The net power output of a truck engine is consumed by numerous forces opposing the truck’s movement on the road. These forces in the case of a heavy-duty truck derive from a number of subsystems or components that consume energy by various forms of friction, by unfavorable pressure differentials, or by energy conversion to power a device. The 21st Century Truck Partnership (21CTP) has identified the areas of energy consumption for a typical Class 8 vehicle operating on a level road at a constant speed of 65 mph with a gross vehicle weight (GVW) of 80,000 lb. In this case, the engine losses are about 322 horsepower (hp), 60 percent of the fuel energy. The truck power demands consume the remaining 40 percent, as summarized in Table 5-1.
Under the described operating conditions, aerodynamic drag and tire rolling resistance are major contributors to energy loss. Although all trucks would benefit from aerodynamic drag reduction, those with high average speed and miles traveled would benefit most. Class 8, over-the-highway, tractor-trailer combination trucks best fit that operational description.
NOTE: Horsepower consumed each hour is an energy term (hp-h).
SOURCE: NRC, 2010, Table 5-4.
The resisting aerodynamic horsepower is proportional to
Cd × A × V3, where Cd = coefficient of drag, A = frontal area, and V = forward velocity (NRC, 2010, p. 28).1 This illustrates the important role of vehicle speed on aerodynamic horsepower consumption. The relationship is shown in Figure 5-1.
An analysis of the consumptions shown in Table 5-1 has illustrated that a 20 percent reduction in Cd results in about a 10.5 percent reduction in fuel consumption. This supports the industry’s rule of thumb that for high–road-speed tractor-trailers, the fuel consumption change is one-half of the drag change.
Although it is typical in truck aerodynamic improvement practice to report fuel consumption at 65 mph, rarely is an average speed of 65 mph achieved without frequently exceeding the common Interstate highway speed limit. In the case of many real-world trucks’ duty cycles with perhaps an average 55 mph, the aerodynamic fuel-consumption reduction is about 9 percent rather than the 10.5 percent associated with a 20 percent Cd reduction.
Also illustrated in Figure 5-1 is the tire-rolling-resistance power consumption.2Figure 5-1 indicates that these two sources of power consumption are equal at about 50 mph, while rolling resistance power consumption is about twice that because of aerodynamic drag at 37 mph, when the tractor-trailer is equipped as a 2008 model pre-SmartWay3 combination vehicle.
1 Cd = coefficient of drag = Force/(1/2 ρ A V2), which is dimensionless; F = force the vehicle must overcome due to air, ρ = density of the air, A = projected area perpendicular to the direction of travel, and V = velocity of the vehicle relative to the fluid (air).
2 “Rolling resistance” is the force at the axle in the direction of travel required to make a loaded tire roll. The coefficient of rolling resistance (Crr) is the value of the rolling resistance force divided by the wheel load.
3 SmartWay is an Environmental Protection Agency (EPA) voluntary certification program for tractor-trailer combinations. The EPA notes that the
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5 Vehicle Power Demands INTRODUCTION The resisting aerodynamic horsepower is proportional to The net power output of a truck engine is consumed by numerous forces opposing the truck’s movement on the road. Cd × A × V³, where Cd = coefficient of drag, A = frontal These forces in the case of a heavy-duty truck derive from a area, and V = forward velocity (NRC, 2010, p. 28).1 This number of subsystems or components that consume energy illustrates the important role of vehicle speed on aerody- by various forms of friction, by unfavorable pressure differ- namic horsepower consumption. The relationship is shown entials, or by energy conversion to power a device. The 21st in Figure 5-1. Century Truck Partnership (21CTP) has identified the areas An analysis of the consumptions shown in Table 5-1 has of energy consumption for a typical Class 8 vehicle operating illustrated that a 20 percent reduction in Cd results in about on a level road at a constant speed of 65 mph with a gross a 10.5 percent reduction in fuel consumption. This sup- vehicle weight (GVW) of 80,000 lb. In this case, the engine ports the industry’s rule of thumb that for high–road-speed losses are about 322 horsepower (hp), 60 percent of the fuel tractor-trailers, the fuel consumption change is one-half of energy. The truck power demands consume the remaining 40 the drag change. percent, as summarized in Table 5-1. Although it is typical in truck aerodynamic improve- Under the described operating conditions, aerodynamic ment practice to report fuel consumption at 65 mph, rarely drag and tire rolling resistance are major contributors to is an average speed of 65 mph achieved without frequently energy loss. Although all trucks would benefit from aero- exceeding the common Interstate highway speed limit. In the dynamic drag reduction, those with high average speed case of many real-world trucks’ duty cycles with perhaps an and miles traveled would benefit most. Class 8, over-the- average 55 mph, the aerodynamic fuel-consumption reduc- highway, tractor-trailer combination trucks best fit that tion is about 9 percent rather than the 10.5 percent associated operational description. with a 20 percent Cd reduction. Also illustrated in Figure 5-1 is the tire-rolling-resistance power consumption.2 Figure 5-1 indicates that these two sources of power consumption are equal at about 50 mph, while rolling resistance power consumption is about twice TABLE 5-1 Heavy-Duty Truck Power Consumption that because of aerodynamic drag at 37 mph, when the (each hour) tractor-trailer is equipped as a 2008 model pre-SmartWay3 combination vehicle. Power Power Operating Load Consumed (hp) Consumed (%) Aerodynamic 114 53 1 C = coefficient of drag = Force/(1/2 r A V2), which is dimensionless; d F = force the vehicle must overcome due to air, r = density of the air, A = Rolling resistance 68 32 projected area perpendicular to the direction of travel, and V = velocity of Auxiliaries 20 9 the vehicle relative to the fluid (air). Drivetrain 12 6 2 “Rolling resistance” is the force at the axle in the direction of travel required to make a loaded tire roll. The coefficient of rolling resistance (C rr) Total 214 100 is the value of the rolling resistance force divided by the wheel load. 3 SmartWay is an Environmental Protection Agency (EPA) voluntary NOTE: Horsepower consumed each hour is an energy term (hp-h). SOURCE: NRC, 2010, Table 5-4. certification program for tractor-trailer combinations. The EPA notes that the 78
