Summary

In 2007 the National Highway Traffic Safety Administration (NHTSA) requested that the National Academies provide an objective and independent update of the technology assessments for fuel economy improvements and incremental costs contained in the 2002 National Research Council (NRC) report Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards. The NHTSA also asked that the NRC add to its assessment technologies that have emerged since that report was prepared. To address this request, the NRC formed the Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy. The statement of task, shown in Appendix B, directed the committee to estimate the efficacy, cost, and applicability of technologies that might be used over the next 15 years.

FINDINGS AND RECOMMENDATIONS

Overarching Finding

A significant number of technologies exist that can reduce the fuel consumption of light-duty vehicles while maintaining similar performance, safety, and utility. Each technology has its own characteristic fuel consumption benefit and estimated cost. Although these technologies are often considered independently, there can be positive and negative interactions among individual technologies, and so the technologies must be integrated effectively into the full vehicle system. Integration requires that other components of the vehicle be added or modified to produce a competitive vehicle that can be marketed successfully. Thus, although the fuel consumption benefits and costs discussed here are compared against those of representative base vehicles, the actual costs and benefits will vary by specific model. Further, the benefits of some technologies are not completely represented in the tests used to estimate corporate average fuel economy (CAFE). The estimate of such benefits will be more realistic using the new five-cycle tests that display fuel economy data on new vehicles’ labels, but improvements to test procedures and additional analysis are warranted. Given that the ultimate energy savings are directly related to the amount of fuel consumed, as opposed to the distance that a vehicle travels on a gallon of fuel, consumers also will be helped by addition to the label of explicit information that specifies the number of gallons typically used by the vehicle to travel 100 miles.

Technologies for Reducing Fuel Consumption

Tables S.1 and S.2 show the committee’s estimates of fuel consumption benefits and costs for technologies that are commercially available and can be implemented within 5 years. The cost estimates represent estimates for the current (2009/2010) time period to about 5 years in the future. The committee based these estimates on a variety of sources, including recent reports from regulatory agencies and other sources on the costs and benefits of technologies; estimates obtained from suppliers on the costs of components; discussions with experts at automobile manufacturers and suppliers; detailed teardown studies of piece costs for individual technologies; and comparisons of the prices for and amount of fuel consumed by similar vehicles with and without a particular technology.

Some longer-term technologies have also demonstrated the potential to reduce fuel consumption, although further development is required to determine the degree of improvement, cost-effectiveness, and expected durability. These technologies include camless valve trains, homogeneous-charge compression ignition, advanced diesel, plug-in hybrids, diesel hybrids, electric vehicles, fuel cell vehicles, and advanced materials and body designs. Although some of these technologies will see at least limited commercial introduction over the next several years, it is only in the 5- to 15-year time frame and beyond that they are expected to find widespread commercial application. Further, it will not be possible for some of these technologies to become solutions for significant technical and economic challenges, and thus some of these technologies will remain perennially 10 to 15 years out beyond a moving reference. Among its provisions,



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Summary In 2007 the National Highway Traffic Safety Adminis- additional analysis are warranted. Given that the ultimate tration (NHTSA) requested that the National Academies energy savings are directly related to the amount of fuel provide an objective and independent update of the tech- consumed, as opposed to the distance that a vehicle travels nology assessments for fuel economy improvements and on a gallon of fuel, consumers also will be helped by addition incremental costs contained in the 2002 National Research to the label of explicit information that specifies the number Council (NRC) report Effectiveness and Impact of Corporate of gallons typically used by the vehicle to travel 100 miles. Average Fuel Economy (CAFE) Standards. The NHTSA also asked that the NRC add to its assessment technologies that Technologies for Reducing Fuel Consumption have emerged since that report was prepared. To address this request, the NRC formed the Committee on the Assessment Tables S.1 and S.2 show the committee’s estimates of of Technologies for Improving Light-Duty Vehicle Fuel fuel consumption benefits and costs for technologies that Economy. The statement of task, shown in Appendix B, are commercially available and can be implemented within directed the committee to estimate the efficacy, cost, and 5 years. The cost estimates represent estimates for the cur- applicability of technologies that might be used over the rent (2009/2010) time period to about 5 years in the future. next 15 years. The committee based these estimates on a variety of sources, including recent reports from regulatory agencies and other sources on the costs and benefits of technologies; estimates FINDINGS AND RECOMMENDATIONS obtained from suppliers on the costs of components; discus- sions with experts at automobile manufacturers and sup- Overarching Finding pliers; detailed teardown studies of piece costs for individual A significant number of technologies exist that can reduce technologies; and comparisons of the prices for and amount the fuel consumption of light-duty vehicles while maintain- of fuel consumed by similar vehicles with and without a ing similar performance, safety, and utility. Each technology particular technology. has its own characteristic fuel consumption benefit and esti- Some longer-term technologies have also demonstrated mated cost. Although these technologies are often considered the potential to reduce fuel consumption, although further independently, there can be positive and negative interactions development is required to determine the degree of improve- among individual technologies, and so the technologies ment, cost-effectiveness, and expected durability. These must be integrated effectively into the full vehicle system. technologies include camless valve trains, homogeneous- Integration requires that other components of the vehicle be charge compression ignition, advanced diesel, plug-in added or modified to produce a competitive vehicle that can hybrids, diesel hybrids, electric vehicles, fuel cell vehicles, be marketed successfully. Thus, although the fuel consump- and advanced materials and body designs. Although some tion benefits and costs discussed here are compared against of these technologies will see at least limited commercial those of representative base vehicles, the actual costs and introduction over the next several years, it is only in the 5- to benefits will vary by specific model. Further, the benefits of 15-year time frame and beyond that they are expected to find some technologies are not completely represented in the tests widespread commercial application. Further, it will not be used to estimate corporate average fuel economy (CAFE). possible for some of these technologies to become solutions The estimate of such benefits will be more realistic using the for significant technical and economic challenges, and thus new five-cycle tests that display fuel economy data on new some of these technologies will remain perennially 10 to 15 vehicles’ labels, but improvements to test procedures and years out beyond a moving reference. Among its provisions, 1

