Review of the 21st Century Truck Partnership: Third Report (2015)

8

SuperTruck Program

INTRODUCTION

The SuperTruck program was designed to provide a full Class 8 tractor-trailer vehicle demonstration of a wide range of technologies, many of which were developed at the component or subsystem level under previous 21st Century Truck Partnership (21CTP) projects.¹ The SuperTruck program aligns with findings and recommendations set out in the NRC Phase 1 review of 2008 (NRC, 2008). For example, NRC Phase 1 Recommendation 1-2 stated that project “goals should be clearly stated in measurable engineering terms.” Recommendation 3-1 called for demonstrating 50 percent brake thermal efficiency (BTE) at an operating point representative of a 65 mile per hour (mph) cruise operation. Recommendation 3-8 called for completing the 50 percent engine BTE demonstration before embarking on a 55 percent effort. The SuperTruck program had already started at the time of the NRC Phase 2 review in 2011, and the project plans were reviewed in Chapter 8 of the NRC Phase 2 report (NRC, 2012).

Four project teams were awarded projects under the SuperTruck program. All of the teams were given the same basic fuel-saving targets, along with a requirement to maintain “comparable vehicle performance”:

• Achieve 50 percent BTE from the engine at a highway cruise operation speed/load point;
• Demonstrate a path to 55 percent BTE from the engine (see Chapter 3); and
• Demonstrate a 50 percent increase in freight efficiency, measured in freight ton-miles per gallon, on a long-haul drive cycle.

In addition to these targets, the Cummins team added a target to measure the effectiveness of its auxiliary power unit (APU) systems, which handle hotel loads when the vehicle is parked. The Daimler team also evaluated freight efficiency over a somewhat different 24-hour cycle. The Cummins target is to demonstrate a 68 percent increase in freight efficiency on a 24-hr duty cycle (drive cycle plus overnight hotel load).

The teams were given some flexibility regarding the targets. For example, each team defined its own long-haul drive cycle(s), and each team derived the cruise operation point for the 50 percent BTE demonstration from its selected drive cycle. The teams also had broad flexibility regarding the selection of specific technologies used to achieve the targets. All four projects were set up with a time frame of approximately 4 years. Table 8-1 compares the overall technical approaches of the four SuperTruck teams.

PROJECT BUDGETS AND RELEVANCE TO 21CTP

The Cummins-Peterbilt project was funded by the Department of Energy (DOE) using money from the American Recovery and Reinvestment Act of 2009 (ARRA).² DOE’s funding is $38.8 million, with the industrial partners contributing $38.8 million, for a project total of $77.7 million. The Daimler SuperTruck project was also funded by DOE with ARRA money. DOE committed $39.6 million to the Daimler project, and the industrial partners also put in $39.6 million, for a total project funding of $79.1 million. As shown in Table 3-1, the project budget was split approximately 60/40 between vehicle and engine work.

The Volvo SuperTruck program was funded by DOE at $18.9 million, from regular DOE appropriations. Volvo also contributed $19.1 million to its program, for a total project funding of $38 million. The Volvo project is smaller in scale, because Volvo is also participating in a European government-funded program along the lines of SuperTruck.

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¹ D. Anderson, 21st Century Truck Partnership, “Vehicle Technologies Office Vehicle and Systems Simulation and Testing,” presentation to the committee, September 3, 2014.

² Budget information provided by Ken Howden, DOE, to the committee in March 2015. Also see Table 3-1.

TABLE 8-1 SuperTruck Team Technical Approaches

NOTE: TBD, to be determined; AMT, automated manual transmission; DCT, dual clutch transmission; RR, rolling resistance; MMC, metal matrix composite; PCP, peak cylinder pressure; HPCR, high-pressure common rail; CR, compression ratio; HVAC, heating, ventilation, and air conditioning; EGR, exhaust gas recirculation; VG, variable geometry (turbocharger); HPL, high pressure loop; GPS, global positioning system; rpm, revolutions per minute; LED, light-emitting diode; ECM, electronic control module; FMEP, friction mean effective pressure.

The Volvo team started about 1 year after the Cummins and Daimler teams, and the project is expected to be complete about a year after Cummins and Daimler. Finally, the Navistar program was assigned $35.8 million in regularly appropriated DOE funding, with $40.4 million in funding committed by the contractor, for a total Navistar project funding of $76.2 million. Navistar put its SuperTruck project on hold for approximately 2 years to deal with the conversion of its engine products from an EGR-only approach to the use of selective catalytic reduction (SCR) for compliance with 2010 emissions standards. Navistar resumed participation in SuperTruck in November 2014, and its completion is expected to be approximately 1.5 years behind that of the Cummins and Daimler teams.

The SuperTruck programs are highly relevant to the goals of the Partnership. As noted in the introduction to this chapter, these programs address recommendations from the NRC Phase 1 report, and the Phase 2 review in 2011 provided a generally positive review of the SuperTruck project plans (NRC, 2008, 2012, see Chapter 8 of the latter report).

CUMMINS-PETERBILT PROJECT

Members of and suppliers to the Cummins-Peterbilt team are listed in Table 8-2. Table 8-2 also lists some of the technology content used in the demonstration truck. One noteworthy aspect of the team structure was that Peterbilt actually did the design and fabrication work for the aerodynamic upgrades of the trailer used for its SuperTruck rather than depending on the trailer manufacturer for this support. The trailer manufacturer was responsible for weight reduction efforts on the trailer. This approach appears to be common to all the SuperTruck projects and is driven by the modest technical capabilities of trailer manufacturers.

TABLE 8-2 Cummins-Peterbilt Project Team Members and Suppliers

Cummins-Peterbilt Technical Approach

Cummins selected the 15 L ISX engine for this program. This is the largest displacement engine to be used in the program. Cummins opted to avoid downsizing the engine in order to take advantage of efficiency technologies that can only be applied to a relatively low brake mean effective pressure (BMEP) engine, such as a very high compression ratio and a combustion strategy that leads to high cylinder pressures. Cummins did aggressively downspeed the engine, which causes the engine to operate at a higher BMEP for a given road load under cruise conditions. Using a large displacement engine increases the challenge of packaging the engine, the waste heat recovery (WHR) system, the exhaust aftertreatment system, and the cooling system into a highly aerodynamic vehicle layout. A large displacement engine also means that efforts to reduce engine friction are particularly important. Finally, a large displacement engine imposes a weight penalty. These disadvantages must be considered in light of the engine efficiency achieved.

According to the Cummins 2014 annual merit review (AMR) presentation (Koeberlein, 2014), conventional diesel combustion was retained, but with revisions to the combustion system (compression ratio, piston bowl, injector specification, and calibration). Turbocharger efficiency was improved, and the EGR circuit was optimized to minimize pumping work (and thus the pressure differential required to drive EGR flow). Extensive efforts were made to reduce friction, and a 30 percent reduction in friction mean effective pressure (FMEP) is claimed. The aftertreatment system design was modified to achieve higher conversion efficiency, which allows higher engine-out oxides of nitrogen (NO_x), and it was increased in size to provide less back pressure on the engine, which reduces the engine’s pumping work. The engine was calibrated to produce 4.3 g/hp-hr NO_x on the Supplemental Emission Test (SET) cycle. A WHR boiler bypass is integrated into the exhaust system. The bypass allows reduced vehicle heat rejection in situations where the cooling fan would otherwise have to be used. Since cooling fan power is greater than the contribution of the WHR system, minimizing fan-on time is important to achieving low on-highway fuel consumption.

Peterbilt elected to use a production Model 579 tractor as the basis for the final SuperTruck demonstration tractor. The Cummins annual merit review presentation shows that the SuperTruck demonstrator has a 46 percent reduction in the coefficient of drag (C_d) from the baseline tractor-trailer configuration, based on computational fluid dynamic (CFD) calculations (Koeberlein, 2014). If the mirrors could be eliminated and replaced with cameras, the benefit would increase to 49 percent. In contrast, a completely clean sheet tractor design achieved a 49.6 percent C_d reduction without mirrors. Given the results of this evaluation, Cummins-Peterbilt decided that there is no need to consider an all-new tractor design. However, the Cummins-Peterbilt tractor and trailer are designed as a matched set. This means that the Peterbilt SuperTruck tractor cannot pull a conventional trailer, and the Cummins-Peterbilt SuperTruck trailer is not compatible with a conventional tractor.

Because WHR introduces an additional heat rejection demand to the vehicle cooling system, the team put effort into improving airflow through the cooling system and under the hood during fan-off operation. Slide 17 of the 2014 Cummins merit review shows some results from a CFD evaluation of cooling package airflow (Koeberlein, 2014).

