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Assessment of Fuel Economy Technologies for Light-Duty Vehicles 7 Non-Engine Technologies INTRODUCTION This chapter focuses on reducing fuel consumption with non-power-train technologies. These technologies affect engine performance either directly or indirectly in a manner that reduces fuel consumption. For example, a significant portion of this chapter discusses the state of readiness, cost, and impact of reducing vehicle mass. Reducing mass reduces the energy necessary to move a vehicle, and thus reduces fuel consumption. The complexity of substituting advanced, lightweight materials affects the redesign of a part or a subsystem, component manufacturing (including tooling and production costs), and joining, and raises interface issues that mixing different materials can pose. The term material substitution oversimplifies the complexity of introducing advanced materials, because seldom does one part change without changing others around it. Advanced lightweight materials show great promise for reducing mass throughout a vehicle’s body structure and interior. Low-rolling-resistance tires and reduction of aerodynamic drag are also discussed as technologies that can lower tractive force and result in reduced fuel consumption. Improvements in energy-drawing devices such as air conditioner compressors and power steering can reduce fuel consumption either by electrification or by improving their efficiency. New transmissions with more gears or that are continuously variable improve power train efficiency. All these options either reduce the demand for power from the engine or enable operating the engine at a more efficient point to reduce fuel consumption. NON-ENGINE TECHNOLOGIES CONSIDERED IN THIS STUDY The committee considers car body design (aerodynamics and mass), vehicle interior materials (mass), tires, vehicle accessories (power steering and heating, ventilation, and air conditioning [HVAC] systems), and transmissions as areas of significant opportunity for achieving near-term, cost-effective reductions in fuel consumption. These will be considered in some detail below. Aerodynamics As discussed in Chapter 2, the force required to overcome drag is represented by the product of the drag coefficient, the frontal area, and the square of speed. The actual formula is F = ½ Cd AV2 where A is the vehicle frontal area, V is velocity, and Cd is the drag coefficient. Cd typically ranges from about 0.25 to 0.38 on production vehicles and depends on several factors with the primary influence coming from vehicle shape and smaller influences from other factors, such as external mirrors, rear spoilers, frontal inlet areas, wheel well covers, and the vehicle underside. Vehicles with higher Cd values (greater than .30) may be able to reduce the Cd by up to 10 percent at low cost without affecting the vehicle’s interior volume. In trying to reduce fuel consumption, certain vehicles achieved very low drag coefficients, for example, GM’s EV1 had a Cd of 0.19, and the third-generation Prius has a Cd of 0.25.1 In the committee’s judgment a Cd of less than 0.25 would require significant changes that could include the elimination of outside rear view mirrors, total enclosure of the car underbody, and other modifications that may be very costly. Vehicles that exist today with a low Cd (below 0.25) are usually specialty vehicles (e.g., sports cars and high-mileage vehicles like the Prius). The 2010 Mercedes E-class is the only production vehicle with a Cd as low as 0.25. However, this is a luxury-class vehicle and retails for $50,000 (or more). Some costs are incurred from incorporating aerodynamic features such as the integrated front spoiler, an option that may not be possible for lower-cost vehicle classes. Further reducing Cd for lower-cost vehicles is expensive and perhaps beyond a point of diminishing returns. Vehicles with higher Cd (e.g., trucks, 1 See http://www.greencar.com/articles/20-truths-gm-ev1-electric-car.php and http://pressroom.toyota.com/pr/tms/toyota/all-new-prius-reveal.aspx, respectively.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles vans, and box-like vehicles such as the Scion and Flex) can reduce Cd, although vehicle functionality is diminished. If the functionality is compromised, then the vehicle’s appeal to the consumer would be reduced. As noted above, the aerodynamic drag is the product of the drag coefficient Cd, the vehicle frontal area, and speed. Reduction in the frontal area, reducing vehicle size, and lower speed limits would also improve fuel consumption; however, exploring these options is outside the committee’s statement of task. Car Body Design and Interiors Optimized car body design focuses on a balance between structural stiffness, noise/vibration/harshness (NVH), safety (crashworthiness), comfort (space), and mass. Today’s priority of reducing fuel consumption places an emphasis on mass reduction, with the assumption that other performance criteria will not be unduly compromised. Vehicle mass can be reduced without compromising size, crashworthiness, and NVH, although countermeasures are often required to restore NVH performance when mass is reduced. The majority of vehicle mass can be attributed to the body structure, closure panels (doors, hood, and deck lid), interior seating and trim components, glass, power train components (engine, transmission, etc.), and the chassis (axles, wheels, brakes, suspension, etc.). Steel, cast iron, fiber/reinforced composites, glass, and aluminum have been the dominant materials for these components, with steel accounting for the majority of mass. Estimates for the amount of these materials in today’s average, high-volume vehicles are listed in Table 7.1 (Carpenter, 2008). The typical baseline vehicle used for comparison is described as a 3,600-lb model-year 2009 comparable to a Toyota Camry or Chevrolet Malibu. High-volume vehicle manufacturing is generally associated with the production of more than about 100,000 vehicles per year (although some might say 50,000). Low volume might be under 25,000 vehicles per year. This is important because different materials become cost competitive at different volumes. Higher-cost materials (composites, aluminum, and magnesium) become more cost competitive at lower volumes because the forming tools in most cases have a lower investment cost offsetting the higher material cost. Steel requires high-cost forming tools but has a lower materials cost, making steel competitive at higher volumes. For example, for some non-structural applications, steel becomes cost competitive vis-à-vis plastic at around 50,000 units. Two key strategies for achieving mass reduction are changing the design to require less material, or substituting lighter-weight materials for heavier materials. Assuming that the car size is essentially fixed, there are design techniques that can reduce mass. Several different body architectures are described below. Material substitution relies on replacing a heavier material with a lighter one while maintaining performance (safety and stiffness). For example, high-strength steel can be substituted for mild steel (and therefore a thinner gauge can be used), aluminum can be substituted for steel, plastic can be substituted for aluminum, and magnesium can be substituted for aluminum. It is often a misnomer to refer to this as material substitution. The part (or subsystem) often has to be redesigned, and the fabrication process may change and the assembly process may be different. In fact, the material cost differential may be insignificant relative to the costs associated with the changes in fabrication and assembly. Body Design and Material Selection The great majority of vehicles produced today are unibody design. The unibody design is a construction technique that uses the internal parts as the principal load-bearing structure. While the closure panels (doors, hood, and deck lid) provide important structural integrity to the body of the vehicle, the outer skin panels, defined as the metal outer panels on the entire automobile that are painted and visible to the consumer, do not. This design has replaced the traditional body-on-frame design primarily because it is a lighter. Body-on-frame designs, where an independent body structure (with its own structural integrity) sits on top of a separate frame (with its own structural integrity), still prevail on some heavier vehicles such as pickup trucks and larger SUVs because of its overall superior strength and stiffness. Another design, the space frame, was recently developed to accommodate aluminum. The forming and joining of aluminum cannot easily or cheaply be replicated in a steel unibody design. A typical space frame is composed of extruded metal connected at the ends, which are referred to as nodes. Both the unibody and the space frame have “hang-on” panels where the skin panels have little to no structural load. A final design architecture, the monocoque, relies on the outer skin surface as a principal load-bearing surface. The TABLE 7.1 Distribution of Materials in Typical Vehicle (e.g., Toyota Camry and Chevrolet Malibu) Material Comments Approximate Content in Cars Today, by Weight (percent) Iron and mild steel Under 480 Mpa 55 High-strength steel ≥ 480 Mpa (in body structure) 15 Aluminum No aluminum closure panels; aluminum engine block and head and wheels 10 Plastic Miscellaneous parts, mostly interior trim, light lenses, facia, instrument panel 10 Other (magnesium, titanium, rubber, etc.) Miscellaneous parts 10
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles monocoque is seen in very low volumes because there are few applications where it is structurally and economically viable. Generally, these three designs are associated with the following materials: Unibody—steel-based structure (mostly steel stampings) usually with steel skin panels but sometimes plastic or aluminum skin panels. This design has high investment (engineering and tooling) costs and is designed for high volume. Space frame—usually an aluminum-based structure (aluminum castings, extrusions, and sheet). This design is less complex than the unibody and has lower investment costs, which are typically offset by higher material costs. Because of the high material costs (that are variable with volume), this is typically a low-volume design. Monocoque—reinforced resin/composite body structure using the skin to bear loads. Today, this architecture is uncommon for passenger automobiles and more common for aircraft or ships. The space frame and monocoque structures are associated today with niche vehicle markets, whereas the unibody with its steel-based structure is common (perhaps found in more than 99 percent of today’s automobiles). These design approaches differ from the body-on-frame design that is well suited for heavier “working” vehicles like trucks and SUVs. Body-on-frame readily achieves all the desired design criteria, except that it is heavy because of the large frame components. Reducing Mass Using Alternative Materials There are several methods to make steel structures lighter, regardless of their design construction: Substitute higher-strength steel for lower-strength steel. Higher-strength steel can be down-gauged (made thinner). There are, however, forming and joining issues with higher-strength steel that limit where it can be applied, and down-gauging can reduce the ability to meet stiffness criteria. Substitute sandwich metal material for conventional steel. Sandwich material has layers of steel or aluminum (usually three), often with the internal layer in the form of honeycomb or foam. Other layered materials can include bonded steel with plastic/polymers. This cladding material can achieve high stiffness and strength levels with low mass. Sandwich material is light, is very stiff, and can be formed for many parts. On the downside, joining it to other parts can be difficult, its availability is limited today, and it is expensive to produce. Introduce new steel designs that are available, such as with laser welded blanks and hydro-formed tubes or