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2 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES TABLE S.1 Committee’s Estimates of Effectiveness (shown as a percentage) of Near-Term Technologies in Reducing Vehicle Fuel Consumption Incremental values - A preceding technology must be included Technologies I4 V6 V8 Spark Ignition Techs Abbreviation Low High A VG Low High AVG Low High AVG 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Low Friction Lubricants LUB 1.3 1.3 1.5 0.5 2.0 0.5 2.0 1.0 2.0 Engine Friction Reduction EFR 2.3 2.5 3.0 1.5 3.0 1.5 3.5 2.0 4.0 VVT- Coupled Cam Phasing (CCP), SOHC CCP 2.3 2.3 2.5 1.5 3.0 1.5 3.0 2.0 3.0 Discrete V ariable Valve Lift (DVVL), SOHC DVVL 5.0 7.5 NA NA NA 4.0 6.0 5.0 10.0 Cylinder Deactivation, SOHC DEAC 1.5 1.5 1.8 1.0 2.0 1.0 2.0 1.5 2.0 VVT - In take Cam Phasing (ICP) ICP 2.0 2.3 2.3 1.5 2.5 1.5 3.0 1.5 3.0 VVT - Dual Cam Phasing (DCP) DCP 2.3 2.5 3.0 1.5 3.0 1.5 3.5 2.0 4.0 Discrete V ariable Valve Lift (DVVL), DOHC DVVL 4.8 5.0 5.3 3.5 6.0 3.5 6.5 4.0 6.5 Continuously Variable V alve Lift (CVVL) CVVL 5.0 7.5 NA NA NA 4.0 6.0 5.0 10.0 Cylinder Deactivation, OHV DEAC 2.3 2.5 3.0 1.5 3.0 1.5 3.5 2.0 4.0 VVT - Coupled Cam Phasing (CCP), OHV CCP 2.0 2.3 2.5 1.5 2.5 1.5 3.0 2.0 3.0 Discrete V ariable Valve Lift (DVVL), OHV DVVL 2.3 2.3 2.3 1.5 3.0 1.5 3.0 1.5 3.0 Stoichiometric Gasoline Direct Injection (GDI) SGDI Turbocharging and Downsizing TRBDS 3.5 5.0 5.0 2.0 5.0 4.0 6.0 4.0 6.0 Diesel Techs 25.0 25.0 15.0 35.0 15.0 35.0 NA NA NA Conversion to Diesel DSL 10.0 10.0 30.0 Conversion to Advanced Diesel ADSL 7.0 13.0 7.0 13.0 22.0 38.0 Electrification/Accessory Techs 2.0 2.0 2.0 Electric Power Steering (EPS) EPS 1.0 3.0 1.0 3.0 1.0 3.0 1.0 1.0 1.0 0.5 1.5 0.5 1.5 0.5 1.5 Improved Accessories IACC Higher Voltage/Improved Alternator HVIA 0.3 0.3 0.3 0.0 0.5 0.0 0.5 0.0 0.5 Transmission Techs 4.0 4.0 4.0 1.0 7.0 1.0 7.0 1.0 7.0 Continuously Variable Transmission (CVT) CVT 2.5 2.5 2.5 2.0 3.0 2.0 3.0 2.0 3.0 5-spd Auto. Trans. w/ Improved Internals 1.5 1.5 1.5 1.0 2.0 1.0 2.0 1.0 2.0 6-spd Auto. Trans. w/ Improved Internals 2.0 2.0 2.0 2.0 2.0 2.0 7-spd Auto. Trans. w/ Improved Internals 1.0 1.0 1.0 1.0 1.0 1.0 8-spd Auto. Trans. w/ Improved Internals 5.5 5.5 5.5 3.0 8.0 3.0 8.0 3.0 8.0 6/7/8-spd Auto. Trans. w/ Improved Internals NAUTO 7.5 7.5 7.5 6.0 9.0 6.0 9.0 6.0 9.0 6/7-spd DCT from 4-spd A T DCT 6/7-spd DCT from 6-spd A T DCT 3.5 3.5 3.5 3.0 4.0 3.0 4.0 3.0 4.0 Hybrid Techs 3.0 3.0 3.0 12V BAS Micro-Hybrid MHEV 2.0 4.0 2.0 4.0 2.0 4.0 34.0 34.0 34.0 Integrated Starter Generator ISG 29.0 39.0 29.0 39.0 29.0 39.0 37.0 37.0 37.0 Power Split Hybrid PSHEV 24.0 50.0 24.0 50.0 24.0 50.0 35.0 35.0 35.0 2-Mode Hybrid 2MHEV 25.0 45.0 25.0 45.0 25.0 45.0 Plug-in hybrid PHEV NA NA NA NA NA NA NA NA NA Vehicle Techs 0.3 0.3 0.3 0.3 0.3 0.3 Mass Reduction - 1% MR1 1.4 1.4 1.4 1.4 1.4 1.4 Mass Reduction - 2% MR2 3.3 3.3 3.3 Mass Reduction - 5% MR5 3.0 3.5 3.0 3.5 3.0 3.5 6.5 6.5 6.5 Mass Reduction - 10% MR10 6.0 7.0 6.0 7.0 6.0 7.0 12.0 12.0 12.0 Mass Reduction - 20% MR20 11.0 13.0 11.0 13.0 11.0 13.0 2.0 2.0 2.0 Low Rolling Resistance Tires ROLL 1.0 3.0 1.0 3.0 1.0 3.0 1.0 1.0 1.0 1.0 Low Drag Brakes LDB 1.0 1.0 Aero Drag Reduction 10% AERO 1.5 1.5 1.5 1.0 2.0 1.0 2.0 1.0 2.0 NOTE: Some of the benefits (highlighted in green) are incremental to those obtained with preceding technologies shown in the technology pathways described in Chapter 9. the Energy Independence and Security Act (EISA) of 2007 of fuel consumed in driving a given distance. Although each requires periodic assessments by the NRC of automobile is simply the inverse of the other, fuel consumption is the vehicle fuel economy technologies, including how such tech- fundamental metric by which to judge absolute improve- nologies might be used to meet new fuel economy standards. ments in fuel efficiency, because what is important is gallons Follow-on NRC committees will be responsible for respond- of fuel saved in the vehicle fleet. The amount of fuel saved ing to the EISA mandates, including the periodic evaluation directly relates not only to dollars saved on fuel purchases of emerging technologies. but also to quantities of carbon dioxide emissions avoided. Fuel economy data cause consumers to undervalue small increases (1-4 mpg) in fuel economy for vehicles in the Testing and Reporting of Vehicle Fuel Use 15-30 mpg range, where large decreases in fuel consumption Fuel economy is a measure of how far a vehicle will travel can be realized with small increases in fuel economy. The with a gallon of fuel, whereas fuel consumption is the amount percentage decrease in fuel consumption is approximately