A diagram of the Cummins WHR system used in the Demonstrator 1 vehicle is shown in Figure 8-1. According to Cummins, the final SuperTruck demonstrator vehicle used a WHR system that includes energy recovered from the engine coolant and lubricant circuits (Koeberlein, 2014). No details were provided on whether these circuits were run at an elevated temperature in order to provide higher quality waste heat. Also, the final demonstrator system fed power back into the front accessory drive belt rather than into the crankshaft through a gear train.

The original project plan called for the use of a solid oxide fuel cell APU to handle hotel loads during the stationary portion of the 24-hr duty cycle. According to Cummins, several problems were encountered with the fuel cell, including a long warm-up time, low thermal efficiency, high weight, and

FIGURE 8-1 Cummins Demonstrator 1 WHR system layout. SOURCE: Koeberlein (2014).

a low peak power capacity (Koeberlein, 2014). After efforts to resolve these issues proved unsuccessful, the fuel cell was replaced with a custom-designed lithium ion battery-based APU. This system has a 13.2 kWh storage capacity, of which 12.2 kWh is used during the hotel load portion of the 24-hr duty cycle. The battery is recharged by a 240 amp engine-driven alternator, and a full system recharge takes 6 hr of driving time. The heating, ventilation, and cooling (HVAC) system was converted to electric power to work with the APU. The Cummins SuperTruck battery APU system weight is about 400 lb, which is comparable to the weight of diesel-engine driven APU systems that are widely used in the field today.

The original project plan called for a dual clutch transmission. In the end, a single clutch automated manual transmission was used. Optimization work was performed on the transmission ratios and to improve the mechanical efficiency of the transmission. Another feature planned early in the program was a turbocharger with its own continuously variable transmission (CVT) (Fleet Owner Magazine, 2010). The idea was to improve transient response by accelerating the turbocharger using crankshaft power when needed, and to generate power to the crankshaft when more than adequate turbine

power was available. The VanDyne turbocharger proved to be not adequately developed for use in a vehicle application, so a more efficient conventional (variable geometry) turbocharger was employed instead. The Cummins approach to the 55 percent BTE requirement is described in Chapter 3.

Cummins-Peterbilt selected a test route running from Denton, Texas, to Vernon, Texas, and back.³ The route is primarily rural, with a couple of traffic lights. Most of the route follows US 380 and US 287, which combine sections of divided highway with stretches of two- and four-lane undivided road. The route length is 311 miles, with 550 feet in elevation change. A figure on Slide 15 of Cummins’ presentation to the committee shows that the distribution of grades on this route is very close to the national average grade distribution of interstate highways in the lower 48 states.⁴

Cummins-Peterbilt Project Results

Table 8-3 shows information on the Cummins-Peterbilt 2009 model baseline tractor-trailer. These data are based on results provided by Cummins-Peterbilt in the AMRs, along with information provided to the committee by Cummins. Note that the 24-hr cycle includes 8 hr of idling or APU use to support cab hotel loads. Table 8-4 summarizes the SuperTruck project results to date.

Based on the results in Table 8-4, some calculations can be made to determine the relative contribution of engine efficiency and vehicle power demand. Assuming that the 2009 baseline Cummins engine had a BTE of 42 percent (Koeberlein, 2014), the reduction in vehicle fuel consumption due to improved engine efficiency is about 17.6 percent. Vehicle fuel consumption on the long-haul cycle was reduced by 40 percent, so about 22.4 percent fuel consumption reduction is due to vehicle power demand reduction. These same data can be expressed in another way: Of the total vehicle fuel savings on the long-haul drive cycle, about 44 percent is due to engine efficiency improvements, and 56 percent is due to vehicle power demand reduction. If the increase in cargo allowed by empty weight reduction is taken into account, the engine efficiency/vehicle efficiency split is 41/59 percent.

Additional results provided by the Cummins-Peterbilt team include:

• Reduction in C_d: 46 percent
• Weight increases:
  • —WHR + aftertreatment upgrades: 950 lb
  • —Aerodynamic devices: 2,500 lb
  • —Idle reduction system: 400 lb
• Weight reductions:
  • —Reduced fuel load, 400 lb

TABLE 8-3 Cummins-Peterbilt 2009 Baseline Data

SOURCE: Koeberlein (2014).

• • —Tractor weight reduction, 2,400 lb
  • —Trailer weight reduction, 2,355 lb
• Net vehicle weight reduction/payload increase: 1,305 lb
• Cummins-Peterbilt SuperTruck freight efficiency on driving cycle (no idle): 178 ton-mi/gal
• Cummins-Peterbilt SuperTruck load specific fuel consumption (LSFC) on driving cycle: 5.64 gal/1.000 ton-mile
• Share of total fuel savings attributed to:
  • —Engine improvements and WHR, 42 percent
  • —Tractor aerodynamic improvements, 14 percent
  • —Trailer aerodynamic improvements, 28 percent
  • —Driveline and tire improvements, 15 percent

The data presented above show one significant issue introduced by the application of fuel-saving technologies: weight increase. In the Cummins-Peterbilt SuperTruck, the weight increase associated with the fuel saving technologies totals 3,850 lb. To achieve the reported increase in payload of 1,305 pounds, the empty weight of the tractor and trailer had to be reduced by 5,155 pounds, or 15.8 percent. Achieving weight reductions of this size in a production truck is likely to be extremely expensive and require extensive analysis and development. Once requirements for cost-effectiveness are applied, it is likely that the application of efficiency technologies will push up empty weight. This has a slight negative impact on fuel consumption but a larger negative impact on freight efficiency, since the maximum legal payload will be reduced.

The vehicle-level demonstration tests were conducted in December 2013. Temperatures were low and winds were high (Damon, 2014). For the 24-hr duty cycle, the average

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³ E. Koeberlein, Cummins-Peterbilt, “Cummins SuperTruck Program: Technology and System Level Demonstration of Highly Efficient and Clean, Diesel Powered Class 8 Trucks,” presentation to the committee, May 14, 2014.

⁴ Ibid.

TABLE 8-4 Cummins-Peterbilt Project Results to Date^a

NOTE: Results are based on a comparison to the reference truck, run on the same route, with the two trucks about 1 min apart.

^aThe results presented in this table are based on data collected by the committee prior to May 2015. At the DOE Annual Merit Review in June 2015, David Koeberlein of Cummins presented the following results: “Developed framework and analysis for 55% thermal efficiency, completed analytical roadmaps for both diesel and dual fuel approaches, and completed targeted engine tests to validate roadmaps” (Koeberlein, 2015). However, the committee was not in a position to review these results from the June 2015 AMR.

wind during the driving portion was 14 mph, with gusts to 28 mph. For the basic drive cycle comparison, the average wind was 13 mph, with gusts to 33 mph. These high winds had the effect of driving up fuel consumption for both the baseline reference truck and the SuperTruck test vehicle. The difference in performance between the baseline and SuperTruck vehicles is likely to be at least slightly related to wind conditions, so a test in milder conditions might give slightly different results. The way the two vehicles’ C_d values vary with yaw angle will account for any difference in wind sensitivity.

The headline trip result of 10.7 mpg was achieved during a later test, where the average wind was 6 mph, with no gusts. This compares to a result of 9.9 mpg on the windy day. Additional results obtained with the Demo 2 (final version) SuperTruck tractor are summarized in Table 8-5. These tests are outside the scope of the program requirements, but they provide valuable insight.

The results shown in Table 8-5 reveal the very modest sensitivity of fuel consumption to weight increases above 65,000 lb but a more significant sensitivity to lower payload. Giving up the aerodynamic SuperTruck trailer and replacing it with a standard trailer with a skirt causes a fuel consumption increase of about 11 percent, which is very significant. Note that these results are affected by variations in wind conditions. Also note that the Table 8-5 results do not look at differences in performance on a given day, where the test truck is compared to a reference truck run at the same time, which is the most accurate way to determine differences.

The Cummins-Peterbilt team had its fleet partner, US Xpress, drive the Demo 1 level vehicle with a commercial load on a 950-mi route in Texas, using US Xpress drivers. US Xpress evaluated vehicle drivability and loading/unloading issues. As a result of this test, the access panel covering the trailer tandem was modified so that it could open 180 degrees for tire inspection. Another change implemented as a result of the fleet test was to make the trailer skirt pneumatically retractable for access to loading docks and for crossing crowned areas such as railroad tracks.

Cummins-Peterbilt Project Management

A committee subgroup visited with Cummins-Peterbilt and Eaton in Columbus, Indiana, on August 28, 2014. With one exception, the subgroup found the project to be well organized and well run. The only exception was that the project team was unaware of the flexibility they had under the contract to change plans. This caused a delay in moving away from use of a fuel cell APU after it became clear that the fuel cell’s issues could not be resolved within the project

TABLE 8-5 Additional SuperTruck Tractor Fuel Economy Results

scope. The subgroup was impressed with the way the project team took advantage of the program to improve their modeling and simulation capability. There were several situations where simulation and test results did not match, and the team reviewed these in detail to understand and resolve the differences. The improved simulation capabilities that resulted had an impact on the program, and they will also increase the ability of the team to deliver improved products in the future.

