The hybridization of medium- and heavy-duty vehicles (MHDVs) is given a high priority among the technology objectives of the 21st Century Truck Partnership (21CTP). The roadmap and technical white papers document issued by 21CTP in 2013 (21CTP, 2013) states that “Hybrid electric vehicle (HEV) technology is a key enabler that will help 21CTP achieve its goals” by allowing MHDV manufacturers “to simultaneously improve fuel economy, emissions, and performance.” The objective of this chapter is to (1) review the progress that the 21CTP has made toward accomplishing its ambitious technology objectives in the hybridization of medium- and heavy-duty vehicles; (2) identify the areas where its efforts to date have fallen short of these objectives; and (3) to provide recommendations for actions that should be taken to enhance the effectiveness of its coordinated project efforts in this area.
Hybrid propulsion systems for MHDVs exhibit both similarities and differences when compared to the more mature versions of this hybrid technology that are available in a growing number of hybrid electric light-duty vehicle (LDV) passenger models. Broadly speaking, the overall objectives of the hybrid drive propulsion equipment are the same in both vehicle classes. That is, hybrid drives are supplementary propulsion drives that augment the core internal combustion engine (ICE) powertrain in order to accomplish one or more of the following objectives:
- Recover braking energy that would otherwise be dissipated as heat and convert it instead to either electrical or hydraulic energy that can be stored and then used later for propulsion or vehicle auxiliary purposes. In addition to reducing fuel consumption and emissions, this approach can dramatically reduce brake wear in some MHDV classes such as urban buses, yielding significant maintenance savings.
- Provide additional acceleration that is added to the baseline ICE acceleration, making it possible to downsize the engine in some cases, resulting in lower fuel consumption and emissions.
- In some hybrid configurations, allow the ICE to spend much more of its operating time in its sweet spot range of torque and speed for maximum efficiency, thereby reducing its fuel consumption and emissions.
- Create opportunities for MHDVs to operate with their engines off (i.e., zero emissions operation) either for operating over some distance in an all-electric mode with zero emissions or for stop/start-mode operation in heavy traffic to eliminate unnecessary fuel consumption and emissions when the vehicle is temporarily stopped.
- Provide a source of stored auxiliary electric or hydraulic power that can be valuable to MHDV operators for a variety of purposes that include the powering of tools and lifts in vocational trucks or the powering of electric generators in long-haul Class 8 trucks in order to achieve idle reduction objectives (see Chapter 6).
Although this list is not exhaustive, it captures the most important operational objectives for incorporating hybrid drives into MHDVs. In many of the demonstration versions of hybridized MHDV trucks that have been designed and built to date, a conscious effort has been made to incorporate as many of the special functions listed above as possible in order to maximize the value extracted from the hybrid propulsion equipment.
Since the details of many alternative hybrid propulsion drive configurations developed for MHDVs have been provided in another NRC report (NRC, 2010), no attempt will be made to reproduce this valuable tutorial information here. However, it does deserve to be pointed out that two major types of hybrid propulsion drives are being developed that on the one hand are complementary and on the other, competitive. The most widely adopted hybrid drive architecture is
based on electric power, using a combination of generators and electric motors and electrical energy storage devices (typically batteries) as the basic building blocks. Since all hybridized passenger LDVs now in production use some version of hybrid electric propulsion drives, this approach is becoming well established in the vehicle manufacturing industry. However, a second type of hybrid propulsion drive has been developed based on hydraulic power, using a combination of hydraulic pumps, motors, and hydraulic energy storage in pressurized accumulators. Although the hybrid hydraulic vehicular drive technology is less mature than its hybrid electric counterpart, the hydraulic hybrid drive exhibits some noteworthy characteristics, including the ability to store short bursts of energy more economically than batteries in electric-based drives. This feature makes the hybrid hydraulic drive appealing for medium-duty delivery and refuse trucks that undergo large numbers of start/stop cycles during a typical day, with short total travel distances.
The commercialization of hybrid propulsion drives for MHDVs has been focused on a few specific segments of the MHDV market that are particularly well-suited to benefit from the performance advantages of the hybrid powertrains. These include
- Class 2b pickup trucks and vans,
- Classes 4-6 box-and-bucket trucks,
- Class 8 refuse trucks, and
- Class 8 urban transit buses (see Annex at the end of this chapter for discussion)
One of the key features that nearly all of these MHDVs share is a typical duty-cycle that includes frequent stops and starts that are well-suited for braking energy recovery using a hybrid powertrain. As a result, each of these vehicles can achieve significant improvements in fuel consumption from hybridization. Several manufacturers have been actively participating in the commercialization of hybrid powertrains for these vehicles, including 21CTP partners Allison, BAE Systems, and Eaton.
Despite the progress, some serious obstacles have impeded the growth of these markets, leading to notable setbacks. In particular, the lower cost of gasoline, diesel fuel, and natural gas and the disappearance of federal financial incentives have made it more difficult for MHDVs to succeed in competitive markets such as Class 4-6 delivery trucks. One notable recent example has been Eaton’s decision to discontinue sales of its diesel-electric hybrid drive system in North America, announced in September 2014 (Eaton, 2014). A year earlier, Eaton had decided to discontinue its mild hydraulic drive system aimed at refuse trucks (Eaton, 2013), and there are indications that other hybrid hydraulic powertrains are encountering similar cost competition problems in the marketplace (21CTP-1, 2014). Other major manufacturers have also encountered serious problems with commercialization of hybrid drive equipment for medium-duty trucks in North America, including Allison Transmission (see section titled “Overview of Medium-Duty Hybrid Vehicles in Classes 2b to 6” later in this chapter for more details).
These setbacks are particularly disappointing since studies and field data confirm that hybrid propulsion systems can make significant contributions to reducing both the fuel consumption and greenhouse gas (GHG) emissions of several different types of heavy-duty trucks (NRC, 2012). This takes on increased importance since Phase I of new federal standards limiting the maximum fuel consumption and GHG emissions of MHDVs became active for the first time in model year (MY) 2014 (EPA, 2011, 2013), and Phase II limits are being formulated by the Environmental Protection Agency (EPA) and the Department of Transportation (DOT).1 Although these standards do not require manufacturers to adopt hybrid drives or any other specific technology, the substantial improvements made possible by hybridization of some classes of MHDVs are expected to become increasingly valuable in the future. As a result, there is a risk that decreases in fuel prices that are unlikely to last forever will retard the development of technology for achieving long-term improvements in the fuel consumption and GHG emissions of MHDVs that are 21CTP objectives.
The current marketplace challenges for hybrid power trains can be largely attributed to the basic problem of payback periods that are too long for MHDV customers to accept. Even though the trucks are expected to have lifetimes longer than 10 years, the payback periods that are acceptable to truck purchasers are often 2 years or less (CALSTART, 2010), making it difficult for hybrid technology to compete for new business. This same CALSTART study includes analysis showing that the shorter the time that a hybrid truck is owned, the more difficult it is for an owner to recoup any premium for the hybrid propulsion equipment before the vehicle is sold.
The payback period barrier to market acceptance of hybrid trucks is recognized by the 21CTP leadership, who have expressed an interest in exploring alternatives, including “regulatory pull, robust incentives, and, perhaps, alternative business models (e.g., battery leasing),” to make up for the cost disadvantage of current hybrid powertrains (21CTP-1, 2014). For example, one approach to addressing the payback period problem would be to extend prorated purchase incentives to the second and subsequent generations of MHDV hybrid truck purchasers, making it easier for vehicle sellers to recoup their investments in this fuel- and emissions-reduction technology. Finally, if the long-term goal of the 21CTP program—to significantly drive down
1 See the National Highway Traffic Safety Administration (NHTSA)/ EPA Phase 2 Notice of Proposed Rulemaking for medium- and heavy-duty vehicle fuel efficiency and GHG standards, June 19, 2015, www.nhtsa.gov/fueleconomy.
the cost of MHDV hybrid equipment—is achieved, MHDV hybrid trucks will progressively compete more effectively in the international truck marketplace as the technology improves and matures.
Although the term “MHDV” covers a wide range of truck vehicles from Class 2b to Class 8 with a wide range of applications and duty cycles, the majority of the development effort for hybridized MHDVs has been focused on four areas: (1) medium-duty Class 3 to Class 6 delivery and electric utility trucks; (2) long-haul Class 8 trucks; (3) urban passenger transit buses; and (4) Class 8 vocational trucks, most notably refuse trucks. The first two of these are addressed in the body of this report in the following two subsections since they focus on truck classes that have been the target of multiple 21CTP R&D projects since the beginning of the Partnership. A discussion of hybrid buses is provided in an Annex to this chapter.