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TABLE S.2 Committee’s Estimates of Technology Costs in U.S. Dollars (2008) NR C 2009 Costs Incremental Values - A preceding technology must be included Technologies SUMMARY I4 V6 V8 AVG w/1.5 AVG w/1.5 AVG w/1.5 Low High AVG Low High AVG Low High AVG RPE RPE RPE Spark Ignition Techs Abbreviation Low Friction Lubricants LUB 4 4 3 5 3 5 3 5 4 6 6 6 Engine Friction Reduction EFR 48 78 64 104 42 63 63 94.5 84 126 32.0 52.0 VVT- Coupled Cam Phasing (CCP), SOHC CCP 35 70 70 35 52.5 70 105 70 105 Discrete Variable Valve Lift (DVVL), SOHC DVVL 130 160 180 210 280 320 145 217.5 195 292.5 300 450 Cylinder Deactivation, SOHC DEAC NA NA 340 400 357 420 NA NA 370 555 388.5 582.75 70 70 VVT - In take Cam Phasing (ICP) ICP 35 70 70 35 52.5 105 105 VVT - Dual Cam Phasing (DCP) DCP 35 70 70 70 70 35 52.5 105 105 Discrete Variable Valve Lift (DVVL), DOHC DVVL 180 220 260 300 145 217.5 200 300 280 420 130 160 Continuously Variable Valve Lift (CVVL) CVVL 290 310 350 390 182 273 300 450 370 555 159 205 Cylinder Deactivation, OHV DEAC NA NA 220 250 255 NA NA 235 352.5 255 382.5 VVT - Coupled Cam Phasing (CCP), OHV CCP 35 35 35 35 52.5 35 52.5 35 52.5 225 300 Discrete Variable Valve Lift (DVVL), OHV DVVL 130 160 210 240 280 320 145 218 338 450 Stoichiometric Gasoline Direct Injection (GDI) SGDI 213 323 117 195 169 256 295 351 156 234 319 485 Turbocharging and Downsizing TRBDS -144 205 525 790 31 658 370 490 430 645 46 986 Diesel T echs 3174 NA NA Conversion to Diesel DSL 2154 2632 2857 3491 NA NA 2393 3590 4761 Conversion to Advanced Diesel ADSL 520 520 683 683 3513 4293 683 3903 520 780 1025 5855 Electrification/Accessory Techs Electric Power Steering (EPS) EPS 70 120 70 120 70 120 95 143 95 143 95 143 80 80 80 Improved Accessories IACC 70 90 70 90 70 90 120 120 120 Higher Voltage/Improved Alternator HVIA 35 35 35 15 55 15 55 15 55 53 53 53 Transmission Techs Continuously Variable Transmission (CVT) CVT 150 170 243 263 243 263 160 240 253 380 253 380 5-spd Auto. T rans. w/ Improved Internals 133 133 133 133 200 133 200 133 200 174 262 174 262 174 262 6-spd Auto. T rans. w/ Improved Internals 133 215 133 215 133 215 7-spd Auto. T rans. w/ Improved Internals 170 300 235 353 235 353 235 353 170 300 170 300 8-spd Auto. T rans. w/ Improved Internals 425 425 425 425 638 425 638 425 638 6/7/8-Speed Auto. T rans. with Improved Inter nals NAUT O 137 425 137 425 281 422 281 422 281 422 137 425 6/7- spd DCT from 6-spd AT DCT -147 185 -147 185 -147 185 19 29 19 29 19 29 6/7- spd DCT from 4-spd AT DCT 193 193 -14 400 -14 400 193 290 290 290 -14 400 Hybrid Techs 12V BAS Micro-Hybrid MHEV 450 550 585 715 720 880 500 665 650 865 800 1064 Integrated Starter Gener ator ISG 1760 2640 2000 3000 3200 4800 2200 2926 2500 3325 4000 5320 Power Split Hybrid PSHEV 2708 4062 3120 4680 4000 6000 3385 4502 3900 5187 5000 6650 6500 8645 6500 8645 6500 8645 2-Mode Hybrid 2MHEV 5200 7800 5200 7800 5200 7800 Series PHEV 40 PHEV 8000 12000 9600 14400 13600 20400 10000 13300 12000 15960 17000 22610 Vehicle T echs Mass Reduction - 1% MR1 37 45 48 58 68 82 41 61 53 80 75 1 13 85 111 156 Mass Reduction - 2% MR2 77 93 100 121 142 170 127 166 234 Mass Reduction - 5% MR5 239 311 439 217 260 283 339 399 479 358 467 659 Mass Reduction - 10% MR10 572 747 1054 520 624 679 815 958 1 150 859 1 120 1581 Mass Reduction - 20% MR20 1650 2475 1700 2550 1750 2625 1600 1700 1600 1800 1600 1900 Low Rolling Resistance T ires ROLL 30 40 30 40 35 53 35 53 35 53 30 40 Aero Drag Reduction 10% AERO 45 45 40 50 40 50 45 68 68 68 40 50 3