hydro-formed sheet metal. The use of tubes and laser blanks can make more optimal use of metal (steel or aluminum) and result in less mass in the structure without compromising design criteria. These methods may increase or decrease costs depending on the application. Most steel and mixed-material vehicles (e.g., steel and aluminum) today are unibody, and aluminum-intensive vehicles tend to be space frame designs, but these are low volume due to cost. The unibody design was developed primarily for steel, and the conventional vehicle today is composed of about 65 percent steel (both mild and high strength). Various components of a unibody can have alternative lightweight materials, including high-strength steel, polymers/composites, and aluminum directly substituted on a part-by-part basis to help reduce mass on a limited basis. Sheet molding compound (SMC plastic) body panels are sometimes used for fenders or exterior closure panels to save weight, and in the case of low-volume vehicles, to save costs. The ability to substitute alternative materials, however, can be limited because of forming (part shape), joining, and interface issues between mixed materials. Steel unibody designs can accommodate polymer/composite or aluminum closure panels because these parts can be easily isolated from the remainder of the structure since they are fastened onto the structure. Many unibody steel-based vehicles made in North America have aluminum hoods and deck lids, but steel doors. Hoods and deck lids are simpler designs than doors (they are flatter and have fewer parts, and therefore are less expensive and less complex to switch over to aluminum). Steel doors could also be converted to aluminum in many cases, as is often done in Europe, but in North America their size and geometry would make this conversion relatively expensive. The mass savings by introducing high-strength steel results from the ability to down-gauge the thickness over mild steel while maintaining the same strength as the thicker mild steel part. Down-gauging reduces stiffness, and so this is not a solution in some cases where stiffness is important. Also, as the strength of steel increases, its ability to be formed into different shapes is reduced (its allowable percent elongation is reduced). This reduced formability also limits where high-strength steel can be applied. The outside panels (skin panels) on a unibody are predominantly non-structural and subject to dents, thus also limiting the ability to down-gauge these panels. The tools that form high-strength steel parts cost more, require greater maintenance because they are subject to wear, and require greater forming pressures in production. In most cases, high-strength steel parts cost more than comparable mild steel parts. New, advanced high-strength steels are being developed to give high-strength steel greater formability and weldability. These advanced high-strength steels, expected to be available within a few years, can reduce mass on some compatible parts by around 35 percent. This is achieved by using high-strength steel to
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles reduce part thickness by 35 percent (e.g., replacing 1.8-mm-thick mild steel with 1.2-mm-thick high-strength steel). Factors such as part geometry and subsystem stiffness can limit viable applications of high-strength steel or constrain the reduction in thickness. An aggressive approach to introducing aluminum into the structure may dictate a totally different body design approach, such as shifting from a unibody to a space frame structure. The space frame design has been developed recently for aluminum-intensive structures. The structure is composed of aluminum castings, extrusions, and sheet. This design is lighter than a comparable steel design and is in production today, but is used only on lower-volume, higher-end vehicles because of its high cost. Introducing an aluminum-intensive structure would necessitate a complete vehicle redesign, requiring several years at extremely high development costs (see the product development process discussion in the section “Timing Considerations for Introducing New Technologies” below in this chapter). Polymer-matrix composites (PMCs) are beginning to be introduced into higher-volume vehicles. Viable options for PMC are for it to be reinforced with glass fibers, natural fibers, or carbon fiber to give it strength. Glass- and natural-fiber-reinforced PMCs are lower cost than carbon fiber, but they have less strength. Since they incur lower cost, it is likely that these applications will be seen on higher-volume vehicles before there is significant use of carbon fiber composites. Carbon fiber is a promising lightweight material for many automotive components. Much like plastic, PMC can be molded into complex shapes, thus integrating several steel or aluminum parts into a single PMC part that reduces complexity and tooling costs. Conservative estimates are that carbon fiber PMC can reduce the mass of a steel structure by 40 to 50 percent (Powers, 2000). Both its strength and its stiffness can exceed that of steel, making it easy to substitute for steel or aluminum while offering equal or better structural performance. The greatest challenges with PMC are cost and carbon fiber availability. Also challenging is connecting composite parts with fasteners, which has delayed the introduction of the latest Boeing 787 Jet. The price of carbon fiber is extremely volatile, with material cost typically in excess of $10/lb. Carbon fiber exceeds the cost of steel and aluminum by approximately 20-fold and 7-fold, respectively. Steel and aluminum can also be formed with high-speed stamping, which is much less costly than forming PMC, which typically involves a fairly slow autoclave process. Research at Oak Ridge National Laboratory (ORNL) is aimed at developing lignin-based carbon fiber to help reduce material cost and improve supply (Compere et al., 2001). This research in conjunction with the FreedomCar program at the United States Council for Automotive Research (USCAR) indicates that the price of carbon fiber has to fall to $5 to $7 per pound (about 50 percent) before it can be cost competitive for high-volume automobiles ( Carpenter, 2008). Lignin-based carbon fiber will also help ensure a greater supply of the base material of PMC. One expert stated that carbon fiber will see wider use in the future, but primarily on lower-volume (fewer than 100,000 vehicles per year), higher-performance vehicles (Carpenter, 2008). The cost differential (by pound) varies significantly for alternative materials. High-strength steel might cost double the price of mild steel ($0.80 versus $0.40 per pound), and aluminum might cost four or five times that of steel (per pound). Other materials such as magnesium and titanium are also expensive and have volatile price fluctuations. It is important to recognize that the comparison of different materials is complicated by many factors, making a cost analysis difficult. Tooling costs and parts fabrication costs differ significantly for different materials. The amount of material (pounds) needed by the lightweight material is different from the incumbent material. Because of part fabrication, the optimal design with the lightweight material may be very different from the design of the original part. For example, some steel parts cannot be formed exactly the same out of aluminum because of formability constraints. Also, if you substitute a material that is cast (magnesium) instead of stamped (steel), the forming cost and the part design are different. The tooling to form the alternative material is likely to be different than the tooling for the incumbent material, and may cost more or less. The processing (part fabrication) process will likely run differently, and may operate much slower than that for the incumbent material (e.g., molding is much slower than stamping, sometimes by a factor of 10). USCAR and the U.S. Department of Energy continue to research reducing body mass by substituting new materials, such as high-strength steel, advanced high-strength steel, aluminum, magnesium, and composites for current materials. The material industries also conduct significant research to advance new materials (for example, through the Auto-Steel Partnership, the American Iron and Steel Institute, the Aluminum Association, and the American Chemistry Council). Increased costs for lighter and stronger parts result from higher material costs and higher costs for component fabrication and joining. Estimates for the body-mass reduction that can be achieved in the near term vary from 10 percent (with mostly conventional and high-strength steels) to 50 percent (with a mostly aluminum/composite structure). Even greater reductions are feasible, but these require very expensive and aggressive use of aluminum, magnesium, and composite structures involving materials such as carbon fiber. Non-Body Mass Reduction Vehicle interiors also offer opportunities to reduce vehicle mass. Some opportunities can be implemented for little
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles cost, whereas others entail significant costs. For example, composite-intensive instrument panels, recycled seating materials, and lighter-weight trim panels can reduce mass by tens of pounds at virtually no cost. However, unlike the car body for which the consumer cannot easily detect what materials are used, the interior is aesthetically critical and closely scrutinized by the consumer. Costs may be incurred by covering over the appearance of some parts. There are quality concerns, such as fit-up of panels, part texture, and appearance issues that constrain interior cockpit design alternatives. Some isolated components can have mass reduced with material substitution such as headlamps (with new resins) and wheels (with new aluminum grades) that actually enhance aesthetics but often increase cost. Non-visual parts, however, also present an opportunity, such as seat belt reinforcements, seating frames/brackets, and fire wall panels. Most non-structural applications that can be light-weighted with plastic already have been. Glass-reinforced sheet molding compound (SMC) is low cost and inexpensive to form but lacks sufficient strength to replace most structural applications responsible for much of the weight. Isolated components on the vehicles are also candidates for aluminum, magnesium, or advanced high-strength steel substitution, such as wheels, engine cylinder heads, suspension arms, transmission cases, brake calipers, steering knuckles, and engine blocks, although many OEMs have already made these substitutions, especially in cylinder blocks and heads. Aluminum heads are more common than aluminum blocks because of performance issues in the block, but other materials including hybrid materials (both aluminum and cast iron) are being applied to the blocks. An even more aggressive approach to introducing aluminum into the structure itself will likely involve aluminum-intensive substructures (e.g., axle assemblies, engine compartment, etc.), and such components are also now starting to penetrate the new-vehicle population. Car glass (windshield, side windows, rear window, mirrors, and sun roofs) is also heavy, and there are opportunities to reduce mass by substituting polycarbonate. Polycarbonate can be coated to provide a durable finish, and this has been applied to non-windshield glass panels where scratching is less a concern. Rolling Resistance Tire rolling resistance is one of many forces that must be overcome in order for a vehicle to move (see discussion in Chapter 2). When rolling, a tire is continuously deformed by the load exerted on it (from the vehicle mass). The repeated deformation during rotation causes energy loss known as rolling resistance. Rolling resistance is affected by tire design (for example, materials, shape, and tread design) and inflation. Underinflated tires increase rolling resistance. The opportunity to improve fuel economy by reducing rolling resistance is already used by OEMs to obtain better “EPA numbers,” and so original