically controlled clutches. Improvements in fuel consump- tion of 3 to 5 percent over a conventional four-speed automatic transmission with hydraulic torque con- verter are possible. However, increased cost, control system complexity, durability, and realizable fuel con- sumption gain versus acceptable shift quality for U.S. customers must be addressed.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 39 â¢ Advanced CVT. Continued advances in methods for high-efficiency, high-torque transfer capability of CVTs are being pursued. New versions of CVTs that will soon enter production incorporate toroidal fric- tion elements or cone-and-ring assemblies with vary- ing diameters. However, these versions also have trade-offs of torque capability vs. frictional losses. These next-generation transmissions have the poten- tial to improve fuel consumption by about 0 to 2 per- cent (relative to current CVTs), with higher torque ca- pabilities for broader market penetration. However, production cost, system efficiency, and customer ac- ceptance of the powertrain operational characteristics must still be addressed. Vehicle Technologies By reducing drag, rolling resistance, and weight, the fuel consumption of vehicles could, in principle, be cut rather sharply in the relatively near term. Manufacturers, however, would quickly run into serious trade-offs with performance, carrying capacity, and safety. Also to be considered are novel vehicle concepts such as hybrid electrics, powered by vari- ous combinations of internal combustion engines and batter- ies or fuel cells. The following discussion reviews both production-intent and emerging vehicle technologies. Production-Intent Vehicle Technologies The following fuel consumption measures are deemed available in the near term (almost immediately after a decision to use them is made): â¢ Aerodynamic drag reduction on vehicle designs. This improvement can be very cost-effective if incorporated during vehicle development or upgrades. However, vehicle styling and crashworthiness have significant influences on the ultimate levels that can be achieved. For a 10 percent reduction in aerodynamic drag, an improvement in fuel consumption of 1 to 2 percent can be achieved. As drag coefficients proceed below about 0.30, however, the design flexibility becomes limited and the relative cost of the vehicle can increase dra- matically. Substituting video minicameras for side- view mirrors (e.g., as is being done for the PNGV con- cept vehicles) would be advantageous but would necessitate a change in safety regulations (NRC, 2000a). â¢ Rolling resistance. Continued advances in tire and wheel technologies are directed toward reducing roll- ing resistance without compromising handling, com- fort, or braking. Improvements of about 1 to 1.5 percent are considered possible. The impacts on per- formance, comfort, durability, and safety must be evaluated, however. â¢ Vehicle weight reduction. Reducing vehicle weight while maintaining acceptable safety is a difficult bal- ance to define. While most manufacturers believe that some reduction in vehicle weight can be accom- plished without a measurable influence on in-use safety, debate continues on how much weight can be reduced without compromising crush space, by using lighter-weight materials and better, more crashwor- thy designs. Emerging Vehicle Technologies Several advanced vehicle technologies are being considered for near-term production. Interest in these technologies has been fostered by the PNGV program. In addition, a wide variety of hybrid vehicle tech- nologies are being explored for initial introduction within the next 5 to 10 years. This section reviews vehicle technolo- gies that have been identified by the industry for introduc- tion within the next 10 years. â¢ Forty-two volt electrical system. Most automotive manufacturers are planning a transition to 42-V elec- trical systems to support the continuing need for in- creased electrical power requirements for next-genera- tion passenger vehicles. Higher voltage will reduce electrical losses and improve the efficiency of many onboard electrically powered systems. It will also al- low new technologies such as electric power steering, which can be significantly more efficient than current technology. Fuel consumption reductions associated with the implementation and optimization of related systems are expected to range from 1 to 2 percent. â¢ Integrated starter/generator (ISG). Significant im- provements in fuel consumption under real-world op- erating conditions can be gained by turning the engine off during idle, while operating the necessary acces- sories electrically (air conditioning presents a major challenge, however). ISG systems providing nearly in- stantaneous engine restart are now planned for pro- duction. Idle stop, under many conditions, is expected to achieve a 4 to 7 percent reduction in fuel consump- tion. Depending on the size and type of battery chosen, it is also possible to recover electrical energy through regenerative braking and subsequent launch assist us- ing ISG technology. Doing so adds cost, complexity, and weight but could improve fuel consumption by a total of 5 to 10 percent. â¢ Hybrid electric vehicles. Hybrid electric vehicles of various types are in different stages: Some are starting to be introduced, others are in advanced stages of de- velopment, and still others are the focus of extensive research by nearly all the large automotive manufac- turers. They include so-called âmild hybridsâ (with regenerative braking, ISG, launch assist, and minimal battery storage); âparallel hybridsâ (with the engine
40 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS powering either or both a mechanical drive train and an electric motor/generator serving as additional pro- pulsion to recharge the battery); and âseries hybridsâ (in which the engine does not drive the wheels but always drives an electric motor/generator to propel the vehicle, recharge the battery, or perform both func- tions simultaneously). The method and extent of hybridization depends on the vehicle type, its anticipated use, accessory pack- age, type of battery, and other considerations. The an- ticipated improvements in fuel consumption can there- fore vary, from about 15 percent for certain mild hybrids to about 30 percent for parallel hybrids. In gen- eral, series hybrids are not yet intended for even lim- ited production, owing to the relatively poor perfor- mance of electric power propulsion and the low efficiencies of current battery systems compared with mechanical drive systems. The varying complexity of the different hybrid types is reflected in large varia- tions in incremental cost. The cost premium of todayâs limited-production mild hybrids is predicted to be $3,000 to $5,000 when they reach production volumes over 100,000 units per year. For fully parallel systems, which operate for significant periods entirely on the electrical drive, especially in city driving, the cost pre- mium can escalate to $7,500 or more. In addition to offering significant gains in fuel consumption, these vehicles have the potential for beneficial impacts on air quality. Further information on hybrids is provided in a separate section below. â¢ Fuel-cell hybrid electric vehicles. The most advanced emerging vehicle technology currently under research and development substitutes an electrochemical fuel cell for the internal combustion engine. In proton ex- change membrane (PEM) fuel cells, hydrogen and oxygen react to produce electricity and water. Since gaseous hydrogen is difficult to store with reasonable energy density, many manufacturers are pursuing the decomposition of a liquid fuel (either methanol or gasoline) as a source of hydrogen, depending on cor- porate perceptions of future fuel availability. State-of- the-art fuel cell systems demonstrate the potential for long-term viability: They could realize high electro- chemical energy conversion efficiencies and very low local exhaust emissions, depending upon the type of fuel chosen and the associated reformation process to produce hydrogen. However, the presence of sulfur in gasoline could pose a significant problemâPEM poi- soning. Owing to its high potential for reducing fuel consumption, this emerging technology is receiving substantial R&D funding. However, most researchers and automotive manufacturers believe that successful commercial application of fuel cells for passenger ve- hicles is at least 10 to 15 years away. Further informa- tion on fuel cells is provided in a separate section later in this chapter. With the exception of fuel cells and series hybrids, the tech- nologies reviewed above are all currently in the production, product planning, or continued development stage, or are planned for introduction in Europe or Japan. The feasibility of production is therefore well known, as are the estimated pro- duction costs. However, given constraints on price imposed by competitive pressures in the U.S. market, only certain tech- nologies are considered practical or cost effective. As noted earlier, the exhaust emission standards in the United States (Tier 2 and SULEV) make the introduction of some high-fuel-economy technologies, such as lean- burn, direct-injection gasoline or high-speed DI diesel en- gines, uncertain. For these technologies to be viable, low- sulfur fuel must be available and particulate traps and NOx emissions controls (lean NOx catalyst, NOx trap, SCR) must be developed. Therefore, current powertrain strate- gies for gasoline-powered engines use mainly stoichio- metric air/fuel mixtures, for which three-way-catalyst aftertreatment is effective enough to meet future emission standards. ESTIMATING POTENTIAL FUEL ECONOMY GAINS AND COSTS To predict the costs associated with achieving improve- ments in fuel consumption, it is necessary to assess applica- tions of the committeeâs list of technologies in production vehicles of different types. The committee estimated the incremental fuel consumption benefits and the incremental costs of technologies that may be applicable to actual vehicles of different classes and intended uses. The commit- tee has hypothesized three successively more aggressive (and costly) product development paths for each of 10 vehicle classes to show how economic and regulatory conditions may affect fuel economy: â¢ Path 1. This path assumes likely market-responsive or competition-driven advances in fuel economy us- ing production-intent technology that may be pos- sible under current economic (fuel price) and regula- tory (CAFE, Tier 2, SULEV) conditions and could be introduced within the next 10 years. It holds ve- hicle performance constant and assumes a 5 percent increase in vehicle weight associated with safety- enhancing features. â¢ Path 2. This path assumes more aggressive advances in fuel economy that employ more costly production- intent technologies but that are technically feasible for introduction within the next 10 years if economic and/ or regulatory conditions justify their use. It also main- tains constant vehicle performance and assumes a 5