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4 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES consumers would pay for a fuel economy technology. It is equal to the percentage increase in fuel economy for values intended to reflect long-run, substantially learned, industry- less than 10 percent (for example, a 9.1 percentage decrease average production costs that incorporate rates of profit and in fuel consumption equals a 10 percent increase in fuel overhead expenses. A critical issue is choice of the RPE economy), but the differences increase progressively: for markup factor, which represents the ratio of total cost of a example, a 33.3 percent decrease in fuel consumption equals component, taking into account the full range of costs of a 50 percent increase in fuel economy. doing business, to only the direct cost of the fully manu- Recommendation: Because differences in the fuel consump- factured component. For fully manufactured components purchased from a Tier 1 supplier,1 a reasonable average RPE tion of vehicles relate directly to fuel savings, the labeling markup factor is 1.5. For in-house manufactured compo- on new cars and light-duty trucks should include information nents, a reasonable average RPE markup factor over variable on the gallons of fuel consumed per 100 miles traveled in manufacturing costs is 2.0. In addition to the costs of mate- addition to the already-supplied data on fuel economy so that rials and labor and the fixed costs of manufacturing, the RPE consumers can become familiar with fuel consumption as a factor for components from Tier 1 suppliers includes profit, fundamental metric for calculating fuel savings. warranty, corporate overhead, and amortization of certain fixed costs, such as research and development. The RPE fac- Fuel consumption and fuel economy are evaluated by the tor for in-house manufactured components from automobile U.S. Environmental Protection Agency (EPA) for the two manufacturers includes the analogous components of the driving cycles: the urban dynamometer driving schedule (city Tier 1 markup for the manufacturing operations, plus addi- cycle) and the highway dynamometer driving schedule (high- tional fixed costs for vehicle integration design and vehicle way cycle). In the opinion of the committee, the schedules installation, corporate overhead for assembly operations, used to compute CAFE should be modified so that vehicle additional product warranty costs, transportation, market- test data better reflect actual fuel consumption. Excluding ing, dealer costs, and profits. RPE markup factors clearly some driving conditions and accessory loads in determining vary depending on the complexity of the task of integrating CAFE discourages the introduction of certain technologies a component into a vehicle system, the extent of the changes into the vehicle fleet. The three additional schedules recently required to other components, the novelty of the technology, adopted by the EPA for vehicle labeling purposes—ones and other factors. However, until empirical data derived via that capture the effects of higher speed and acceleration, air rigorous estimation methods are available, the committee conditioner use, and cold weather—represent a positive step prefers the use of average markup factors. forward, but further study is needed to assess to what degree Available cost estimates are based on a variety of sources: the new test procedures can fully characterize changes in in- component cost estimates obtained from suppliers, discus- use vehicle fuel consumption. sions with experts at automobile manufacturers and suppli- Recommendation: The NHTSA and the EPA should review ers, publicly available transaction prices, and comparisons of the prices of similar vehicles with and without a particular and revise fuel economy test procedures so that they better technology. However, there is a need for cost estimates reflect in-use vehicle operating conditions and also provide based on a teardown of all the elements of a technology the proper incentives to manufacturers to produce vehicles and a detailed accounting of materials and capital costs that reduce fuel consumption. and labor time for all fabrication and assembly processes. Such teardown studies are costly and are not feasible for Cost Estimation advanced technologies whose designs are not yet finalized and/or whose system integration impacts are not yet fully Large differences in technology cost estimates can result understood. Estimates based on the more rigorous method of from differing assumptions. These assumptions include teardown analysis would increase confidence in the accuracy whether costs are long- or short-term costs; whether learning of the costs of reducing fuel consumption. by doing is included in the cost estimate; whether the cost Technology cost estimates are provided by the committee estimate represents direct in-house manufacturing costs or for each fuel economy technology discussed in this report. the cost of purchasing a component from a supplier; and Except as indicated, the cost estimates represent the price which of the other changes in vehicle design that are required an automobile manufacturer would pay a supplier for a to maintain vehicle quality have been included in the cost finished component. Thus, on average, the RPE multiplier estimate. Cost estimates also depend greatly on assumed of 1.5 would apply to the direct, fully manufactured cost to production volumes. obtain the average additional price consumers would pay for In the committee’s judgment, the concept of incremental a technology. Again, except where indicated otherwise, the retail price equivalent (RPE) is the most appropriate indicator of cost for the NHTSA’s purposes because it best represents the full, long-run economic costs of decreasing fuel con- 1A Tier 1 supplier is one that contracts directly with automobile manu - sumption. The RPE represents the average additional price facturers to supply technologies.