The subgroup asked the project team about its experience with DOE research programs. Cummins-Peterbilt emphasized the value of long-term (3- to 4-year) system integration projects. These projects are long enough to enable the contractors to recover and change plans when issues are encountered, and still successfully meet the project goals. In a short-term project, companies must take less risk in order to succeed. The project team felt that long-term system integration projects also provide extensive learning opportunities, develop useful relationships among partners, speed the progress of technology development, and build momentum toward production.

The committee asked Cummins about the relative value of one large, longer duration project, compared to several smaller projects. Cummins told the committee that they see more value in large, long-duration projects, even where limited funding means a lot of competition to win these projects.

DAIMLER-DETROIT DIESEL PROJECT

Table 8-6 lists the Daimler team members and their responsibilities.

Daimler used the 14.6 L DD15 engine for the 2009 baseline vehicle, the 12.8 L DD13 engine for its A-Sample truck, and a 10.7 L engine for the B-Sample (final demonstration) truck.⁵ Note that the 10.7 L engine is not currently offered in the North American market. It is sold in Mercedes trucks in Europe, under the name OM470. The 10.7 L OM470 represents a significant downsizing from the baseline DD15 engine. The smaller displacement brings weight, heat rejection, and packaging advantages over the baseline engine. On the other hand, power and torque are substantially reduced, and durability in long-haul applications is likely to be compromised. Power is down from 455 hp and 1,550 lb-ft in the baseline truck to 390 hp and 1,400 lb-ft with the 10.7 L engine, according to the Detroit Diesel 2014 AMR presentation (Singh, 2014) and subsequent communication from Daimler. Daimler did a study of vehicle performance on the selected SuperTruck routes and ensured that the SuperTruck achieved comparable performance on the following metrics: overall trip time, time spent at less than 30 mph, and time spent in top gear.

TABLE 8-6 Daimler Project Team Members

Based on these criteria, Daimler believes that the SuperTruck provides comparable performance to the baseline truck. Reduced vehicle power demand and assistance from the hybrid system are able to compensate for the lower engine power. However, certain aspects of performance, such as vehicle speed on a long grade, are still likely to suffer.

Conventional diffusion burn diesel combustion was retained, but with revisions to the combustion system

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⁵ D. Kayes, D. Rotz, and S. Singh, Daimler Truck North America LLC, “Super Truck Team Presentation: Daimler,” presentation to the committee, May 15, 2014.

(compression ratio, piston bowl, injector specification, and calibration) (Singh, 2014). Turbocharger efficiency is not discussed, but the EGR circuit was modified to reduce EGR flow, and the turbocharger was reoptimized to match the lower EGR rates. Changes were made to reduce cylinder kit friction. A variable-speed water pump is used to reduce parasitic power (as in one version of the current production DD15), and low viscosity oil is employed at a higher than normal operating temperature in an effort to reduce friction. The aftertreatment system was upgraded to allow for higher engine-out NO_x and lower backpressure. The engine was calibrated to produce higher engine-out NO_x on the SET cycle than the baseline engine, although the engine-out NO_x level is not specified. A waste heat recovery boiler bypass is integrated into the exhaust system. The bypass allows reduced vehicle heat rejection in situations where the cooling fan would otherwise have to be used. Since cooling fan power can be greater than the contribution of the WHR system, minimizing fan-on time is important to achieving low on-highway fuel consumption.

Singh (2014) mentions that engine downsizing and some of the engine efficiency measures result in challenges for cylinder block and head design, and for long-term high-load durability. These issues are driven by increased peak cylinder pressures (PCPs) and reduced oil film thicknesses. Noise, vibration, and harshness (NVH) and emissions are also mentioned as potential issues with the SuperTruck combustion system. Detroit Diesel Corporation worked with MIT on modifications to reduce heat rejection through the cylinder liners. Considerable effort has been made to implement model-based controls for the engine and the hybrid system.

Daimler made extensive modifications to the production truck cab to create the final SuperTruck demonstration tractor. The cab was widened to match the sleeper width, and the windshield has been raked back. The shape of the hood has been extensively modified to optimize aerodynamic efficiency with the smaller engine and angled cooling system. Mirrors were retained, but at the legal minimum size (about 1/3 of the baseline size) and with extensive aerodynamic optimization. The mirrors are supplemented by cameras. Daimler told the committee that the overall wind-averaged C_d (a weighted calculation of drag based on time spent at each yaw angle and wind speed)⁶ of the final demonstrator truck, including both the tractor and trailer, is about 50 percent lower than the baseline. Most of the improvement in C_d came from the trailer, despite extensive development work on the tractor.

If waste heat recovery works on an energy stream (such as EGR flow) that must be cooled anyway, there is no additional heat rejection demand on the vehicle. However, when exhaust energy downstream of the aftertreatment is captured by a WHR system, this represents heat that otherwise would simply flow out of the exhaust pipe. A portion of this heat will be converted into work, but the remainder must be rejected by the tractor’s cooling system. Because WHR and the cooling system for the hybrid battery place an additional heat rejection demand on the tractor’s cooling system, the team put significant effort into improving airflow through the cooling system and under the hood during fan-off operation. The cooling package is mounted at an angle, with the top of the package being farther back in the tractor. This makes an engine-driven fan impractical, so a hydraulic motor-driven fan is used. In addition, Daimler added active shutters to limit cooling air flow under the hood when it is not required. According to Slide 10 of the Daimler 2014 AMR (Rotz, 2014), the shutters improve C_d by 6 percent at zero yaw when they are closed, while reducing underhood airflow by 60 percent. It should be noted that the 6 percent represents C_d improvement measured on SuperTruck only, with its unique hood, cooling package, and underhood configuration. The shutter system is not expected to produce the same results on a production vehicle.

A diagram of the Detroit Diesel WHR system used in the final demonstrator vehicle is shown on Slide 11 of the Daimler 2014 AMR (Rotz, 2014). The basic layout is similar to the Cummins system shown in Figure 8-1, but there are a number of detail differences. Detroit Diesel uses ethanol rather than a refrigerant as the working fluid, and the Detroit Diesel system does not use a recuperator. The Detroit Diesel system uses a scroll expander rather than the turbine used by Cummins. The condenser on the Detroit Diesel system is an ethanol to water heat exchanger. The water then goes to the front of the truck to reject heat. In the Cummins system, the working fluid condenser is part of the cooling package at the front of the truck. The Detroit Diesel system description does not mention using energy from the coolant and lube circuits. Finally, the Detroit Diesel WHR system power output is used to generate electricity rather than being fed back to the engine crankshaft. The electricity can be used to power the vehicle HVAC system and other hotel loads, to power the hybrid motor, or to recharge the hybrid system batteries. It is worth noting that to the extent the SuperTruck engines reduce EGR flow (as they increase engine-out NO_x), the supply of high-quality heat for the WHR system is reduced. This has the effect of reducing the potential power that the WHR system can generate.

The Daimler hybrid system is a parallel system with a 120 kW motor and a relatively small 2.4 kWh battery. The motor power rating falls approximately midway between ratings for so-called “mild” and “full” hybrid drive systems for a Class 8 truck (NRC, 2010), while the battery capacity falls toward the mild end of the hybrid spectrum. As a result, the hybrid system represents an engineering compromise solution that prevents the battery from capturing most of the truck’s available braking energy, but it is significantly lighter, smaller, and less expensive than a comparable full hybrid drive system for this vehicle.

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⁶ See http://www.uwal.org/download/temp/Heavy%20Duty%20Truck%20Aerodynamics.pdf.

Daimler made a significant effort to get as much value as possible from the hybrid system. This was accomplished by a high level of integration of the hybrid drive into the vehicle’s overall system design, making it possible to use the same equipment for several different purposes. The hybrid system in the Daimler SuperTruck plays a role in engine starting, waste heat recovery, idle reduction, enabling electric air conditioning, and providing torque fill during transmission shifting. Torque fill is a feature that uses the electric motor to drive the axle during a shift event, while power from the diesel engine is interrupted, thus providing smoother vehicle acceleration.

Daimler Trucks uses the hybrid system battery to handle hotel loads during sleeper use. The 2.4 kWh battery cannot cover hotel loads for the entire night, so the engine will restart automatically when required to recharge the battery. The hybrid system battery also provides engine start power, eliminating all but one of the 12 V lead acid batteries. The hybrid battery has four sources of power: regenerative braking, the waste heat recovery system, solar panels on the trailer roof, and, finally, engine power fed to the motor/generator. Engine power is not used to charge the battery on the highway because of the power transformation losses involved. Despite the extensive system integration effort, Daimler told the committee that the hybrid system was not cost-effective, given its high cost, its modest fuel savings on a long-haul cycle, and competition from the low-cost eCoast functionality. The eCoast feature provides a significant portion of the fuel savings that can be achieved by a hybrid in a long-haul application, but eCoast is only a software control feature, with no additional hardware required.