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 41 percent increase in vehicle weight associated with safety-enhancing features. â¢ Path 3. This path assumes even greater fuel economy gains, which would necessitate the introduction of emerging technologies that have the potential for substantial market penetration within 10 to 15 years. These emerging technologies require further develop- ment in critical aspects of the total system prior to com- mercial introduction. However, their thermodynamic, mechanical, electrical, and control features are consid- ered fundamentally sound. High-speed, direct-injec- tion diesel engines, for instance, are achieving sig- nificant market penetration in Europe. However, strict exhaust emission standards in the United States neces- sitate significant efforts to develop combustion or ex- haust aftertreatment systems before these engines can be considered for broad introduction. For each product development path, the committee esti- mated the feasibility, potential incremental fuel consumption improvement, and incremental cost for 10 vehicle classes: â¢ Passenger cars: subcompact, compact, midsize, and large; â¢ Sport utility vehicles: small, midsize, and large; and â¢ Other light trucks: small pickup, large pickup, and minivan. The three paths were estimated to represent vehicle devel- opment steps that would offer increasing levels of fuel economy gain (as incremental relative reductions in fuel con- sumption) at incrementally increasing cost. The committee has applied its engineering judgment in reducing the other- wise nearly infinite variations in vehicle design and technol- ogy that would be available to some characteristic examples. The approach presented here is intended to estimate the potential costs and fuel economy gains that are considered technically feasible but whose costs may or may not be recoverable, depending on external factors such as market competition, consumer demand, or government regulations. The committee assembled cost data through meetings and interviews with representatives of automotive manufactur- ers and component and subsystem suppliers and through published references. Cost estimates provided by component manufacturers were multiplied by a factor of 1.4 to approxi- mate the retail price equivalent (RPE) costs for vehicle manu- facturers to account for other systems integration, overhead, marketing, profit, and warranty issues (EEA, 2001). Experience with market competition has shown that the pricing of products can vary significantly, especially when the product is first introduced. Furthermore, marketing strat- egies and customer demand can greatly influence the RPE cost passed along to customers. Retail prices vary greatly, especially for components required to meet regulatory stan- dards (such as catalytic converters, air bags, or seat belts). The baseline fuel economies for these evolutionary cases are the lab results (uncorrected for on-road experience) on the 55/45 combined cycle for MY 1999 for each vehicle class (EPA, 2001a). Both the average fuel economy (in mpg) and the initial fuel consumption (in gallons/100 miles) are shown in Tables 3-1 through 3-3. The incremental improvements, however, were calculated as percentage reductions in fuel consumption (gallons per 100 miles). (The two measures should not be confused; a 20 percent decrease in fuel consumption, for example, from 5 gallons per 100 miles to 4 gallons per 100 miles, represents a 25 percent increase in fuel economy, from 20 mpg to 25 mpg.) The technology baseline for each vehicle class was set according to whether the majority of vehicles employed a given technology. Thus, all cars (but not trucks) are assumed to have four valves per cylinder and overhead camshafts even though a substantial number sold in the United States still have two valves, espe- cially large cars. The results of this technology assessment are summarized for passenger cars in Table 3-1, for SUVs and minivans in Table 3-2, and for pickup trucks in Table 3-3. The distinc- tion between âproduction-intentâ and âemergingâ technolo- gies for engines, transmissions, and vehicles is maintained. For each technology considered, the tables give an esti- mated range for incremental reductions in fuel consumption (calculated in gallons per 100 miles). The ranges in fuel con- sumption improvement represent real-world variations that may result from many (sometimes competing) factors, in- cluding the baseline state of the engine, transmission, or ve- hicle; effectiveness in implementation; trade-offs associated with exhaust emissions, drivability, or corporate standards; trade-offs between price and performance; differences be- tween new system design, on the one hand, and carryover or product improvement on the other; and other calibration or consumer acceptance attributes such as noise and vibration. Similarly, the ranges of incremental cost in these tables represent variations to be expected depending on a number of conditions, including the difference between product improvement cycles and new component design; variations in fixed and variable costs, depending on manufacturer- specific conditions; commonality of components or sub- systems across vehicle lines; and evolutionary cost reduc- tions. In addition, since many of the cost figures were supplied by component and subsystem suppliers, a factor of 1.4 was applied to the supplied cost to arrive at the RPE to the consumer. The analysis presented here is based on the average fuel consumption improvement and cost of each incremental technology, as shown in Tables 3-1, 3-2, and 3-3. For each vehicle class, the average fuel consumption improvement for the first technology selected is multiplied by the baseline fuel consumption (adjusted for the additional weight for safety improvements). This is then multiplied by the average improvement of the next technology, etc. Costs are simply added, starting at zero. Figures 3-4 to 3-13 show the incre-
42 T A B L E 3 -1 F ue l C on su m pt io n T ec hn ol og y M at ri xâ P as se ng er C ar s R et ai l P ri ce F ue l E qu iv al en t ( R P E ) C on su m pt io n ($ ) S ub co m pa ct C om pa ct M id si ze L ar ge B as el in e: o ve rh ea d ca m s, 4 -v al ve , f ix ed ti m in g, as el in e Im pr ov em en t B as el in e: r ol le r fi ng er f ol lo w er . % L ow H ig h 1 2 3 1 2 3 1 2 3 1 2 3 P ro du ct io n- in te nt e ng in e te ch no lo gy E ng in e fr ic ti on r ed uc ti on 1- 5 35 14 0 x x x x x x x x x x x x L ow -f ri ct io n lu br ic an ts 1 8 11 x x x x x x x x x x x x M ul ti va lv e, o ve rh ea d ca m sh af t ( 2- V v s. 4 -V ) 2- 5 10 5 14 0 V ar ia bl e va lv e ti m in g 2- 3 35 14 0 x x x x x x x x x x x x V ar ia bl e va lv e li ft a nd ti m in g 1- 2 70 21 0 x x x x x x x x C yl in de r de ac ti va ti on 3- 6 11 2 25 2 x E ng in e ac ce ss or y im pr ov em en t 1- 2 84 11 2 x x x x x x x x x x x x E ng in e su pe rc ha rg in g an d do w ns iz in g 5- 7 35 0 56 0 x x P ro du ct io n- in te nt tr an sm is si on te ch no lo gy F iv e- sp ee d au to m at ic tr an sm is si on 2- 3 70 15 4 x x x x x x C on ti nu ou sl y va ri ab le tr an sm is si on 4- 8 14 0 35 0 x x x x x x A ut om at ic tr an sm is si on w /a gg re ss iv e sh if t l og ic 1- 3 â 70 x x x x S ix -s pe ed a ut om at ic tr an sm is si on 1- 2 14 0 28 0 x x x P ro du ct io n- in te nt v eh ic le te ch no lo gy A er o dr ag r ed uc ti on 1- 2 â 14 0 x x x x x x Im pr ov ed r ol li ng r es is ta nc e 1- 1. 5 14 56 x x x x x x x x x x x x S af et y te ch no lo gy S af et y w ei gh t i nc re as e â3 to â 4 0 0 x x x x x x x x x x x x E m er gi ng e ng in e te ch no lo gy In ta ke v al ve th ro tt li ng 3- 6 21 0 42 0 x x x x C am le ss v al ve a ct ua ti on 5- 10 28 0 56 0 x x x x V ar ia bl e co m pr es si on r at io 2- 6 21 0 49 0 x x x x E m er gi ng tr an sm is si on te ch no lo gy A ut om at ic s hi ft /m an ua l t ra ns m is si on ( A S T /A M T ) 3- 5 70 28 0 x x A dv an ce d C V T sâ al lo w s hi gh to rq ue 0- 2 35 0 84 0 x x E m er gi ng v eh ic le te ch no lo gy 42 -V e le ct ri ca l s ys te m s 1- 2 70 28 0 x x x x x x In te gr at ed s ta rt er /g en er at or ( id le o ff âr es ta rt ) 4- 7 21 0 35 0 x x x x E le ct ri c po w er s te er in g 1. 5- 2. 5 10 5 15 0 x x x x x x V eh ic le w ei gh t r ed uc ti on ( 5% ) 3- 4 21 0 35 0 x N O T E : A n x m ea ns th e te ch no lo gy is a pp li ca bl e to th e pa rt ic ul ar v eh ic le . S af et y w ei gh t a dd ed ( E P A b as el in e + 3 .5 % ) to in it ia l a ve ra ge m il ea ge /c on su m pt io n va lu es .