equipment tires tend to have lower rolling resistance than consumer-replaced tires because typical values for the coefficient of rolling resistance (ro) values differ between them (NRC, 2006). This represents an interesting value tradeoff. The OEMs are more interested in getting low-rolling-resistance tires to show improved fuel economy, and people buying replacement tires are more interested in low cost and durability. Therefore the total opportunity for fuel consumption reduction is defined by the fraction of the tires on the road that falls into each category. Education of the public on the subject of low-rolling-resistance tires for replacement tires and the continued introduction of tire pressure monitoring systems, which is discussed below, may help improve in-use performance of tires for fuel consumption reduction. There are performance tradeoffs involving tires that tire manufacturers consider during design and manufacturing. These tradeoff variables include, for example, tread compound, tread and undertread design, bead/sidewall, belts, casing, and tire mass. Important tire performance criteria affected by design and manufacturing include rolling resistance, tire wear, stopping distance (stopping distance or grip can be evaluated over different surfaces, such as wet or dry), and cornering grip. Wear and grip are closely correlated to tread pattern, tread compound (e.g., softer compounds grip better but wear faster), and footprint shape. The impact of emphasizing one performance objective (such as low rolling resistance) over other performance criteria is inconclusive. Some studies have shown that tires with low rolling resistance do not appear to compromise traction, but may wear faster than conventional tires. Another study in 2008 by Consumers Union and summarized by Automotive News (Automotive News, 2008) concluded that there may be a reduction in traction, because of low-rolling-resistance tires, that increases stopping distance. The study is not rigorously controlled, and other influences may confound the results. The response by one tire manufacturer, Michelin ( Barrand and Bokar, 2008), argues that low-rolling- resistance tires can be achieved without sacrificing performance factors by balancing the design and manufacturing process variables. Tire makers are continuing to research how to get optimal performance (including fuel economy) without sacrificing other criteria such as safety or wear. Goodyear points out that performance tradeoffs between rolling resistance, traction, and tread wear can be made based on materials and process adjustments, which also affect cost (Goodyear Tire & Rubber Company, 2009). The incremental cost for low-resistance tires may not be significant, but the cost-benefit tradeoff with increased stopping distance, wear, and possibly noise, vibration, and harshness issues are important for the consumer. Rolling resistance can also be affected by brakes. Low-drag brakes reduce the sliding friction of disc brake pads on rotors when the brakes are not engaged because the brake pads are pulled away from the rotating rotor. Most
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles new vehicles have low-drag brakes. The impact over conventional brakes may be about a 1 percent reduction of fuel consumption. Rolling resistance is also affected by tire inflation, and so any technology that affects inflation levels can also affect fuel economy. Reducing tire inflation levels increases rolling resistance, which in turn increases fuel consumption. A tire pressure monitoring system (TPMS) can be set to different pressure thresholds, and the average deviation from the recommended inflation level would be 1/2 the threshold level. For example, if the threshold is set at 10 psi, the average deviation from the recommended level would be 5 psi. Michelin believes that an accurate TPMS with an appropriately set threshold could reduce fuel consumption by up to 0.7 percent (J. Barrand, personal communication, May 12, 2009). Vehicle Accessories Some automakers are beginning to introduce electric devices (such as motors and actuators) that can reduce the mechanical load on the engine, reduce weight, and optimize performance, resulting in reduced fuel consumption. Of course, the electrical power used by these devices must be furnished by the engine driving the alternator. Thus the most advantageous opportunities for converting mechanical devices to electrical are devices that operate only intermittently, such as power steering and air-conditioning compressor. The benefits from electric and/or electro-hydraulic power steering and greater efficiency in air-conditioning (A/C) are not credited by current EPA fuel economy tests (since neither operates during the test), and so manufacturers are reluctant to implement them because of added costs. With the new EPA test procedures, some of the benefits will be reflected in the “sticker,” and improvements in these areas are relatively “low hanging fruit.” Heating, ventilating, and air-conditioning (HVAC). A more efficient system starts with (larger) heat ex changers that transfer high heat more effectively and a thermal expansion valve that controls the evaporator temperature. The compressor uses the majority of the energy of the A/C system, and variable displacement piston compressors are available and in use that significantly reduce fuel use over fixed displacement compressors. There are many other technologies, such as increased use of recirculated air, elevation of evaporator temperature, use of pulse-width modulated blower speed controllers, and internal heat exchangers, that can further reduce fuel usage. Further reductions in fuel use can be achieved by decreasing A/C load through the use of low-transmissivity glazing (reducing both heat and ultraviolet penetration), reflective “cool” paint, and cabin ventilation while parked. Suppliers are investigating the use of directly cooling the seat either through ducting or by thermoelectric materials. Although this may increase comfort, it is not clear whether this will significantly improve fuel economy (Rugh et al., 2007). Exhaust heat recovery. Recent improvements in thermoelectric materials for HVAC and exhaust energy recovery appear promising. Research is directed primarily at new materials with higher “thermoelectric figure of merit” (Heremans et al., 2008; Hussain et al., 2009). This is accomplished by increasing the thermoelectric effect (Seebeck coefficient) and reducing the thermal conductivity. Good results have been obtained with nanomaterial processing, but at this time these are costly. Improvements in potentially low-cost bulk materials are needed for automotive applications. BMW has announced a planned introduction on production vehicles in the 2012/2013 model year.2 It presented a model of an application at the 2006 DEER Conference3 and in the press.4 A DOE presentation gave more information on this vehicle and presented a rather optimistic view of energy recovery.5 In the view of the committee significant improvements need to be made in the performance of bulk materials and in the processing of nanomaterials before thermoelectric heat recovery from the exhaust can be applied in mass production. The committee thinks that this will not happen in the 10-year horizon considered here. Transmission Technologies Transmission technologies can reduce fuel consumption in two ways, first by moving engine operation to more efficient regions of the engine map (cf. Figure 2.3 in Chapter 2) and second by continued reduction of the mechanical losses within transmissions. Of these two, moving engine operation to more efficient regions of the engine map (e.g., higher torque (or brake mean effective pressure; BMEP) and lower speeds) offers the largest potential gains. The major approaches to achieving this movement are by increasing the number of speeds in the transmission (whether manual, automatic, or continuously variable) and lowering final drive ratio. Five-speed automatic transmissions are already a standard for many vehicles; 6-, 7-, and 8-speed automatic transmissions have been available on luxury cars and are penetrating into the non-luxury market. This new wave of automatic transmissions has been enabled by new power flow configurations and improved controls capability that are enabling larger numbers of speeds to be achieved at a lower cost increment over 4-speed automatics than would be the case for adding speeds to previous automatic transmission designs. 2 See http://www.motorward.com/2009/02/new-details-on-next-generation-bmw-5-series/. 3 See http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2006/session6/2006_deer_lagrandeur.pdf. 4 See http://www.autobloggreen.com/2008/09/25/bmw-wins-koglobe-2008-award-for-thermoelectric-generator/. 5 See http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2006/session6/2006_deer_fairbanks.pdf.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles This cost improvement resulted from transmission gear train synthesis optimization studies using computational tools that uncovered gear trains requiring fewer discrete elements because some of the elements (e.g., planetary gear trains) are utilized for multiple speeds. However, increasing the number of speeds always adds some components and their associated cost. Along with higher numbers of transmission speeds, which allow operating engines in more efficient parts of their fuel consumption map, transmission internal losses are also being reduced, thus further improving power train efficiencies. In addition to planetary-based automatic transmissions, advanced versions of manual transmissions are also being introduced that can be more efficient than automatics since torque converters are replaced by computer-controlled clutches, which slip less than torque converters. These new clutches not only are used to launch the vehicle from a stop but also enable rapid automated shifting of the manual gears since one clutch can start engagement before the other clutch has completely released. This class of manuals is called dualclutch automated manual transmissions (DCTs).6 With this concept, new-design manual transmissions are arranged with two parallel gear trains, one for odd-numbered speeds and the other for even-numbered speeds: for a 6-speed DCT, one gear train would contain the first, third, and fifth speed gears while the other gear train would include the second, fourth, and sixth speed gears. DCTs are then coupled to the engine through two clutches integrated into the transmission, one linking the odd-speed gear train to the engine and the other clutch linking the even-speed gear train to the engine. Finally, the clutches are actuated with electro-hydraulic systems calibrated to provide smooth launch and rapid and smooth shifting, making them automatic in their interface to the driver. In most of the current implementations of these clutches, they are immersed in transmission oil, thus providing the cooling necessary for acceptable durability. Dry-clutch versions are now also being developed for vehicles with lower torque requirements, making oil cooling unnecessary. Dry-clutch DCT designs are expected to be less costly to produce and lighter than their wet-clutch counterparts. In addition, dry-clutch DCTs will be more efficient through elimination of the hydraulic pump work to cool the wet clutches. Both automatic and DCT transmissions feature a discrete number of gear ratios that determines the ratio of engine speed to vehicle speed. In contrast, a continuously variable transmission (CVT) offers a theoretically infinite choice of ratios between fixed limits, which allows engine operating conditions to be optimized for minimizing fuel consumption. CVT technology has tended to be used in lower-horsepower vehicles because of maximum-torque limitations with the most common metal-belt design. A few OEMs offer CVTs that utilize other drive schemes allowing usage with larger engines. CVTs have achieved some penetration into the market, but recent trends suggest that their usage may not grow further due to higher than expected costs and lower than