Overview of Medium-Duty Hybrid Vehicles in Classes 2b to 6
While heavy-duty long-haul tractor-trailers may travel 80,000 to more than 225,000 miles per year, medium-duty (MD) trucks in Class 6 are much more varied in configuration and often referred to as “work trucks” or, more specifically, as “vocational trucks” in regulations (see, e.g., Figure 4-1). In many cases, the specialized equipment on the truck (such as the bucket for an electric-utility vehicle or the suction pumps on specialized vehicles for cleaning sewers) can greatly exceed the cost of the truck itself. Since these vehicles are intended to perform work, often in stationary positions, their annual mileage may be as low as 20,000 miles (NRC, 2010). There are several vocational truck applications for which the same electric power converter equipment originally developed for use in hybrid power trains has been adapted to power the apparatus mounted on the vehicle for use in stationary operation.
FIGURE 4-1 Odyne Class 6 plug-in hybrid utility lift truck. SOURCE: Green Fleet Magazine (2008). Courtesy of Odyne Systems, LLC.
In addition to vehicles in the heavier classes, there is activity in battery-electric and hybrid vehicles (both electric and hydraulic) for package delivery vehicles and small commercial vehicles. These are typically categorized in Classes 2b to 5 based on their weights. The CALSTART organization has published a useful collection of photos illustrating the many different types of MD hybrid vehicles (HTUF, 2014).
Similar to the case of heavy-duty (HD) hybrid trucks, the cost of the constituent powertrain parts and the resulting payback period have slowed the market acceptance of MD hybrid vehicles. Since many of these vehicles approach the size and weight of passenger vehicles, including sport utility vehicles and vans, the idea of leveraging technology developed for passenger cars becomes increasingly reasonable as the vehicle class number drops. However, the special needs of commercial vehicle operation, including vibration, higher lifetime miles traveled, longer hours of operation, and temperature, need to be specifically factored into research and development activities aimed at these vehicles.
Previous studies have shown that hybrid powertrains in MD vocational trucks can provide as much as a 30 percent improvement in fuel consumption (NRC, 2010). Much of that savings comes from not idling the engine while operating the equipment on the vehicle. However, this drop in idling time can also be achieved in MD trucks with conventional ICE powertrains if the apparatus mounted on the vehicle does not depend on a running engine for operation. For example, the bucket of an electric-utility vehicle can be designed for operation without a running engine using power electronics, motors, and batteries that share a common heritage with the electric traction drive equipment that would be used in a hybrid-electric drivetrain. This type of MD vocational truck helps to reduce fuel consumption for the fleet but would not be classified as a hybrid vehicle, even though it benefits from the significant work done on components and subsystems developed for hybrid-electric powertrains.
There are other benefits of applying this electric drive technology to truck-mounted apparatus, including quieter operation in residential areas. Effort has also been devoted to implementing remote control of the engine so that the vehicle can make limited movements under the control of the person in the raised bucket. This feature improves the efficiency of the vehicle’s operation, providing a tangible financial benefit that helps to pay for the technology.
Since many of the MD vehicles are operated in urban environments, there is an opportunity for turning off the engine whenever the vehicle is stopped in traffic, a feature commonly referred to as stop/start operation. Since the electric drive equipment in a stop/start system is used primarily to start the internal combustion engine and to provide modest support for acceleration and regenerative braking, the power ratings and cost of the hybrid-electric equipment can be reduced from a “full” hybrid to a “mild” or “micro”
hybrid configuration. For example, UPS (United Parcel Service) previously worked with Eaton and Daimler to enable its package delivery vehicles to stop their engines in traffic whenever the vehicle’s brake is depressed and the vehicle is stopped for more than a preset short time. The system restarts the engine as soon as the driver releases the brake pedal in order to avoid any perceptible delay in accelerating the vehicle due to restarting the engine. This stop/start feature is commonplace in European passenger cars and is in the process of becoming available in passenger vehicles in the United States. This passenger car technology is expected to find its way into medium-duty and some heavy-duty commercial vehicles.
One of the keys to applying hybrid drive technology in these MD vocational truck applications and to meeting the required commercial payback threshold is understanding how the vehicle is used. This understanding makes it possible for the hybrid equipment to be tailored to optimize the cost/benefit ratio. The SuperTruck program that has been supported by the 21CTP for HD trucks helped to better understand fuel use in HD Class 8 long-haul trucks by standardizing based on a 24-hour duty cycle. Using this approach, fuel use required during off-hours to keep the driver comfortable and entertained is included in the fuel consumption calculations. (Interested readers are encouraged to read Chapter 8, which is devoted to the SuperTruck program as well as the “Class 8 Long-Haul Trucks” section in this chapter for more details.)
This fuel use issue is even more important for vocational trucks because of their complicated and varied duty cycles, which include long periods of stationary operation. In November 2013,2 Allison Transmission presented to the National Research Council (NRC) an analysis of the duty cycles of vocational trucks. Southwest Research Institute presented the results of its analysis of various technologies for saving fuel in both MD and HD trucks to the NRC in April 2014, followed by a workshop with EPA in December 2014.3 The duty cycles used for the various analyses included several that are tailored for Class 6 vocational and delivery trucks, such as Parcel Cycle High-Efficiency Truck Users Forum (HTUF) Class 6 and the California Air Resources Board (CARB) truck urban cycle (Heavy-Heavy Duty Diesel Truck [HHDDT] Phase 1 GHG).
Several funded projects are collecting real-world data on duty cycles for MD vocational and delivery trucks. Examples include monitoring programs for UPS hydraulic package-delivery vehicles, FritoLay battery-electric package-delivery vehicles, Smith Electric vehicles, and Odyne plug-in hybrid electric vehicles. A significant effort is the Fleet DNA project led by NREL,4 which is collecting information on hundreds of vocational vehicles in multiple locations around the country. This project is expected to deliver valuable information for understanding real-world operation of these MD vehicles, as well as to provide guidance for future hybrid system development and fuel consumption regulations.
A case history that illustrates both the technology opportunities and market barriers encountered by manufacturers of hybrid drivetrain equipment for trucks is provided by the H 3000 hybrid transmission developed for commercialization by Allison Transmission (Allison, 2015). Allison is one of the major commercial developers of hybrid transmissions systems for installation in buses and medium-duty trucks (H 40/50 EP series), with over 6,600 hybrid systems currently operating in transit buses. These transmissions are designed to recover braking energy from vehicles that have frequent stops and use this energy to reduce the vehicle’s fuel consumption, power accessory equipment, and reduce brake wear (see Figure 4-2). Target applications for the H 3000 transmission are MD vocational trucks for applications including pickup and delivery, shuttle buses, utility service, and small refuse trucks in the Class 5 to light Class 8 weight ranges. Fuel savings are projected to be up to 25 percent depending on the truck duty cycle. The U.S. Department of Energy (DOE) has made an investment of $68 million in this program using American Recovery and Reinvestment Act (ARRA) stimulus funds. This support has been used to help develop this technology and to help build a new factory capable of building as many as 20,000 units of the H 3000 hybrid transmission annually. Although field demonstrations have been successful, the H 3000 hybrid transmission has not yet officially been brought to market, reflecting the market barriers to commercial acceptance currently being encountered by hybrid drive equipment manufacturers such as Allison. Since the ARRA-funded H 3000 development was not carried out as a project in the 21CTP portfolio of funded projects, no further evaluation of this project is included in this report.
Despite the commercial barriers to greater use of MD battery-electric and hybrid vehicles of all types in Classes 2b to 6, there continues to be interest in the industry and incentives to drive it forward. California provides a Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project (HVIP) incentive and lists a number of MD vehicles available for this compensation through its website (HVIP, n.d.). New York also provides incentives; eligible vehicles are listed in NY Truck VIP (2015). The city of Chicago has provided incentives for battery-electric vehicles and buses, and new regulations are expected to extend the incentives to include MD hybrid trucks (Drive Clean Chicago, 2015). DOE main-
2 M. Howenstein, Allison Transmission, “Transmission Technology and Fuel Consumption.” Presentation to NRC Committee on Assessment of Technologies and Approaches for Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, Phase 2, on November 21, 2013.
3 T. Reinhart, Southwest Research Institute, “Technologies for MD/HD GHG and Fuel Efficiency,” Presentation to NRC Committee on Assessment of Technologies and Approaches for Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, Phase 2, on April 29, 2014.
4 D. Anderson, “Vehicle Systems Simulation and Testing,” Presentation to the committee on September 3, 2014.
FIGURE 4-2 Allison H 3000 hybrid transmission major components. SOURCE: Allison (2015). © Allison Transmission 2011. All rights reserved.
tains a list of available vehicles in the Alternative Fuels Data Center (DOE, 2014). Some additional products can be found by looking at the member list for HTUF (HTUF, 2014).