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79 VEHICLE POWER DEMANDS 120 100 Consumption (HP) 80 60 40 20 0 60 70 0 10 20 30 40 50 Aero-hp w/Cd=0.625 Speed (MPH) Tires-hp w/Crr=0.0068 FIGURE 5-1 Aerodynamic and tire power consumption for tractor-trailer combination. SOURCE: NESCCAF/ICCT (2009). 5-1.eps REDUCTION GOALS FROM THE PARTNERSHIP only, of a Class 8 tractor [EPA/NHTSA, 2011; NRC, WHITE PAPERS 2010].) (Also, see footnote 3 in this chapter.) 3. Goal 3 (reference level of 9 percent auxiliaries’ power The goal of the 21CTP is to conduct research, provide consumption): Reduce essential auxiliary loads by hardware demonstrations, and validate and deploy cost- 50 percent. (The baseline for this goal is a Class 8 effective, reliable, and durable technologies that reduce vehi- highway tractor-trailer with sleeper, operating 5 days cle power demands. The Partnership will continue to utilize in over-the-highway operations at 80,000 lb gross a vehicle system approach to continually track the benefits combined vehicle weight [GCVW].) of individual technologies on overall vehicle efficiency and 4. Goal 4: Reduce tare weight by 10 percent, and for the performance. Five primary technology goals applicable to long-term stretch goal by 20 percent, from a 34,000 lb the target tractor-trailer truck are to be achieved over the next base tractor-trailer capable of an 80,000 lb GCVW op- 10-year period (DOE, 2011). eration, and comprised of a tractor (19,500 lb), trailer (13,500 lb), and fuel (1,500 lb). 1. Goal 1 (reference level of 53 percent aerodynamic 5. Goal 5: Thermal Management, and Friction and Wear power consumption): Reduce the aerodynamic drag Reduction coefficient by 20 percent (from a Cd of 0.69). Evaluate a. hermal Management Systems: Increase heat-load T a stretch goal of 30 percent reduction in aerodynamic rejected by 20 percent without increasing radiator drag. (The baseline is from the Environmental Protec- size. tion Agency/National Highway Traffic Safety Admin- b. Friction and Wear (reference level of 6 percent istration [EPA/NHTSA] final rule “Greenhouse Gas drivetrain power consumption): Reduce powertrain Emissions Standards and Fuel Efficiency Standards for and drivetrain consumptions by 50 percent (NRC, Medium- and Heavy-Duty Engines and Vehicles” for 2010).4 a conventional Class 8 tractor with high-roof sleeper. [EPA/NHTSA, 2011; NRC, 2010].) (Also, see footnote The committee appreciates these carefully formulated 3 in this chapter.) goals statements. The committee believes that these goals 2. Goal 2 (reference level of 32 percent rolling resistance are achievable within the 10-year period specified, but only power consumption): Reduce tire rolling resistance by if adequate research and development efforts are expended. 35 percent from tractors equipped with dual-tire drive Typically, achieving some goals will be found more prob- wheels. (The baseline Crr is 0.0082 from the EPA/ lematic than achieving others. In the more problematic NHTSA rule for tires of the dual tire drive wheels, 4 Notes to Goals 1 and 2 were prepared to compare these current numeri- SmartWay brand identifies products and services that reduce emissions, such cal goals to those stated in the DOE (2006) White Paper Roadmap, as well as as greenhouse gas emissions. Certification using EPA test methods allows to compare certain Cds and Crrs corresponding to other frequent descriptions carriers, manufacturers, and shippers to apply the SmartWay logo. See the (current available, SmartWay, Advanced SmartWay). See Appendix G in this EPA website at http://www.epa.gov/smartwaylogistics/basic-information/ report. The baseline for these goals is a Class 8 highway tractor-trailer with index.htm and NRC (2010) for more detailed information. sleeper operating at a steady 65 mph at 80,000 lb GCVW.
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80 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT areas, typically of higher technology risk and cost, 21CTP reductions related to each region that are estimated to be processes are very important. The ability of the Department achievable in the near term. of Energy (DOE) to assist in understanding how to achieve The DOE funded a $4.2 million study, initiated in 2007, the goals through its Vehicle Technologies Program, includ- on trailer aerodynamic improvements to reduce fuel con- ing specifically the Vehicle Systems Simulation and Testing sumption and presented a project status report to the com- (VSST) protocols (DOE, 2010b), should be very beneficial mittee (DOE, 2010a). The authors provided the committee and is particularly encouraged. a pre-publication draft of their results and analysis. The study combined CFD studies with a large battery of full- size tractor-trailer wind tunnel tests at 65 mph in the huge AERODYNAMICS National Full-Scale Aerodynamics Complex (NFAC) at the Aerodynamic drag arises principally from the pressure National Aeronautics and Space Administration (NASA) differentials on fore and aft body surfaces. Surface friction Ames Research Center. This research was supported by is a much less significant issue if surfaces are substantially numerous industrial partners. These data are reported as smooth, which is a common but not yet a universal design yaw-wind averaged drag, which is acquired only in a wind feature; a notable example is container boxes (DOE, 2010a). tunnel, and which most aerodynamicists agree represents Full-truck on-road testing following Society of Automotive the best on-road performance figure. The study clearly is an Engineers (SAE) protocols (e.g., SAE J1263 coast-down test- excellent one, with very thorough evaluation of numerous ing; SAE J1321, Type II over-the-road testing with control candidate design improvements for all three of the trailer truck) is relatively imprecise for evaluating the aerodynamic regions in Figure 5-2. The analysis is quite insightful, provid- effect of design changes. Wind tunnel tests, also following ing very helpful commentary to clarify why certain design SAE protocols (e.g., SAE J1252), are an improvement in pre- details yield the observed results. The best performance cision and, importantly, allow an evaluation of the effects of observed for the case of a 2008 long sleeper tractor and off-axis forces (yaw) due to prevailing wind. Computational straight frame (LS/SF) tractor-trailer was a Cd reduction of fluid dynamics (CFD) is often useful for fine-tuning compo- 23 percent. The draft did not proffer a base case Cd for this nent design to take account of the aerodynamic contribution, LS/SF combination. However, if a Cd of 0.63—used in this but it is in limited use for full-truck behavior. chapter for a 2006-2008 pre-SmartWay tractor—is assumed, Historically, the truck manufacturers have not reported a fuel-consumption reduction of about 12 percent would be Cd values for tractors. This situation is likely due to the expected. This can be compared to the average fuel consump- competitive nature of those values, especially in light of the tion of 9.3 percent for a full package described in the section imprecision of prevailing standard test procedures. below titled “TIAX Summary” and Figure 5-3. Four regions of the tractor-trailer combination truck are amenable to aerodynamic design improvements. These EPA SmartWay Transport Program regions include (1) the various tractor-related “aero” details, (2) the tractor-trailer gap, (3) the trailer skirt (or underbody), In 2004 the EPA developed and implemented SmartWay, and (4) the trailer “base” fairing, which are all illustrated in an organized effort to specify a collection of current and Figure 5-2, along with the approximate fuel-consumption emerging technologies for creating fuel-efficient tractor- FIGURE 5-2 Tractor-trailer (T-T) combination truck showing areas of energy-saving opportunities. NOTE: Percentage changes refer to fuel 5-2.eps consumption with base Cd = 0.625. SOURCE: Personal communication, Richard M. Wood, Solus, LLC. bitmap