expected internal efficiencies (EPA, 2008). The issues discussed above generally apply to both SI and CI engines. However, the effects of moving engine operating points to lower-speed and higher-torque regions of the engine map are more beneficial for SI engines than for CI engines because intake throttling losses are reduced for SI engines, whereas CI engines are not throttled. Nonetheless, for both CI and SI engines, fuel consumption is reduced by moving to higher-torque and lower-speed regions of the engine maps because the relative effect of engine friction losses is reduced. Another important transmission issue difference between SI and CI engines is their peak torque. As noted in Chapter 5, CI engines produce higher maximum torques than do SI engines. Maximum torque capacity is one of the most important criteria for durable transmission design, and so CI engines generally are mated with different, higher-torque-capacity transmissions than SI engines even in the same vehicle platform. Sometimes, a given transmission used for SI engines can be upgraded to higher torque capacity by more extensive and more expensive heat treating of the gears and clutch upgrading, but frequently, different transmissions originally designed for higher maximum torque capacity must be used with CI engines, thus increasing cost, weight, and to some extent internal losses. Another transmission-related technology that is applicable to both SI and CI engines is called idle-stop. This technology is useful primarily for operation in cities and involves turning off the engine at idle. Benefits from idle-stop involve eliminating most of the idle fuel consumption during the idle-stop period. Since idle fuel consumption is relatively large for SI engines due to throttling losses and the use of ignition retard for smooth operation when accessories turn on and off, FC reductions on the Federal Test Procedure (FTP) driving cycle range from 3 to 5 percent. The real-world gain for congested city driving (e.g., New York City) could be as high as 10 percent since engines would be idled much more than on the FTP test cycle. All idle fuel consumption losses are not eliminated since some accessories may need to operated while the engine is stopped (e.g., A/C in hot climates), which not only consumes some fuel but also increases component cost by the necessity of replacing belt-driven accessories with electrically driven ones. For the CI diesel vehicle, idle-stop benefits are smaller than those attained with idle-stop for SI gasoline vehicles because diesel engines have much lower idle FC than their gasoline counterparts. The estimated gain on the U.S. cycle for CI vehicles is about 1 percent, although the real-world gain for congested city driving (e.g., in New York City) could be much higher. Other studies of vehicle fuel consumption (e.g., NRC, 2002) have generally considered potential gains from transmission technologies in a separate category from engine efficiency technologies. In the present study, potential gains 6 See http://www.dctfacts.com/hmStory1b.asp.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles from transmission technologies are considered together with those for engines. This choice was made for the following reasons. For SI engines, the major opportunity for reducing fuel consumption (as is discussed extensively in Chapter 4) is reducing pumping losses. Many of the technology measures discussed in Chapter 4 reduce pumping losses in one way or another. As noted above, the major impact of transmission technologies toward reducing fuel consumption is to move the operation of the engine toward higher torque (or BMEP) and lower speeds at which pumping losses will be reduced. As a result, there are significant interactions between engine technologies that reduce pumping losses (e.g., valve event modulation) and transmission changes that also move engine operation to lower speeds and loads, such as increasing the number of ratios and the associated ratio spread.7 A good example of these interactive effects is cylinder deactivation, as discussed in Chapter 4. When cylinder deactivation is used, the benefit of moving the engine operating point to lower speeds and higher torques and higher BMEP is reduced compared to engines not using cylinder deactivation, because the working cylinders are already running at higher BMEP, thereby reducing pumping losses. Thus the fuel consumption reductions possible from increasing the number of transmission ratios from 4 to 6, for example, would be lower for engines using cylinder deactivation than for those not using cylinder deactivation. This demonstrates how transmission-derived fuel reductions of fuel consumption cannot readily be separated from engine-technology-derived fuel consumption reductions. This choice is reflected in the technology paths discussed in Chapter 9. FUEL CONSUMPTION BENEFITS OF NON-ENGINE TECHNOLOGIES The tractive force that is needed to propel a vehicle can be written simply as the sum of three forces: where Fm accelerates the mass, Fr overcomes rolling resistance, and Fa overcomes aerodynamic drag. The integral of this force over a given driving cycle gives the amount of energy required at the wheels. Using typical values in Equation 2.1 one can calculate that for the EPA combined cycle about one-third of the tractive energy goes into each of these three components (see Table 2.7). However, as Table 2.7 shows for the urban cycle, Fm is around 60 percent of the total and for the highway cycle, Fa is about half. Before giving estimates of the benefits of fuel-saving technologies, it is necessary to make two important points. Merely reducing tractive energy does not translate into a directly proportional reduction of fuel consumption because of (1) the accessory load and (2) the possibility that the power train may then operate at worse efficiency points. To take care of the power train efficiency it is necessary, at the same time, to downsize the engine and/or change transmission shift points, because with a lighter load, the efficiency of the power train is reduced, especially with SI engines that will then operate with more throttling. Unfortunately, many studies on the impact of reducing Fm and Fa do not change the engine operating points. For example, Barrand and Bokar (2008) do an excellent job of investigating the effect of rolling coefficient by changing tires without changing the power train. Only an OEM designing a vehicle with low-rolling-resistance tires, for example, can fully take advantage of rolling-resistance changes by reoptimizing the power train. Theoretically reducing any one of the three components by, say, 10 percent should reduce fuel consumption by roughly 3.3 percent since, as stated above, each component accounts for roughly one-third of the total tractive energy. In fact the size of the engine is determined by acceleration performance requirements, as well as the tractive energy. Therefore all that can be said for certain is that reduction of all three components by an amount (say, X percent) would result in a reduction in fuel consumption by roughly the same amount (X percent), assuming the power train were reoptimized. Aerodynamics As discussed above, vehicles with higher Cd values (over .30) may be able to have the Cd reduced by 5 percent or so (up to 10 percent) at low cost. The associated impact on fuel consumption and fuel economy could be 1 to 2 percent, and this assumes that the engine operating regime is not modified. If lower acceleration can be tolerated and the engine operates at the same efficiency, the improvement with a 10 percent reduction of aerodynamic drag could be as high as 3 percent (10 percent × 0.3). Argonne calculations for the improvement in fuel consumption show that without engine modifications a 10 percent reduction in aerodynamic drag would result in about a 0.25 percent reduction in fuel consumption for the urban cycle and a 2.15 percent change for the highway cycle. Car Body Design and Interiors It is well established that a reduction in vehicle mass reduces fuel consumption. The specific relationship between mass reduction and fuel consumption, however, is complex and depends on many factors: Amount of mass reduction, Driving cycle, Type of engine, and Secondary benefits, such as whether or not other vehicle systems are redesigned to match the new vehicle 7 Ratio spread is defined as the ratio of first gear divided by the ratio of the top gear. As an example, for a typical 6-speed automatic transmission, the low-gear ratio would be 4.58:1 while that of the sixth gear would be 0.75:1. The ratio spread would then be 4.58/0.75, which equals 6.1.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles mass, as with, for example, engine downsizing, retuned transmission, and reduced components for crash management, braking, fuel storage, and so on. A midsize car body structure with closure panels (no trim or glass) can weigh approximately 800 pounds (about 25 percent of the vehicle’s total curb weight). Should the mass reduction be significant, a secondary benefit can accrue from reducing the size of the needed power train, braking systems, and crash management structures. These secondary benefits are difficult to estimate but can potentially approach an additional 30 percent reduction in mass, and these secondary benefits can help offset the cost of the initial effort (IBIS Associates, 2008). A basic estimate of the relationship between fuel economy and mass is provided by the Department of Energy ( Carpenter, 2008) and also by the Laboratory for Energy and Environment at the Massachusetts Institute of Technology (Cheah et al., 2007). A rule of thumb is a 6 to 8 percent improvement in fuel economy (or, equivalently, a reduction of 5.7 to 7.4 percent in fuel consumption) for every 10 percent drop in weight when secondary benefits are included that indirectly accrued from having lower mass. In a study conducted by Ricardo, Inc. (2007), and sponsored by the Aluminum Association, this relationship was simulated for several vehicles loaded with from 2 to 5 passengers. The gasoline-powered vehicles simulated are listed in Table 7.2. Two scenarios for these vehicles were simulated. The first scenario evaluated the impact on fuel economy when everything about the vehicle remained unchanged except for a reduction in vehicle mass. The second scenario resized the engine to reflect comparable vehicle performance (the benefits of other reductions in mass such as a smaller gas tank, smaller brakes, etc. were not included). In this scenario, the engine required less power because of the reduction in mass, and therefore, fuel economy was further improved. The vehicle type was not a major differentiator of fuel economy impact; Table 7.3 shows the range of impact on fuel economy for all types. Table 7.3 shows the results of the Ricardo, Inc., simulation calculating the potential impact on fuel consumption from reduction of mass. The range shown in the results is due to summarizing a composite of simulation runs for different vehicle models and power trains. This discrepancy (range of fuel economy impact) in fuel economy improvement increases for different vehicle types as the reduction in mass increases from 5 to 20 percent. However, if the engine is resized to match each level of mass reduction (to maintain original vehicle performance), the range of fuel economy improvement across the vehicle classes is fairly small. This observation points to the importance of matching engine performance to vehicle mass. For small (under 5 percent) changes in mass, resizing the engine may not be justified, but as the reduction in mass increases (greater than 10 percent), it becomes more important for certain vehicles to resize the engine and seek secondary mass reduction opportunities. Physical vehicle testing has confirmed the reductions in fuel consumption associated with reductions in vehicle mass. For an internal combustion engine, the effect of mass reduction is greater with a city driving cycle versus a highway cycle because of the frequent acceleration/deceleration of mass. For example, vehicles (combination of compact, midsize, and SUV classes) powered by internal combustion engines can reduce fuel consumption approximately as follows (Pagerit et al., 2006): 0.1 gallon per 100 miles driven can be saved with, approximately, 190 pounds mass reduction—city cycle, and 285 pounds mass reduction—highway cycle. As discussed in Pagerit et al. (2006) and further supported by the Ricardo, Inc., study, the improvement gained from reduction of mass (expressed as fuel consumption and not miles per gallon) is the same regardless of the weight of the vehicle. Unlike changes in rolling resistance and aero dynamics, re- TABLE 7.2 Vehicle Mass Assumptions for Ricardo, Inc. (2007) Study to Assess Effects of Mass Reduction on Fuel Economy Type of Vehicle Initial Weight (lb) Load Weight (lb) 5% Reduction (lb) 10% Reduction (lb) 20% Reduction (lb) Small car 2,875 300 3,031 2,888 2,600 Midsize car 3,625 450 3,894 3,713 3,350 Small SUV 4,250 550 4,588 4,735 3,950 Large SUV 5,250 750 5,738 5,475 4,950 NOTE: The 5 percent, 10 percent, and 20 percent mass reduction applies to the initial vehicle weight and not the load. TABLE 7.3 Impact on Fuel Consumption Due to Reduction of Mass in Study by Ricardo, Inc. (2007) Vehicle Mass Reduction from Baseline Vehicle 5% Mass Reduction 10% Mass Reduction 20% Mass Reduction Mass reduction only 1-2% 3-4% 6-8% Mass reduction and resized engine 3-3.5% 6-7% 11-13%