HTUF, founded several years ago by CALSTART (CALSTART, n.d.), is a valuable source of information about the commercialization of MD hybrid vehicles. Bill Van Amburg, the senior vice president of CALSTART, has provided the committee with a list of 29 manufacturers from around the world that are currently actively involved in the development and production of MD hybrid and battery-electric trucks5 Although the list is not reproduced here, the significant number of manufacturers reflects the continuing international interest in the development and commercialization of MD hybrid trucks. It should be noted that many of the manufacturers on this list are currently focused on research or development activities and are not yet offering their vehicles for sale, often attributable to the very soft market conditions that currently prevail for hybrid MDHVs in North America. This reflects the immature state of the MD hybrid technology in this field as well as the challenging market conditions noted earlier.
Class 8 Long-Haul Trucks
Heavy-duty Class 8 long-haul trucks present a challenging target for hybrid powertrain equipment. On the one hand, they do not fit the standard pattern for the other popular HD vehicle targets for hybrid drives. That is, the large majority of Class 8 long-haul trucks travel long distances without stopping, preventing these vehicles from taking advantage of the hybrid drive’s special ability to recover energy from frequent stops and starts. Studies have indicated that the potential fuel consumption reduction benefits from hybridization fall into a range of 2 to 8 percent depending on assumptions about the duty cycle and the frequency and amplitude of elevation changes (i.e., hilliness) along the truck route (NRC, 2010). These reductions are much smaller than comparable numbers for other MHDV candidates such as Class 6 delivery trucks. Nevertheless, the fact that the total fuel consumption of Class 8 long-haul trucks is higher than that of any other MHDV type means that even small percentage reductions in fuel consumption can yield impressively large total reductions in fuel use and emissions.
The Daimler SuperTruck team chose to incorporate a hybrid-electric drive into its vehicle and is close to completing its evaluation. The Navistar SuperTruck team dropped its preliminary plans to include a full hybrid drive in its truck and is now evaluating microhybrid units for possible inclusion in its demonstrator truck (see Chapter 8 for more details). Despite the success of the Daimler SuperTruck demonstrator vehicle in achieving its goal of a 50 percent increase in freight efficiency (freight ton-miles per gallon), corresponding to a 33 percent reduction in its fuel consumption per ton-mile, the net contribution of the hybrid drive to this reduction is modest, making it difficult to justify the cost of the hybrid drive in the Daimler demonstrator truck. As discussed earlier in this chapter, the payback period for the hybrid drive equipment is typically much longer than the short periods of 2 years or less demanded by vehicle owners for justifying their investments. As a result of experiences such as this one in the Daimler Supertruck project, the future of the hybrid electric drive for Class 8 long-haul trucks is cloudy.
5 Van Amburg, personal communication, 2014.
One of the questions left unanswered by the Daimler SuperTruck program is whether the trade-off between vehicle performance (measured in terms of fuel consumption, GHG emissions, and other metrics) and cost could be improved significantly by changing the ratings of the battery, electric motor, or power electronics. This is a serious question that applies not only to hybrid drive systems in Class 8 long-haul trucks, but also to a much wider range of vehicle sizes and applications, including vocational trucks and buses described in the preceding sections. In some cases, the adoption of mild hybrid systems having smaller motors and batteries, also referred to as microhybrids, can provide better performance vs. cost trade-offs than larger full hybrid drives. Since work on the simulation of MHDV hybrid trucks has already been carried out using federal funding at Argonne National Laboratory (ANL) (ANL, 2013) and the National Renewable Energy Laboratory (NREL) (NREL, 2014), the prospect of combining these simulations with real-world data collected from hybrid truck programs such as the Daimler SuperTruck demonstrator vehicle suggests some opportunities for investigating hybrid drive optimization.
An additional factor for consideration is the development by Daimler engineers of a vehicle speed control algorithm called eCoast, which modulates the truck speed on grades so that the vehicle mass becomes the energy storage means (via potential energy) for reducing the vehicle’s fuel consumption without the need for expensive batteries or hybrid drive equipment (NACFE, 2014). This eCoast software algorithm is capable of delivering much of the value of the hybrid drive equipment at a fraction of the cost. On the other hand, the hybrid electric drive is tightly integrated into the overall vehicle propulsion drive, allowing it to play a role in enabling several advanced vehicle features. This fact complicates the engineering matter of deciding whether a hybrid drive can be justified or not. This example illustrates the challenges faced by truck vehicle designers in choosing which technologies to add or remove as they design new truck propulsion systems that can meet complex combinations of performance criteria in addition to achieving the demanded reductions in fuel consumption and emissions.
In its 2013 roadmap document (21CTP, 2013), the 21CTP states its strategic approach in five thrusts, summarized as follows: (1) Develop hybrid propulsion systems for MHDVs; (2) overcome the technical barriers that inhibit the technologies; (3) educate interested parties on the importance of MHDV hybrid systems; (4) stimulate market demand for MHDV hybrid products; and (5) establish confidence in MHDV hybrid technologies by providing unbiased testing and evaluation of hybrid MHDVs.
The material presented to the committee by 21CTP indicates that most of the Partnership’s effort has been focused on the first, second, and fifth thrust, with much less evidence of initiatives focused on either hybrid MHDV education or market stimulation.
In this same document, the top priority R&D areas that require government funding to meet 21CTP’s hybrid vehicle technology goals are identified as (1) drive unit optimization; (2) drive unit cost; (3) energy storage system reliability; and (4) energy storage system cost. It is notable that all four of these identified R&D areas focus on components or subsystems in a hybrid propulsion unit and not on the integrated hybrid system. The implications of this intentional focus on component and subsystem R&D rather than integrated hybrid drive systems will be addressed in more detail later in this chapter.
Other key 21CTP initiatives that have a significant impact on MHDV hybrid drive systems include the following:
- The SuperTruck program for long-haul Class 8 trucks. The Daimler project includes a full hybrid drive system and the Navistar team is investigating mild hybrid options. This is discussed in more detail in Chapter 8.
- Participation in development of test procedures for MHDV powertrains that include both conventional and hybrid powertrain configurations, using the Vehicle Systems Integration (VSI) Laboratory at Oak Ridge National Laboratory (ORNL) (Smith et al., 2014).
Review of 21CTP Hybrid Vehicle Technology Goals
In 2006 the 21CTP established three hybrid technology goals for 2012. These goals established design life and cost targets for the hybrid drive unit and the energy storage system, as well as fuel economy and emission improvement targets for a heavy hybrid propulsion system operating on an urban driving cycle. Progress toward achieving these goals was reviewed in the NRC Phase 2 report (NRC, 2012), and this discussion will not be repeated or updated here since the target date for those three goals has passed.
Instead, this report will focus its discussion on six stretch goals for MHDV hybrid propulsion technology that were defined by the 21CTP in February 2011 (DOE, 2011). The target areas for these stretch goals are generally the same as those targeted by the three 2006 goals, but the six stretch goals are updated and made more specific. The reason these goals were explicitly designated as “stretch” goals when they were created is that these goals “can only be accomplished with increased funding through the 21st Century Truck Partnership” (21CTP, 2013). Since little funding has been allocated to MHDV hybrid component R&D since FY 2007 (NRC, 2012, Table 4-2), these stretch goals remain unfulfilled from the standpoint of 21CTP. As a result, a thorough discussion of each of the six stretch goals would not be meaningful under the circumstances.
However, hybrid drive and energy storage R&D, primarily for light-duty passenger vehicles, are being supported by DOE. The objectives of this R&D program overlap the needs of the MHDVs to some degree. As stated in the 21CTP roadmap document, “There is a common perception that investments in passenger car (LDVs) technology benefit HD trucks. This is not entirely true” (21CTP, 2013). In light of this observation, it makes sense to broadly address the relevance and impact of this DOE-sponsored R&D on the MHDV stretch goals. These six goals will be reviewed in sequence. (The goal text is summarized; the complete version is available in the hybrid propulsion white paper dated February 28, 2011 (DOE, 2011)).
Goal 1—Electric Machines. Develop advanced motor technology that will deliver electric machines with improved durability, lower cost, better power density, and alternatives to rare earth permanent magnets.
- —Greater than 1 million miles (Class 8 line-haul application) or 15 years of life (vocational applications).
- —Power density for some motor designs today is at approximately 0.5 kW/kg. The objective is to nearly double the power density to approximately 1 kW/kg. A cost target of $50/kW by 2016 has been established.
- —Motors and generators have efficiencies typically at approximately 94 percent today. The objective is 96 to 97 percent by 2016.
- —Demonstrate a nonpermanent magnet motor technology in a commercial vehicle application that would equal or meet current hybrid system requirements by 2013.