The Daimler SuperTruck uses a production 12-speed automated manual transmission (AMT) made in-house by Daimler. The production design was modified to allow incorporation of the hybrid system motor. The calibration of the AMT was revised to accommodate the hybrid system and to keep the engine closer to its optimum operating point. A feature called eCoast has been added (Rotz, 2014, Slide 6). This feature disconnects the engine from the driveline when the vehicle power demand is zero and allows the engine to drop to idle. eCoast comes into play on gentle downhill grades and any time the driver wants to gradually slow the truck. The use of e-Coast preserves vehicle inertia, since the energy is not used to spin the engine. That inertia then reduces the fuel required the next time the vehicle demands power. In other words, the vehicle is its own energy storage device, in which energy is stored in the form of kinetic energy. Volvo Trucks currently offers a similar feature in some of its production trucks under the trade name Eco-Roll (Volvo Trucks, n.d.), and Cummins has announced a similar system for 2015 production availability.

The Detroit Diesel approach to the 55 percent BTE requirement is described in Chapter 3. Daimler Trucks and Detroit Diesel selected two routes on which to evaluate their SuperTruck vehicles (Rotz, 2014). A third route was added later (conference call with Rotz, 2015). The first route runs from Dallas to San Antonio in Texas, using I-35. This route has frequent minor grade fluctuations of ±0.5 percent to 1 percent) due to numerous underpasses, along with a few more significant hills of up to ±5 percent grade. The I-35 route is run at 65 mph, which tends to favor aerodynamic improvements. This route was given a 64 percent weighting on a time basis by Daimler, meaning that 64 percent of the driving portion of the 24-hour drive cycle consisted of the I-35 route. The second route is from Portland to Canyonville in Oregon, using I-5. This route has significant segments that are flat or nearly flat, along with some hills with grades up to about 6 percent. The Oregon route is run at 58 mph, just above the state speed limit of 55 mph. This route was given a 28 percent weighting, since there are more states with a truck speed limit of 65 mph or greater than states with a 55 mph limit. Daimler Trucks did not compare the grade distribution on these routes to that of the national road network, but they appear to the committee to represent reasonably typical routes. The third route, which was given an 8 percent weighting, used local urban highways in the Portland area. This route was meant to represent getting from the loading dock out to the long-haul route.

Because the Daimler SuperTruck includes a hybrid system, the results reported below are based on having the battery in the same state of charge at the beginning and end of each test. The headline test result of 12.2 mpg on the San Antonio to Dallas I-35 route is an average of 5 round-trip runs of approximately 400 miles each, all made at a cruise speed of 65 mph. This result was publicly announced at the Mid-America Truck Show in March 2015. The 12.2 mpg number translates to 206 ton-mi/gal, or 4.85 gal/1,000 ton-mi. These are the best results reported so far in the SuperTruck program, but remember that test routes and test conditions vary, so results are not directly comparable.

Daimler-Detroit Diesel Project Results

Based on Table 8-7, some calculations can be made to determine the relative contribution of engine efficiency and vehicle power demand. Assuming that the 2009 baseline Detroit engine had a BTE of 44 percent, the reduction in vehicle fuel consumption due to improved engine efficiency is about 12.4 percent. Average vehicle fuel consumption on the two long-haul cycles was reduced by 47.4 percent, so about 35 percent fuel consumption reduction is due to vehicle power demand reduction, including the effect of the hybrid system. These same data can be expressed in another way: Of the total vehicle fuel savings on the long-haul drive cycle, about 26 percent is due to engine efficiency improvements and 74 percent to vehicle power demand reduction. Additional results include these:

• Reduction in C_d: 54 percent (final demonstrator, scale model wind tunnel result) (Rotz, 2014, Slide 14).

TABLE 8-7 Daimler Trucks and Detroit Diesel Project Results to Date^a

NOTE: FC, fuel consumption.

^aThe results presented in this table are based on data collected by the committee prior to May 2015. At the DOE Annual Merit Review in June 2015, Sandeep Singh of Detroit Diesel Corporation presented the following results: “Achieving 55% BTE is expected to require advanced combustion strategies such as DF-LTC (dual fuel and low temperature combustion), plus additional improvements in parasitic reductions, component efficiencies, WHR, etc. beyond those achieved during SuperTruck. Daimler and ORNL look to continue DF-LTC efforts beyond SuperTruck to address these issues” (Singh, 2015). However, the committee was not in a position to review these results from the June 2015 AMR.

• Net vehicle weight reduction/payload increase: 1,550 lb (A-Sample truck) (Rotz, 2014, Slide 12) and 2,800 lb on the final demonstrator (conference call between Tom Reinhart, committee member, and Derek Rotz, Daimler, April 19, 2015)
  • —Details of weight reduction/increases were not provided.
• Distribution of aerodynamic drag reduction:
  • —Trailer aerodynamic improvements: 72 percent of the total vehicle improvement, with 1/3 of the aerodynamic engineering effort.
  • —Tractor aerodynamic improvements: 28 percent of the total vehicle improvement, with 2/3 of the aerodynamic engineering effort.

It is somewhat surprising that Daimler’s wind tunnel test results show that tractor and trailer aerodynamic benefits are independent of each other (Rotz, 2014, Slide 14). In a simple test that involved swapping between the baseline and final demonstration levels of tractor and trailer, no synergy was found for the highly aerodynamic final demonstration tractor and trailer. Other researchers have found that tractor and trailer aerodynamics do depend on each other, so this result may represent an unusual case. It is also worth noting that the Daimler Trucks trailer design is compatible with standard tractors, unlike the Cummins-Peterbilt trailer design, where the tractor and trailer form a matched set.

In many cases, when individual technologies are combined into a package, the fuel saving is less than the sum of the individual contributions. This is always the case where multiple technologies target the same source of energy loss, but it can also occur when unrelated technologies are combined. For example, if average vehicle power demand is reduced by lowering aerodynamic drag and tire rolling resistance, the engine may spend more time at light load, where it is less efficient. On the other hand, Daimler reported at least one instance where the whole benefit from a package of features is greater than the sum of the parts. Reducing vehicle power demand has the effect of increasing the performance of the eCoast feature, since as aerodynamic drag and tire rolling resistance are reduced, the vehicle power demand drops below zero more often. In other words, it takes less of a negative grade to produce a zero power demand condition as C_d and C_rr go down, so the eCoast feature has more kinetic energy to work with.

Daimler-Detroit Diesel Project Management

A committee subgroup visited Daimler Trucks North America in Portland, Oregon, on October 17, 2014. Another subgroup visited Detroit Diesel Corporation on November 24, 2014. The subgroup that visited Daimler Trucks was impressed with the way the project team was taking advantage of the program to improve its modeling and simulation

capability for vehicle aerodynamics, and its fuel economy test capability. The improved simulation and test capabilities had an impact on the program, but they will also increase the ability of the team to deliver improved products in the future.

Detroit Diesel feels that the single operating point 55 percent BTE target is not as attractive as improving efficiency over a realistic on-road duty cycle. It also pointed out the advantages of a system integration project like SuperTruck compared to component-level development projects. When integrating the complete system, Daimler made some discoveries about the real-world performance of certain technologies that were quite different than projections from simulation and test cell operation. SuperTruck drove the integration of many engine and vehicle technologies that had been previously considered only on a stand-alone basis.

Some Daimler suggestions for future research opportunities are these:

1. Development of WHR systems to achieve lower cost, weight, and complexity, along with higher performance;
2. Development of advanced combustion technologies such as dual fuels; and
3. Development of friction reduction technologies for a high-cylinder-pressure engine.

Overall, Daimler was very enthusiastic about the SuperTruck program. One manager called it “one of the best government projects ever.” By doing a complete vehicle, Daimler learned about the potential of many technologies, as well as issues and limitations that stand in the way of introducing some of these technologies.

VOLVO PROJECT

Because the Volvo SuperTruck project did not begin until June 2011, it was not included in the NRC Phase 2 report on 21CTP. The project is expected to be completed by June 2016. Volvo elected to divide the project into two phases. Phase 1 delivered a concept evaluation vehicle (VEV-1, or mule). This vehicle was used to validate candidate technologies during 2013. Phase 2 will deliver a final SuperTruck demonstrator that will include the technologies validated in Phase 1, as well as additional technologies and refinements.

The total cost of the project is projected to be $38 million, with 50 percent cost sharing. This total is about half of the budget for the other SuperTruck projects. As of September 2014 the total spent was $24 million; as of June 2015, $26 million was spent (Amar, 2015). A list of the key team members and their contributions is provided in Table 8-8.