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles ducing mass not only reduces the amount of tractive energy needed but also permits a reduction in power train (engine downsized or transmission shift changes) without adversely affecting performance (acceleration). A 10 percent reduction in mass and power for the reference vehicle should reduce fuel consumption by about 5.7 to 7.4 percent (or 6 to 7 percent). In a conventional vehicle, the energy used to accelerate the mass is mostly dissipated in the brakes, whereas in a hybrid, a significant fraction of this braking energy is recovered, sent back to the battery, and reused. Thus, mass reduction in hybrid vehicles is less important than in conventional vehicles. The complexity of mass reduction increases when a conventional vehicle is compared with either a hybrid (which incurs additional battery mass) or a CI engine (which has greater power train mass). While reducing mass will always provide a fuel economy benefit, changing technology pathways (between SI, CI, or hybrid designs) has to recognize the impact that the new technology has on mass. Rolling Resistance A report on tires and fuel economy (NRC, 2006) estimates that a 10 percent reduction in rolling resistance will reduce fuel consumption by 1 to 2 percent. This reduction, however, is without changes in the power train. If the power train could be adjusted to give the same performance, then the benefit of a 10 percent reduction would be on the order of as much as 3 percent. Underinflated tires that are 20 percent below recommended inflation pressure (say, 35 psi) increase rolling resistance by 10 percent, and thus increase fuel consumption by 1 to 2 percent (Goodyear Tire & Rubber Company, 2009). Again as discussed above under “Aerodynamics,” if a reduction in rolling resistance is combined with a reduction in aerodynamics and mass, the power train can be significantly modified to improve efficiency. As indicated in Chapter 2, rolling resistance accounts for about a third of the energy going to the wheels for the city as well as the highway cycles. Reducing mass, aerodynamics, and rolling resistance by 10 percent reduces fuel consumption by about 10 percent with power train resizing and other drive train adjustments (e.g., changes in transmission shift points, axle ratios). As noted earlier, vehicle mass reduction for a hybrid is not as effective since some of the energy going to the brakes is recovered. Vehicle Accessories The opportunity may exist to decrease fuel consumption (in gallons per 100 miles driven) by about 3 to 4 percent with a variable-stroke HVAC compressor and better control of the amount of cooling and heating used to reduce humidity (Table 7.4). Estimates for further reductions that can be achieved by decreasing air conditioner load through the use of low-transmissivity glazing, reflective “cool” paint, and cabin ventilation while parked have not been determined. According to a Deutsche Bank report, electro-hydraulic power steering (EHPS) would reduce fuel consumption by 4 percent with an incremental cost of $70, while electric power steering could improve 5 percent with an incremental cost of $120, but there is little information on how this estimate was obtained (Deutsche Bank, 2008). A TRW study ( Gessat, 2007) showed that while a conventional hydraulic power steering system consumed 0.35 L/100 km, the best TRW electro- hydraulic steering system consumed 0.07 and an electric power steering system 0.02. These figures are relative to a small vehicle with a 1.6-L engine. In its study of CO2-reducing technologies for the EPA (EPA, 2008), Ricardo, Inc., found that electric power steering (EPS) reduced combined fuel consumption by about 3 percent based on FSS calculations. From this and the estimates provided in recent regulatory activities by NHTSA and EPA, the committee estimated that EPS reduces combines fuel consumption by about 1 to 3 percent on the EPA 55/45 combined cycle, which is the basis for the CAFE standard. However, the committee recognizes that the reduction of fuel consumption could be as high as 5 percent under in-use driving conditions. Transmission Technologies Fuel consumption reductions generally increase with additional transmission speed ratios, although interaction effects between engine technologies that reduce pumping losses and increase the number of transmission speeds are important, as noted earlier. However, since the costs also increase and the marginal gain for each additional speed gets smaller, there are diminishing returns. Table 7.5 lists the transmission technologies and estimated reductions in fuel consumption. The basis of this table is baseline engines TABLE 7.4 Potential Reduction of Fuel Consumption with the Use of Vehicle Accessories Vehicle Accessory Reduction in Fuel Consumption (%) Comments Variable-stroke HVAC compressor 3-4 Improved cooling, heating, and humidity control Low-transmissivity glazing, cool paint, parked-vehicle ventilation ~1 Lower heat buildup in vehicle decreases air-conditioning load Electrohydraulic power steering 4 Combined electric and hydraulic power for midsize to larger vehicles reduces continuous load on engine Electric power steering 1-5 Electric power steering for smaller vehicles reduces continuous load on engine—smaller benefits (1-3%) estimated for the FTP
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles without significant valve event modulation technologies or cylinder deactivation. TIMING CONSIDERATIONS FOR INTRODUCING NEW TECHNOLOGIES The timing for introducing new fuel consumption technologies can significantly influence cost and risk. The maturity of a technology affects its cost and reliability. Automobile companies have sophisticated product and process validation procedures that must be adhered to before products can be scaled up for mass production, or they expose themselves to large warranty or product liability concerns. Many vehicle changes are timed for implementation around the product development process to minimize cost and quality concerns. Lower-volume and higher-end vehicles often have new technologies applied first for several reasons. The lower volumes mitigate the exposure to risk, and the higher-end vehicles can bear the higher initial early cost of a new technology. During this period, competition brings the technology cost down while the supply chain develops for higher volumes in the future. An important consideration for introducing new technologies that have broad impact concerns the product development process of new vehicles. Aggressive use of lightweight materials to obtain secondary benefits; power train modifications; and body shape modifications (to improve aerodynamics), for example, may have to be timed with future product development phases. Although material substitution for components can occur throughout the life cycle of a car in many cases, the mass saved in this way is relatively minor. Considering how to reduce mass to achieve greater energy savings requires a broad systems evaluation and reengineering of the vehicle. Once a vehicle has been validated and tooled for a specific design and production has begun, new development costs are planned for future model changes. Most significant modifications have to occur around various phases of the vehicle’s production life. Automobile manufacturers differ significantly in their approach to introducing new products. Manufacturers based in Asia, for example, are known for having shorter product life cycles but often implementing lower levels of engineering redesign at changeover. Manufacturers based in Europe and North American have traditionally had longer product cycles with a greater amount of engineering applied at changeover. There are always exceptions to these generalities even within a manufacturer, depending on the vehicle model. The strategy to implement engineering changes on a regional vehicle (e.g., North America only) versus a global platform can greatly impact timing and cost. Entire textbooks have been written around product timing for manufacturers, and so a discussion here can at best only introduce the inherent issues that affect cost and timing for any manufacturer. Generally, 2 to 3 years is considered the quickest time frame for bringing a new vehicle to market. A significant amount of carryover technology and engineering from other models (or previous vehicle models) is usually required to launch a new vehicle this quickly. In some cases, so much of the vehicle is replicated that the new vehicle is considered a “freshened” or “re-skinned” model. The ability to significantly influence vehicle performance (e.g., through light-weighting, changing power trains, etc.) is minimal because so much of the vehicle is unchanged. More substantial changes to the vehicle occur over longer periods of time. Newly styled, engineered, and redesigned vehicles can take from 4 to 8 years, each with an increasing amount of new content. Automobile producers generally have product development programs (PDPs) spanning at least 15 years. PDPs are extremely firm for 3 to 5 years due to the need for long-lead-time items such as tooling or supplier development requirements, and the need for extensive testing of major items such as those required for fuel economy, emissions, and safety regulations, and confirmation of reliability and durability. In general, model changeovers can be categorized into five areas (freshen, re-skin, restyle, reengineer, TABLE 7.5 Transmission Technologies and Estimated Reductions in Fuel Consumption Technology Fuel Consumption Reductiona (%) Comments Five-speed automatic transmissions 2-3 Technology can also improve vehicle performance Six-speed automatic transmissions 3-5 Seven-speed automatic transmissions 5-7 Eight-speed automatic transmissions 6-8 Dual-clutch automated manual transmissions (6-speed) (DCT) 6-9 Original automatic transmissions with conventional manual transmissions supplemented with electro-hydraulic clutch and shift actuators have been replaced with DCTs Continuously variable transmissions 1-7 Some issues related to differences in feel and engine noise; improvements depend on engine size NOTE: Values based on EEA (2007) with adjustments to reflect range of values likely to occur. aImprovements are over a 2007 naturally aspirated SI-engine vehicle with 4-speed automatic transmission of similar performance characteristics.