43 T A B L E 3 -2 F ue l C on su m pt io n T ec hn ol og y M at ri xâ S U V s an d M in iv an s R et ai l P ri ce B as el in e (s m al l S U V ): o ve rh ea d ca m s, 4 -v al ve , f ix ed ti m in g, F ue l E qu iv al en t ( R P E ) B as el in e: r ol le r fi ng er f ol lo w er . C on su m pt io n ($ ) S m al l S U V M id S U V L ar ge S U V M in iv an Im pr ov em en t B as el in e (o th er s) : 2 -v al ve , f ix ed ti m in g, r ol le r fi ng er f ol lo w er . (% ) L ow H ig h 1 2 3 1 2 3 1 2 3 1 2 3 P ro du ct io n- in te nt e ng in e te ch no lo gy E ng in e fr ic ti on r ed uc ti on 1- 5 35 14 0 x x x x x x x x x x x x L ow -f ri ct io n lu br ic an ts 1 8 11 x x x x x x x x x x x x M ul ti va lv e, o ve rh ea d ca m sh af t ( 2- V v s. 4 -V ) 2- 5 10 5 14 0 x x x x x x x x x V ar ia bl e va lv e ti m in g 2- 3 35 14 0 x x x x x x x x x x x x V ar ia bl e va lv e li ft a nd ti m in g 1- 2 70 21 0 x x x x x x x x C yl in de r de ac ti va ti on 3- 6 11 2 25 2 x x x x x E ng in e ac ce ss or y im pr ov em en t 1- 2 84 11 2 x x x x x x x x x x x x E ng in e su pe rc ha rg in g an d do w ns iz in g 5- 7 35 0 56 0 x x x x P ro du ct io n- in te nt tr an sm is si on te ch no lo gy F iv e- sp ee d au to m at ic tr an sm is si on 2- 3 70 15 4 x x x x x x x x x C on ti nu ou sl y va ri ab le tr an sm is si on 4- 8 14 0 35 0 x x x A ut om at ic tr an sm is si on w /a gg re ss iv e sh if t l og ic 1- 3 0 70 x x x x x S ix -s pe ed a ut om at ic tr an sm is si on 1- 2 14 0 28 0 x x x x x P ro du ct io n- in te nt v eh ic le te ch no lo gy A er o dr ag r ed uc ti on 1- 2 0 14 0 x x x x x x x x Im pr ov ed r ol li ng r es is ta nc e 1- 1. 5 14 56 x x x x x x x x x x x x S af et y te ch no lo gy S af et y w ei gh t i nc re as e â3 to â 4 0 0 x x x x x x x x x x x x E m er gi ng e ng in e te ch no lo gy In ta ke v al ve th ro tt li ng 3- 6 21 0 42 0 x x x x C am le ss v al ve a ct ua ti on 5- 10 28 0 56 0 x x x x V ar ia bl e co m pr es si on r at io 2- 6 21 0 49 0 x x x x E m er gi ng tr an sm is si on te ch no lo gy A ut om at ic s hi ft /m an ua l t ra ns m is si on ( A S T /A M T ) 3- 5 70 28 0 x x x x A dv an ce d C V T sâ al lo w s hi gh er to rq ue 0- 2 35 0 84 0 x E m er gi ng v eh ic le te ch no lo gy 42 -V e le ct ri ca l s ys te m s 1- 2 70 28 0 x x x x x x x x In te gr at ed s ta rt er /g en er at or ( id le o ff âr es ta rt ) 4- 7 21 0 35 0 x x x x x x x x E le ct ri c po w er s te er in g 1. 5- 2. 5 10 5 15 0 x x x x x x x V eh ic le w ei gh t r ed uc ti on ( 5% ) 3- 4 21 0 35 0 x x N O T E : A n x m ea ns th e te ch no lo gy is a pp li ca bl e to th e pa rt ic ul ar v eh ic le . S af et y w ei gh t a dd ed ( E P A b as el in e + 3 .5 % ) to in it ia l a ve ra ge m il ea ge /c on su m pt io n va lu es .
44 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS TABLE 3-3 Fuel Consumption Technology MatrixâPickup Trucks Retail Price Baseline: 2-valve, fixed timing, roller finger follower. Fuel Equivalent (RPE) Small Large Consumption ($) Pickup Pickup Improvement (%) Low High 1 2 3 1 2 3 Production-intent engine technology Engine friction reduction 1-5 35 140 x x x x x x Low-friction lubricants 1 8 11 x x x x x x Multivalve, overhead camshaft (2-V vs. 4-V) 2-5 105 140 x x x x x x Variable valve timing 2-3 35 140 x x x x x Variable valve lift and timing 1-2 70 210 x x x x Cylinder deactivation 3-6 112 252 x x x Engine accessory improvement 1-2 84 112 x x x x x x Engine supercharging and downsizing 5-7 350 560 x x x Production-intent transmission technology Five-speed automatic transmission 2-3 70 154 x x x x x Continuously variable transmission 4-8 140 350 x Automatic transmission w/aggressive shift logic 1-3 0 70 x x x Six-speed automatic transmission 1-2 140 280 x x x Production-intent vehicle technology Aero drag reduction 1-2 0 140 x x x x Improved rolling resistance 1-1.5 14 56 x x x x x x Safety technology 5% safety weight increase â3 to â4 0 0 x x x x x x Emerging engine technology Intake valve throttling 3-6 210 420 x x Camless valve actuation 5-10 280 560 x x Variable compression ratio 2-6 210 490 x x Emerging transmission technology Automatic shift/manual transmission (AST/AMT) 3-5 70 280 x x Advanced CVTs 0-2 350 840 x Emerging vehicle technology 42-V electrical systems 1-2 70 280 x x x x Integrated starter/generator (idle offârestart) 4-7 210 350 x x x x Electric power steering 1.5-2.5 105 150 x x x x Vehicle weight reduction (5%) 3-4 210 350 NOTE: An x means the technology is applicable to the particular vehicle. Safety weight added (EPA baseline + 3.5%) to initial average mileage/consumption values. mental results. Table 3-4 summarizes the results for the end point of each path. Further details of the methodology can be found in Appendix F. No weight reduction was considered except in Path 3 for large passenger cars (Table 3-1) and medium and large SUVs (Table 3-2), where a 5 percent weight reduction is assumed as part of the 9- or 10-year forward projections. The following example will assist the reader in under- standing the relationship between Tables 3-1 through 3-3 and the results of the analysis, as summarized in Table 3-4. The average fuel consumption of midsize SUVs (based on 1999 sales-weighted averages) is 4.76 gal/100 miles, or 21.0 mpg. The assumed weight increase associated with future safety-enhancing features will result in a 3.5 percent increase in fuel consumption, to 4.93 gal/100 mile, or 20.3 mpg. This example is shown in the âMidsize SUVâ column of Table 3-2 and the âBase FC w/Safety Weightâ column of Table 3-4. Within the Path 1 assumption for midsize SUVs, the tech- nologies applied for incremental reductions in fuel consump- tion included engine friction reduction (1 to 5 percent); low- friction lubricants (1 percent); four-valve overhead cam (OHC) from two-valve overhead valve (OHV) or two-valve OHC (2 to 5 percent); variable intake valve timing (1 to 2 percent); cylinder deactivation (3 to 6 percent); engine ac- cessory improvement (1 to 2 percent); five-speed automatic transmission (2 percent over four-speed automatic); aggres- sive shift logic (1 to 3 percent); and improved rolling resis- tance (1 to 1.5 percent). Multiplying the averages of these reductions yields a Path 1 estimated fuel consumption for midsize SUVs of 4.0 gal/100 miles, or 25.3 mpg. The incre-