Goal 2—Inverter Design/Power Electronics. Develop technologies that will improve the cycle life of critical components within the inverter and other power electronics within the hybrid system.
- —Develop an improved switching device (insulated gate bipolar transistors [IGBTs] or other) that has a broader operating temperature range and a top temperature higher than today’s 50°C and offers improved system life and durability. Develop this improved switching system and demonstrate benefits by 2016.
- —By 2016, reduce the overall weight of inverter designs by 20 percent through more efficient switching devices with higher operating temperatures and potential integration with engine cooling systems.
Goals 1 and 2 focus on achieving significant improvements in the performance, lifetime, and cost of the electric machine and power electronic inverter, respectively. The good news is that technology trends in these areas, supported in part by the DOE investments in R&D aimed at LDVs, are yielding improvements, in particular in the performance and power density of the power electronics. However, the likelihood of developing electric machines that do not contain high-grade rare earth magnets that exceed the performance and power density of the existing machines that use these magnets, as called for in the first goal, is low. Nevertheless, this R&D effort is spurring the development of so-called non-rare-earth traction machines that are likely to be attractive for some hybrid applications that do not need the weight and efficiency advantages provided by rare-earth magnets.
Progress toward achieving the cost targets and lifetimes called for in these first two goals is less clear and more difficult to evaluate. Project principal investigators employed by established suppliers of this equipment make positive claims about progress toward these objectives, but lifetime and cost are notoriously difficult to evaluate quantitatively. Indications are that the trends are in the right direction, but significant work still needs to be done to reach the aggressive targets. It should be noted that the lifetime targets for MHDVs are more challenging than those for passenger vehicles, both because of the length of the MHDV lifetime goal (15 years, compared to <10 years for passenger vehicles), and the more challenging physical environment (e.g., temperature, vibration, corrosive agents) experienced by hybrid drive equipment in MHDV applications.
Goal 3—Energy Storage Systems. Develop an energy storage system with 15 years of design life, a broader allowable temperature operating range, improved power density and energy density, and significantly lower cost.
- —Develop a system that can provide a cycle life of 5,000 full cycles, which should achieve the target of 1 million miles (on the highway) or 15 years (vocational). Current state-of-the art energy storage systems are typically rated for 8 years of life.
- —By 2017, extend the acceptable operating temperature range for lithium ion batteries, currently at 0°C, to 55°C.
- —Develop battery technologies that will significantly increase power and energy densities.
- —Proposed cost targets:
- $45/kW and/or $500/kWh for an energy battery by 2017;
- $40/kW and/or $300/kWh for a power battery by 2020; and
- By 2016, the cost of the overall battery pack should not exceed the cost of the cells themselves by more than 20 percent.
- —Establish an “end-of-life” strategy for advanced batteries and provide the necessary funding related to either the remanufacturing or recycling of batteries by 2017.
The status of the third goal, which targets power density, cost, and lifetime targets, but for energy storage equipment (primarily batteries) rather than electric machines and power electronics. This has been the single largest area for R&D investment of any of the five stretch goals during the past 5 years, although the focus has been on energy storage components for LDVs, not MHDVs. Steady progress is being reported on increasing both the energy and power density of new batteries for propulsion applications, but their ability to meet the challenging lifetime and cost targets for hybrid MHDVs, as stated in the goals, is much less certain. The specialized aspects of the hybrid MHDV application that distinguish them from the LDV hybrid system, together with the much lower volumes associated with the MHDV market, combine to make these targets particularly challenging for commercial suppliers to meet.
Goal 4—Hybrid System Optimization, Medium Duty. To develop and demonstrate medium-duty hybrid system technology that can deliver substantial increases in fuel economy, beyond what is available with today’s systems:
- —Potential applications for demonstration include MD shuttle buses, vocational trucks, and on/off highway MD work trucks.
- —A vehicle demonstration program that provides a platform for developing these medium-duty technologies (similar to the SuperTruck program for heavy-duty technologies) is one potential approach, with development and demonstrations to be completed by 2017.
Goal 5—Hybrid System Optimization, Heavy Duty. An overarching goal is to develop and demonstrate HD hybrid system technology that can deliver substantial increases in fuel economy.
- —For urban, heavy start-and-stop driving cycles, a stretch goal of 60 percent (38 percent reduction in fuel consumption) has been identified.
- —For regional haul and line-haul applications, the percentage improvements would be more modest, with a stretch goal of 25 percent (20 percent reduction in fuel consumption).
- —Additional review and development need to be considered for those vehicles that would possess alternative anti-idling devices that could be provided without additional infrastructure changes.
Stretch goals 4 and 5 are different from the first three goals by virtue of targeting hybrid system optimization objectives for MD and HD vehicles, respectively. The intent of these two stretch goals to focus R&D effort on system design issues rather than components is highly commended because the value proposition for hybrid systems in MHDVs can be significantly improved by carefully integrating such systems into the MHDV systems, where it can contribute to the implementation of several valuable and innovative features that support 21CTP objectives. As noted earlier, the Daimler SuperTruck team6 adopted this approach in its demonstrator truck. The specific targets included in these two goals were purposely chosen to extend well beyond the objectives of the current SuperTruck projects, and the cited target numbers (e.g., 20 percent fuel consumption reduction for line-haul trucks) are very ambitious, exceeding anything that has been demonstrated to date. As of this time, no funding has been allocated to achieving these goals. There is little sign that MHDV equipment or vehicle manufacturers will make these R&D investments on their own. The 21CTP program is in the process of revising its goals in this area, as discussed later in this chapter in the section “21CTP Hybrid Team Restructuring,” and the committee supports these efforts, as reflected in its Recommendation 4-1.
Goal 6—Electrified Power Accessories. Develop robust, durable, efficient electric power accessories for use with medium- and heavy-duty hybrid systems:
- —Electrifying accessories such as power steering, air compressors, and air-conditioning compressors can significantly reduce parasitic losses by powering them on-demand.
- —Target date for availability of such improved accessories: 2016.
The final stretch goal, Goal 6, focuses on the development of electrified power accessories such as power steering and air-conditioning compressors that are “robust, durable, [and] efficient.” Unlike the preceding five goals, there are no quantitative targets established for this goal because of its breadth. This goal is closely related to the preceding two because the MHDV system integration and optimization efforts associated with Goals 4 and 5 can be expected to extend into the areas of electric accessories, as was the case in the Daimler SuperTruck project.7 Although there has been no R&D funding invested in the development of electric accessories specifically for MHDVs, some of the results of R&D efforts that have been supported to advance accessory electrification technology in LDVs will broadly benefit MHDVs as well. However, as noted previously, the specialized nature of the MHDV specifications, the challenging physical environment for this equipment, and the longer lifetime targets make it difficult to directly apply the results from passenger vehicle R&D projects without significant additional effort tailored to MHDVs.
Before closing this section, it should be said that the 21CTP leadership, in response to a committee question, answered that it had “not conducted a full planning effort
6 D. Kayes, D. Rotz, and S. Singh, Daimler Truck North America LLC, “SuperTruck Team,” Presentation to the committee on May 15, 2014.
for reviewing these goals and defining the specific budget required to meet each one. . .” (21CTP-1, 2014) even though this was a specific recommendation of the NRC Phase 2 report. (See discussion on H-6 Revised Hybrid Goals, Recommendation 4-5, in the section “21CTP Response to Recommendations in NRC 2nd Review Report” near the end of this chapter for more details.) In this same response, the 21CTP leadership said “the Hybrid team has been revisiting the goals in light of the current and near-term future outlook for hybrid technology in commercial trucks” (21CTP-1, 2014). The latest information from the 21CTP leadership indicates that the hybrid team is in the process of undergoing reorganization, and it is expected that this process, when completed, will have a significant impact on the future of these goals. More details about this reorganization can be found in the section “21CTP Hybrid Team Restructuring” later in this chapter.
Assessment of Progress and Key Accomplishments
The committee has reviewed available information about several projects funded by federal agencies in the Partnership that relate to battery-electric vehicles, hybrid-electric vehicles, and hybrid-hydraulic vehicles. Information provided by 21CTP leadership indicates that total expenditures by three of the 21CTP-affiliated federal agencies (DOE, DOD, and DOT) on hybrid electric drive technology for both LDVs and MHDVs during the 2012-2014 totaled $63.4 million. Table 4-1 lists all of the electric drive technologies projects identified by the 21CTP leadership as part of 21CTP project portfolio. This funding can be broken into two main portions, one consisting of projects that are specifically focused on MHDVs with hybrid and battery-electric drives. The other portion of the projects claimed by 21CTP is focused on developing electric drive technology for LDVs, accompanied by the claim that the technology targeted by these projects is applicable to larger MHDVs.