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles and redesign; see Automotive News, July 14, 2008, p. 28). These five categories and their potential for effecting fuel consumption improvements are described in Table 7.6. It is not accurate to say that every vehicle progresses through every one of these phases. It is possible to skip a re-skin and jump to a restyle, for example. Also, not every vehicle will be redesigned in 6 to 8 years because many factors affect this timing (market demand, finances, etc.). The potential for impacting fuel consumption is only a rough approximation, and none of these estimates consider the inclusion of hybrid or alternative power trains. The estimates for reducing fuel consumption shown in Table 7.6 are not additive (from previous changeover phases). Fuel consumption estimates also assume comparable vehicles of the same size and performance (including crash worthiness, electronic content, and other factors that are often adjusted with new vehicles). The engine development process often follows a path separate from those of other parts of the vehicle. Engines have longer product lives, require greater capital investment, and are not as critical to the consumer in differentiating one vehicle from another as are other aspects of the car. Also, consumer-driven changes for styling change faster than the need to introduce new power train technologies. The power train development process evolves over closer to a 15-year cycle, although refinements and new technologies will be implemented throughout this period. Also, because of the complexity, costs, and resources required to launch a new power train, it is unusual to launch a new engine-related transmission simultaneously. The development of new technologies over a 15-year life cycle can be substantial, and the performance improvement for fuel consumption can be substantial with a new power train. The estimates in Table 7.6 are based on business as usual. The “frequency” is the time from concept through prototyping, production vehicle design, tooling release, verification testing on preproduction vehicles, and start of full-scale production. Shorter time frames are possible, especially if more vehicle content is carried over between PDPs to reduce engineering, testing, etc., but this limits the degree of model changeover. Urgency to introduce new vehicles (e.g., smaller and more fuel efficient vehicles) can accelerate the nominal duration of each PDP phase, but the investment cost will grow. Modest improvements in fuel consumption can be achieved early in the PDP cycle (e.g., freshen and re-skin stages) by introducing more aerodynamic designs and low-rolling-resistance tires. A greater impact on reducing fuel consumption can come from changes in engine, transmission, and mass reduction later in the PDP when the vehicle is re designed or reengineered. Restyled vehicles allow for material substitution on a part-by-part basis, but without changing entire subassembly structures. Often, the substitution might be for a higher-strength metal with a thinner gage in place of the current material. Tooling and assembly processes may be altered somewhat to accommodate the new material. A re engineered vehicle allows for changing the design of major sub assemblies (engine compartment, closure panels, body sides, etc.), thus allowing for entirely new approaches to reducing mass. Reengineered vehicles normally require crashworthiness testing TABLE 7.6 Vehicle Product Development Process (non-power train) and Timing Implications to Effect Fuel Economy Changes Type of Model Change Frequency (Years) Description Fuel Consumption Reduction Opportunities to Impact Fuel Consumption Investment Cost Freshen 2-3 Sheet metal untouched, may include new grille, fascia, headlights, taillights, etc. Little to none (≤3%) Minor impact on mass; possible impact with aerodynamics and tires Low Re-skin 3-5 Minor changes to sheet metal Little to none (≤5%) Same as above and vehicle accessories Modest Re-style 4-8 Extensive changes to exterior and interior Minimal (5-8%) Some impact on mass (mostly interior components); possible impact with aerodynamics, tires, and vehicle accessories High Re-engineer 4-8 Extensive makeover of vehicle’s platform, chassis, and components to reduce noise, vibration, and harshness and improve qualities such as ride, handling, braking, and steering (this degree of change or the next may require recertification and crash testing), body restyling often concurrent with this phase Moderate (7-14%) Mass reduction opportunity with part-by-part material substitution (e.g., aluminum or high-strength steel); possible impact with aerodynamics, tires, and vehicle accessories Very high Redesign A 6-8 New platform, new interior and exterior styling; engine and transmission carried over; some structural subsystems possibly reengineered Significant (13-18%) Entire vehicle structure—opportunity to introduce lightweight materials throughout entire vehicle; impact from aerodynamics, tires, and vehicle accessories Very high
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles and incur significant additional costs because of the reengineered designs. The redesigned vehicles start with a “clean sheet” affording the benefits of a reengineered vehicle, along with more optimal matching of the power train to the lighter-weight structure. In general, a redesign results in a new vehicle platform that in many cases replaces existing vehicles. Aerodynamics Reductions of drag coefficient Cd by 5 percent or so (up to 10 percent) have been taking place and will continue. A 5 percent reduction in aerodynamics can be achieved with minimal cost through vehicle design, and larger reductions can be achieved by sealing the undercarriage and installing covers/shields (e.g., in the wheel well areas and underbody). Elimination of outside rear view mirrors will require changes in safety regulations and improvement in vision systems. Since these changes can be costly, they are unlikely to be implemented soon except on high-end vehicles. In the longer term (about 10 years), 5 to 10 percent reductions in aerodynamic drag are plausible, but this may come with some compromise in vehicle functionality. Car Body Design and Interiors Reductions in weight have been taking place and will continue in the near term with reductions from 10 percent (with mostly conventional and high-strength steels) to 25 percent (with high-strength steel structures, aluminum closure panels, and body/interior components made from various lightweight materials). Table 7.7 provides an overview of the timelines for the introduction of new materials for various vehicle components. Today’s new vehicles already are composed of upward of 40 to 50 percent high-strength steel (over 480 MPa yield strength), but higher-strength steels (advanced high-strength steels) are being developed (up to 1,000 MPa) that could replace even the current high-strength steel. Various vehicle components for which isolated material substitution can take place will also be the norm. For example, Ford recently indicated that aluminum calipers replaced steel ones, thus saving 7.5 pounds per vehicle. Also, aluminum wheels replaced steel wheels, resulting in 22 pounds saved per vehicle. More aggressive application of aluminum to car doors can also save another 20 pounds per door, but at a higher cost. Substitution of material in other components can also be expected, including the wiring harness. Substituting copper-clad aluminum wiring for all copper wiring can save 10 or more pounds per vehicle, but usually at a higher cost. More aggressive reduction of mass is feasible at higher cost if aggressive targets of greater than 25 percent are set. Reduction of mass at the 50 percent level can be attained in the body with a mostly aluminum structure (probably using a space frame design), but this approach will be cost prohibitive under most conditions for high-volume vehicles. The use of composite structures involving materials such as carbon fiber will need significant cost reduction and supply chain development over the next 15 years. The committee does not expect to see significant inroads in this time frame by this technology except in low-volume (specialized applications), high-performance vehicles. Other polymer/reinforced composites, etc. will continue to make inroads in the vehicle interior where steel or aluminum is used currently for strength. For example, all-polymer/reinforced composite instrument panels (without rear steel reinforcements) are likely to make it to production soon. As production processes continue to be developed, broader application of both magnesium and titanium can be expected, such as for magnesium engine blocks that weigh approximately 30 pounds less than aluminum ones (see Table 7.7). Magnesium will likely make inroads for component parts such as suspension arms and interior dash panels and seating brackets. Titanium will continue to find application in suspension springs, valve springs, valves, connecting rods, and exhaust systems, resulting in 35 to 40 percent savings in mass over steel components. Rolling Resistance Low-rolling-resistance tires are already used by OEMs. The committee does not expect significant additional improvements without sacrificing performance. Since replacement tires are on most vehicles on the road today, a campaign to educate purchasers of replacement tires of the possibility of fuel savings is a good way to reduce fuel consumption. More vehicles today are being offered with low-tire-pressure monitors to warn the driver of underinflated tires for safety and fuel economy. Vehicle Accessories Variable stroke compressors and reduction of subcooling are being developed and should appear in vehicles in the next 3 to 5 years. Because the current duty cycle measuring fuel consumption does not recognize HVAC systems, there is no motivation to introduce these systems because they incur additional costs. However, the proposed new EPA test procedure may cause new interest in introducing this technology. COSTS OF NON-ENGINE TECHNOLOGIES Aerodynamics A 5 percent reduction in aerodynamics can be achieved with minimal cost through vehicle design. Slightly more aggressive reductions can be achieved by sealing the undercarriage and installing covers/shields (e.g., in the wheel well areas and underbody) costing in the tens of dollars. A 10 percent reduction in aerodynamics may be aggressive, calling for wind deflectors (spoilers) and possibly elimination of rear view mirrors, which would cost a few hundred dollars.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles TABLE 7.7 Estimated Timeline for Introduction of New Materials by Type of Component Timing High-Strength Steel Aluminum Magnesium Plastics and Polymer—Composites Current or near term (3-5 years) Body rails, door sills, B-pillar, side roof rails, underbody, front suspension subframe, bumper beams, cross-members, brackets and reinforcements, exterior body panels, body side ring, longitudinal rails, wheels Hood, deck lid, engine block and cylinder lining, front suspension subframe, bumper beams, rear suspension knuckles, steering hanger beam, power train components (castings), condenser/radiator wiring harness Instrument panel, seat components Brackets Crash structures Intake manifold Truck box Outer skin panels (doors, fenders, etc.) Instrument panel Bumpers Trim Engine parts (intake manifold, cover, etc.) Future (5-10 years) Same as above, only with higher-strength steels Doors, exterior body panels (fender, roof) Door, inner Engine block Body side ring Roof Side pillar (B or C) Underbody Seat components Sound dampening Glass (polycarbonate) Long term (>10 years) New steels with greater formability allowing application to more complex part shapes and exterior panels; less steel overall in the vehicle Increased applications (depending on material cost); subassemblies such as engine compartment, chassis, instrument panels; overall, more aluminum in the vehicle Limited increase in applications; possibly transmission parts New materials will be developed with higher strength, allowing them to be applied to more structural parts. Mixed-material bonding will be developed. Overall, more plastics/polymers will be in the vehicle. Car Body Design and Interiors The term “material substitution” often misrepresents the complexity and cost comparison when one material is substituted for another