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 45 TABLE 3-4 Estimated Fuel Consumption (FC), Fuel Economy (FE), and Incremental Costs of Product Development Base FC Average Average Fuel Average w/Safety Fuel Consumption Cumulative Weight Class Base FE Base FC Weight Economy (mpg) (gal/100 mi) Cost ($) Path 1 Subcompact 31.3 3.19 3.31 34.7 2.88 465 Compact 30.1 3.32 3.44 33.4 2.99 465 Midsize 27.1 3.69 3.82 30.0 3.33 465 Large 24.8 4.03 4.17 27.9 3.58 675 Small SUV 24.1 4.15 4.29 26.7 3.74 465 Mid SUV 21.0 4.76 4.93 25.3 3.96 769 Large SUV 17.2 5.81 6.02 20.7 4.84 769 Minivan 23.0 4.35 4.50 26.5 3.78 587 Pickupâsmall 23.2 4.31 4.46 27.2 3.68 682 Pickupâlarge 18.5 5.41 5.59 21.2 4.71 587 Path 2 Subcompact 31.3 3.19 3.31 37.5 2.67 1,018 Compact 30.1 3.32 3.44 36.6 2.73 1,088 Midsize 27.1 3.69 3.82 36.0 2.78 1,642 Large 24.8 4.03 4.17 34.5 2.90 2,167 Small SUV 24.1 4.15 4.29 31.4 3.18 1,543 Mid SUV 21.0 4.76 4.93 30.8 3.25 2,227 Large SUV 17.2 5.81 6.02 24.7 4.05 2,087 Minivan 23.0 4.35 4.50 34.0 2.94 2,227 Pickupâsmall 23.2 4.31 4.46 34.0 2.94 2,227 Pickupâlarge 18.5 5.41 5.59 28.2 3.55 2,542 Path 3 SubCompact 31.3 3.19 3.31 43.9 2.28 2,055 Compact 30.1 3.32 3.44 42.9 2.33 2,125 Midsize 27.1 3.69 3.82 41.3 2.42 3,175 Large 24.8 4.03 4.17 39.2 2.55 3,455 Small SUV 24.1 4.15 4.29 36.5 2.74 2,580 Mid SUV 21.0 4.76 4.93 34.2 2.92 3,578 Large SUV 17.2 5.81 6.02 28.4 3.52 3,235 Minivan 23.0 4.35 4.50 36.6 2.73 2,955 Pickupâsmall 23.2 4.31 4.46 36.6 2.73 3,298 Pickupâlarge 18.5 5.41 5.59 29.5 3.39 2,955 mental costs are estimated to average $769. Table 3-4 shows the end points of all 3 paths for all 10 vehicle classes. For the application of other incremental technologies in Path 2 and Path 3, only incremental benefits relative to prior technol- ogy applicationsâsuch as âvariable valve lift and timingâ added to âvariable valve timingâ aloneâwere assumed, in an attempt to eliminate double counting. Likewise, the incremental cost was added on top of the previous cost increment. Although not shown in the figures, the uncertainty increases with each step along the path. The level of uncertainty is quite high in Path 3. For minivans, SUVs, and other light trucks, the potential for reductions in fuel requirements is much greater than for smaller passenger cars. A review of the data shows that the technologies evalu- ated as emerging under Path 3 for the larger vehicles include camless valve actuation systems combined with a variable compression ratio andâpossiblyâclutched supercharging. A competing technology that could exceed the fuel consump- tion gains for such vehicles is turbocharged, intercooled, di- rect-injection diesel engines. This advantage is demonstrated by the growing popularity of such powertrains, which power almost all vehicles over 5,000 lb in Europe and 30 to 40 percent of all private passenger vehicles, even compact and subcompact classes. However, the ability of these powertrains to meet federal for Tier 2 and California SULEV emissions standards is un- proven, mainly because of shortcomings in exhaust gas aftertreatment. Therefore, the most efficient stoichiometric gasoline strategies (excluding hybrid vehicles, discussed be- low) were chosen to represent emerging technologies with proven thermodynamic advantages, which can employ rela- tively conventional three-way-catalyst aftertreatment systems.
46 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 2.002.202.402.602.803.003.203.403.60 Fuel Consumption (Gallons/100 Miles) C os t Path 3 Path 2 Path 1 FIGURE 3-5 Compact cars. Incremental cost as a function of fuel consumption. FIGURE 3-4 Subcompact cars. Incremental cost as a function of fuel consumption. $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 1.501.701.902.102.302.502.702.903.103.303.50 Fuel Consumption (Gallons/100 Miles) C os t Path 3 Path 2 Path 1
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 47 FIGURE 3-6 Midsize cars. Incremental cost as a function of fuel consumption. $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 2.002.202.402.602.803.003.203.403.603.804.00 Fuel Consumption (Gallons/100 Miles) C o st Path 3 Path 2 Path 1 $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 $4,000.00 2.502.702.903.103.303.503.703.904.104.304.50 Fuel Consumption (Gallons/100 Miles) C os t Path 3 Path 2 Path 1 FIGURE 3-7 Large cars. Incremental cost as a function of fuel consumption.
48 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS FIGURE 3-9 Midsize SUVs. Incremental cost as a function of fuel consumption. $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 2.503.003.504.004.505.00 Fuel Consumption (Gallons/100 Miles) C o st Path 3 Path 2 Path 1 $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 2.502.702.903.103.303.503.703.904.104.304.50 Fuel Consumption (Gallons/100 Miles) C os t Path 3 Path 2 Path 1 FIGURE 3-8 Small SUVs. Incremental cost as a function of fuel consumption.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 49 FIGURE 3-10 Large SUVs. Incremental cost as a function of fuel consumption. $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 3.504.004.505.005.506.006.50 Fuel Consumption (Gallons/100 MIles) Path 3 Path 2 Path 1 C os t $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 2.503.003.504.004.505.00 Fuel Consumption (Gallons/100 Miles) C os t Path 3 Path 2 Path 1 FIGURE 3-11 Minivans. Incremental cost as a function of fuel consumption.