Phase 1 Technologies and Results

The tractor selected for the Phase 1 mule (VEV-1) was a model VNL 670 (Figure 8-2). The wheel fairings were modified for reduced drag. LED lighting was used for both internal and external lights to reduce electrical power demand and weight. The trailer was also equipped with LED lighting. Volvo calculates that equipping both tractor and trailer with efficient LED lighting in place of the standard incandescent system can save up to 120 gal/yr of fuel (DOE VTO, 2013). The use of LED lighting allowed the use of light gauge wiring for weight reduction.

TABLE 8-8 Volvo SuperTruck Collaborators and Partners

According to Volvo’s 2013 FY progress report for vehicles systems simulation and testing, VEV-1 was upgraded with a new and lighter 6 × 2 axle configuration, a prototype proprietary lighter weight suspension, lightweight aluminum wheels, and wide-based low rolling resistance tires (DOE VTO, 2013). In addition, the standard two-piece driveshaft was replaced with an aluminum one-piece unit that provided a 25 percent reduction in weight. The total weight savings from these components was approximately 900 lb.

FIGURE 8-2 Volvo VEV-1 preliminary demonstration vehicle. SOURCE: Amar (2013).

The Volvo team used complete vehicle CFD simulations to design and optimize aerodynamic parts or add-on devices for the tractor and the trailer. Freight Wing’s latest designs for trailer aerodynamic devices were used as a starting point for the vehicle aerodynamic simulations. In parallel with the aerodynamic optimization activities, Freight Wing explored opportunities to make the trailer add-on devices more practical from an operational perspective. In particular, new methods for enabling the tail fairing geometry to fold and provide convenient access to cargo were investigated. Different materials including reinforced composite panels were also evaluated for opportunities to improve product durability. The intent was to make the aerodynamic geometry that has proven to be effective in prior work as practical as possible for real-world utilization and production.

Prototype parts corresponding to the designs simulated through CFD were fabricated and installed on VEV-1. Primarily these included tractor wheel skirts, trailer skirts, and a trailer tail, which were tested under real-world conditions during the fuel economy tests. Tests results demonstrated a 13 to 15 percent fuel consumption reduction for the complete vehicle, compared with the MY 2009 baseline (DOE VTO, 2013). This correlated very well with the simulated aerodynamic drag reduction of 30 percent for the corresponding geometry, and confirmed the accuracy of the CFD methods.

For Phase 1, Volvo chose its 13 L engine (DOE VTO, 2013). This choice was made because the 13 L is Volvo’s highest volume production engine, and the 2009 baseline vehicle was equipped with a 13 L engine. The basic engine improvements included high-pressure common rail fuel injection (in place of the production engine’s unit injectors), revised piston bowl geometry, reduced-friction power cylinder components, advanced lube and coolant pumps that reduce parasitic losses, and a mechanical turbocompound system.

A Generation 1, Rankine-cycle WHR system was also included in Phase 1. The WHR system exceeded previous performance in steady-state operation, despite the addition of a more efficient combustion chamber and turbocompounding, both of which reduced the heat available to the system. Energy recovery was possible during nearly all positive power operation, with interruptions during coasting or engine brake operation. The advanced power train system installed in the VEV-1 chassis successfully completed multiple on-road tests with varying route profiles and vehicle loads (DOE VTO, 2013).

The lower exhaust temperatures resulting from the turbocompound and improved combustion efficiency created some additional challenges for efficient function of the exhaust aftertreatment system (EATS). A chemical model of the EATS was developed for the unit delivered as part of VEV-1, allowing for transient evaluation of the EATS in the SuperTruck environment.

TABLE 8-9 Volvo 2009 Baseline Test Results

The transmission choice for Phase 1 was a 12-speed dual clutch unit (DOE VTO, 2013). A dual clutch transmission eliminates power interruptions during shifts. The elimination of power interruptions enables performance improvements for both WHR and turbocompounding, since they no longer need to deal with the rapid changes in engine gas flow and temperature that are characteristic of normal shifting with a manual transmission or an AMT. The dual clutch transmission also allows for further engine downspeeding, since shifts are both more comfortable and without power interruption. As a result, a driver will tolerate higher shift frequency with a dual clutch than with an AMT.

Advanced lower-friction lubricants were used in all power train components as well as axle bearings. These lubricants include synthetic low viscosity oil for the transmission and axle. Volvo provided the committee with baseline test results for its 2009 model truck. These results were measured at a steady speed of 65 mph on level ground. Results are averaged for two directions to minimize the impact of wind and minor grade fluctuations. These results, shown in Table 8-9, cannot be directly compared to results from the SuperTruck test program, which are run over a defined on-highway drive cycle. However, the baseline test results do give a good view of the starting point for the Volvo SuperTruck work. SuperTruck results against the program goals for Phase 1 are shown in Table 8-10. Phase 2 (final) results of the Volvo program are expected in 2016.

Volvo Phase 2 Plans and Progress

The Phase 2 vehicle is referred to as VEV-2 or as the demonstrator. A very aggressive approach was taken for weight reduction for the demonstrator. A prototype ultralightweight frame assembly was designed in 2013 and delivered on schedule in the first quarter of 2014 (see Figure 8-3). The weight savings achieved was 800 lb, exceeding the internal target of 40 percent compared with the equivalent steel frame ladder. The subsequent assembly of axles and chassis-mounted components uncovered no issues with the design. Work is under way to build a second vehicle for track evalu-

TABLE 8-10 Volvo SuperTruck Phase 1 Results^a

SOURCE: Amar (2014).

^aThe results presented in this table are based on data collected by the committee prior to May 2015. At the DOE Annual Merit Review in June 2015, John Gibble of Volvo presented the following results: “50% BTE engine component development is complete. System integration and test is ongoing” (Gibble, 2015). Volvo also reported simulation results suggesting that 56.2% BTE could be possible, and 48% BTE without waste heat recovery. The final demonstrator vehicle build is under way. However, the committee was not in a position to review these results from the June 2015 AMR.

ation and data collection and to perform further analysis on the chassis assembly.

For the Phase 2 (final) demonstrator truck, Volvo selected its 11 L engine, which is 400 lb lighter than the 13 L used in VEV-1 (Gibble, 2014). The 11 L is calibrated to produce 425 hp, compared to 485 hp for the 2009 baseline 13 L engine. Volvo expects the 11 L to at least match the 1,650 lb-ft torque of the 13 L. It projects that the lower vehicle power demand will result in comparable vehicle performance, although there may be slight misses in low-speed acceleration rate and in speed on steep grades. Similar fuel efficiency improvement technologies that were incorporated into the 13 L engine in Phase 1 are included in the Phase 2 11 L engine: high-pressure common rail fuel injection, revised piston bowl geometry, reduced friction power cylinder components, advanced lube and coolant pumps, and turbocompounding. The final demonstrator vehicle will also include an aftertreatment system with new developments to improve conversion efficiency and reduce package size.

For the Phase 2 WHR system, Volvo is focusing its efforts on weight and cost reduction and improved reliability. Working toward the goal of 50 percent BTE, Volvo has operated three engines in test cells, as well as six component-level test stands. These activities are maturing the various technologies in parallel.

In order to maximize overall HVAC system efficiency, cab insulation was increased, and the efficiency of the heating and cooling systems was improved. The energy management system is designed to always select the most efficient energy source/storage system to power typical hotel mode loads (DOE VTO, 2013).

To investigate the potential for various idle reduction concepts, it was necessary to understand the detailed energy usage and balance over a 24-hour period. Several shorter road cycles were combined with a number of stops and engine-off events to form 24-hour cycles. The proportion of the different types of roads (flat, hilly, etc.) was verified by Volvo to be representative of typical North American long-haul operation. A 24-hr electrical load consumption profile was developed using representative electrical configurations, historical weather conditions, and other factors, in order to help size and optimize the hotel load systems. With such a

FIGURE 8-3 Prototype Volvo aluminum tractor frame. SOURCE: Amar (2014).

load profile, it was possible to establish rough requirements for energy storage capacity and potential fuel savings.

The requirements established for the APU included 10,000 Btu for cooling, 10,000 BTU for heating, flexibility to operate during driving and when parked in hotel mode, and the ability to operate from a battery pack or from shore power. A supplier has been selected, and the design direction was decided in early 2013. The first prototype system was bench tested in late 2013, and the first chassis installation took place early in 2014 to identify any changes necessary to the design prior to the final assembly.

The application of intelligent controls includes both a more fuel-efficient “look-ahead” GPS-type cruise control and the management of power-consuming auxiliaries. In cruise, the vehicle will legally accelerate on downgrades but will hold a gear and reduce speed slightly while cresting a hill. Auxiliaries will be engaged during downhill operation to maximize the use of available vehicle kinetic energy. Modeling work done by Volvo predicts that these intelligent controls will provide the following fuel economy improvements: rolling terrain 3 to 5 percent, and hilly terrain 5 to 8 percent. The development of the Phase 2 power train and vehicle is progressing. A technology package to enable the 11 L engine to meet the 50 percent BTE target at cruise has been defined, and performance development work is under way. Volvo told the committee that it plans to have the final demonstration vehicle completed and begin testing it in the fourth quarter of 2015.