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81 VEHICLE POWER DEMANDS 14% Fleet Tests Track 12% Wind Tunnel or CFD Average Not included in average 10% 9.3% 8% 6% 5.8% 5.2% 4.3% 4% 3.5% 2.2% 2% 1.3% 0% Full Pkg Partial Gap Full Gap Partial Skirts Full Skirts Base Flaps Partial Pkg 0 FIGURE 5-3 Summary of trailer aerodynamic device fuel consumption reduction (baseline C d of 0.625). CFD, computational fluid dynam- ics. SOURCE: TIAX (2009). 5-3.eps trailer combinations with the best environmental performance pre-SmartWay specifications by virtue of their aerodynamic in terms of both air pollution and emissions of greenhouse and tire-rolling-resistance changes alone. gases (GHGs) (EPA, 2011; NRC, 2010). SmartWay tractors must have an aerodynamic profile that includes a high-roof California Regulation Based on SmartWay Program sleeper, integrated roof fairings, cab side extenders, fuel tank side fairings, and aerodynamic bumpers and mirrors. One of the most significant consequences of the Smart- They must be powered by a 2007 or newer engine, with a Way certification program is action taken by the California SmartWay-approved option for idle reduction. The tires must Air Resources Board (CARB) to reduce the state’s GHG be SmartWay-approved, low-rolling-resistance tires. All six emissions to 80 percent of 1990 levels by 2020 (ARB, 2008). major U.S. truck manufacturers have one or more complying In response to the California legislature’s Global Warming tractors. Thousands of carriers, shippers, and manufacturers Solutions Act of 2006, the CARB required all tractor-trailers are SmartWay members or affiliates, attributing to the excel- to implement SmartWay technologies. lent success of this voluntary efficiency program. Beginning in January 2010, with the 2011 model SmartWay dry van trailers are 53 ft long and must have year, all sleeper cab tractors on California highways that side skirt fairings, a front gap or rear fairing, and SmartWay- pull 53-ft or longer box van trailers must be SmartWay- approved low-rolling-resistance tires. Trailer fairings and certified. Day cab tractors must have SmartWay-approved tires can be either provided by the original equipment manu - low-rolling-resistance tires. At the same time, in model facturer (OEM) on new trailers or retrofitted to older trailers year 2011 and beyond, all 53-ft van trailers must also be by more than a dozen manufacturers that have developed SmartWay-certified. these aerodynamic components. The SmartWay program has provided an important TIAX Summary visibility in the heavy-duty truck industry to the benefits of adapting manufacturer-developed aerodynamic trailer TIAX provided data on the performance of a collection features and low-rolling-resistance tires. SmartWay com- of aerodynamic modifications to trailers, including packages binations consume a minimum of 8 percent less fuel than of various combinations, using various testing methods.
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82 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT These are reported in Figure 5-3. The full package includes nent improvements are typically not additive. Appropriately, the partial gap filler, full or partial trailer skirt, and base the perspective of the 21CTP for the SuperTruck projects is flaps (base fairings and boat tails). TIAX also reported that to utilize a vehicle systems approach for the validation of next-generation aerodynamic tractors would improve fuel research and development results. consumption by 3 to 4 percent in the 2013-2015 time period Finding 5-2. The aerodynamic test procedures may not be (TIAX, 2009). It might be helpful to note here that a 0.63 Cd base was sufficiently precise, and only wind tunnel testing accounts for used in several earlier documents, including the previous important yaw effects, so that competitive pressures discour- Partnership White Papers (DOE, 2006), the performance- age truck-tractor manufacturers from publishing Cd figures. Recommendation 5-15 from the National Research Council’s improvement estimates in Figure 5-2, and the TIAX (2009) study. Further, the current Partnership white paper (DOE, 2010 report titled Technologies and Approaches to Reducing 2011) adopted the proposed EPA/NHTSA GHG rule Cd base the Fuel Consumption of Medium- and Heavy-Duty Vehicles of 0.69 for application to the new goal. This difference in goal provided good suggestions for standardizing Cd reporting. between the current and previous white papers represents a Finding 5-3. T he proposed EPA/NHTSA greenhouse fuel consumption penalty increment of about 4 percent for the tractor-trailer operating condition described for Table 5-1. gas emissions standards rule chose not to regulate trailer Adjusting these TIAX data to the 0.69 new Cd base, the operational efficiency. Regardless of the reasons, this seems committee believes that in the 2013-2015 time frame, a 13 a significant omission, because both trailer aerodynamic percent reduction in fuel consumption is achievable at 65 devices and low-rolling-resistance tires that are currently mph when utilizing the trailer “full package” average of 9.3 production-available can provide an immediate, combined percent reduction. Note that this performance represents a fuel consumption reduction of about 13 percent (compared Cd reduction of about 25 percent, compared to the expressed to the rule’s baselines). goal of 20 percent. Finding 5-4. Aerodynamic design packages are expected In the 2015 to 2020 time period, if it is assumed that the performance of the trailer individual devices at the 75th per- to improve tractor-trailer fuel consumption by 19 percent at centile would eventually be achieved, then the combined full 65 mph when fully developed in the 2015-2020 time period. package (of partial gap, full skirt, and base flaps) would be This reduction corresponds to a Cd reduction of nearly 40 16 percent (Cd base adjusted to 0.69). Combining that trailer percent (from the newly adopted 0.69 Cd baseline). performance with the forecast next-generation tractor perfor- Recommendation 5-1. The Partnership should consider set- mance would yield a 19 percent reduction in fuel consumption (a Cd reduction of about 38 percent) achievable at 65 mph, ting an aerodynamic drag stretch goal of 40 percent instead in the 2015-2020 time period. This result is derived through of 30 percent. a method of multiplication of fuel-consumption reductions (DOE, 2010a). Take particular note that these packaged solu- TIRE ROLLING RESISTANCE tions include a boat tail or similar device that might interfere with trailer docks, and must be appropriately accommodated. When tires roll under a truck’s weight, their shape changes At least one manufacturer of such devices reported that its boat cyclically, deforming and recovering with inherent hyster- tail folds flat onto the doors in 6 seconds (ATDynamics, 2010). esis. That deformation energy is converted into heat and the Navistar, with partners Kentucky Trailer and Freight tire’s environment dissipates the heat accumulation, and the Wing, initiated a Cooperative Research and Development heat dissipated is due to the tire’s rolling resistance. The Agreement (CRADA) with the DOE beginning in December power consumed by the tires is proportional to truck weight, 2008 to bring to market a tractor-trailer combination and tire speed, and the coefficient of rolling resistance (Crr) (NRC, package that can reduce the fuel consumption of a heavy- 2010, p. 28). Rolling resistance is influenced by many fac- duty vehicle by at least 15 percent. After completion of the tors, including design and construction features, materials, project, the team members will make this fuel-efficient tech- internal pressure, and tread design, which may be different nology package available for sale (Navistar, 2008). according to intended tire use at steer, drive, or trailer loca- All three of the SuperTruck projects will investigate tractor tions. The change from bias to radial ply in the 1970s and and trailer aerodynamic features (see Chapter 8 in this report). 1980s reduced Crr by 25 percent. These projects will provide appropriate next steps under the A common 18-wheeler highway tire specification for 21CTP for many of the vehicle power demand topics. today (pre-low rolling resistance) will have an average Crr Findings and Recommendations 5 “Regulators should require that aerodynamic features be evaluated on a wind-averaged basis that takes into account the effects of yaw. Tractor and Finding 5-1. Aerodynamic improvement studies need to trailer manufacturers should be required to certify their drag coefficient become increasingly integrated, because individual compo- results using a common industry standard” (NRC, 2010).