Closer examination of the projects that make up this inventory reveals that the dominant portion of this project funding (>75%) is directed at vehicle demonstration projects, and much of the funding was supplied by the ARRA stimulus program. Although such demonstration (pilot) programs are valuable, it should be noted that less that 20 percent of this funding is associated projects that can be objectively categorized as R&D.
Attention will first be addressed to projects that specifically address MHDVs. A review of information available to the committee reveals that these 21CTP-affiliated MHDV projects, with only a couple exceptions, can be placed in one of four categories:
|Agency||Subgrouping||Internal Project Title||Recipient||2012 Funding||2013 Funding||2014 Funding|
|DOD||Non-Rare-Earth Materials for Motors||N/A||1,500,000||500,000||500,000|
|DOD||Modeling and Optimization of Electrified Propulsion Systems||N/A||98,000|
|DOD||High Energy Density Asymmetric Capacitors||N/A||99,000|
|DOD||Powertrain Thermal Management - Integration and Control of a Hybrid Electric Vehicle Battery Pack, E-Motor Drive, and Internal Combustion Engine Multiple Loop Cooling System||N/A||50,000|
|DOD||Advanced Models for Electric Machines||N/A||78,000|
|DOE||Advanced Electric Drive Technologies R&D||Various (see Annual Report, http://energy.gov/sites/prod/files/2014/04/f15/2013_apeem_report.pdf)||3 National labs (ORNL, NREL, Ames), universities, and industry partners||13,266,940||11,053,327||9,704,789|
|DOE||Electric Drive Technologies||Various (see Annual Report, http://energy.gov/sites/prod/files/2014/04/f15/2013_apeem_report.pdf)||6 Industry (GE, UQM, GM, Sigma, APEI, Synthesis Partners) and 1 lab (ANL)||5,500,000||9,587,357||11,500,000|
|Total for 2012-2014||63,437,413|
Category 1. Projects that support specific truck manufacturers to develop new MHDV hybrid or battery-electric trucks or improve existing models and then collect data about their performance during field tests. In some cases, the project involves building significant numbers of the vehicles. Examples of these projects include ARRA VT072, “Smith Electric Vehicles: Advanced Vehicle Electrification & Transportation Sector Electrification” (Mackie, 2014) and ARRA VT083, “Plug-In Hybrid Electric Commercial Fleet Demonstration and Evaluation” (Cox, 2014). These projects are by far the largest of all the projects associated with hybrid drive technology that are part of the 21CTP portfolio, representing a total federal funding commitment of $77 million over 5 years for these two named projects. They were both made possible using funding provided to DOE under the 2009 ARRA, and they are the only current 21CTP projects that use federal funding to design and construct new MD hybrid trucks (780 total vehicles for the two projects) that are then placed in the field for testing and data collection. (One of the ARRA-funded SuperTruck projects also includes a hybrid drive as part of its drivetrain; see Chapter 8.) Both projects have suffered setbacks that have delayed their completion, but progress is being made by each toward meeting their truck delivery targets during 2015. Preliminary field test results look promising for achieving reduced fuel consumption and emissions, but more field testing is necessary to provide a more complete evaluation.
Category 2. Projects that support work at the national laboratories or third-party organizations to evaluate the performance of several different types and models of MHDV hybrid or battery-electric trucks (or buses) without requiring government funding to directly support the development and manufacturing of those vehicles. Examples of these projects include NREL VSS001, “MHDV Field Evaluations” (Walkowicz, 2014), and the project led by the South Coast Air Quality Management District (SCAQMD), VSS115, “Zero Emissions HD Drayage Truck Demonstration”) (Choe, 2014). Both projects involve agreements with multiple truck manufacturers who are responsible for developing and building the hybrid trucks, which are field-tested by an independent third-party organization, which collects extensive data. Federal funding for projects in this group is typically $600,000 or less per year, approximately ten times smaller than annual federal expenditures for projects in the first group. The skills of the funded researchers are applied primarily to directing the data collection, followed by rigorous evaluation. Results from these projects range from very promising in the case of VSS001, cited above, to disappointing in the case of another project, VSS116, “Hydrogen Fuel Cell Electric Hybrid Truck and Zero-Emission Delivery Vehicle Deployment” (Carr and Williams, 2014), which has been significantly delayed by problems with the manufacturers that were originally selected to provide the vehicles. It should be noted that this last-mentioned project included funding to provide financial incentives for customers to purchase the fuel-cell-powered vehicles for field testing, contributing to its larger total DOE budget of $2.4 million over 3 years.
Category 3. Projects that involve a closer relationship between one or more national laboratories and a manufacturer of hybrid or battery-electric MHDVs to pursue the development of improved vehicle technology involving the architecture, subsystems, or control of the drivetrain. Examples of this group of projects include VSS133, “Cummins MD & HD Accessory Hybridization CRADA,” which combines the efforts of Cummins and ORNL (Deter, 2014), and VSS134: “Vehicle Thermal System Modeling in Simulink,” which represents a collaboration between NREL and three truck industry partners (Lustbader and Kiss, 2014). Typically, these projects are organized so that the national laboratory focuses its efforts on modeling, analyzing, and, in some cases, testing the new technology while the industry partner takes responsibility for implementing the new technology in hardware and/or software, as appropriate. The key difference between this project group and the preceding one is that, in this group, national laboratory researchers are more directly involved in technical activities such as modeling, analysis, and laboratory testing that directly influence the development of the new technology that is being conducted under the leadership of the industry partners. Annual funding levels for these projects are typically $600,000 or less per year, again far less than the annual budgets for projects in the first group. These projects are particularly appealing since they provide opportunities to harness the special technical skills of researchers at the national laboratories to provide valuable assistance to the manufacturers in areas that complement the skills of their in-house technical staffs. Of the two projects, the first one, involving the Cummins-ORNL cooperative research and development agreement (CRADA), is further along due to its earlier start date, and the technical results to date from the modeling and simulation work appear to be very promising.
The plans to test prototype hardware and software developed during the course of the Cummins-ORNL project on dynamometers in the new Vehicle Systems Integration (VSI) Power Train Test Laboratory at ORNL will provide a welcome opportunity to demonstrate the unique strengths and features of this impressive new facility (Smith et al., 2014). The facility includes two high-power (500 kW), high-performance dynamometers that can be used to test large truck engines and hybrid drivetrains using sophisticated controls and instrumentation that can apply any desired drive cycle to the engine
system while a thorough set of measurements are being made, including fuel usage and exhaust emissions (see Figure 4-3). The VSI Laboratory also includes high-speed computers and high-quality real-time control equipment that make it possible to conduct tests that combine actual equipment with simulated components or controllers in the same experiment. There are very few test facilities like this in the world today specifically designed for testing MHDV truck engines and powertrain equipment.
Category 4. Projects that address issues associated with the introduction of MHDV hybrid and battery-electric trucks from a higher level by developing models to analyze and project the performance, cost, market opportunities, and the resulting reductions in fuel consumption and emissions of these vehicles for several years in the future on a regional and national scale.
Examples of this last group of projects include VAN001, “Impact Analysis: VTO Baseline and Scenario (BaSce) Activities,” led by ANL (Stephens, 2014), and VAN012, “Modeling for Market Analysis: HTEB, TRUCK, and LVChoice,” led by an ANL contractor, TA Engineering, Inc. (Birky, 2014). Although the number of projects in this group and the total annual funding (<$700,000 for the two projects listed above) are lower than for the other three groups, these modeling studies can play an important role in helping 21CTP leadership to evaluate the areas in which their future project funding can have the largest positive impact for achieving the Partnership objectives of reducing fuel consumption and emissions. This effort takes on special importance because of the challenging conundrums associated with evaluating the trade-offs between the national benefits of hybridization in MD trucks (higher percentage benefits per truck but lower total fleet fuel savings) and HD trucks (lower percentage benefits per truck but higher total fleet fuel savings). Unfortunately, the validity and credibility of these models is heavily dependent on the quality of the input data which, in some cases, requires detailed cost and sales data that manufacturers are traditionally hesitant to provide. Regardless of the inevitable debates about the accuracy of their future projections, the models developed as a result of these projects play a useful role by encouraging leaders in both government and industry to consider the high-level impact issues when deciding on future technology investments.
FIGURE 4-3 500 kW dynamometer with diesel engine-under-test in ORNL VSI Laboratory with truck outline overlay. SOURCE: Smith et al. (2014).