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5 SUMMARY cost estimates provided are based on current conditions and consumption and can also cause a slight increase in engine do not attempt to estimate economic conditions and hence performance, which offers a potential opportunity for en- predict prices 5, 10, or 15 years into the future. gine downsizing. There are many different implementations of VEM, and the costs and benefits depend on the specific engine architecture. Fuel consumption reduction can range Spark-Ignition Gasoline Engine Technologies from 1 percent with only intake cam phasing, to about 7 per- Spark-ignition (SI) engines are expected to continue to be cent with a continuously variable valve lift and timing setup. the primary source of propulsion for light-duty vehicles in The incremental RPE increase for valve-event modulation the United States over the time frame of this report. There ranges from about $50 to $550, with the amount depending have been and continue to be significant improvements in on the implementation technique and the engine architecture. reducing the fuel consumption of SI engines in the areas of Variable compression ratio, camless valve trains, and friction reduction, reduced pumping losses through advanced homogeneous-charge compression ignition were all given valve-event modulation, thermal efficiency improvements, careful consideration during the course of this study. Because cooled exhaust gas recirculation, and improved overall of questionable benefits, major implementation issues, or engine architecture, including downsizing. An important uncertain costs, it is uncertain whether any of these technolo- attribute of improvements in SI engine technologies is that gies will have any significant market penetration in the next they offer a means of reducing fuel consumption in relatively 10 to 15 years. small, incremental steps. This approach allows automobile manufacturers to create packages of technologies that can Compression-Ignition Diesel Engine Technologies be tailored to meet specific cost and effectiveness targets, as opposed to developing diesel or full hybrid alternatives that Light-duty compression-ignition (CI) engines operating offer a single large benefit, but at a significant cost increase. on diesel fuels have efficiency advantages over the more Because of the flexibility offered by this approach, and given common SI gasoline engines. Although light-duty diesel the size of the SI engine-powered fleet, the implementation vehicles are common in Europe, concerns over the ability of SI engine technologies will continue to play a large role of such engines to meet emission standards for nitrogen in reducing fuel consumption. oxides and particulates have slowed their introduction in the Of the technologies currently available, cylinder de- United States. However, a joint effort between automobile activation is one of the more effective in reducing fuel manufacturers and suppliers has resulted in new emissions consumption. This feature is most cost-effective when ap- control technologies that enable a wide range of light-duty plied to six-cylinder (V6) and eight-cylinder (V8) overhead CI engine vehicles to meet federal and California emissions valve engines, and typically reduces fuel consumption by standards. The committee found that replacing a 2007 model 4 to 10 percent at an incremental RPE increase of about year SI gasoline power train with a base-level CI diesel $550. Stoichiometric direct injection typically affords a 1.5 engine with an advanced 6-speed dual-clutch automated to 3 percent reduction in fuel consumption at an incremen- manual transmission (DCT) and more efficient accessories tal RPE increase of $230 to $480, depending on cylinder packages can reduce fuel consumption by about 33 percent count and noise abatement requirements. Turbocharging on an equivalent vehicle performance basis. The estimated and downsizing can also yield fuel consumption reduc- incremental RPE cost of conversion to the CI engine is tions. Downsizing—reducing engine displacement while about $3,600 for a four-cylinder engine and $4,800 for maintaining vehicle performance—is an important strategy a six-cylinder engine. Advanced-level CI diesel engines, applicable in combination with technologies that increase which are expected to reach market in the 2011-2014 time engine torque, such as turbocharging or supercharging. frame, with DCT (7/8 speed) could reduce fuel consump- Downsizing simultaneously reduces throttling and friction tion by about an additional 13 percent for larger vehicles and losses because downsized engines generally have smaller by about 7 percent for small vehicles. Part of the gain from bearings and either fewer cylinders or smaller cylinder bore advanced-level CI diesel engines comes from downsizing. friction surfaces. Reductions in fuel consumption can range The estimated incremental RPE cost of the conversion to the from 2 to 6 percent with turbocharging and downsizing, de- package of advanced diesel technologies is about $4,600 for pending on many details of implementation. This technology small passenger cars and $5,900 for intermediate and large combination is assumed to be added after direct injection, passenger cars. and its fuel consumption benefits are incremental to those An important characteristic of CI diesel engines is that from direct injection. Based primarily on an EPA teardown they provide reductions in fuel consumption over the entire study, the committee’s estimates of the costs for turbocharg- vehicle operating range, including city driving, highway ing and downsizing range from close to zero additional cost, driving, hill climbing, and towing. This attribute of CI diesel when converting from a V6 to a four-cylinder (I4) engine, to engines is an advantage when compared with other technol- almost $1,000, when converting from a V8 to a V6 engine. ogy options that in most cases provide fuel consumption Valve-event modulation (VEM) can further reduce fuel benefits for only part of the vehicle operating range.