Volvo has listed some issues and barriers that need to be dealt with before certain SuperTruck technologies can go into production (Gibble, 2014):

• Cost-effective and timely evaluation of advanced components and configurations;
• Added weight, packaging difficulty, and complexity of certain technologies;
• Reduced aftertreatment efficiency at low exhaust temperatures (a natural result of engine efficiency improvement and vehicle power demand reduction);
• Integration of interdependent technologies; and
• Operational effectiveness and end-user acceptance of advanced concepts.

Volvo’s 55 percent BTE effort is discussed in Chapter 3.

Volvo Program Management

Volvo, like the other original equipment manufacturers (OEMs), also noted how SuperTruck allowed much more extensive technology development and learning from system integration. A large integration program like SuperTruck allows:

• A wide scope of technologies to be evaluated,
• A range of technologies from short term to exotic to be evaluated, and
• Vehicle-level targets drive more innovation than component-level targets.

Volvo noted that a number of graduate students have been developed as a result of SuperTruck funding, and several of them are now working in the industry, making use of the ideas they worked on under the program. Volvo expects some of the features developed under the SuperTruck program to be in production soon. The committee was shown a 2016 model tractor, which incorporates some aerodynamic features first developed for SuperTruck. Volvo had some suggestions for potential follow-on projects:

• Platooning,⁷
• Regional haul, and
• Vocational trucks

The discussion around regional haul focused on one main question: Is the regional haul duty cycle different enough from the long-haul cycle to drive different technical solutions? This is a question that could itself form the basis of a research project. One difficulty with a vocational truck project is that there are so many types of vocational operations to choose from, not one of which accounts for a really large portion of medium- and heavy-duty vehicle fuel consumption. Some care would be needed to define a vocational project that would develop technologies applicable across a fairly wide range of vocational applications.

NAVISTAR PROJECT

The Navistar SuperTruck project is unique among the projects in one way: the Navistar project was initiated in the fourth quarter of 2010 but put on hold in the third quarter of 2012. Navistar resumed work on November 1, 2014, after a 2-year pause. As a result, this project will be completed well after the other SuperTruck projects. The current schedule calls for completion at the end of 2016. Navistar provided a listing of project partners and suppliers in 2011, but in its November 2014 presentation to the committee, it stated that it had reduced the list of partners from 8 to 2 (Zukouski, 2014, slide 2) without identifying them to the committee. The Navistar presentation to the committee did list Wabash as the trailer partner, Michelin as the tire partner, and Lawrence Livermore National Lab as an aerodynamics partner. A revised list of partners and suppliers has not been provided to the committee. Navistar presented their plans and results to date to the committee on November 18, 2014 (Zukouski, 2014). Navistar will retain the baseline 13 L engine, with extensive changes to reduce friction, reduce heat loss, improve combustion efficiency, and reduce parasitic

________________

⁷ See Chapter 9 for further discussion of platooning.

losses. Work is under way to improve the efficiency of the air handling system (EGR, turbocharger, ports, and valve events). Navistar has not defined if or by how much the SuperTruck power and torque curves might vary from the baseline engine.

Navistar’s November 18 presentation shows that conventional diesel combustion was retained, but with revisions to the combustion system (compression ratio, piston bowl, injector specification, and calibration) (Zukouski, 2014). Several turbocharger efficiency options will be evaluated, including ball bearings, e-boost (an electric motor/generator that can either help spool up the turbocharger when more boost is required, or extract electrical energy from the exhaust when boost is adequate), and turbocompound. However, initial results with turbocompounding show a net loss at the cruise point (Zukouski, 2014, slide 14). Changes were made to reduce cylinder kit friction. A variable-speed water pump and variable-displacement oil pump are used to reduce parasitic power, and low-viscosity oil is employed at a higher than normal operating temperature in an effort to reduce friction. The aftertreatment system was upgraded to allow for higher engine-out NO_x and lower back pressure. The engine was calibrated to produce higher engine-out NO_x than the baseline engine. In response to a question during the public session of the November 18 committee meeting, Navistar stated that engine-out NO_x would increase to 6 g/hp-hr.

The original Navistar plan called for a 360 kW, 700 V series hybrid system. This system proved to be very heavy, expensive, and complex for a modest fuel saving performance, so it was dropped from the project. Navistar is still considering a 48 V mild hybrid system that would recuperate some braking energy and allow for electrification of accessories. The system includes a 48 V motor/generator, a supercapacitor, an electric A/C compressor, and a nickel-zinc (NiZn) battery (Zukouski, 2014, slide 25).

Navistar plans to use a direct drive automated manual transmission combined with a prototype axle ratio of 1.91:1 (Zukouski, 2014, slide 8). This would provide a cruise rpm of just under 1,050 rpm at 65 mph in a direct drive top gear. An alternative ratio of 2.05:1 would allow a cruise speed of about 1,125 rpm with a direct-drive top gear. Navistar projects the fuel savings from a direct top gear to be 1.5 percent, with additional fuel savings coming from the low cruise rpm.

Navistar is considering a couple of aerodynamic technologies that are not in the other SuperTruck team plans. One is active ride height and pitch control, which is the subject of an invention disclosure. Another item is an active trailer gap/flow control device. The list of controls features such as smart cruise control, and parasitic power demand reduction features is similar to that of the other SuperTruck teams. One possibly unique feature is “intelligent air control with dryer,” which is not further described (Zukouski, 2014, slide 31).

Navistar’s weight reduction plans include a large weight reduction effort on the trailer, where a 3,700 lb weight reduction is projected (Zukouski, 2014, slide 29). Trailer features include composite nose, sides, roof, rear door, and skirts, along with a 1.125 in. thick aluminum composite floor, aluminum cross members, light weight landing gear, and a new boat tail. The tractor weight reduction is targeted at 3,250 pounds, including:

• Composite cab (240 lb),
• MMC brakes (tractor and trailer, 600 lb),
• Light driveshaft and axles (190 lb),
• Aluminum wheel hubs and bearings (150 lb),
• Aluminum engine and transmission mounts (50 lb),
• Aluminum intensive rear suspension (370 lb),
• Thin wall, advanced material, and downsized fuel tanks (500 lb),
• Aluminum wide base single wheels (350 lb), and
• Michelin wide-base single tires (350 lb).

Navistar Project Results

Table 8-11 lists the results achieved by the Navistar team as of April 2015. Keep in mind that work has just resumed, after a 2-yr hold.

Navistar’s 55 percent BTE effort is discussed in Chapter 3.

Navistar Program Management

Because Navistar has been out of the SuperTruck program until recently, the committee is not in a position to review program management.

OVERALL SUPERTRUCK PROGRAM REVIEW

The consensus of the committee is that the SuperTruck projects have provided a significant advancement in the state of the art. By combining a large number of technologies into complete, running vehicles, many useful results have been obtained, such as

• Some entirely new technologies have been developed and implemented;
• Some existing technologies have had their performance improved;
• Technology combinations that have never been tried before were evaluated;
• Cost/benefit information on many technologies has been developed, although most of this information will remain proprietary to the companies involved;
• Participating companies have improved their fuel efficiency simulation and test capability;
• Participating companies have already selected certain technologies for either continued development or production implementation; and
• Importantly, participating companies have the information to decide which technologies are not worth further development.

TABLE 8-11 Navistar Project Results to Date^a

^a The results presented in this table are based on data collected by the committee prior to May 2015. At the DOE Annual Merit Review in June 2015, Russ Zukouski of Navistar presented the following results: Engine BTE of 48.3% demonstrated, and 50% planned in early 2016 (Zukouski, 2015). The remaining plans presented in the 2015 AMR match the table above. However, the committee was not in a position to review these results from the June 2015 AMR.

The two teams that have finished their vehicle demonstrations (Cummins-Peterbilt and Daimler/Detroit) have produced results substantially better than the targets called for in the SuperTruck contracts. Their results are very impressive and represent substantial achievements by the two teams. Both teams just cleared the 50 percent engine BTE target, but they went well beyond the goals for overall freight efficiency improvement. It is clear to the committee that competition among the teams drove them to go well beyond the contract requirements. The remaining two teams are expected to try to match or beat the results already posted.

The program could be criticized on the grounds that the four SuperTruck teams have in many cases converged on similar technical solutions. However, there are enough differences between the four trucks to provide alternative approaches to many technologies. For example, there are hybrid and nonhybrid vehicles, and there are single and dual clutch transmissions. There is also some variation in the approach to aerodynamics. One team chose an integrated tractor-trailer approach, where the vehicle must be used as a set. Other teams chose an independent approach, where the SuperTruck tractor could pull a standard trailer, or the SuperTruck trailer could go behind a current tractor. Several other features could be listed that are unique to one or two of the teams.