In addition to the projects that are specifically focused on MD and HD trucks discussed above, a number of other projects are being funded by DOE and DOD to develop technology for automobiles and combat vehicles that may be applicable to hybrid and battery-electric MHDVs in the future. Although the specific objectives and status of these projects will not be discussed in detail here, it should be stated that none of the DOE-funded projects are defined to directly address the technical demands that distinguish light-duty automobiles from medium- and heavy-duty trucks. However, there are some projects that address these issues indirectly. For example, there are a few projects, such as APE063, “Performance and Reliability of Bonded Interfaces for High-Temperature Packaging” (DeVoto, 2014), and APE061, “Cost-Effective Fabrication of High-Temperature Ceramic Capacitors for Power Inverters” (Balachandran, 2014), that address important technical challenges associated with achieving rugged and reliable power electronics in hostile high-temperature environments with semiconductor junction temperatures up to 200°C, conditions that are relevant to the longer lifetimes expected for power electronics operating in future hybrid/electrified trucks. Several of the other projects, such as those focused on developing traction motors that do not use expensive rare-earth magnetic material, could eventually lead to scaled-up versions that would be useful in hybrid drives for trucks, but when this might happen is uncertain.
There are also a few projects identified by DOD that could yield electric drive technology that matches or exceeds the power ratings and ruggedness requirements for electric drives in commercial MHDVs. One example is a project funded by the U.S. Army Tank Automotive Research, Development and Engineering Center (TARDEC) named “Integrated Starter Generator (ISG)” (DOD, 2014) that is developing high-performance electric machines and inverters with ratings of 120 kW and 160 kW for use in future combat vehicles—power ratings that fall within the range required for hybrid drive systems in HD trucks. This is a multiyear project led by General Dynamics Land Systems (GDLS) that began in FY2013 with a planned duration of 6 years and a total budget of $26.9 million. The project is planned to include significant efforts to build prototype ISG hardware that will be tested in both the laboratory and actual combat vehicles (the Army’s Stryker). Although the technical details provided by DOD about this project are quite limited, it is interesting to note that the project leaders specifically call out “Intelligent Engine Start/Stop” as one of the target operating modes, highlighting its potential relevance to MHDV hybrid trucks.
Before closing this section, it is worth noting that the ARRA-funded projects that comprise the dominant share of the 21CTP projects in the hybrid electric drives area are due to end in FY2015. As a result, the annual expenditures in the future 21CTP budgets associated with hybrid electric drive technology are likely to drop significantly for FY2016 and beyond unless hybrid-related projects emerge to take the place of the ARRA-funded projects. The committee supports investments by 21CTP in longer-term R&D projects focused on promising approaches that might lead to significant improvements in hybrid-related technology, as reflected in Recommendation 4-2.
Summary of Key Barriers and Future Opportunities
The environment for the hybridization of MHDVs has changed significantly during the past 5 years. Some of the factors influencing these changes include (1) experience is being gained with hybrid drives in MHDVs for a variety of vehicle classes and applications that has been clarifying the real-world fuel consumption improvements that can be achieved and (2) natural gas and petroleum prices have dropped considerably, reducing the economic attractiveness of commercially offered hybrid drivetrains. Against this backdrop, the key barriers and issues that are slowing the commercial acceptance of hybrid trucks include the following:
- While the prices of key components—including the power electronics, motors, and batteries—in hybrid drivetrains for light-duty passenger cars are decreasing, the rate of decrease is not been sufficiently fast to allow hybrid drivetrains to meet payback period criteria set by the truck purchasers under current conditions of falling fuel prices and the absence of any direct price for emissions other than regulatory limits. The cost of batteries or alternative energy storage components has been particularly troublesome despite continuing progress on reducing battery costs.
- Despite claims that the significant investment by the federal government in hybrid drive technology R&D for LDVs is directly applicable to MHDVs, there are substantive differences between the requirements of LDVs and MHDVs that create important gaps in the technology readiness of commercial hybrid drive components for truck drivetrain applications.
- The truck manufacturing industry is characterized by a significant number of small- to medium-size firms compared to the smaller number of much bigger passenger vehicle manufacturers. This difference makes it much less likely that truck manufacturers will invest in the long-term R&D needed to develop mature and cost-effective hybrid drivetrain technology for their future truck products.
- One of the biggest conundrums is that while hybrid technology is most beneficial for MD trucks that experience large numbers of start/stop cycles, collectively, these Classes 3 to 6 trucks combined consume less than half of the total fuel consumed by long-haul Class 8 trucks, which do not benefit as much from the
introduction of hybrid drivetrains (NRC, 2010). This has made it more difficult for the 21CTP to justify R&D investments in hybrid technology for any of the MD truck classes.
- Federal test procedures for evaluating fuel consumption and emissions are still incomplete for hybrid truck drivetrains, complicating the process of quantitatively evaluating their performance for the purpose of qualifying for regulatory credits or state tax incentives. Historically, these fuel consumption and emissions tests for conventional MHDVs have always been conducted using the diesel engine alone. More details are provided in the subsection “Hybrid Vehicle Fuel Consumption and Emissions Certification,” later in this chapter.
- The early years of hybrid truck manufacturing, the past 10-15 years, have been marked by a number of immature products that resulted in poor vehicle experiences for the buyers, as well as orphaned products caused by manufacturers who prematurely left the market or went out of business. This checkered history has hurt resale values and discouraged fleets from adopting hybrids.
The net impact of these barriers on the current market for hybrid trucks has been summarized by Deborah Gordon, executive director of Regulatory Issues and Hybrid Programs at Allison, as follows:
When considering volume production over the next 10 years for commercial truck hybrids, Allison believes that fleet operators and vehicle manufacturers currently lack a viable business case to support widespread deployment. At least a few considerable barriers remain; the technology is considered somewhat unproven in terms of ‘real world’ reliability in truck vocations, a lack of significant financial incentives to offset costs, and the current impact of low fuel prices (Gordon, personal communication, 2015).
Despite this discouraging assessment of the hybrid truck market in North America, it should be noted that the market for hybrid trucks is much stronger in other parts of the world, including China and Europe, where concern about air pollution is high, particularly in densely populated urban environments. For example, a recently completed study by Frost & Sullivan predicted that global sales of MD hybrid and electric trucks will grow from 2,200 annually in 2013 to 84,000 annually in 2022, corresponding to a compound annual growth rate (CAGR) of nearly 50 percent (Frost & Sullivan, 2014). The projections of that same study for HD hybrid and electric trucks are even more attention-grabbing, predicting global annual sales growth from 300 in 2013 to 51,000 in 2022, corresponding to a CAGR value of 77 percent. The study predicts that the largest purchaser of these hybrid and electric trucks will be China, with sales driven primarily by government mandates. Consistent with these predicted trends, Dr. Mihai Dorobantu, the Eaton representative on the 21CTP hybrid team, has noted that Eaton’s sales of hybrid truck drivetrain equipment are very strong in China for MHDV applications such as city buses (see Figure 4-4), despite the fact that Eaton’s U.S. sales dropped to the point of causing it to suspend market activities in North America, as noted earlier in this chapter (Dorobantu, personal communication, 2015).
These sharply countervailing trends suggest that, while the technology and market barriers to hybrid MHDVs are currently high, particularly in North America, the long-term international market opportunities are substantial. In this situation, the role of the 21CTP in applying its R&D resources to achieve positive long-term objectives could have a significant impact on the prospects for U.S.-based manufacturers to succeed in the future domestic and international markets for hybrid MHDVs.
21CTP Hybrid Team Restructuring
The 21CTP organization includes a hybrid team that consists of representatives of 21CTP industry partner companies that have a commercial interest in hybrid drive components, subsystems, or complete vehicles. This hybrid team provides advice to the 21CTP executive committee and to the leadership of the overall 21CTP program inside DOE.
During its recent meetings in July and November 2014, members of the hybrid team reviewed the special challenges associated with the commercialization of MHDV hybrid drive equipment and the vehicles in which they are installed. An important topic of discussion during those meetings was that, beyond hybrid drives, “there are opportunities for efficiency gains in the remainder of the drivetrain (conventional, automatic, or AMT transmissions, axles, etc.)” (21CTP-1, 2014). Members of the hybrid team are now in the midst of reorganizing the group to broaden its focus to include advanced drivetrains. To this end, the currently proposed name of this reorganized team is the Hybrid and Drivetrain
FIGURE 4-4 HD hybrid city buses in Jining City, China, built with Eaton hybrid drives. SOURCE: Eaton Corporation, “Eaton drops hybrids in North America,” Fleets & Fuels, June 26, 2013. http://www.fleetsandfuels.com/fuels/hybrids/2014/06/eaton-dropshybrids-in-north-america/.
Working Group. Although the changes are not official, it is expected that the terms of the team restructuring will be worked out with the 21CTP leadership and completed by midyear in 2015.