50 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS FIGURE 3-13 Large pickups. Incremental cost as a function of fuel consumption. $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 3.003.504.004.505.005.506.00 Fuel Consumption (Gallons/100 Miles) C o st Path 3 Path 2 Path 1 $- $500.00 $1,000.00 $1,500.00 $2,000.00 $2,500.00 $3,000.00 $3,500.00 2.503.003.504.004.505.00 Fuel Consumption (Gallons/100 Miles) C o st Path 3 Path 2 Path 1 FIGURE 3-12 Small pickups. Incremental cost as a function of fuel consumption.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 51 HYBRID VEHICLES The concept of hybrid electric vehicles (HEVs) is not new, but the technology for application in vehicles advanced significantly in the last decade. Hybrid vehicles combine the power output of an internal combustion engine with a bat- tery or other energy source to gain energy efficiency, reduce exhaust emissions, or, in some cases, improve acceleration. HEVs have received significant attention in the Partnership for a New Generation of Vehicles (PNGV). Ford, GM, and DaimlerChrysler have announced plans to introduce PNGV- developed hybrid technologies into production beginning in MY 2003. Toyota and Honda have already begun offering MY 2001 HEVs in limited production in the United States. Readers who desire further information on HEVs may con- sult a variety of sources, including Automotive News (2001) and An (2001), as well as a National Research Council re- port on the PNGV program (NRC, 2000a). Figure 3-14 shows the power relationship between an internal combus- tion engine and an electric motor for hybrid vehicles. In the future, HEVs may be viable in situations involving increasingly stringent emissions regulations or demands to reduce oil dependence. For automotive use, however, two important parameters directly influence the practicality of the energy storage system: (1) the energy storage density (compared with liquid petroleum-derived fuel) and (2) the ability to rapidly receive or release stored energy. Various energy storage techniques have been evalu- ated for light-duty vehicle applications, including batter- ies, capacitors, flywheels, and hydraulic/pneumatic systems. Despite restrictions in their energy transfer rate, batteries remain of high interest due to their relatively high power density. A survey of key vehicle and powertrain characteristics is summarized in Table 3-5. Breakdowns of the relative contri- butions of powertrain modifications, including downsizing and dieselization, are shown in Figure 3-15. The data clearly show that vehicle and powertrain features can, on their own (that is, apart from true hybridization), result in significant fuel economy gains. Ford has announced plans to introduce a hybrid version of its Escape SUV in MY 2003. It will reportedly have a four-cylinder engine and achieve about 40 mpg in the EPA combined (55/45) cycle. Its electric motor will reportedly produce acceleration performance similar to that of a larger six-cylinder engine (if the battery is sufficiently charged). GMâs hybrid powertrain, called ParadiGM, is reportedly being considered for application in several vehicles. It ap- parently combines a 3.6-liter V6 engine with a pair of elec- tric motors. The engine shuts off at idle and low speed, and the vehicle can reportedly accelerate from a stop using only electric power. DaimlerChrysler is apparently planning to offer a hybrid Dodge Durango SUV in 2003. It will reportedly combine a 3.9-liter V6 engine driving the rear wheels with an electric motor driving the front wheels. Its performance is reported to equal that of the current V8, four-wheel-drive version (again with sufficient battery charge) at a somewhat higher FIGURE 3-14 Relationship between the power of an internal combustion engine and the power of an electric motor in a hybrid electric vehicle. 0 20 40 60 80 100 120 140 90 80 70 60 50 40 20 30 10 0 P ow er o f E le ct ric M ot or ( kZ W ) Power of Internal Combustion Engine (kW) 80 hp 107 hp 134 hp 214 hp DC S-Klasse Hybrid DC C-Klasse Hybrid Volvo Power Split Hybrid DC Durango Hybrid (â03) Honda Insight (â99) Chrysler ESX3 Toyota Prius (â98) GM Precept Ford Prodigy Audi Duo Fiat Ibrida WW Golf Hybrid Mitsubishi SUW Advance Ford Escape Hybrid (â03)
52 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS TABLE 3-5 Published Data for Some Hybrid Vehicles Power Engine Engine Motor Trans- Weight Plant Size Power Battery Peak mission CAFE 0â60 Data HEV Vehicle Type Status (lb) Type (L) (hp) Type (kW) Type (mpg)a (sec) Source Toyota Priusb Gasoline hybrid Com. 2,765 SI I-4 1.5 70 NiMH 33 CVT 58 12.1 c Honda Insight Gasoline hybrid Com. 1,856 SI I-3 1.0 67 NiMH 10 M5 76 10.6 d, e Ford Prodigy Gasoline hybrid Prot. 2,387 CIDI I-4 1.2 74 NiMH 16 A5 70 12.0 d, f DC ESX3 Gasoline hybrid Prot. 2,250 CIDI I-3 1.5 74 Li-ion 15 EMAT-6 72 11.0 d, g GM Precept Gasoline hybrid Prot. 2,590 CIDI I-3 1.3 59 NiMH 35 A4 80 11.5 d, h NOTE: SI, spark ignition; CIDI, compression ignition, direct injection; CVT, continuously variable transmission; M, manual; A, automatic; EMAT, electro- mechanical automatic transmission. SOURCE: An (2001). a CAFE fuel economy represents combined 45/55 highway/city fuel economy and is based on an unadjusted figure. b U.S. version. c EV News, 2000, June, p. 8. d NRC (2000a). e Automotive Engineering, 1999, October, p. 55. f The starter/generator rated 3 kW continuous, 8 kW for 3 minutes, and 35 kW for 3 seconds. We assume 16 kW for a 12-s 0â60 acceleration. g Automotive Engineering, 2000, May, p. 32. h Precept press release; the front motor is 25 kW and the rear motor is 10 kW, so the total motor peak is 35 kW. 0 0 8 7 8 3 7 2 4 59 11 19 21 26 38 46 262626 151414 13 8 0 10 20 30 40 50 60 70 80 90 US Prius Honda Insight Ford Prodigy DC ESX3 GM Precept M P G Hybrid optimization Engine downsizing Load reduction Dieseli- zation Baseline Com. Veh. P N G V C iv ic H x B as el in e C or ol la (1 .8 L) P N G V B as el in e P N G V B as el in e ( 1. 6L ) FIGURE 3-15 Breakdown of fuel economy improvements by technology combination. SOURCE: An (2001).
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 53 cost, but it will achieve fuel economy similar to its V6, two- wheel-drive equivalent. Advanced HEVs cost much more than more conventional vehicles. In addition, overall system efficiencies must con- tinue to improve, especially energy conversion, power trans- fer, electrochemical battery storage, and power output from the motors. These developments will allow greater overall fuel efficiency and system trade-offs that would result in reduced battery and motor sizes, extended electric-only pro- pulsion range, improved power density, and reduced vehicle weight. During the early introduction of these technologies, sev- eral obstacles must be addressed. First, warranty periods must be defined and, hopefully, extended with time. Second, the rate at which battery power systems can accept energy generated during a hard regenerative braking event must be improved. Finally, the potential safety consequences of a depleted battery (loss of acceleration power) must be clarified. FUEL CELLS The emerging technology of fuel cells is also receiving increasing attention and R&D funding on the basis of its potential use in passenger vehicles. A few concept vehicles are now in operation, and a few commercial vehicles may appear in niche markets in the next few years. Figure 3-16 schematically represents their principle of operation, using hydrogen as a fuel. Hydrogen enters the fuel cell through the porous anode. A platinum catalyst, applied to the anode, strips the electrons from the hydrogen, producing a positive hydrogen ion (a proton). The electrons pass through the load to the cathode as an electric current. The protons traverse the electrolyte and proceed to the porous cathode. Ultimately, through the application of a catalyst, the protons join with oxygen (from air) and the electrons from the power source to form water. Different types of fuel cells employ different materials. According to Ashley (2001), âthe proton exchange mem- brane (PEM) variety has emerged as the clear favorite for automotive use.â Another type, the solid oxide fuel cell (SOFC), considered by Ashley and others as a less likely alternative, is represented by the alkaline air cell. The big- gest difference between the SOFC and PEM technologies is their operating temperatures. While PEM cells run at 80Â°C, SOFC units run at 700Â° to 1000Â°C. If hydrogen is used as the fuel, no atmospheric pollutants are produced during this portion of the energy cycle of fuel cells, since water is the only by-product. No hydrocarbons, carbon monoxide, NOx, or particulates are produced. It is important to note that hydrogen could also be used as the fuel for an internal combustion engine. Louis (2001) quotes BMW as stating that a âspark ignition engine running on hydrogen is only slightly less efficient than a direct hydro- gen fuel cell.â The internal combustion engine will produce a certain level of NOx during combustion. However, due to FIGURE 3-16 Working principles of a PEM fuel cell.