Another difficulty with the SuperTruck program is the lack of a common point for comparing the results of the four SuperTruck teams. Each team chose its own baseline (a 2009 model engine and vehicle, not all of which were identically equipped) and its own test routes (similar in concept, but never identical). As a result, if two teams both state that they achieved an x percent reduction in fuel consumption, this does not necessarily mean that they ended up with identical fuel consumption. Their baselines and test routes differ, so x improvement for one team cannot be directly compared to x for another team. The same issue applies to results such as x miles per gallon or y gallons per 1,000 ton-miles. Since these results were obtained on different test routes, they are not directly comparable. Unfortunately, there are no plans to test either the baseline vehicles or the final demonstration vehicles under comparable conditions.

Another issue that the committee found in the SuperTruck program is that teams are allowed to take any net reductions in empty vehicle weight and increase the payload to maintain the same operating weight. For vehicles that run at maximum legal weight (80,000 lb in most cases), this is an appropriate approach. However, many vehicles “cube out,” i.e., run with the trailer full at a gross vehicle weight (GVW) of less than 80,000 lb. To account for this, the SuperTruck program specified a 65,000 lb test weight. To allow the teams to take credit for increased payload at a 65,000 lb GVW artificially inflates the apparent benefits of the weight reductions achieved by the SuperTruck teams. A more realistic accounting for the benefit of weight reductions would factor in the limited percentage of vehicles that can actually turn an empty weight reduction into increased payload.

DOE has selected the working GVW for 21CTP at 65,000 lb, which is near the average GVW value but not necessarily representative of typical truck operating weights. In practice, trucks tend to run near 80,000 lb when full (with exceptions), and then near 34,000 lb when running empty. This is shown by weigh-in-motion (WIM) data collected by DOT, as shown in Figure 5-4 (Quinley, 2010). The figure shows that 65,000 lb is actually a rather unusual operating condition.

It is also clear that a 65,000 lb truck is an inefficient vehicle by international standards in terms of cargo mass capacity (the amount of payload weight that can be carried, which in turn affects LSFC). This makes a 65,000 lb truck inconsistent with the essential requirements of an exemplar future truck. The consequences of low-cargo-weight limited vehicles could be significant, because more efficient vehicles would require fewer trips for a given freight task, thereby reducing fuel use and emissions by virtue of the lower number of trips required (exposure). Weight limits would also influence crash frequency, given that they are related to exposure (Woodrooffe, 2001; Montufar et al., 2007). A further possible unintended safety consequence of choosing the lower GVW target of 65,000 lb is that engine downsizing and power reduction become viable strategies for reducing

fuel consumption, which can have an impact on vehicle speed performance in the fully loaded condition, particularly on grades. The resulting speed differentials relative to other vehicle classes may constitute a safety hazard. It appears that the four SuperTrucks in the current program have enough power to comply with the contract requirement calling for comparable performance, with the possible exception of speed on a long grade in the case of the Daimler/Detroit and Volvo trucks.

Safety systems development and evaluation were not part of the contractual requirements of the SuperTruck program, so there has been no reported safety development activity.

The committee did not observe any apparent safety issues with the SuperTruck vehicles. One technology that will require some safety related review as development continues is the waste heat recovery systems. These systems often use a flammable working fluid under considerable pressure, so provisions to mitigate fire risk must be in place.

Appropriate Federal Role

The SuperTruck program covered a range of technologies from relatively straightforward items that can be quickly implemented to high-complexity, high-risk, long-term technologies such as WHR systems. It could be argued that the government role does not extend to the short-term, low-risk technologies, but never before have so many fuel-saving technologies been brought together into actual vehicles for on-road testing. The committee finds that the industry on its own would never have put together such an extensive vehicle integration project. The high level of learning and advancement of the state of the art that came from the SuperTruck program is exemplary for the sort of results that government-sponsored R&D is meant to achieve.

SuperTruck Future

The committee believes that there are roles for a range of R&D projects under the 21st Century Truck Partnership. These could range from gathering and analyzing data from field operations, to the development of specific technologies, to large technology integration programs like SuperTruck. The clear benefits of the SuperTruck programs mean that follow-on projects would be welcome. However, budget realities mean that it will not be possible to fund four projects of such a magnitude at the same time in the foreseeable future. An alternative approach would be to competitively fund one large program every year or two. Potential future topics are discussed in the Program Management sections of this chapter and in the Findings and Recommendations section.

One of the ideas for a follow-on project—a SuperTrailer program—is brought up in Recommendation 8-2. The idea for such a program stems from the following circumstance: Trailer manufacturers have little engineering capability in aerodynamics despite the fact that trailer aerodynamics accounts for a significant portion of the fuel savings for all of the SuperTruck programs. Because trailer makers have limited capability, truck OEMs and specialist suppliers took the lead in developing SuperTruck trailer aerodynamic features. A SuperTrailer program could help to grow an engineering capability among trailer manufacturers.

In considering possible future vehicle integration programs, DOE and 21CTP need to consider a number of issues, such as

• Does the regional haul duty cycle differ enough from long haul that it would result in a significantly different technical solution from the current SuperTruck program?
• Can a vocational SuperTruck project be defined that covers enough vocational applications to represent a worthwhile portion of total medium- and heavy-duty fuel consumption?
• Would a SuperTrailer program have sufficient research content to justify government funding?
• Should a project target 55 percent BTE at the best point, or should some other metric be devised that better represents actual on-road engine efficiency?

At the February 17, 2015, committee meeting, Ken Howden of DOE explained that the DOE is planning to start a SuperTruck 2 project in 2015. Under the current plan, there will be a single winning team, and the goal will be a 100 percent improvement in freight efficiency over a 24-hour duty cycle (50 percent LSFC reduction). This project is meant to build on the existing accomplishments of the SuperTruck teams. The project may also involve consideration of regional haul applications. This presentation was made before Daimler/Detroit announced its 115 percent freight efficiency improvement over a 24-hour cycle, so the goals may be revised.

21CTP Partnership Responses to NRC Phase 2 Recommendations

Recommendation 3-2 in the NRC Phase 2 report (NRC, 2012) asked DOE to ensure that the 50 percent engine BTE requirement gets a sufficient share of the SuperTruck funding and that previous DOE-funded research be utilized to give a good chance of success. The Partnership replied that this was indeed the case, and that the contractors working on the SuperTruck programs had already participated in a number of DOE-funded research projects related to engine efficiency, with considerable success. Given the success to date of the three SuperTruck teams who have been working continuously on the 50 percent BTE goal since 2011, the committee agrees that the Partnership has done a good job of promoting development of 50 percent BTE engines. Two SuperTruck teams have met the 50 percent BTE goal, and the other two teams have plausible plans in place to meet the goal.

The NRC Phase 2 Recommendation 5-1 suggested that the Partnership consider setting a stretch goal of a 40 percent reduction in aerodynamic drag, compared to the existing goal of 30 percent. The Partnership responded that it would consider adjusting its goals,based on results obtained from the SuperTruck program. Cummins-Peterbilt claims a 46 percent C_d reduction from 2009,⁸ while Daimler/Detroit Diesel has shown 39 percent C_d reduction in scale-model wind tunnel testing (Singh, 2014) and Volvo has demonstrated 30 percent C_d reduction but plans to reach over 40 percent.⁹ It now appears that all four SuperTruck programs will probably approach or even exceed the 40 percent target suggested in the NRC Phase 2 report.

The NRC Phase 2 Finding 6-3 and Recommendation 6-3 concluded that the Delphi solid oxide fuel cell APU prototype was, after 10 years of DOE funding and development, far from meeting performance criteria suitable for truck applications. A reassessment of the solid oxide fuel cell program was called for to determine whether it made sense to continue development. This recommendation was not taken up by the Partnership, but after another year of continuing development issues, the two SuperTruck teams using the solid oxide fuel cell dropped it. Delphi has since discontinued its effort to develop the solid oxide fuel cell APU.

The NRC Phase 2 Recommendation 8-1 asked that LSFC be used as the metric for the SuperTruck program (gallons per 1,000 ton-miles). The Partnership responded that the fuel economy metrics of ton-miles per gallon had been part of the initial solicitation and could not be changed. However, the Partnership promised that it would “present the results for SuperTruck … in terms of reductions in fuel consumption … wherever possible.” In reviewing reports on SuperTruck activity, such as the Annual Merit Reviews and presentations made to the committee, the committee finds no indication that the Partnership has actually started to provide results in terms of LSFC. Indeed, the LSFC values in this report had to be calculated by the committee from fuel economy data provided by the SuperTruck teams.