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83 VEHICLE POWER DEMANDS of about 0.0068. This results from the tire combination of 2 This level of reduced fuel consumption has been validated steers, 8 drives, and 8 trailers from a range represented by in an extensive on-highway test series conducted by the Oak data such as in Figure 5-4. (See Appendix G of this report Ridge National Laboratory (ORNL) in cooperation with for the tire weighting values used in this averaging.) Simi- a carrier, Schrader Trucking, and using Michelin-supplied larly, the EPA SmartWay 18-wheeler average threshold Crr tires (ORNL, 2009). Six well-instrumented tractors and six is 0.0063 based on the values from Figure 5-4, and might be trailers all with a mix of standard dual tires and NGWBSTs achieved with low-rolling-resistance dual tires. accumulated more than 688,000 miles at an aggregated The tire industry has taken additional initiative, spurred average speed of 58 mph traveling through 39 eastern and by competitive market forces, to develop next-generation midwestern states and Canada. Every combination of tires wide-base single tires (NGWBSTs), which have substantially that included some mix of NGWBSTs provided statisti- reduced Crr and are becoming the current state of the art; some cally significant fuel-consumption reductions at all three fleets are replacing dual tires with the NGWBST systems of the selected gross weight groupings. Those applications when new trucks are ordered. Figures for Crr in the low 0.004s that replaced both tractor and trailer duals with NGWBSTs are available for some tire positions (trailers). A currently achieved a 9.3 to 9.6 percent reduction in fuel consumed available set of tractor-trailer tires, including wide-base low- when carrying medium and high payloads. rolling-resistance designs, provide a Crr of 0.0055. A combined tractor-trailer Crr of 0.0045 is achievable As noted above in Goal 2, the 21CTP has recently in the next 5 years (TIAX, 2009, p. 4-53) and could yield adopted the Crr baseline used by the EPA for tractor tires a fuel-consumption reduction of about 15 percent. These on dual drive wheels, from the proposed truck GHG/fuel reductions are compared to the supposed EPA non-low- efficiency rule promulgated by the EPA and NHTSA (EPA/ rolling-resistance tractor-trailer 0.0077 Crr weighted baseline NHTSA, 2010). To put the Goal 2 drive tires’ Crr baseline noted above, and result from the corresponding 40 percent of 0.0082 in perspective for an 18-wheeler, one must create reduction in Crr. a combination that includes the EPA/NHTSA rule’s selec- Potential pavement damage due to changes in tire shape tion for steer tires, 0.0078, along with a committee-assumed and load is a high concern for regulators. Road wear and trailer tire value of 0.0072. That tractor-trailer combined damage are known to be directly controlled by contact weighted average Crr then is about 0.0077. Now, by compari- (hertz) stress. This stress increases with the 4th power of son, the current NGWBST combined weighted average Crr unit load. As a result, vehicle weight and the distribution of is a reduction of nearly 30 percent, to 0.0055, and yields a that weight over the tire contact patches are critical factors in fuel-consumption reduction of about 10.5 percent. (Note that determining the durability of road surfaces. Studies show that 18-wheelers become 10-wheelers when their current 8 pairs NGWBSTs do not increase contact stress in the pavement of duals are replaced by single wide-base tires.) compared to the stress generated by standard dual tires. As a FIGURE 5-4 Example rolling resistance coefficients for heavy-duty truck tires. (Data in this figure are C rr × 1,000). Acronyms are defined 5-4.eps in Appendix I. SOURCE: Courtesy of Michelin Tire North America. C. Bradley and S. Nelson, Michelin Tire North America, “Truck Tires and Rolling Resistance,” presentation to the National Research Council Committee to Assess Fuel Economy Technologies for Medium- and bitmap Heavy-Duty Vehicles, February 4, 2009, Washington, D.C.
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84 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT rolling resistance characteristics: they are the SAE J1269 result, pavement damage is expected to be similar for these multi- and single-point, and the draft International Orga- two types of tires for primary roads. nization for Standardization (ISO) 28580 single-point with Some of the concerns regarding pavement damage interlaboratory correlation procedure. Unfortunately, tire can be attributed to past experiences and studies of the manufacturers have not voluntarily collaborated in efforts original 65-series on-off-road and regional single tires (e.g., to facilitate the comparison of rolling resistance and other 385/65R22.5 and 425/65R22.5). These tires are normally characteristics across company boundaries. Furthermore, operated at elevated service inflation pressures, with conse- given that Crr is not constant over the tread life of tires, it quently reduced tire footprint size and peak tire-road contact would be a great improvement toward tire selection if such stresses that surpass those of traditional dual tires. Studies laboratory procedures added a requirement to measure Crr of the original “65-series singles” concluded that increased at the tire mid-life (circa 150,000 miles). This is an area road damage could be attributed to these tires, and this natu- needing DOT or DOE attention, because fuel-consumption rally generated concern for state and federal departments of benefits are being lost because of limited carrier acceptance transportation when NGWBSTs were developed and put in of the NGWBSTs. use (Al-Qadi, 2007a,b). Other issues still concerning users of NGWBSTs are tread life, truck stability in blowout, running on a flat, Response to Recommendations from NRC Phase 1 Review availability of nearby repair facilities, and integrity of drive The 21CTP agreed that it is appropriate for the DOT, EPA, traction. Tire manufacturers believe that these issues have and DOE to report tire performance data to buyers and sell- been resolved (Al-Qadi, 2007a,b). Many carriers have been ers. It noted that the EPA SmartWay Transport Partnership replacing duals on existing equipment with NGWBSTs at publicly reports the fuel-savings capability of low-rolling- an accelerated pace, seeking the anticipated fuel savings resistance tires, including the wide-base single families of contribution of NGWBSTs. A recent trade press article tires (see 21CTP response in Appendix C to Recommenda- identified eight medium and large carriers that have been tions 5-9 on Parasitics from [NRC, 2008]). The DOE also converting, some beginning many years ago (TT, 2011). It recently reported the favorable results of its testing with has been observed that when replacement of dual with wide NGWBSTs. single tires are made to existing axles, manufacturers cau- tion that improper wheel selection can reduce load-carrying capability (AM, 2010). Carriers need to be made aware of Findings and Recommendations the importance of such caveats. Potential safety issues asso- Finding 5-5. N ext-generation wide-base single tires ciated with blowouts of NGWBSTs do not appear to have (NGWBSTs) can provide a combination tractor-trailer with become a remarkable problem. Nevertheless, the Department an immediate 10.5 percent fuel-consumption reduction and of Transportation (DOT) should thoroughly review the real- up to a 15 percent reduction in the next 5 years, but many world ramifications of documented NGWBST blowouts. fleets do not yet embrace the technology. M any carriers are routinely using NGWBSTs because they are satisfied that these issues are minimal, but many Recommendation 5-2. The DOE should set the goal for other fleet owners will need to be convinced. Most Class 8 reduced rolling resistance for the tires of the combination tractor-trailer combination trucks can benefit from the fuel- tractor-van trailer, rather than for the tractor drive wheels consumption reductions contained in NGWBSTs. There are only, because improved-performance trailer tires are equally some application issues that carriers must become aware of, important to realizing the full benefit of reduced rolling such as trailer spread-axle configurations. In short, carriers resistance designs. This benefit can be achieved by combin- must monitor the details of conversion as well as new pur- ing the EPA base values for steer and drive tires in the EPA/ chases. Another benefit of using NGWBSTs is an 800 lb or NHTSA GHG rule, with an assumed trailer tire Crr value of greater weight reduction for an 18-wheeler, when used with about 0.0072. aluminum wheels. Maintenance of tire pressure is important both to tire life Finding 5-6. Carriers need to follow carefully the recom- and rolling resistance. A 20 percent pressure reduction in all mendations of axle manufacturers for replacing dual tires tires causes a fuel-consumption increase of 2 to 3 percent, with single-wide tires to ensure that the integrity of the load associated with an increase in rolling resistance (NRC, 2010, system is not compromised. p. 114). Tire pressure monitoring systems with in-wheel sen- sors have become available in recent years and are gaining Recommendation 5-3. The 21CTP should consider produc- acceptance in fleet application. As usual, the cost/benefit ing a comprehensive summary that can be updated giving the trade-off is an important element in the acceptance of such prescriptions and precautions that carriers should consider new technologies. when retrofitting NGWBSTs onto original equipment axles At least two standard laboratory test procedures are in fitted with dual wheels and tires. This effect might best be common use for determining truck (and light-duty vehicle)