54 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS the very lean flammability limit of hydrogen, the NOx con- centration will be much lower than when using normal hy- drocarbon fuels. Energy is consumed, however, and exhaust emissions are likely to be generated in producing, transporting, and storing the hydrogen. The energy efficiency of a fuel cell cycle, âfrom well to wheels,â includes energy losses and emissions from all of the steps of production, refining, and distribution of the fuel (see Attachment 4A). Since hydro- gen is not naturally available, as are conventional fuels, it must be extracted from other hydrogen-containing com- pounds such as hydrocarbons or water. Unless the extrac- tion is performed onboard, the hydrogen must be trans- ported from the extraction point to the user. Hydrogen distribution systems are beyond the scope of this report, but this section evaluates two fuel cell systems that use a fuel reformer to generate hydrogen onboard the vehicle from either methanol (which can be produced from natural gas or biomass) or gasoline. Onboard reformers have several common difficulties that must be overcome for commercial acceptance. They typi- cally operate significantly above room temperature, with energy conversion efficiencies of 75 to 80 percent. The hy- drogen is removed from the fuel by either catalysis or com- bustion. In addition, optimal operation occurs at process pressures above atmospheric. Furthermore, the response time and transient power requirements for vehicle application necessitate some form of onboard storage of hydrogen. For commercial success in passenger vehicles, the volume and weight parameters of the fuel reformer, fuel cell, and electric drive must be relatively competitive with current power trains and fuel tanks. Using methanol as the liquid fuel offers the advantage of sulfur-free conversion (normal gasoline contains sulfur, which poisons fuel-cell stacks). Methanol has its own prob- lems, however. It is toxic if ingested, highly corrosive, soluble in water (thereby posing a potential threat to under- ground water supplies), and currently relatively expensive to produce, compared with gasoline. However, proponents of methanol cite the toxicity of existing hydrocarbon fuels (gasoline or diesel fuel) and point out the low evaporative emissions, the absence of sulfur, and the potential for pro- duction from renewable sources. All major automotive manufacturers are actively pursu- ing fuel cell systems using an onboard reformer. The com- mittee believes, however, that advanced internal combustion engine-powered vehicles, including HEVs, will be over- whelmingly dominant in the vehicle market for the next 10 to 15 years. This conclusion is supported by the recently released study by Weiss et al. (2000). Figure 3-17 shows the state of the art in fuel cell systems and the targets set by the Department of Energy for longer- term development. The figure shows that significant devel- opment advances are necessary to allow the fuel cell to be- come competitive with the internal combustion engine as a source of power. It is also important to note that the internal 34 31 120 120 300 150 40 33 250 250 125 5044 35 325 325 45 10 0 50 100 150 200 250 300 350 % % W /L W /k g $/ kW 0. 1 se c Efficiency @ 25% Load Efficiency @ full Load Power Density Specific Power Cost Resp. Time (10%-90%) Current Status Project Goal Long-Term Goal FIGURE 3-17 State of the art and future targets for fuel cell development.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 55 combustion engine will continue to advance as the fuel cell is being developed. An additional issue that must be addressed is the reduced efficiency at higher loads, as shown in Figure 3-18. Substan- tial development will be required to overcome this character- istic and other challenges associated with power density, spe- cific power, production cost, and system response time, before fuel cells can be successfully commercialized in an HEV. REFERENCES An, F. 2001. Evaluating Commercial and Prototype HEVâs. SAE 2001-01- 0951. Warrendale, Pa.: Society of Automotive Engineers (SAE). Ashley, S. 2001. âFuel Cells Start to Look Real.â Automotive Engineering International. March. CARB (California Air Resources Board). 1998. Particulate Emissions from Diesel-Fueled Engines As a Toxic Air Contaminant, November 3. Available online at <http://www.arb.ca.gov/toxics/dieseltac/ dieseltac.com>. CFR (Code of Federal Regulations). 2000. No. 40âPart 600, Office of the Code of Federal Regulations. National Archives and Records Adminis- tration, Washington, D.C., July. Chon, D., and J. Heywood. 2000. Performance Scaling of Spark-Ignition Engines: Correlation and Historical Analysis of Production Engine Data. SAE Paper 2000-01-0565. Warrendale, Pa.: SAE. DOE (Department of Energy). 2000. Fuel Cell and CIDI Engine R&D. Solicitation #DE-RP04-01AL67057, November. Ecker, H.-J. 2000. Downsizing of Diesel Engines: 3-Cylinder/4-Cylinder. SAE Paper 2000-01-0990. Warrendale, Pa: SAE. EEA (Energy and Environmental Analysis, Inc.). 2001. Technology and Cost of Future Fuel Economy Improvements for Light-Duty Vehicles. Final Report. Prepared for the committee and available in the National Academiesâ public access file for the committeeâs study. EPA (Environmental Protection Agency). 1999. Regulatory Impact Analy- sisâControl of Air Pollution from New Motor Vehicles: Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur Control Require- ments. EPA 420-R99-023. Washington, D.C., December. EPA. 2000a. Light-Duty Automotive Technology and Fuel Economy Trends 1975 Through 2000. EPA 420-R00-008. Washington, D.C., December. EPA. 2000b. Regulatory Impact AnalysisâHeavy-Duty Engine and Ve- hicle Standards and Highway Diesel Fuel Sulfur Control Requirements, December. Leone, T.G., E.J. Christenson, and R.A. Stein. 1996. Comparison of Vari- able Camshaft Timing Strategies at Part Load. SAE Paper 960584. Warrendale, Pa.: SAE. Louis, J. 2001. SAE 2001-01-01343. Warrendale, Pa.: SAE. NRC (National Research Council). 1992. Automotive Fuel Economy: How Far Should We Go? Washington, D.C.: National Academy Press. NRC. 2000a. Review of Research Program of the Partnership for a New Generation of Vehicles: Sixth Report. Washington, D.C.: National Academy Press. NRC. 2000b. Review of the U.S. Department of Energyâs Heavy Vehicle Technologies Program. Washington, D.C.: National Academy Press. Pierik, R.J., and J.F. Burkhanrd. 2000. Design and Development of a Me- chanical Variable Valve Actuation System. SAE Paper 2000-01-1221. Warrendale, Pa.: SAE. Pischinger, M., W. Salber, and F. Vander Staay. 2000. Low Fuel Consump- tion and Low EmissionsâElectromechanical Valve Train in Vehicle Operation. Delivered at the FISITA World Automotive Congress, June 12â15, Seoul. Riley, R.Q. 1994. Alternative Cars in the 21st Century. Warrendale, Pa.: SAE. Sierra Research. 2001. A Comparison of Cost and Fuel Economy Projec- tions Made by EEA and Sierra Research. Prepared for the committee and available in the National Academiesâ public access file for the committeeâs study. Weiss, M., J.B. Heywood, E.M. Drake, A. Schafter, and F.F. AuYeung. 2000. On the Road in 2020: A Life Cycle Analysis of New Automobile Technologies. Energy Laboratory, Massachusetts Institute of Technol- ogy, October. Cambridge, Mass.: MIT. Wirbeleit, F.G., K. Binder, and D. Gwinner. 1990. Development of Pistons with Variable Compression Height for Increasing Efficiency and Spe- cific Power Output of Combustion Engines. SAE Paper 900229. Warrendale, Pa.: SAE. Zhao, Fu-Quan, and Ming-Chia Lai. 1997. A Review of Mixture Prepara- tion and Combustion Control Strategies for Spark-ignited Direct-injec- tion Gasoline Engines. SAE Paper 970627. Warrendale, Pa.: SAE. FIGURE 3-18 Typical fuel cell efficiency. 0 10 20 30 40 50 0.30 0.35 0.40 0.45 0.50 pmax = 2.5 bar pmax = 2.0 bar pmax = 1.5 bar pmax = 1.0 bar Effective Power [kW] S ys te m E ffi ci en cy