one. The cost to change materials in the vehicle, from an incumbent material to a lighter-weight material, is a function of capital and variable costs: Fixed Costs (up-front investment costs) Design and engineering Prototype development and testing Tooling: fabrication, dimensional measurement, and assembly Variable Costs (a function of the volume of production) Production and assembly labor cost Production equipment Material Joining (welding, adhesive, sealing, riveting, etc.) An added complexity results with material substitution because part design is material dependent, and the redesigned part may provide (and often does) different functionality than the original part. For example, a molded plastic part can take on more complexity than a formed steel part, and so the direct comparison should also take the difference in functionality into account. Also, two or more parts may get integrated into a single part with one material versus that of another, and so the subsystem of parts has to be evaluated for a cost and performance comparison. Most cost-effective materials today for reducing mass are high-strength steel and aluminum. Both materials can replace many incumbent steel parts or assemblies, and the structural components that are among the heaviest parts offering the greatest opportunity will be targeted. Plastics, composites, and other metals (magnesium and titanium) will be used on a somewhat limited basis because of cost. In recent years, reductions in mass have been realized in the body, interior, and power train by introducing new materials such as high-strength (and advanced high-strength) steels, plastics (not including carbon fiber), and aluminum. Magnesium has also been used to reduce mass, but to a much lesser extent. In the near future (5 years), the committee expects continued mass reduction following the same pattern; through continued introduction of more and higher-strength steels, aluminum, plastics/polymers, and to a lesser extent other materials such as magnesium. Although there are research and development costs to develop new high-strength steels and new manufacturing processes for them, once developed they have minimal net long-term incremental cost over mild steel. Tooling, fabrication, and joining costs tend to be higher for these materials because of the material strength, which has to be added to the net cost difference. Although the cost per pound of high-strength steel is higher than mild steel, less of it is needed. Hence, a 10 or 20 percent material cost premium will be offset by using 10 to 20 percent thinner steel. As high-strength steels are introduced, their net incremental cost approaches zero after a period of maturity. The DOE estimates that, on average, substituting high-strength steel for mild steel results in about a net increase in material cost of 10 percent (see Carpenter, 2008). The cost to reduce mass (cost per pound of mass reduced) increases as the amount of reduced mass increases. The “low
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles hanging fruit” of mass reduction using high-strength steel in basic applications can result in less than a 10 percent cost premium. However, increasingly aggressive reduction of mass requires more difficult parts and materials whose cost exceeds the 10 percent premium. For example, a 1 percent reduction in mass can generally be achieved at a multiplier of 1.0 to 1.1. More aggressive applications likely require more expensive materials or more expensive fabrication and joining methods, or affect the costs of other parts in the vehicle. As the aggressiveness increases (to 5 percent, 10 percent, or even 20 percent), more materials and processing options need to be considered that further increase cost. The committee believes that a 10 percent reduction in mass is achievable with a mix of materials (high-strength steels, aluminum, composites, and other metals) for approximately $2.00 per pound of mass eliminated (see Table 7.8). More aggressive reductions will cost more than $2.00 per pound. Aluminum costs more than steel and has some forming and joining limitations that prevent its use in some applications. An incremental cost of aluminum over steel body parts in the range of 30 to 100 percent has been estimated (Carpenter, 2008; Bull, 2008). The Aluminum Association estimates that the average increment is 30 percent at the low end (premium cost per pound of mass eliminated). At the mid-point of this range, the incremental cost is $1.65/pound of mass eliminated. Higher costs will be incurred (approaching $2.00/lb cost premium) as more aggressive reduction of mass reduction is attempted. The body of a baseline vehicle (mostly steel) weighs approximately 800 pounds. An aluminum-intensive body weighs approximately 45 percent less, or 440 pounds. The estimated cost for this savings in weight is in the range of $468 ($1.30/lb) to $594 ($1.65/lb). Mass reduction in other vehicle systems such as power train, wheels, chassis, and interior would typically come at similar or slightly higher incremental cost per pound saved. Vehicle interiors (including seats, door trim, headliners, instrument panel components, etc.) constitute approximately one-third of the vehicle mass (1,000 pounds in a 3,000-pound vehicle). By using lightweight materials, Byron Foster at Johnson Controls plans to eliminate 30 percent of the interior mass (Forbes, 2008). If the same incremental cost used for the body is assumed, approximately 300 pounds eliminated would cost $390 ($1.30/lb) to $495 ($1.65/lb). Other opportunistic components in the vehicle include the power train, chassis, and wheel components. Many of these components have been light-weighted already with high-strength steel and aluminum where practical. One next step would be to transition to more magnesium, which comes with a cost premium of perhaps 50 percent or more over that for aluminum. Secondary Savings Benefits An important consideration with mass reduction is that its effects on fuel consumption can cascade. As the mass of a vehicle is reduced in, say, the body or interior, other components of the vehicle can be reduced in size as a consequence. For example, brakes, fuel system, power train, and even crash-management structures can all be downsized for a lighter vehicle. In the study conducted by Ricardo, Inc., (2007) for the Aluminum Association, the rule of thumb generated was that for every pound eliminated in the vehicle structure, an additional 0.30 lb (30 percent) of mass could be reduced in other areas of the vehicle. If this rule of thumb is applied and mass reduction comes at a cost of $1.65/lb, then at an additional 30 percent of secondary mass savings (0.3 lb) the net cost per pound becomes $1.65/1.3 lb, which becomes $1.27/lb. It is important to note that achieving secondary savings typically requires reengineering one or more systems on the vehicle, and this would likely be performed according to the product development timing plan (see above the section “Timing Considerations for Introducing New Technologies”). So the 30 percent secondary benefit is achieved in the long term and not necessarily when the initial reduction in mass is achieved. Rolling Resistance The incremental cost for low-rolling-resistance tires is estimated to be $2 to $5 per tire, but there is some evidence that suggests that these tires may slightly compromise stopping distance. One tire manufacturer suggested that tires that do not compromise stopping distance or tread wear could cost 10 to 20 percent more than conventional tires. (Note: The uncertainty about low-rolling-resistance tires with respect to increased tread wear and stopping distance is the reason for increasing the estimated cost beyond the $1.00 per tire cost cited in NRC (2006). The NRC (2006) study recognized that an acceptable increase in tread wear and stopping distance might occur. However, to eliminate this increase, additional costs can be expected over the $1.00 estimate.) TABLE 7.8 Committee’s Estimate of Cost to Reduce Vehicle Mass (based on 3,600-lb vehicle) Mass Reduction (%) Low Cost/lb ($) High Cost/lb ($) Average Cost/lb ($) Mass Saved (lb) Low Total Cost ($) High Total Cost ($) 1 1.28 1.54 1.41 36 46.08 55.30 2 1.33 1.60 1.46 72 95.76 114.91 5 1.50 1.80 1.65 180 270.00 324.00 10 1.80 2.16 1.98 360 648.00 777.60
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles Vehicle Accessories Table 7.9 shows the committee’s estimates of the costs for vehicle accessories that could improve the fuel consumption of light-duty vehicles. Transmission Technologies The estimated retail price equivalent for each transmission technology is provided in Table 7.10. As was the case for the engine technology chapters (e.g., Chapters 4 and 5), the baseline for transmission costs is the 4-speed automatic typical of 2007 model-year vehicles. Cost estimates are from the two sources considered (EEA, 2007; Martec Group, Inc., 2008). As can be seen from Table 7.10, the cost estimates for the 5-, 6-, 7-, and 8-speed automatic transmission replacements for the baseline 4-speed automatic have a considerable numerical range. In addition to the cost estimates, Table 7.10 also includes cost estimates converted to RPE using the RPE multiplier of 1.5. Besides the estimates for 5-, 6-, 7-, and 8-speed automatic transmission replacements, estimates are also included for DCTs and CVTs. The DCT estimates reflect an even wider numerical range than those for the automatics. For example, the 6-speed automatic cost estimates range from $133 to $215, whereas the estimates for the wet-clutch, 350 N-m torque capacity range from $140 to $400. Although DCT units have been in high-volume production for a number of years, until recently only the VW-Audi group, working closely with one supplier, has produced such a transmission. As a result, the number of cost estimates available to the committee was limited. When additional information was sought by the committee, the results reflected the still-emerging knowledge base about this transmission type. One estimate, based on a detailed teardown study conducted by FEV, Inc., for the EPA, estimated the cost of 6-speed DCTs with 350 N-m torque capacity and wet clutches at over $147 less than that for a 6-speed automatic (Kolwich, 2010). However, OEMs considering tooling up their own equivalent units had also made careful estimates of the high-volume piece cost increase of DCT6s. These OEM estimates were that high-volume DCT6s would cost nearly $200 more than 6-speed automatics. Thus, the range between estimates was approximately $350. At the present time, insufficient information is available to narrow this wide range. SUMMARY There is a range of non-engine technologies with varying costs and impacts to consider. Many of these technologies are continually being introduced to new vehicle models based on the timing of the product development process. Coordinating the introduction of many technologies with the product development process is critical to maximizing their impact and minimizing their cost. Relatively minor changes that do not involve reengineering the vehicle can be implemented within a 2- to 4-year time frame. This could include efforts such as aiming for minor reductions TABLE 7.9 Estimated Incremental Costs for Vehicle Accessories That Improve Fuel Consumption Description Source of Cost Estimate Estimate HVAC—variable stroke, increased efficiency (humidity control, paint, glass, etc.) U.S. Environmental Protection Agencya $70-$90 Electric and electric-hydraulic power steering Deutsche Bank $70-$120 Thermoelectric energy recovery Several hundred dollars aThe U.S. EPA has estimated the cost associated with improving the energy efficiency of the A/C system and reducing refrigerant leakage from the system at less than $110 to the consumer (ANPR-HQ-OAR-2008-0318; FRL 8694-2). With an RPE of 1.75 the cost to the original equipment manufacturer would be just over $60. TABLE 7.10 Estimates of Replacement Costs for Transmission Technologies Relative to 2007 4-Speed Automatic Transmissions Transmission Type $Cost (EEA, 2007) $RPE (EEA, 2007) $Cost (Martec, 2008) $RPE (Martec, 2008) 5-speed automatic 133 200 — — 6-speed automatic 133 205 215 323 7-speed automatic 170 255 — — 8-speed automatic — — 425 638 DCT (dry clutch, 250 N-m) — — 300 450 DCT (wet clutch, 350 N-m) 140 210 400 600 CVT (engine <2.8 liter) 160 240 — — CVT (engine >2.8 liter) 253 380 — — NOTE: RPE values were determined using a cost multiplier of 1.5.