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85 VEHICLE POWER DEMANDS managed in conjunction with the American Trucking Associa- road at 65 mph, assuming unchanged brake thermal efficiency tion’s (ATA’s) Technology and Maintenance Council, which (BTE). Auxiliary power requirements are derived from many has drafted such a Recommended Practice and is a specialist in vehicle functions, as described above (DOE, 2011). creating such directives for ATA membership (ATA, 2007). The most often imagined solution for removing these loads from their current drive is the electrification of the vari- Finding 5-7. There is no rolling resistance test procedure ous drives, which was called the More Electric Truck project with interlaboratory correlation universally employed as an in the 21CTP. Electrically driving many of these systems industry standard. can achieve power on demand, using energy only when and where it is needed. In that way, nonpropulsion energy like Recommendation 5-4. The 21CTP, strongly supported by that from waste heat recovery (WHR) systems, hybrid system DOT and EPA (the latter through its SmartWay program), regenerative braking systems, or auxiliary idle reduction should conduct an authoritative study of the several barriers systems might supply the needed electricity. A 21CTP goal (e.g., related to tread life, truck stability in blowouts, run-flat identified for hybrid drive units in Chapter 4 (see revised tires, and other topics) to the widespread carrier adoption Goal 1) provides for “electrification of power accessories of NGWBSTs. The DOT should specifically support reduc- with goals of reduced weight and cost, operation in engine- tion of barriers to NGWBST acceptance by requiring the off conditions and a service life of 1 million miles/15 years.” universal use by tire manufacturers of a rolling resistance Truck electrification will have to be achieved without a deg- test procedure like that in ISO (International Organization radation of current subsystem durability and reliability, and for Standardization) 28580, to ensure that comparative inter- advanced electrical systems will have to be cost-effective. laboratory data exist. Multiple projects were initiated and successfully completed in the 21CTP program by the end of 2007. Average power savings of up to 2 percent of fuel are the largest estimated in AUXILIARY LOADS the NRC Phase 1 report (NRC, 2008, p. 74). Auxiliary loads are typically driven by a mechanical drive Two of the SuperTruck platforms will investigate electri- from the propulsion engine. Examples include compressed cally driven auxiliaries, as those projects integrate WHR, air for brake systems; air conditioning compressors; electri- hybrid-electric, and idle-reduction systems. It is expected cal energy for lighting, hotel loads, heating, ventilation, and that those projects may be better able to quantify the actual air-conditioning (HVAC) fans and battery-charging systems; savings of electrically driven auxiliaries in real-world duty. power-steering pumps; and power take-off (PTO) drives, Chapters 4 and 6 of this report are devoted to hybrid systems where used. Trailer refrigeration loads are normally satisfied and idle reduction, respectively. with a second, dedicated engine. Power demand on the pro- pulsion engine for these functions might range up to 9 per- Response to Recommendations from NRC Phase 1 Review cent, depending on the truck duty cycle and environment. Seemingly missing from this list of “auxiliaries” is the The 21CTP reported that it is exploring the cost and bene- engine cooling fan. However, this is not a significant omis- fits of continuing R&D in the auxiliaries area compared to the sion when the principal truck operation perspective is to be potential for efficiency improvements by other heavy-truck a line-haul tractor-trailer at high road speed. The line-haul technologies (see Appendix C, response to Recommendation fan power consumption has been summarized for a 1,800 5-1 on parasitics from NRC, 2008). engine rpm fan-on condition as 40 to 60 hp. However, for high road speed, the fan-on time was estimated at 5 percent Finding and Recommendation (NRC, 2010, p. 110). Together these figures suggest a time Finding 5-8. The More Electric Truck may achieve about average consumption of 2 to 3 hp, sufficiently small not to warrant attention. However, the committee notes that there one-third of the auxiliaries’ reduction goal for a loaded are operating conditions, for example, at lower road speeds, tractor-trailer. Better quantification is expected to result climbing hills, and with the air conditioner on, when the fan through two of the SuperTruck projects. on will be consuming 20 to 50 hp for appreciable periods. A Recommendation 5-5. The Partnership should renew R&D variable-speed fan drive can reduce the necessary fan speed and accompanying power consumption to only that neces- efforts to further reduce fuel consumption related to auxiliary sary to achieve both radiator and air-conditioner-condenser power demands. temperatures and pressure. Goal 3 above requires a reduction in essential auxiliary WEIGHT REDUCTION loads by 50 percent. In Table 5-1, auxiliary load is identi- fied as 9 percent of the demand on the engine. A 50 percent Truck weight reduction affects fuel consumption by reduction, to 4.5 percent of the demand, would provide a corre- reducing tire rolling resistance and unrecovered energy used sponding 4.5 percent reduction in fuel consumption on a level when accelerating or grade climbing. The energy required to
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86 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT overcome resistances is approximately linearly dependent increase issues will be encountered—for example, with the on the weight of the vehicles. Generally for Class 8 trucks, use of tractor aerodynamic components and idle reduction there is more incentive for reducing the vehicle weight components. for weight-limited trucks, which can replace the reduced For these reasons, the 21CTP reinstated funding of tare weight with cargo. For a 35,000 lb tractor-trailer fully the lightweight materials research beginning late in 2010 loaded with 45,000 lb of cargo, reducing weight by 1,000 ($500,000) and into 2011 ($2.12 million) (see Chapter 1, lb increases load-carrying capacity by the same amount Table 1-2). The FY 2011 budget of $2.12 million will be and therefore reduces payload-specific fuel consumption, directed to lightweight materials initiatives for the Super- expressed in gallons per 1,000 ton-miles, by a little more Truck projects. Several weight-reduction initiatives are than 2 percent. Unfortunately, for a volume full (cubed-out) funded under the SuperTruck projects themselves. trailer application, the fuel-consumption reduction is only about 0.5 percent per 1,000 lb of tare weight reduction, Weight-Reduction Goals because payload remains constant (NESCCAF/ICCT, 2009, p. 50). Approximately 60 percent of tractor-trailer loads are Weight-reduction goals vary by vehicle; the targets for cubed-out before grossed out (weight full) (NRC, 2010). all vehicle classes range from 10 to 33 percent. For Class 8 Opportunities for fuel efficiency impact vary considerably by tractor-trailer combinations the goal had been from 15 to 20 truck type and class and duty cycle. Vehicle weight effects percent, with the specific goal of 5,000 lb. Recently the goal are more important for duty cycles with frequent starts and has been modified. The new goal is a 10 percent reduction in stops (NRC, 2010, Table 5-16). For urban delivery vehicles, weight for a baseline tractor-trailer tare weight of 34,000 lb a 10 percent reduction in weight can reduce fuel consumption (specific goal of 3,400 lb) along with a longer-term stretch by as much as 7 percent. goal of 20 percent