56 Measuring the fuel economy of vehicles in miles per gal- lon (mpg) alone does not provide sufficient information to evaluate a vehicleâs efficiency in performing its intended function. A better way to measure the energy efficiency of vehicles is needed, one that has a sound engineering basis. This attachment presents two weight-based parameters as examples of approaches that take the intended use of a ve- hicle into consideration. One is based on a vehicleâs curb weight and the other includes its payload (passenger plus cargo). Because of the short time frame for the committeeâs study, an analysis sufficiently detailed to draw conclusions as to the value of these or other parameters was not possible. MILES PER GALLON VERSUS GALLONS PER MILE AND HOW TO MEASURE The physics of vehicle design can form the basis for pa- rameters that more accurately represent system energy effi- ciencies and could be used by EPA in fuel economy testing. Mpg is not by itself a sufficient parameter to measure effi- ciency, since it is inherently higher for smaller vehicles and lower for larger vehicles, which can carry more passengers and a greater cargo load. Although CAFE standards currently characterize vehicles by miles driven per gallon of fuel consumed, the inverse, gallons per mile, would be more advantageous for several reasons. As shown in Figure 3A-1, gallons per mile mea- sures fuel consumption and thus relates directly to the goal of decreasing the gallons consumed. Note that the curve is relatively flat beyond 30 or 35 mpg because fuel savings become increasingly smaller as mpg increases. Also, the use of fuel consumption (gallons per mile) has analytical advan- tages, addressed in this attachment. To aid and clarify the analysis and make the numbers easier to comprehend, the term to be used is gallons per 100 miles (gal/100 miles). A vehicle getting 25 mpg uses 4 gal/100 miles. For reproducibility reasons, fuel consumption measure- ments are made on a chassis dynamometer. The driving wheels are placed on the dynamometer rollers; other wheels do not rotate. Thus rolling resistance, as with aerodynamic drag, must be accounted for mathematically. Vehicle coast- down times are experimentally determined (a measure of aerodynamic drag); an auxiliary power unit (APU) ensures that dynamometer coast-down times are in reasonable agree- ment with road-tested coast-down times. Test reproducibil- ity is in the few percent range. The driver follows two differ- ent specified cycles, city and highway, which were deduced from traffic measurements made some 30 to 40 years ago. A change in the test cycle is not a minor itemâmuch engineer- ing know-how is based on the present cycle, which is also used for exhaust emissions measurements. WEIGHT-SPECIFIC FUEL CONSUMPTION Figure 5A-4 (in Chapter 5) plots gal/100 miles versus vehicle weight for MY 2000 vehicles. The vertical scatter along a line of constant weight reflects the fact that vehicles Attachment 3A A Technical Evaluation of Two Weight- and Engineering-Based Fuel-Efficiency Parameters for Cars and Light Trucks 0 2 4 6 8 10 12 10 15 20 25 30 35 40 45 50 55 60 Fuel economy (miles per gallon) F ue l c on su m ed ( ga llo ns p er 1 00 m ile s) Series1 FIGURE 3A-1 Dependence of fuel consumption on fuel economy. SOURCE: NRC (2000).
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 57 of the same weight may differ in the efficiency of their drive trains or rolling resistance or aerodynamic drag (and thus in the number of gallons used to travel a given distance). While gal/100 miles is a straightforward parameter for measuring fuel consumption, it does not reflect the load-carrying ca- pacity of the vehicle. Smaller cars, with lower fuel consump- tion, are designed to carry smaller loads, and larger cars and trucks, larger ones. For engineering analysis purposes, it is convenient to nor- malize the data in Figure 5A-4, that is, divide the y value (vertical scale) of each data point by its curb weight in tons. The resulting new vertical scale is the weight-specific fuel consumption (WSFC). The units shown in Figure 3A-2 (and Figure 5A-5) are gal/ton of vehicle weight/100 miles. The straight horizontal line is a reasonable representation of the average efficiency of fuel use data for a wide variety of ve- hicle types and weights. It shows that the efficiency (WSFC) is approximately the same for this variety of different ve- hicle types (MY 2000, 33 trucks and 44 cars) and weights. Note that some vertical scatter is to be expected; all vehicles having approximately the same weight do not necessarily have the same drive-train efficiency. Figure 3A-3 shows on-the-road data taken by Consumer Reports (April 2001). Their measurements were based on a realistic mixture of expressway, country-road, and city driv- ing. Again, the efficiency of fuel use for their on-the-road tests is reasonably represented by a horizontal straight line. Figure 3A-3 illustrates the analytical utility of this approach. The lowest car point, at a little less than 3,000 lb, is a diesel engine; its WSFC is around 1.8 compared with around 2.7 for the average. The two hybrid points also show lower WSFC than the average but higher than the diesel. Figure 3A-4 illustrates possible realistic reductions in WSFC. EPA has fuel-consumption data for more than a thou- 0 1 2 3 4 2000 2500 3000 3500 4000 4500 5000 5500 Weight, lb W S F C , G al lo ns /T on o f V eh ic le W ei gh t - 1 00 M ile s Premium Small Comp VAN Entry Small Comp PU Midsize STD PU Near Luxury Midsize Small SUV Luxury Midsize Comp SUV Large Luxury Comp SUV Luxury Large Large SUV Average Cars Trucks FIGURE 3A-2 Weight-specific fuel consumption versus weight for all vehicles. 0 1 2 3 4 5 0 2000 4000 6000 8000 vehicle weight (pounds)W S F C , g al lo ns p er to n pe r 10 0 m ile s AUTO LTR&SUV HYBRID FIGURE 3A-3 Fleet fuel economy. Based on information from Consumer Reports (April 2001).