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles in mass (material substitution), improving aerodynamics, or switching to low-rolling-resistance tires. More substantive changes require longer-term coordination with the PDP because reengineering and integration with other subsystems are necessary. This could include resizing the power train/transmission or aggressively reducing mass (e.g., changing the body structure). Substantive changes like this will take 4 to 8 years to adopt. The cost estimates provided in this chapter all assume coordination with the PDP to help contain costs and achieve maximum impact. Two important technologies impacting fuel consumption addressed in this chapter are light-weighting and transmissions. Light-weighting has almost unlimited potential because vehicles can be made very light with exotic materials, albeit at potentially high cost. The incremental cost to reduce a pound of mass from a vehicle tends to increase as the total amount of reduced mass increases, leading to a curve with diminishing returns. About 10 percent of vehicle mass can be eliminated at a cost of roughly $700 (or about $2.00/lb; see Table 7.11). If the aggressiveness to reduce mass increases much beyond 10 percent, it is necessary to begin addressing body structure design (such as considering an aluminum-intensive car), and the cost per pound increases. A 10 percent reduction in mass over the next 5 to 10 years appears to be within reach for the typical automobile, considering the current baseline. Transmission technology has significantly improved and, like other vehicle technologies, shows a similar curve of diminishing returns. Planetary-based automatic transmissions can have five, six, seven and eight speeds, but with incremental costs increasing faster than their impact on fuel consumption. Continuously variable transmissions have been available on the market for a number of years, but their rate of implementation seems to have flattened out, suggesting that future new implementations will be limited in number. DCTs are in production by some vehicle OEMs (e.g., VW/Audi DSG), and new DCT production capacity has been announced by other vehicle OEMs and suppliers. It is therefore expected that the predominant trend in transmission design will be conversion both to 6- to 8-speed planetary-based automatics and to DCT automated manuals, with CVTs remaining a niche application. Because of the close linkage between the effects of fuel-consumption-reducing engine technologies and those of transmission technologies, the present study has considered primarily the combined effect of engines and transmission combinations rather than potential separate effects. TABLE 7.11 Summary of the Committee’s Findings on the Costs and Impacts of Technologies for Reducing Light-Duty Vehicle Fuel Consumption Fuel Consumption Technology Description and Approximate Manufacturing Cost Impact on Fuel Consumption (%) Comments Mass reduction (assume 3,600-pound vehicle) 1% (36 lb); $46-$55 0.25 Material substitution 5% (180 lb); $270-$324 3-3.5a Material substitution 10% (360 lb); $648-$778 6-7a Aggressive material substitution 20% (720 lb); $1,600+ 11-13a Redesigned body with aluminum and composite-intensive structures Transmission Five-speed automatic transmissions; $133 2-3 Can also improve vehicle performance Six-speed automatic transmissions; $133-$215 3-5 Can also improve vehicle performance Seven-speed automatic transmissions; $170-$300 5-7 Can also improve vehicle performance Eight-speed automatic transmissions; $425 6-8 Can also improve vehicle performance Dual-clutch automated (DCT) manual transmissions (6/7 speed); $300 (dry clutch), –$14-$400 (wet clutch <350 N-m) 6-9 DCTs have replaced original automated manual transmissions Continuously variable transmissions; $150 (<2.8 L), $263 (>2.8 L) 1-7 Possible engine noise; not applicable to large engines Aerodynamics 5 to 10% reduction in Cd (coefficient of drag); $40-$50 1-2 Wheel well and underbody covers, body shape, mirrors, etc.; bigger impact on highway drive cycle Rolling resistance Low-rolling-resistance tires; approximately $10 apiece ($30-$40) 1-2b Stopping distance and durability can be compromised with inferior materials; optimal materials drive up costs Tire-inflation monitor; becoming standard equipment 0.7 Depends on monitor settings and driver behavior Low-drag brakes; becoming standard equipment 1 Most cars equipped already today Electrical accessories HVAC—variable stroke, increased efficiency (humidity control, paint, glass, etc.); $70-$90 3-4 Current FTP does not capture benefit (benefits reduced to 0.5-1.5% within Table 9.1) Electric and electric-hydraulic power steering; $70-$120 1-5 Electric for small cars, electric-hydraulic for bigger cars—benefits for the FTP are smaller (1-3%). aWith resized power train. bThree percent may be feasible with resized power train.
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Assessment of Fuel Economy Technologies for Light-Duty Vehicles Accessories are also being introduced to new vehicles to reduce the power load on the engine. Higher-efficiency air-conditioning systems are available that more optimally match cooling with occupant comfort. This includes, for example, humidity control, air recirculation, and increased compressor efficiency using a variable-stroke compressor. Electric and electric-hydraulic power steering also reduces the load on the engine by demanding power (electric) only when the operator turns the wheel, whereas the older technology relied on hydraulic power supplied by the engine all the time. An important motivating factor affecting the introduction of these accessories is whether or not their impact is measured during the official CAFE certification tests. The certification test currently does not take the air conditioner into account, and so there is little motivation to improve its efficiency and incur added cost; however, this situation may change with newly proposed test procedures. Estimates for these technologies and several others are summarized in Table 7.11. The fuel consumption estimates assume ideal conditions, and there are important interaction effects among different technologies. Generally, it is not possible to apply two or more of the technologies in Table 7.11 and algebraically add the impacts on fuel consumption. The typical impact from multiple technologies will be less than the sum of their individual fuel consumption estimates. FINDINGS Finding 7.1: Refresh/redesign. With respect to reducing fuel consumption, recognition of product development process timing is important for minimizing the cost of implementing many new vehicle technologies. Only relatively modest changes can be made when vehicles are restyled, and secondary benefits from mass reduction are unlikely. The reengineering or redesign phases of product development offer the greatest opportunity for implementing new fuel-saving technologies, and this can occur from 4 to 8 years after initial introduction. Significant changes to power train and vehicle structure and materials can be made more easily at this time. Finding 7.2: Mass reduction. Reduction of mass offers the greatest potential to reduce vehicle fuel consumption. To reduce mass, vehicles will continue to evolve with a broad mix of replacement materials that include high-strength steels, aluminum, magnesium, and reinforced plastics. These materials will be introduced on a component-by-component basis as companies move up the learning curve and continue to design for them. More aggressive efforts to reduce mass (by, say, 5 to 10 percent) will require system solutions (as opposed to material substitution solutions). Achieving a mass reduction of greater than 10 percent (as high as 20 percent) will require a significant change in vehicle design (such as a shift to an aluminum-intensive body or aggressive use of other higher-cost materials like carbon fiber) and will incur a significant increase in costs. The uncertainty and instability of commodity prices (e.g., for carbon fiber, resins, and aluminum versus steel) increase the risk to the vehicle manufacturer of adopting these new materials. Finding 7.3: Transmissions. Another promising technology for reducing vehicle fuel consumption is transmissions with an increased ratio spread between the low and the high gears (e.g., 6-8 speeds) and dual-clutch transmissions that eliminate torque converters. Finding 7.4: Lower-energy-loss accessories. A collection of relatively low-cost vehicle technologies can have a positive impact on reducing fuel consumption. Low-rolling-resistance tires, improvements to vehicle aerodynamics, and electric power steering can all cost less than $200 in total while reducing fuel consumption by about 10 percent, if HVAC is included as a component of real-world driving. Other technologies that can yield incremental reductions in fuel consumption are increased HVAC compressor efficiency, ultraviolet filtering, glazing, and cool/reflecting paints, but these technologies are not currently pursued very aggressively because they are not taken account of in the official CAFE certification tests. It would take more than the addition of HVAC in one of the five test schedules used to report fuel economy on the vehicle sticker to have a significant impact on the penetration of these technologies. REFERENCES Automotive News. 2008. A big fuel saver: Easy rolling tires (but watch braking). July 21. 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Assessment of Fuel Economy Technologies for Light-Duty Vehicles Gessat, J. 2007. Electrically powered hydraulic steering systems for light commercial vehicles. SAE Paper 2007-01-4197. SAE International, Warrendale, Pa. Goodyear Tire & Rubber Company. 2009. Letter from Donald Stanley, Vice President, Product Quality and Plant Technology, April 13, 2009; e-mail exchanges with Donald Stanley, January, 28, 2009, and February 25, 2009. Heremans, J.P., V. Jovovic, E.S. Toberer, A. Saramat, K. Kurosaki, A. Charoenphakdee, S. Yamanaka, and G.J. Snyder. 2008. Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states. Science 321:554. Hussain, Q., C. Maranville, and D. Brigham. 2009. Thermoelectric exhaust heat recovery for hybrid vehicles. SAE Paper 2009-01-1327. SAE International, Warrendale, Pa. IBIS Associates. 2008. Benefit Analysis: Use of Aluminum Structures in Conjunction with Alternative Power Train Technologies in Automobiles. IBIS, Waltham, Mass. Kolwich, G. 2010. Light-Duty Technology Cost Analysis—Report on Additional Case Studies. Prepared for U.S. Environmental Protection Agency. FEV, Inc., Auburn Hills, Mich. Martec Group, Inc. 2008. Variable Costs of Fuel Economy Technologies. Prepared for Alliance of Automobile Manufacturers. June 1; amended September 26 and December 10. NRC (National Research Council). 2002. Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards. Washington, D.C.: National Academy Press. NRC. 2006. Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance—Special Report 286. Washington, D.C.: The National Academies Press. Pagerit, S., A. Rousseau, and P. Sharer. 2006. Fuel economy sensitivity to vehicle mass for advanced vehicle powertrains. SAE Paper 2006-01-0665. SAE International, Warrendale, Pa. Powers, W. 2000. Automotive materials in the 21st century. Advanced Materials and Processes, May. Ricardo, Inc. 2007. Impact of Vehicle Weight Reduction on Fuel Economy for Various Vehicle Architectures. Prepared for the Aluminum Association, Inc. Rugh, J.P., L. Chaney, J. Lusbader, J. Meyeer, M. Rustagi, K. Olson, and R. Kogler. 2007. Reduction in vehicle temperatures and fuel use from cabin ventilation, solar-reflective paint, and a new solar-reflective glazing. SAE Paper 2007-01-1194. SAE International, Warrendale, Pa.