reduction in weight. Because of budget reductions for the 21CTP, no funding was provided for lightweight materials (other than for pro- Opportunities and New Initiatives pulsion materials) from FY 2007 through FY 2009. However, prior to the FY 2007 budget reduction, there had been numer- For a Class 8 truck there are numerous opportunities ous projects aimed at vehicle weight reduction. Several for reducing vehicle weight by introducing lighter-weight projects involving the national laboratories and industry led materials, albeit often at a cost premium. The more obvious to useful examples of weight reduction. A complete list of opportunities lie in the body structure (~19 percent of total 21CTP projects up to 2007 can be found in the 21CTP Quad tractor weight), the chassis/frame components (~12 percent), Sheets (DOE, 2007). and wheels and tires (~10 percent). Truck manufacturers have been substituting lightweight materials for a number of components in the cab, chassis, and wheels. Examples New Incentives for Vehicle Weight Reduction include composite structure in the cab, aluminum panels, The incentive for reducing the weight of weight-limited aluminum wheels, and aluminum fuel tanks. There are also Class 8 trucks has taken a new urgency as trucks have been weight-reduction opportunities afforded by extensive use a dding weight particularly with emissions-compliance of aluminum for both tractor and trailer (NRC, 2010, see devices. Emissions control components have added as much Figure 5-38). as 400 lb to the typical tractor. Aerodynamic devices are The Pacific Northwest National Laboratory (PNNL), in slowly growing in popularity, adding several hundred pounds cooperation with PACCAR, Novelis, and Magna, is develop- ing an aerodynamic lightweight cab structure.6 The objective in some cases, especially trailer devices (the trade-off of add- ing weight to improve aerodynamics is a good one, because is to develop a low-cost forming method using aluminum aerodynamic drag is a major contributor to fuel consumption alloy that allows the use of aluminum instead of steel or at highway speeds). Weight reduction will be needed to offset other materials. A target of 40 percent weight savings is the other components such as auxiliary power units (~400 lb) objective. PNNL forming equipment will be used, and its added to reduce fuel consumption normally expended dur- impact on corrosion and ability to be painted will be evalu- ing idle. For city buses and urban delivery vehicles, weight ated. The forming technology will be transferred to Magna reduction becomes important to offset the hybrid systems for the fabrication of a full-scale cab. The project will begin that many of these vehicles are adding. in FY 2011. Furthermore, the new EPA/NHTSA standards to reduce As part of the SuperTruck projects, additional lightweight f uel consumption and greenhouse gas emissions from materials initiatives are planned. For example, Navistar, medium- and heavy-duty vehicles are expected to achieve which of the 21CTP industry partners provided the most reductions in CO2 and fuel-consumption from 7 to 20 per- cent reduction from current, 2010, baselines (EPA/NHTSA, 6 Jerry Gibbs, DOE, “Materials Support for the 21st Century Truck: 2011). As selected truck tractor technologies are expected Lightweighting and Propulsion Materials,” presentation to the committee, to build on the EPA SmartWay configurations, some weight November 15, 2010, Washington, D.C.
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87 VEHICLE POWER DEMANDS detail for its weight-reduction effort, plans to explore the The DOE recently issued a Funding Opportunity following.7 A n nouncement (FOA) that includes opportunities for additional cost-shared research in the area of lightweight • Use of composites in cab-in-white, materials. It includes additional research in magnesium and carbon-fiber composites.8 • Use of composites in trailer floor, • Carbon composite drums, • Lightweight rotors and aluminum calipers, Response to Recommendations from NRC Phase 1 Review • Plastic fuel tanks, • Single lightweight driveshaft, and Because of severe reductions in the 21CTP budget, no • Aluminum cross-members. budget was allocated to lightweight materials research from 2007 through 2009. In the NRC Phase 1 report (NRC, It may also be possible to transfer and expand technical 2008), it was recommended (Recommendation 5-2) that work that had been carried out on light-duty vehicle activities scarce budget resources be allocated to projects with higher to heavy-truck applications. Two examples were presented potential payoff for fuel-consumption reduction (e.g., engine to the committee (see footnote 6). The first example involves efficiency) than payoff through the application of lightweight the potential application of magnesium. Studies at the PNNL materials. Furthermore, the NRC Phase 1 report suggested and ORNL will explore the possibility of improving the duc- that it should be the responsibility of the truck manufacturers tility of magnesium and its low-temperature formability. The to take the next steps of system integration, product valida- researchers will also explore the development of new joining tion, and production application of lightweight materials. methods (magnesium to steel), as conventional automotive joining methods are not applicable to magnesium. Galvanic Finding corrosion limits applications of magnesium currently—the Finding 5-9. Several projects that were carried out prior to team will explore the application of low-cost ceramic coat- ings as a solution to this problem. 2007 have shown the potential for the reduction in weight The second example involves the processing of carbon of individual components and subsystems. However, to date fiber for composite applications. Although glass-reinforced there has been no integrated full-vehicle project to show that composites, often in the form of sheet molding compound, the goal of reducing the weight of a Class 8 tractor-trailer have been used in high-volume automotive and in heavy- by 3,400 lb can be achieved. Moreover, the NRC Phase 1 truck applications for years, higher-performance carbon- report had recommended that such a project, using prototype reinforced composites have not. The primary obstacle has components, vehicle integration, and full-vehicle system been the cost of the carbon fiber itself. However, there analysis, should be carried out by industrial partners—led are other issues associated with the application of high- by original equipment manufacturers. The new SuperTruck performance carbon composites. The fabrication process is program appears to be a response to this suggestion. slow compared with steel stamping processes. Furthermore, assembly is complicated by the fact that joining methods THERMAL MANAGEMENT typical of automotive assembly processes are not applicable. Other issues needing resolution include coloration, recycling Thermal management projects have been coordinated methods, and the ability to repair damaged parts. with the DOE Heavy Vehicle Systems Optimization Pro- Progress is being made, however, in adapting carbon gram. The primary focus has been on increasing cooling composites for automotive applications. Indeed, carbon radiator capacity without increasing size. Heat rejection and composites have been used for years in the motor-sports radiator size are issues that have several effects on truck industry, and they are more recently finding applications design. Incurring higher heat rejection normally mandates in low-volume specialty automotive products. And, in fact, a larger cooling package, which adds weight and cost. The certain characteristics of carbon composites are superior to larger cooling package also requires more airflow, and the conventional steel. Clearly the higher strength and stiffness air passes through the turbulent and restrictive areas under of carbon composites enable part-to-part weight reduction. the hood, increasing the vehicle aerodynamic drag. A larger Composites offer opportunities for part consolidation as cooling package also requires changes to the shape of the well as the ability to form complex shapes that could not truck’s front, which limits aerodynamic design options and be achieved by steel stamping. Composites are corrosion- results in increased drag. Because of these factors, lower heat resistant. For low volumes, tooling costs can be lower than rejection and/or a more efficient cooling system contribute to those typical of metal stamping. lower aerodynamic drag, lower truck weight, and potentially lower cost. 7 Anthony 8 Cook, Navistar, Inc., “Navistar’s SuperTruck Program,” pre- Financial Assistance Funding Opportunity Announcement, Number: sentation to the committee, September 8, 2010, Washington, D.C. DE_FOA-0000239, December 16, 2010.