58 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS sand MY 2000 and 2001 vehicles. A horizontal line was drawn on a WSFC (highway) graph for these vehicles such that 125 vehicles were below this arbitrary line. The results for the 125 vehicles are shown in Figure 3A-4. The average WSFC value for all vehicles was 1.7; the average for the 125 vehicles was around 1.4. Since these were production ve- hicles, it would appear that application of in-production tech- nologies to the entire fleet could produce significant reduc- tions in WSFC. LOAD-SPECIFIC FUEL CONSUMPTION For a heavy-duty truck designed to carry a large payload, the most meaningful parameter would be normalized by di- viding the gallons per mile by the tons of payload, to arrive at a load-specific fuel consumption (LSFC), that is, gallons per ton of payload per 100 miles. This number would be lowest for vehicles with the most efficient powertrain sys- tem and the least road load requirements (lightest weight, low accessory loads, low rolling resistance, and low drag) while moving the largest payload. Similarly, a reasonable parameter for a fuel-efficient bus would be gallons per pas- senger-mile. The parameter LSFC is more difficult to define for light- duty vehicles than for heavy-duty trucks or buses, because the payloads are widely different (and harder to define) for these vehicles. This report calculates a total weight capacity by multiplying passenger capacity (determined by the num- ber of seat belts) by an average weight per person (150 lb) and adding cargo weight capacity, which is the cargo vol- ume multiplied by an average density (say, 15 lb/ft3).1 For pickup trucks, the difference between gross vehicle weight (GVW) and curb weight was used to determine payload. The weight of the passengers and cargo could be added to the vehicleâs weight, and the sum used in the EPA fuel economy test to determine engine loading for the test cycle. Alterna- tively, the present fuel economy data could be used with the above average passenger plus cargo weight. The fuel con- sumption on the city and highway cycle would be measured and expressed as gallons/ton (passenger plus cargo weight)/ 100 miles. Figure 3A-5 plots fuel economy against payload in tons for heavy-duty and light-duty vehicles. Lines of constant mpg-tons are also shown, with larger numbers representing more efficient transport of payloads. LSFC, the inverse of mpg-tons, is also shown on the lines, with lower numbers representing lower normalized vehicle fuel consumption. The point representing the PNGV goal is also shown. Fuel economy measures based on this parameter would drive engineers to maximize the efficiency with which ve- hicles carry passengers and cargo while minimizing struc- tural weight. This new fuel consumption parameter has the potential to be a better parameter to compare different types and sizes of vehicles. Figure 3A-6 graphs the same light-duty vehiclesâ fuel consumption (in gal/100 miles) as a function of the payloads in Figure 3A-8. This figure shows the large difference in fuel consumption between cars (2.5 to 4 gal/100 mi) and trucks (3.5 to 5.5 gal/100 mi); the CAFE standards for both types of vehicles are included for reference. Figure 3A-7 shows LSFC (in gallons per ton of passengers plus cargo) for the same vehicles. LSFC appears to normalize fuel consumption, bridging all types of vehicles. Both types of vehicleâre- gardless of size and weightâare represented above and be- low the average line. This finding suggests that LSFC is a good engineering parameter for both cars and trucks. COMPARING THE TWO WEIGHT-BASED PARAMETERS The WSFC essentially normalizes the fuel consumed per 100 miles to take out the strong dependence on vehicle weight. Different weight vehicles can be compared more equitably. Lower WSFC parameters indicate lower road load requirements and/or higher powertrain efficiencies with lower accessory loads. Figure 3A-9 shows fuel economy versus vehicle curb weight for the 87 light-duty vehicles. Constant efficiency lines (in mpg Ã tons of vehicle weight) are shown along with WFSC. Figure 3A-10 shows fuel economy versus ve- hicle payload for the 87 vehicles. The constant efficiency lines in mpg Ã tons of payload are shown along with LSFC. The utility of this plot is that it shows the interrelationship of fuel economy, payload, and LSFC in gallons/payload tons/100 miles. LSFC and WSFC show similar utility in determining whether certain types of vehicles are either above or below the average lines in Figures 3A-2 and 0 0.4 0.8 1.2 1.6 0 2000 4000 6000 Vehicle weight (pounds) W SF C , g al lo ns p er to n pe r 1 00 m ile s AUTOS LT TRUCKS HYBRIDS FIGURE 3A-4 Best-in-class fuel-efficiency analysis of 2000 and 2001 vehicles. 1This is an estimated density for cargo space. GM uses about 11 lb/ft3 across a range of vehicles. Further study needs to be done to determine a representative design density to use.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 59 0.25 10mpg x 40Ton 1.1 10 mpg x 10 Ton 0.5 5 mpg x 40 Ton10 mpg x 4Ton 2.5 Heavy-Duty Vehicles Light-Duty Vehicles PNGV 8.3 24 mpg x 0.5Ton 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 Payload, tons F ue l E co no m y, m pg LSFC, gallons/Payload Ton -100 miles y = 0.001x + 0.6132 R2 = 0.804 0 1 2 3 4 5 6 7 8 9 10 2000 2500 3000 3500 4000 4500 5000 5500 Payload/lb F C , g al lo ns / 1 00 m ile s Premium Small Comp VAN Entry Small Comp PU Midsize STD PU Near Luxury Midsize Small SUV Luxury Midsize Comp SUV Large Luxury Comp SUV Luxury Large Large SUV CAFE Standard for Cars CAFE Standard for Trucks Cars Trucks FIGURE 3A-6 Fuel consumption versus payload. FIGURE 3A-5 LSFC versus payload for a variety of vehicles.
60 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS 0 1 2 3 4 5 6 7 8 9 10 2000 2500 3000 3500 4000 4500 5000 5500 Weight, lb LS F C , g al lo ns / 1 00 m ile s - T on s of P as se ng er s pl us C ar go Premium Small Comp VAN Entry Small Comp PU Midsize STD PU Near Luxury Midsize Small SUV Luxury Midsize Comp SUV Large Luxury Comp SUV Luxury Large Large SUV Average Cars Trucks E nt ry S m al l P re m iu m S m al l M id si ze S m al l S U V C om p P U N ea r Lu xu ry M id si ze Lu xu ry M id si ze La rg e C om p V A N Lu xu ry L ar ge C om p S U V S T D P U Lu xu ry C om p S U V La rg e S U V y = 51.59x + 821.64 R2 = 0.4757 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 P ay lo ad , l b In order of increasing average weight FIGURE 3A-7 Payload versus LSFC. FIGURE 3A-8 Payload for a variety of vehicles.
TECHNOLOGIES FOR IMPROVING THE FUEL ECONOMY OF PASSENGER CARS AND LIGHT-DUTY TRUCKS 61 38 mpg x 1Ton 2.6 2.1 22 mpg x 2Ton 2.3 24 mpg x 2Ton 3.1 32 mpg x 1Ton 27 mpg x 2Ton 3.8 A ve P re m iu m S m al l A ve E nt ry S m al l A ve N ea r Lu xu ry M id si ze A ve L ar ge A ve L ux ur y La rg e A ve M id si ze A ve L ux ur y M id si ze A ve C om p V A N A ve C om p P U A ve S T D P U A ve S m al l S U V A ve L ux ur y C om p S U V A ve C om p S U V A ve L ar ge S U V 1.9 26 mpg x 1Ton 0 5 10 15 20 25 30 35 40 45 50 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 Weight, lb F ue l E co no m y, m pg Cars Premium Small Entry Small Midsize Near Luxury Midsize Luxury Midsize Large Luxury Large Trucks Comp VAN Comp PU STD PU Small SUV Comp SUV Luxury Comp SUV Large SUV WSFC, gallons/Ton of Vehicle Weight -100 miles 3A-8. Using LSFC, however, would encourage manufac- turers to consider all aspects of vehicle design, including materials, accessory power consumption, body design, and engine and transmission efficiency. The use of the LSFC number will show high-performance, heavy, two-seat sports cars without much cargo space and large luxury cars to be on the high side compared with vehicles designed to be fuel- and payload-efficient. WSFC does not account for the load-carrying capacity of FIGURE 3A-9 Fuel economy as a function of average WSFC for different classes of vehicles. certain vehicles such as pickups, vans, and SUVs. The vans and large SUVs in Figure 3A-8 are shown below the average fit line and below the average WSFC line in Figure 3A-2, indicating they have highly efficient powertrain technologies and low road load/accessory load requirements. Pickups (PUs) are above the average WSFC line in Figure 3A-2, showing that it is difficult to design a truck that has low aerodynamic drag and is fuel efficient. When the fuel consumptions of these vehicles (vans, pickups, and SUVs) are normalized to pay-
62 EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS load, they are below the average LSFC line in Figure 3A-8, indicating they are well designed for their intended use. CONCLUSION Both the WSFC and LSFC parameters have potential util- ity as fuel-efficiency parameters for vehicles, but their appli- cability requires additional study. FIGURE 3A-10 Fuel economy versus average payload for different classes of vehicles. 12.5 16 mpg x 0.5Ton 8.3 24 mpg x 0.5Ton 6.3 32 mpg x 0.5Ton 4.2 48 mpg x 0.5Ton A ve P re m iu m S m al l A ve E nt ry S m al l A ve N ea r Lu xu ry M id si ze A ve L ar ge A ve L ux ur y La rg e A ve M id si ze A ve L ux ur y M id si ze A ve C om p V A N A ve C om p P U A ve S T D P U A ve S m al l S U V A ve C om p S U V A ve L ux ur y C om p S U V A ve L ar ge S U V 5.0 40 mpg x 0.5Ton 0 5 10 15 20 25 30 35 40 45 50 0 400 800 1200 1600 2000 2400 Payload, lb F ue l E co no m y, m pg Cars Premium Small Entry Small Midsize Near Luxury Midsize Luxury Midsize Large Luxury Large Trucks Comp VAN Comp PU STD PU Small SUV Comp SUV Luxury Comp SUV Large SUV LSFC, gallons/Payload Ton -100 miles REFERENCE NRC (National Research Council). 2000. Automotive Fuel Economy: How Far Should We Go? Washington, D.C.: National Academy Press. p. 156.