The NRC Phase 2 Recommendation 8-2 asked that the SuperTruck contractors agree on “at least one common vehicle duty cycle that will be used to compare the performance of all three [now four] SuperTruck vehicles.” The Partnership responded that different OEMs were developing with different customers in mind, and that using a common test protocol for all the vehicles would be prohibitively expensive. The committee finds the first objection to be questionable, given that all four SuperTruck projects are aimed at long-haul vehicles with identical payloads and performance targets. However, while getting all four vehicles together for joint testing (or at least the three vehicles likely to be available soon) would admittedly be quite expensive, getting accurate data for comparison does require running vehicles over the same route at the same time. The committee believes that a comparison test under identical conditions would be very useful, and suggests that additional funding be found to support such a test.

FINDINGS AND RECOMMENDATIONS

Finding 8-1. Overall, the committee finds the SuperTruck program to be a great success, and that the system integration aspect of SuperTruck was a key to the program’s success. The SuperTruck program drove technology development at a faster pace than industry would have achieved on its own. SuperTruck teams used the program to do the following:

• Increase both test and analysis capabilities, and improve the correlation between test and analysis;
• Use simulation results to drive improved experimental techniques, and use experimental results to help improve simulation techniques;
• Integrate combinations of technologies that had never been tested on a complete vehicle before;
• Learn about opportunities, issues, and trade-offs with fuel saving technologies in real-world vehicle testing; and
• Understand the challenges that must be overcome in order to make certain technologies cost effective.

Finding 8-2. The Cummins-Peterbilt and Daimler SuperTruck teams have met the goal of an engine with 50 percent brake thermal efficiency (BTE) at the cruise power point, and the other two teams are working to meet this goal. The Cummins and Daimler teams have also exceeded by a wide margin the goal of a 50 percent increase in freight efficiency (33 percent reduction in LSFC) over a long-haul drive cycle. The other two teams are also working to meet or exceed the program goal in 2015 (Volvo) and early 2016 (Navistar).

Finding 8-3. The Cummins-Peterbilt SuperTruck team has comfortably exceeded a self-imposed goal of a 68 percent increase in freight efficiency (40.5 percent reduction in LSFC) over a 24-hr long-haul duty cycle. They achieved an 86 percent increase in freight efficiency (46 percent reduction in LSFC). The Daimler Trucks North America team demonstrated a 115 percent increase in freight efficiency (53.5 percent reduction in LSFC) on a different 24-hour duty cycle. This 24-hour goal does not apply to the Volvo program, and Navistar’s status is yet to be determined.

Finding 8-4. Fuel-saving technologies such as extensive aerodynamic features, a WHR system, and an APU to handle hotel loads all add substantial weight (3,850 pounds in the

________________

⁸ E. Koeberlein, Cummins-Peterbilt, “Cummins SuperTruck Program: Technology and System Level Demonstration of Highly Efficient and Clean, Diesel Powered Class 8 Trucks,” presentation to the committee, May 14, 2014.

⁹ A. Greszler, Volvo Group Truck Technology “SuperTruck: Development and Demonstration of a Fuel-Efficient Class 8 Highway Vehicle,” presentation to the committee, May 15, 2014.

Cummins-Peterbilt truck). This weight penalty represents a significant challenge for improved efficiency trucks, and project teams had to work very hard and implement some very expensive weight reduction features to achieve an overall vehicle empty weight reduction.

Finding 8-5. All project teams report that the bulk of the aerodynamic improvements achieved in SuperTruck projects result from features added to the trailer, despite the fact that most of the engineering effort went into tractor improvements. This highlights the critical role of the trailer in achieving real-world fuel savings.

Finding 8-6. Using the results available to date, about 26 to 44 percent of the total vehicle fuel savings are due to engine efficiency improvements, while about 56 to 74 percent are due to vehicle power demand reduction. In the Cummins-Peterbilt project, 42 percent of fuel savings are due to the engine and WHR, 14 percent to tractor aerodynamics, 28 percent to trailer aerodynamics, and 15 percent to tire and driveline improvements. In the Daimler SuperTruck, engine improvements account for 26 percent of the total fuel savings while 74 percent is a result of vehicle power demand reductions, including the effect of the hybrid system.

Finding 8-7. SuperTruck project results show a limited potential impact on long-haul duty cycles for hybrid systems using currently available technology. Much of the benefit of a hybrid system can be captured with much less expensive and not as heavy alternatives, such as a GPS-based cruise control that uses the vehicle as a kinetic energy storage device. Microhybrid systems (smart control of auxiliary power demand, possibly combined with limited energy storage to handle auxiliary and/or hotel loads) may be a more promising hybrid approach for long-haul trucks.

Finding 8-8. Additional component-level R&D is required to generate new technologies that could enable a future SuperTruck program to exceed the results achieved by the current program. Promising areas of research include the engine and power train system, controls features, and the trailer and its integration with the tractor.

Finding 8-9. The SuperTruck vehicles incorporate technologies with a wide range of production readiness: Some will be going into production soon; some will never become cost-effective with technology that is now known. The outstanding fuel savings achieved in this program thus need to be treated carefully. Actual production vehicles achieving SuperTruck fuel savings may not be cost-effective for several decades, unless fuel costs increase substantially.

Finding 8-10. The SuperTruck contract goals required testing at 65,000 lb gross combined weight (GCW) in recognition of the fact that many trucks cube out rather than gross out (fill the trailer with cargo without reaching the weight limit). The goals also allow teams that achieve an empty weight reduction to add freight to maintain the 65,000 lb GCW. This gives a very large benefit in terms of freight efficiency for any weight reduction achieved. Since an operator that cubes out would not be able to take advantage of a weight reduction in practice, the project goals tend to overemphasize the benefit of vehicle weight reduction.

Finding 8-11. The SuperTruck program allowed each OEM to select different 2009 baseline vehicles and test routes, so the results are not directly comparable. This limits the ability to compare the results of the four vehicles.

Finding 8-12. Although it did not conduct a detailed safety analysis, the committee believes that it is unlikely that most of the efficiency technologies under consideration in the SuperTruck program will have a negative impact on safety. However, due to elevated temperatures and pressures and potentially flammable working fluids, the safety aspects of WHR systems will need to be considered during their development.

Finding 8-13. DOE is still using fuel economy (FE) in miles/gallon and freight efficiency in ton-miles/gallon for their fuel use metric, while NHTSA regulations that were published 5 years ago use fuel consumption (FC) in gallons/100 miles and load specific fuel consumption (LSFC) in gallons/1,000 ton miles. When experimental or modeling studies of percent improvement for technologies are calculated, a 50 percent increase in FE results in a 33 percent reduction in FC. FC and LSFC are the correct metrics to use since they are used in the regulations and they also multiply directly by miles driven to get fuel usage while FE and freight efficiency are inversely related to miles driven to get fuel usage. This nonlinear relationship is harder to understand without doing a calculation.

Recommendation 8-1. The SuperTruck demonstration vehicles represent a very large investment. DOE should consider ways of extracting additional research results from this investment by using the trucks that have been built to evaluate additional technologies. Some possibilities include:

• Evaluation of additional technologies, such as microhybrid;
• Comparison of SuperTrucks on identical test cycles, with additional work to help understand any differences in performance;
• Vehicle evaluation of hardware resulting from future system or subsystem research projects; and
• Exploration of a range of routes and payloads to determine the sensitivity of technologies to various applications.

Recommendation 8-2. Because of the great value demonstrated by the SuperTruck program, DOE should maintain at least one vehicle integration project at any given time. Owing to likely funding limitations, however, it will probably not be possible to have three or four similar projects running. A range of integration projects are possible, such as:

• A regional haul SuperTruck;
• A heavy-duty vocational SuperTruck (refuse, dump, etc.);
• A SuperTrailer program (to help trailer manufacturers build engineering capability); and
• A delivery truck of Class 3, 4, 5, or 6.

Recommendation 8-3. Any future system integration program with more than one team should entail performance testing on identical duty cycles, so that differences in the performance of specific technologies can be better understood. The vehicle should also maintain the acceleration and speed-on-grade performance of the baseline truck.

Recommendation 8-4. Future complete vehicle programs should account for the benefit of weight reductions in an appropriate way (at 80,000 lb only for a tractor-trailer), taking into account that because only a portion of a vehicle fleet runs at the legal weight limit, only that portion of the fleet could carry additional cargo if vehicle empty weight is reduced.

Recommendation 8-5. It is important for the 21CTP, probably through DOT, to monitor and analyze in detail the technologies implemented in the SuperTruck projects to verify that they do not have a negative effect on safety, since one or more of these technologies may be considered for future production vehicles.

Recommendation 8-6. DOE should use FC and LSFC in its studies in order to be consistent with EPA/NHTSA regulations and to provide in the literature the percent improvements in terms that relate to the metrics used in the regulations. Also, DOE should take the lead in changing the culture so that FC and LSFC metrics become accepted by industry.

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