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88 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT Good progress has been achieved by the application of to optimize coolant boiling to reduce coolant system size nanoparticle-containing coolants. Nanofluids contain highly and power consumption (ANL, 2010a). This second project conductive particles (1 to 100 nanometers) suspended in could support these same themes but was not reported by liquids to provide significantly increased heat transfer from the SuperTruck participants. These projects are illustrative cooled systems, compared to conventional glycol-water of areas in which technology development cost and risk can systems. These nanofluid coolant projects were planned for be managed under the DOE VSST protocol (DOE, 2010a). 7-year duration, with completion anticipated in 2012. The Further, the Partnership has identified a number of potential nanofluid cooling system work has been managed at the topics that might make a big contribution to the breakthrough Argonne National Laboratory (ANL), evidently with limited sought, such as advanced window glazing, concepts for direct trucking company involvement. Nevertheless, a heavy-duty heating and cooling of the vehicle occupants, heat-generated truck demonstration is planned for the nanofluid coolant cooling techniques, and thermoelectrics (DOE, 2011). project(s). Research status forecasts a radiator size reduction Other next steps appear to be to provide consistent funding of more than 10 percent (ANL, 2009a, 2010b). to permit nanofluid performance-enhancing discoveries to be Modeling of underhood cooling airflow has also been tested in truck-cooling demonstrations in aerodynamically pursued. Both technologies were driven by the engine efficient trucks, thereby integrating several technologies. manufacturers’ addition of cooled exhaust gas recircula- tion (EGR) beginning in 2002 to lower NOx by combustion Response to Recommendations from NRC Phase 1 Review modification. EGR rates have continued to increase in some of those engines to enable compliance with the latest NOx The DOE has continued to emphasize the cooling sys- standard reduction in calendar year 2010. The committee tem nanofluid developments through a series of ongoing has not found that high-technology cooling radiator designs, projects at the ANL. It has also initiated the two CRADAs coordinated with increased EGR, have been incorporated noted above: Cooling Boiling in Head Region-PACCAR, in heavy truck systems to date. It is noted that there is an Integrated Underhood Thermal and External Aerodynamics- ANL project associated with the nanofluid projects, called Cummins, VSS004 (ANL, 2010a). The Cummins Super- Efficient Cooling in Engines with Nucleated Boiling. This Truck project will evaluate tractor frontal shape as affected project is attempting to exploit the fact that the boiling by cooling system capacity/efficiency needs. heat-transfer coefficient is more than five times the liquid The DOE also agreed to find methods to provide status heat-transfer coefficient. A two-phase boiling heat-transfer reporting as part of its overall assessment of the Partner- regime is sought, then altering the cooling system to man- ship’s processes and progress. The DOE believes that the age a continuous gas-liquid condition. Such a two-phase SuperTruck projects provide a unique opportunity to bring heat-transfer system with a net higher heat-transfer than a together manufacturers and suppliers for coordinated sys- conventional nonboiling cooling system further supports the tems R&D. notion to reduce radiator size (ANL, 2009b). The committee believes that the removal of barriers to Finding and Recommendation production implementation is a key next-step action. The Finding 5-10. H eavy-duty truck thermal management project leaders have listed barriers for nanofluids: adequate heat-transfer coefficient increase, high viscosity of nano- objectives are growing in importance as new systems to fluids, pumping power increase, and fluid production costs improve both engine and truck efficiency, particularly waste (ANL, 2009a); and for the nucleate boiling radiators: cool- heat recovery systems, become reality. These are accompa- ant boiling heat-transfer coefficients, coolant two-phase nied by new heat management issues and are expected to be pressure-drop data, and acceptable boiling limits of both added to trucks in the current decade. critical heat flux and flow instability (ANL, 2009b). Recommendation 5-6. The Partnership should continue Furthermore, current efforts to achieve a major fuel- consumption reduction by means of the addition of WHR and priority support of nanofluid and high-efficiency underhood hybrid electric systems will add yet higher cooling demands cooling systems, as well as review other potential technical on the radiator system. Given the fuel-consumption reduc- concepts, and validate them as an integrated system. tion goal, aerodynamics needs to be improved substantially, and smaller radiators would facilitate changes to the frontal FRICTION AND WEAR tractor shape for reduced air pressure and aero-friction. Cum- mins noted in its SuperTruck presentation to the committee The DOE initiated a study focused on developing a com- that it would address this issue of tractor frontal shape as prehensive friction model for engine and drivetrain systems. affected by cooling system capacity/efficiency needs. And The project purports to improve existing computational the DOE has initiated a new CRADA with Cummins with models, which are based only on fluid film lubrication. Not- this intention, reported at the June 2010 DOE Merit Review ing that most engine and driveline components operate under presentations. There is an associated CRADA with Peterbilt, both mixed and boundary lubrication regimes, a comprehen-
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89 VEHICLE POWER DEMANDS sive model that can adequately predict friction in both sliding • Integration of friction and wear models to reduce pow- and rolling contact regimes is the objective. ertrain loss, Completed work identified that friction at a lubricated • Development of advanced coatings for reduced friction interface (especially under the boundary regime) is a com- and wear, and plex phenomenon involving the shearing of the lubricant • Down-selection and demonstration of engineered sur- fluid film, the tribochemical boundary films, and the near- face applications for reduced wear and friction. surface material. Next steps will attempt to quantify and model all three regimes. The expected 6-year project was Revision of Goal 5 within the new Vehicle Power Demand begun at the ANL in 2010 (ANL, 2010c). This project is Orientation also illustrative of one in which technology development cost and risk can be managed under the DOE VSST protocol. It The “friction and wear” component of Goal 5 requires the is noted that no truck OEM companies are yet collaborating following: “Develop and demonstrate technologies that reduce with the contractor in this project. powertrain and driveline losses” (DOE, 2011, p. 3). Note that As described in the subsection titled “Lubricants” in this deals with both powertrain and drivetrain friction. Chapter 3, the Engine Manufacturers