Some valuable insights into the objectives and future directions of this reorganized working group have been provided by Mihai Dorobantu, director of Technology Planning and Government Affairs in the Eaton Vehicle Group, who is a member of the current hybrid team (Dorobantu, 2014, personal communication). He has been actively involved in the team restructuring process and is well versed in the current status of hybrid MHDV technology and markets. According to Dr. Dorobantu, the current hybrid team members collectively have a much better understanding of the capabilities of today’s hybrid technology in MHDVs as well as the commercial obstacles that it currently faces. At the same time, there is a much better understanding of the need to take a more integrated systems view of future MHDVs, including the role of the powertrain beyond the engine as well as the broader electrification trends that are affecting all forms of land transportation, including LDV automobiles. Armed with their years of collective experience in the hybrid MHDV field, the team members are proposing that the scope of the new working group should be broadened to include a wider variety of technologies that can provide cost-effective reductions in truck fuel consumption and GHG emissions.
Questioned about the role of hybrids in the scope of the new working group, Dr. Dorobantu indicated that it was not the intention of the team members to eliminate hybrid technology from the 21CTP program since there are specific market segments (e.g., urban buses) and market locations (e.g., China) where hybrid technology is experiencing considerable market success. Instead, a goal of the new working group will be to determine how hybrid technology can be utilized in innovative ways as part of a broader powertrain electrification process to achieve critical technology breakthroughs that will be commercially successful in a wider range of MHDV classes and application categories. For example, Dr. Dorobantu expressed optimism about the longer-term market opportunities for advanced power train technology in HD Class 8 long-haul trucks because of emerging market trends toward regional-haul trucks with smaller engines that spend considerably more of their operating time in congested urban environments requiring frequent stops and starts.
Based on this discussion and other information provided by the 21CTP leadership cited above, it is apparent that one of the important achievements of this hybrid team restructuring, when completed, will be a greater focus on the interactions and potential integration of several key subsystems in the vehicle, starting with the engine. This proposed system focus contrasts with the current 21CTP strategy of focusing on the development of component technology, a topic that will be addressed in more detail later in this chapter.
Hybrid Vehicle Fuel Consumption and Emissions Certification
The fuel consumption and emissions certification of a conventional diesel-powered MHDV is currently accomplished by running the engine over a combination of transient and steady-state operating conditions on an engine dynamometer. The certification process is considerably more complicated for hybrid trucks since the emissions cannot be accurately determined unless the complete hybrid powertrain, including both the engine and the electric machine(s), is tested as an integrated unit. Progress has been made by the National Highway Traffic Safety Administration (NHTSA) and EPA in recent years toward defining alternative approaches to evaluating the fuel consumption and emissions of hybrid MHDVs using either simulation, dynamometer testing of hybrid drivetrain power packs without the rest of the vehicles, or chassis dynamometer testing of the complete hybrid truck. However, these evaluation procedures are marginal for the Phase I MHDV fuel consumption and emissions regulations issued in 2011 (EPA, 2011), hindering their ability to accurately evaluate the fuel consumption and emissions characteristics of production hybrid MHDVs.
Improved validation techniques will give the industry and the regulators the information needed to assure compliance with new fuel consumption and GHG emissions standards in a way that reflects the benefits that hybridization provides to vehicle performance. The need for these MHDV test procedures has been apparent for several years, providing the basis for one of the recommendations (Recommendation 4-8) in the NRC Phase 1 report (NRC, 2008). The current committee received promising reports about the recent completion of the Vehicle Systems Integration Laboratory at ORNL,8 including reports that this facility will be used in the development of MHDV hybrid power pack test procedures in collaboration with EPA and other agencies. However, no specific date has been set for the completion and release of the new test procedures.
Role of the Federal Government and the States
Hybrid Truck Incentives and Tax Credits
Incentives were established to help accelerate the development and implementation of high-efficiency HD vehicles, taking the form of fuel consumption credits. More specifically, manufacturers earn credits for HD vehicles and engines they produce that exceed the fuel consumption standards. Credits are calculated at the end of each model year based on
8 D. Smith, Vehicle Systems Integration (VSI) Laboratory, Oak Ridge National Laboratory, Presentation to the committee on November 18, 2014.
the fleet average fuel consumption. A manufacturer is permitted to average, bank, or trade credits that it accumulates by complying with the standards. Carbon dioxide (CO2) credits can be used to offset compliance with the nitrous oxide (N2O) and methane (CH4) vehicle standards (i.e., 0.10 g/bhp-hr N2O and 0.10 g/bhp-hr CH4 for engine testing of long-haul tractors and vocational vehicles in 2014 and beyond for compression ignition [CI] engines, and 2016 and beyond for spark ignition [SI] engines).
Several states have adopted incentives (NCSL, 2014) for the purchase of hybrid vehicles or for conversions. These state incentives take a variety of forms, including grants, rebates/vouchers, loans, tax credits, or tax exemptions. California has a hybrid truck and bus voucher program. New York has an alternative fuel vehicle voucher/incentive program. Colorado offers tax credits for either the purchase or lease of qualified vehicles or for qualified conversions. These Colorado credits apply to battery-electric and plug-in hybrid-electric vehicles, hydraulic hybrid trailers, and to alternative fuel vehicles (AFV), including liquefied natural gas, compressed natural gas, liquefied petroleum gas or hydrogen. The Texas Clean Fleet Program (TCFP) offers grants to replace HD on-road diesel vehicles with alternative fuel and hybrid vehicles.
The Federal Transit Administration (FTA) provides incentives for mass transit buses, including those powered by conventional diesel engines (alone), hybrid powertrains, and by other types of nondiesel engines. The federal incentive is 80 percent of the purchase price for buses with conventional diesel engines, plus 90 percent of the differential price for a bus equipped with a hybrid powertrain. If the bus is powered by a nondiesel (e.g., natural gas) engine, 82 percent of the differential price is covered by the federal incentives.
Fuel Efficiency Standards
In 2011 the EPA and NHTSA announced the Heavy-Duty National Program, establishing standards that reduce GHG emissions and improve the fuel efficiency for medium- and heavy-duty engines and vehicles. These standards require that the HD tractors used in tractor-trailer combinations for long-haul service reduce fuel consumption and GHG emissions by 9 to 23 percent compared to their 2010 baseline values, starting in model year (MY) 2017 (EPA, 2011). The standards apply to HD long-haul trucks (Class 7 or 8), large pickup trucks (Class 2b), and vocational vehicles (Classes 2b to 8). The rules cover both engines and vehicles.
Two approaches for phase-in of the 2018 standard have been established to provide manufacturers with some flexibility on how they comply with the new standards. One of these is based on an engine averaging, banking, and trading (ABT) program and the other is based on a vehicle ABT program. Both programs are designed to apply with increasing stringency during the 5-year period from MY 2014 to MY 2018.
The EPA and NHTSA together with CARB plan to extend the HD program beyond 2018 to achieve further reductions in fuel consumption and GHG emissions. In establishing these standards, the EPA will likely have to consider new technologies that are not currently in production such as advanced forms of hybridization.
H-2 Hybrid Goals. NRC Phase 2 Recommendation 4-1. The DOE should provide an up-to-date status with respect to the heavy-duty hybrid goals. The DOE should partition the available hybrid funds between heavy-duty and light-duty hybrid R&D technology to promote the R&D required for the development of heavy-duty hybrid technologies, since heavy-duty hybrid requirements are significantly different from light-duty requirements.
21CTP Response: DOE does not have specific hybrid goals for light-duty hybrids. Research and Development (R&D) and corresponding goals are for component technologies (e.g. batteries, electric motors, etc.). These technologies and the R&D advances should be scalable across vehicle weight classes in many cases.
Committee Comment on Response to 4-1
In the DOE 21CTP roadmap and technical white papers (21CTP, 2013), Section 2/10.1 summarizes six stretch goals for the MHDV Hybrid Group; these were originally formulated and published in 2011 (DOE, 2011). The goals address motor technology, power electronics, energy storage, system optimization for MHDVs, and electrified power accessories. In response to a question posed by the committee to the 21CTP management about the status of work on these stretch goals, the following response was received:
Although we have not conducted a full planning effort for reviewing these goals and defining the specific budget required to meet each one, the Hybrid team has been revisiting the goals in light of the current and near-term future outlook for hybrid technology in commercial trucks (21CTP-1, 2014).
No further information has been received from the 21CTP management team regarding the results of the hybrid team’s efforts to revisit the goals, suggesting that a significant amount of uncertainty still exists in this area. It is important for these goals to be clarified as soon as possible so that definite plans can be made for accomplishing those goals.
H-3 Hybrid Goals. NRC Phase 2 Recommendation 4-2. The DOE should determine what is needed for the battery cells and other electric drive components in the ARRA-Transportation Electrification programs aimed at development and manufacturing in the United States, as specified in the objectives of these programs.