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6 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES The market penetration of CI diesel engines will be tric vehicles (i.e., with driving range, trunk space, volume, strongly influenced by both the incremental cost of CI diesel and acceleration comparable to those of vehicles powered power trains above the cost of SI gasoline power trains and with internal-combustion engines) depends on a battery cost by diesel and gasoline fuel prices. Further, while technology breakthrough that the committee does not anticipate within improvements to CI diesel engines are expected to reach mar- the time horizon considered in this study. However, it is clear ket in the 2011-2014 time frame, technology improvements that small, limited-range, but otherwise full-performance to SI gasoline and hybrid engines will also enter the market. battery electric vehicles will be marketed within that time Thus, competition between these power train systems will frame. Although there has been significant progress in fuel continue with respect to reductions in fuel consumption and cell technology, it is the committee’s opinion that fuel cell to cost. For the period 2014-2020, further potential reduc- vehicles will not represent a significant fraction of on-road tions in fuel consumption by CI diesel engines may be offset light-duty vehicles within the next 15 years. by increases in fuel consumption as a result of changes in engines and emissions systems required to meet potentially Non-engine Technologies for Reducing Vehicle Fuel stricter emissions standards. Consumption There is a range of non-engine technologies with varying Hybrid Vehicle Technologies costs and impacts. Many of these technologies are continu- Because of their potential to eliminate energy consump- ally being introduced to new vehicle models based on the tion when the vehicle is stopped, permit braking energy to timing of the product development process. Coordinating the be recovered, and allow more efficient use of the internal introduction of many technologies with the product devel- combustion engine, hybrid technologies are one of the opment process is critical to maximizing impact and mini- most active areas of research and deployment. The degree mizing cost. Relatively minor changes that do not involve of hybridization can vary from minor stop-start systems reengineering the vehicle or that require recertification for with low incremental costs and modest reductions in fuel fuel economy, emissions, and/or safety can be implemented consumption to complete vehicle redesign and downsizing within a 2- to 4-year time frame. These changes could in- of the SI gasoline engine at a high incremental cost but with clude minor reductions in mass (achieved by substitution of significant reductions in fuel consumption. For the most materials), improving aerodynamics, or switching to low- basic systems that reduce fuel consumption by turning off rolling-resistance tires. More substantive changes, which re- the engine while the vehicle is at idle, the fuel consumption quire longer-term coordination with the product development benefit may be up to about 4 percent at an estimated incre- process because of the need for reengineering and integration mental RPE increase of $670 to $1,100. The fuel consump- with other subsystems, could include resizing the engine and tion benefit of a full hybrid may be up to about 50 percent transmission or aggressively reducing vehicle mass, such as at an estimated incremental RPE cost of $3,000 to $9,000 by changing the body structure. The time frame for substan- depending on vehicle size and specific hybrid technology. A tive changes for a single model is approximately 4 to 8 years. significant part of the improved fuel consumption of full hy- Two important technologies impacting fuel consumption brid vehicles comes from the complete vehicle redesign that are those for light-weighting and for improving transmis- can incorporate modifications such as low-rolling-resistance sions. Light-weighting has significant potential because tires, improved aerodynamics, and the use of smaller, more vehicles can be made very light with exotic materials, albeit efficient SI engines. at potentially high cost. The incremental cost to reduce a In the next 10 to 15 years, improvements in hybrid vehicles pound of mass from the vehicle tends to increase as the total will occur primarily as a result of reduced costs for hybrid amount of reduced mass increases, leading to diminishing power train components and improvements in battery perfor- returns. About 10 percent of vehicle mass can be eliminated mance such as higher power per mass and volume, increased at a cost of roughly $800 to $1,600 and can provide a fuel number of lifetime charges, and wider allowable state-of- consumption benefit of about 6 to 7 percent. Reducing mass charge ranges. During the past decade, significant advances much beyond 10 percent requires attention to body struc- have been made in lithium-ion battery technology. When ture design, such as considering an aluminum-intensive car, the cost and safety issues associated with them are resolved, which increases the cost per pound. A 10 percent reduction lithium-ion batteries will replace nickel-metal-hydride bat- in mass over the next 5 to 10 years appears to be within reach teries in hybrid electric vehicles and plug-in hybrid electric for the typical automobile. vehicles. A number of different lithium-ion chemistries are Transmission technologies have improved significantly being studied, and it is not yet clear which ones will prove and, like other vehicle technologies, show a similar trend most beneficial. Given the high level of activity in lithium- of diminishing returns. Planetary-based automatic transmis- ion battery development, plug-in hybrid electric vehicles will sions can have 5, 6, 7, and 8 speeds, but with incremental be commercially viable and will soon enter at least limited costs increasing faster than reductions in fuel consumption. production. The practicality of full-performance battery elec- DCTs are in production by some automobile manufacturers,