Association initiated In Table 5-1, drivetrain load is identified as 6 percent of a lubricant project beginning in April 2010 as the EPA/ the demand (50 percent reduction of the load will reduce NHTSA GHG/fuel efficiency rule was anticipated. The fuel consumption by 3 percent, assuming unchanged engine primary objective is an improved fuel efficiency contribu - BTE). The drivetrain loads are those resulting from engine tion through implementation of a High Temperature High torque transmitted through units like a transmission(s) and Shear (HTHS) viscosity property. Early industry testing rear axle(s) gearing, and not including auxiliaries or tires, as with HTHS controlled oils has shown promise for fuel- partitioned in the DOE (2011) white paper. Drivetrain loads consumption reduction while other parameters continue to derive from windage of gears running in lubricant and fric- provide traditional performance. The notion of this HTHS tion within components of the geared units. property is believed to be applicable to drivetrain units as Goal 5 has been carried over from the DOE (2006) white well as engines. This potential should be considered within paper “Parasitics,” which included powertrain components, the projects that the 21CTP considers for friction and wear often referred to as engine accessories, that are needed to reduction. operate an engine on a dynamometer and on the EPA Federal In addressing the committee, two of the SuperTruck Test Procedure (FTP). These are the oil pump, fuel pump, presenters indicated that friction reduction was included in water pump, and any other engine fluid pump (like an EGR their projects. However, it is believed that these efforts are pump). Those loads are integral to engine operation con- being directed toward engine friction specifically and not to tributing to the brake thermal efficiency and not to vehicle driveline or auxiliaries. power demand. To represent only the power consumptions of The DOE presented fuel and lubricants development vehicle power demand, it is appropriate that the term “pow- plans to the committee.9 The DOE suggested that it might ertrain” be removed from the Goal 5.b statement. play a valuable role in developing an understanding of There is also a need for an updated study of the current microfluidic transport and tribological film formation. The driveline power demand of 12 hp. It is noted that this 12 hp, first project noted above appears to be a good beginning. reported in the most recent white paper (DOE, 2011), is the The DOE cited the long-standing engine and drivetrain same value as that in the previous white paper (DOE, 2006) friction-reduction needs, anticipating that half of the target which represented both powertrain and driveline “parasitic” improvement might be achieved with engine oil enhance - (friction) losses together. The committee expects that the ments. The DOE surely can make a helpful contribution, driveline-only power demand (friction) will be significantly but it will need to become engaged with driveline and revised downward. auxiliary system developers and manufacturers as well as becoming involved in the heavy-duty-engine-industry oil Response to Recommendations from NRC Phase 1 Review development process. The 21CTP certainly provides an appropriate forum. The NRC Phase 1 review report (NRC, 2008) estimated The DOE (2011) white paper identified a list of friction that a 50 percent reduction in drivetrain losses would reduce and wear activities that were proposed to begin in 2011 and fuel consumption by 1.2 percent. Similarly, that review sug- to be completed in 2018. These activities may well make gested that a 50 percent reduction in powertrain (engine) fric- a needed contribution in this difficult area. A project plan tion losses would reduce fuel consumption by 3.7 percent. needs to be developed within the Partnership to solidify this The two losses sum to about 5 percent, somewhat lower list (see below) and begin the work. than the stated goal. Further, Recommendation 5-8 from that review suggested that the DOE reassess the technical feasi- bility of these 50 percent reductions while retaining adequate 9 Kevin Stork, DOE, “DOE Fuel & Lubricant Technology R&D,” presen - durability and reliability (NRC, 2008, p. 80). tation to the committee, November 15, 2010, Washington, D.C.
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90 REVIEW OF THE 21ST CENTURY TRUCK PARTNERSHIP, SECOND REPORT The Partnership responded that it agreed with the rec- and determine whether any technologies to reduce vehicle ommendation (see Appendix C), and that each of the three power demand are not being adequately addressed by the SuperTruck teams will continue the research in these areas SuperTruck program. The DOE should define projects and of friction, wear, and lubrication in the engine and drivetrain. find funding to support the development of technologies Both Daimler and Navistar have friction-reduction phases in beyond the scope of SuperTruck. their projects. The DOE believes that the 50 percent reduc- tion goal feasibility (combined powertrain and driveline REFERENCES losses) will receive reasonably thorough evaluation through the SuperTruck projects. The committee suggests that the Al-Qadi, I. 2007a. New Generation of Wide-Base Tire and Its Impact on DOE will need to be proactive with the SuperTruck contrac- Trucking Operations, Environment, and Pavements. Transportation Research Board 86th Annual Meeting. Paper No. 07-2432. January tors to ensure that they allocate adequate resources in order 21-25. Washington, D.C. to achieve the expected thorough evaluation. Al-Qadi, I. 2007b. Impact of Wide-Based Tires on Pavement and Trucking Operation. Presented at the International Workshop on the Use of Wide- Base Tires, Federal Highway Administration, Turner-Fairbank Highway Findings and Recommendation Research Center. October 25-26. McLean, Virginia. AM (ArvinMeritor, Inc.). 2010. Product Information Letter #515, Rear Drive Finding 5-11. There is a need for an updated study of the Axle Application Guidance and Recommendations for Single Wide-Base current driveline power demand of 12 hp. Furthermore, to Tires Mounted on Outset Wheels. January. 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There has been no apparent collaboration on merit_review_2010/propulsion_materials/pm008_routbort_2010_o.pdf. lubricant projects between the DOE and OEM partners. Accessed May 5, 2011. ANL. 2010c. Friction Modeling for Lubricated Engine and Drivetrain C omponents. Ajayi. June. Available at h ttp://www1.eere.energy. OVERALL FINDING AND RECOMMENDATION gov/vehiclesandfuels/pdfs/merit_review_2010/propulsion_materials/ pm026_ajayi_2010_p.pdf. Accessed June 1, 2010. Finding 5-13. Summarizing the committee’s findings on ARB (Air Resources Board). 2008. Final Regulation Order to Reduce vehicle power demands: Project prioritization by the 21CTP Greenhouse Gas Emissions from Heavy-Duty Vehicles. Available at roughly follows the consumption ranking of the several http://www.arb.ca.gov/regact/2008/ghghdv08/ghgfro.pdf. Accessed heavy-duty truck operating loads listed in Table 5-1 and May 5, 2011. ATA (American Trucking Association). 2007. New Generation Wide Based technology risk. 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