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7 SUMMARY and new production capacity for this transmission type has Comparisons of FSS modeling and PDA estimation sup- been announced. It is expected that the predominant trend in ported by lumped parameter modeling have shown that the transmission design is conversion to 6- to 8-speed planetary- two methods produce similar results when similar assump- based automatics and to DCTs, with continuously variable tions are used. In some instances, comparing the estimates transmissions remaining a niche application. Given the close made by the two methods has enhanced the overall valid- linkage between the effects of fuel-consumption-reducing ity of estimated fuel consumption impacts by uncovering engine technologies and transmission technologies, the inadvertent errors in one or the other method. In the com- present study has for the most part considered the combined mittee’s judgment both methods are valuable, especially effects of engines and transmission combinations rather than when used together, with one providing a check on the other. potential separate effects. However, more work needs to be done to establish the accu- Accessories are also being introduced to new vehicles racy of both methods relative to actual motor vehicles. to reduce the power load on the engine. Higher-efficiency T he Department of Transportation’s Volpe National air conditioning systems are available that more optimally Transportation Systems Center has developed a model for match cooling with occupant comfort. Electric and electric/ the NHTSA to estimate how manufacturers can comply with hydraulic power steering also reduces the load on an engine fuel economy regulations by applying additional fuel sav- by demanding power only when the operator turns the wheel. ings technologies to the vehicles they plan to produce. The An important motivating factor affecting the introduction model employs a PDA algorithm that includes estimates of of these accessories is whether or not their impact is mea - the effects of interactions among technologies applied. The sured during the EPA driving cycles used to estimate fuel validity of the Volpe model could be improved by taking consumption. into account main and interaction effects produced by the FSS methodology described in Chapter 8 of this report. In particular, modeling work done for the committee by an Modeling Reductions in Fuel Consumption Obtained from outside consulting firm has demonstrated a practical method Vehicle Technologies for using data generated by FSS models to accurately assess The two primary methods for modeling technologies’ the fuel consumption potentials of combinations of dozens reduction of vehicle fuel consumption are full system simula- of technologies on thousands of vehicle configurations. A tion (FSS) and partial discrete approximation (PDA). FSS is design-of-experiments statistical analysis of FSS model runs the state-of-the-art method because it is based on integration demonstrated that main effects and first-order interaction effects alone could predict FSS model outputs with an R2 of the equations of motion for the vehicle carried out over the speed-time representation of the appropriate driving or of 0.99. Using such an approach could appropriately com- test cycle. Done well, FSS can provide an accurate assess- bine the strengths of both the FSS and the PDA modeling ment (within +/–5 percent or less) of the impacts on fuel methods. However, in the following section, the committee consumption of implementing one or more technologies. recommends an alternate approach that uses FSS to better The validity of FSS modeling depends on the accuracy of assess the contributory effects of the technologies applied representations of system components. Expert judgment is in the reduction of energy losses and to better couple the also required at many points and is critical to obtaining ac- modeling of fuel economy technologies to the testing of such curate results. Another modeling approach, the PDA method, technologies on production vehicles. relies on other sources of data for estimates of the impacts of fuel economy technologies and relies on mathematical Application of Multiple Vehicle Technologies to Vehicle summation or multiplication methods to aggregate the effects Classes of multiple technologies. Synergies among technologies can be represented using engineering judgment and lumped Figures 9.1 to 9.5 in Chapter 9 of this report display the parameter models2 or can be synthesized from FSS results. technology pathways developed by the committee for eight Unlike FSS, the PDA method cannot be used to generate classes of vehicles and the aggregated fuel consumption ben- estimates of the impacts of individual technologies on fuel efits and costs for the SI engine, CI engine, and hybrid power consumption. Thus, the PDA method by itself, unlike FSS, train pathways. The results of the committee’s analysis are is not suitable for estimating the fuel consumption impacts that, for the intermediate car, large car, and unibody standard of technologies that have not already been tested in actual truck classes, the average reduction in fuel consumption for vehicles or whose fuel consumption benefits have not been the SI engine path is about 29 percent at a cost of approxi- estimated by means of FSS. mately $2,200; the average reduction for the CI engine path is about 37 percent at a cost of approximately $5,900; and the average reduction for the hybrid power train path is about 2 Lumped parameter models are simplified analytical tools for estimating 44 percent at a cost of $6,000. These values are approximate vehicle energy use based on a small set of energy balance equations and empirical relationships. With a few key vehicle parameters, these methods and are provided here as rough estimates that can be used for can explicitly account for the sources of energy loss and the tractive force qualitative comparison of SI engine-related technologies and required to move the vehicle.

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8 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES other candidates for the reduction of vehicle fuel consump- vehicles. Combining the results of such testing with FSS tion, such as light-duty diesel or hybrid vehicles. modeling, and thereby making all simulation variables and subsystem maps transparent to all interested parties, would allow the best opportunity to define a technical baseline Improvements to Modeling of Multiple Fuel Economy against which potential improvements could be analyzed Technologies more accurately and openly than is the case with the current Many vehicle and power train technologies that improve methods employed. fuel consumption are currently in or entering production or The steps in the recommended process would be as are in advanced stages of development in European or Asian follows: markets where high consumer fuel prices have made com- mercialization of the technologies cost-effective. Depending 1. Develop a set of baseline vehicle classes from which a on the intended vehicle use or current state of energy-loss characteristic vehicle can be chosen to represent each reduction, the application of incremental technologies will class. The vehicle may be either real or theoretical produce varying levels of improvement in fuel consump- and will possess the average attributes of that class as tion. Data made available to the committee from automobile determined by sales-weighted averages. manufacturers, Tier 1 suppliers, and other published studies 2. Identify technologies with a potential to reduce fuel also suggest a very wide range in estimated incremental consumption. cost. As noted above in this Summary, estimates based on 3. Determine the applicability of each technology to the teardown cost analysis, currently being utilized by the EPA various vehicle classes. in its analysis of standards for regulating light-duty-vehicle 4. Estimate each technology’s preliminary impact on fuel greenhouse gas emissions, should be expanded for develop- consumption and cost. ing cost impact analyses. The committee notes, however, that 5. Determine the optimum implementation sequence cost estimates are always more uncertain than estimates of (technology pathway) based on cost-effectiveness and fuel consumption. engineering considerations. FSS modeling that is based on empirically derived power 6. Document the cost-effectiveness and engineering train and vehicle performance and on fuel consumption judgment assumptions used in step 5 and make this data maps offers what the committee believes is the best information part of a widely accessible database. available method to fully account for system energy losses 7. Utilize modeling software (FSS) to progress through and to analyze potential improvements in fuel consumption each technology pathway for each vehicle class to achievable by technologies as they are introduced into the obtain the final incremental effects of adding each market. Analyses conducted for the committee show that the technology. effects of interactions between differing types of technolo- gies for reducing energy loss can and often do vary greatly If such a process were adopted as part of a regulatory rule- from vehicle to vehicle. making procedure, it could be completed on 3-year cycles to allow regulatory agencies sufficient lead time to integrate Recommendation: T he committee proposes a method the results into future proposed and enacted rules. whereby FSS analyses are used on class-characterizing ve- hicles, so that synergies and effectiveness in implementing CONCLUDING COMMENTS multiple fuel economy technologies can be evaluated with what should be greater accuracy. This proposed method would A significant number of approaches are currently avail- determine a characteristic vehicle that would be defined as a able to reduce the fuel consumption of light-duty vehicles, reasonable average representative of a class of vehicles. This ranging from relatively minor changes to lubricants and tires representative vehicle, whether real or theoretical, would to large changes in propulsion systems and vehicle platforms. undergo sufficient FSS, combined with experimentally Technologies such as all-electric propulsion systems have determined and vehicle-class-specific system mapping, to also demonstrated the potential to reduce fuel consumption, allow a reasonable understanding of the contributory effects although further development is required to determine the of the technologies applied to reduce vehicle energy losses. degree of improvement, cost-effectiveness, and durability. Data developed under the United States Council for Automo- The development and deployment of vehicles that consume tive Research (USCAR) Benchmarking Consortium should less fuel will be influenced not only by technological factors be considered as a source for such analysis and potentially but also by economic and policy factors whose examination expanded. Under the USCAR program, actual production is beyond the scope of this study. Future NRC committees vehicles are subjected to a battery of vehicle, engine, and will be responsible for periodic assessments of the cost and transmission tests in sufficient detail to understand how each benefits of technologies that reduce vehicle fuel consump- candidate technology is applied and how they contribute to tion, including how such technologies might be used to meet the overall performance and fuel consumption of light-duty new fuel economy standards.