Partnership Response: The objective of the ARRA Transportation Electrification grants are to demonstrate, collect data, and evaluate potential grid impacts of electric-drive vehicles that are ultimately produced in the United States. While DOE encourages domestic sourcing of components used in the vehicles, there is no requirement that the components be manufactured in the United States.
Committee Comment on Response to 4-2
From the context of this recommendation and its associated finding (Finding 4-1) in the NRC Phase 2 report, it appears that the Phase 2 report was recommending that DOE make an effort to deliver information about its battery and motor drive component development programs to the major industry recipients of ARRA-funded awards who were using the federal funding to develop both battery-electric and hybrid trucks and buses. No specific action was apparently taken by DOE in response to this recommendation, and the time that has now elapsed since the ARRA awards were made makes the recommendation moot at this point.
H-4 Hybrid Emissions Certification. NRC Phase 2 Recommendation 4-3. As partners of the 21CTP, EPA and DOT’s NHTSA should work with CARB to develop test procedures for the certification process for criteria emissions so that the emissions benefits of hybridization will be recognized, allowing the reduction in size or simplification of the emission control system of hybrid heavy-duty vehicles to be realized.
Partnership Response: DOE agrees that the proposed test procedure development should be performed by EPA and DOT’s NHTSA.
Committee Comment on Response to 4-3
The importance of the development of these test procedures has been discussed earlier in this chapter and will not be repeated here. Recommendations to accelerate the development of these test procedures date back to the NRC Phase 1 report in 2008 and an updated version of this recommendation is included in this report in order to spur further development of these certification procedures.
H-5 Hybrid Business Case/Break-even Time. NRC Phase 2 Recommendation 4-4. Dual paths should be pursued to achieve a break-even time of 5 years for heavy-duty hybrid vehicles. First, the DOE should use its vehicle simulation tools to determine the advanced technologies needed to meet the goal of 60 percent improvement in fuel economy (38 percent reduction in fuel consumption), from the current status of 20 to 40 percent improvement (17 to 29 percent reduction in fuel consumption) and initiate R&D programs to develop these technologies. Second, manufacturers should be encouraged to explore modular, flexible designs, which could yield higher production volumes and thus achieve significant reductions in capital costs of hybrid systems.
Partnership Response: DOE is prepared to assist industry in these types of studies. DOE does not plan to conduct or initiate hybrid centric R&D programs. DOE’s focus is on electric-drive component R&D to develop technologies that can be integrated by manufacturers into advanced technology vehicles.
Committee Comment on Response to 4-4
There is significant value in taking a systems approach to designing hybrid drive systems for trucks, as was demonstrated in the SuperTruck program results. At least two of the six stretch goals set by 21CTP for its hybrid truck program in 2011 are specifically focused on system optimization of MD and HD hybrid trucks (Goals 4 and 5), and the available evidence indicates that R&D efforts on systems-based objectives is justified. For example, the 21CTP federal agencies, including DOE and EPA, are encouraged to make their vehicle simulation tools available to their industry partners to evaluate vehicle-level approaches to maximizing the benefits of hybrid drive systems for a variety of truck applications, in keeping with the 21CTP goals. Despite the ambitious quantitative objectives set in the 21CTP stretch goals, opportunities for applying smaller microhybrid units in MDHVs to achieve more modest fuel consumption and emissions reductions should be included in these evaluations if they can achieve significant improvements in the value proposition for new mild hybrid truck configurations.
H-6 Revised Hybrid Goals. NRC Phase 2 Recommendation 4-5. The 21CTP should establish plans and develop realistic budgets for accomplishing the six new stretch goals for heavy-duty hybrid vehicles in accordance with the committee’s findings, explain the rationale behind the new goals, and provide the current status of the applicable technology for each of the goals so that the magnitude of the tasks for each can be assessed.
21CTP Response: The Partnership concurs that planning for these updated goals is critical: the Partnership industry and government members will be working as a team to conduct these planning efforts and identify the appropriate parameters for successful achievement of the goals, subject to available funding. Ongoing research results will inform goal revisions. Two of the SuperTruck teams are developing and integrating full hybrid systems into Class 8 vehicles. In addition, ORNL will be installing and testing a full heavy-duty hybrid system in a dedicated test cell. 21CTP will use these project findings to revise goals as appropriate.
Committee Comment on Response to 4-5
This recommendation is closely associated with Recommendation 4-1. As noted in the Comment on Response 4-1, the 21CTP hybrid team has not developed a plan for addressing the six stretch goals and is now in the process of revisiting the goals in conjunction with the restructuring of the team.
The MHDV hybrid propulsion initiative currently comprises a major thrust within the strategic approach defined for the 21CTP technology program. Despite some significant technical accomplishments that have been cited in this chapter, the MHDV hybridization program finds itself at a crossroads with countervailing forces and some internal inconsistencies that the 21CTP leadership must acknowledge and resolve in order to set a clear direction for moving forward. A couple of striking examples include these:
- The 2013 21CTP roadmap continues to place a high priority on hybridization in its technology plan for achieving major reductions in fuel consumption and emissions, yet no funding has been requested or allocated to explicit MHDV hybrid R&D projects for the past 7 fiscal years. Although claims are made by the 21CTP leadership that DOE expenditures on component-oriented R&D for LDV hybrid drives is sufficient to meet the requirements for MHDV hybridization, the 2013 21CTP roadmap document makes a special point of emphasizing the differences between the technology needs for LDV and MHDV hybrid systems (21CTP, 2013).
- Several MHDV hybridization projects funded by federal agencies and private industry have clearly demonstrated that these hybrid systems can successfully deliver major reductions in fuel consumption and emissions, but the cost of the hybrid drive equipment does not meet typical payback period requirements set by the MHDV truck purchasers. In some of these cases, the breakeven period for the hybrid drive equipment falls well within the expected lifetime of the MHDV and its propulsion drive, even without applying any price on the carbon that is released. However, the tight payback period, 2 years or less, that is typically required by industry (CALSTART, 2010) significantly impedes the ability of MHDV hybrid drive equipment to succeed in the marketplace. Reasons cited by truck purchasers for insisting on such short payback periods include the high cost of capital and typically short new truck ownership periods of 3 to 5 years, with little confidence that the new buyers will compensate them for any premium-cost features that reduce fuel consumption.
The demonstrated long-term benefits of hybridization for reducing fuel consumption and emissions in several types of MHDVs are too large to ignore despite the cost barriers faced by many of today’s hybrid drive manufacturers for their commercial offerings. More stringent fuel consumption and GHG emissions standards for MD and HD trucks are now being developed by the federal government for the years beyond MY 2018, making it important for 21CTP to support the development of advanced technology, such as battery-electric and hybrid drives, that will help to meet those goals. Unfortunately, the cost of hybrid drive equipment is not likely to fall sufficiently fast to meet payback requirements in the near future. The following findings and recommendations have been formulated with the objective of learning as much as possible from past and current 21CTP projects focused on hybrid MHDV equipment, and applying these lessons to the future development of more cost-effective hybrid systems that can overcome the current market barriers.
Finding 4-1. The 21CTP is considering a proposal to restructure its hybrid team so that it can work on other drivetrain efficiency improvements, including other types of system integration opportunities that incorporate hybrid drive equipment.
Recommendation 4-1. The 21CTP hybrid team should use this opportunity to redefine its mission in a manner that will lead to vehicle efficiency and emissions reduction improvements via a range of technology options, including promising opportunities for electrification and other types of innovative drivetrain improvements. During the course of this restructuring, the six R&D stretch goals developed in 2011 for the MHDV hybridization program should be redefined as part of the development of strategic objectives of the restructured advanced drivetrain initiative. At the conclusion of this process, the 21CTP leadership, working together with DOE and the other 21CTP partner federal agencies, should make a serious effort to secure funding to pursue whatever goals emerge so that they have a realistic chance of being achieved.
Finding 4-2. Several manufacturers have commercialized MD hybrid trucks during the past several years and successfully demonstrated their ability to significantly reduce fuel consumption and emissions, particularly in vocational and delivery truck applications. Despite this progress, the high cost of the hybrid drive train equipment and batteries, combined with dropping prices for natural gas and oil, have significantly retarded their market penetration in the United States. This has caused economic hardships for many hybrid truck manufacturers, causing a widespread reevaluation of the current hybrid truck business viability, at least in North America. At the same time, there is evidence that business opportunities for MHDV hybrid equipment are growing in other parts of the world, particularly in China, where government mandates are having a major impact.
Recommendation 4-2. Recognizing the advantages that hybridization can offer in trucks, 21CTP should support the development of new technology that offers promise for significantly improving the performance and cost-effectiveness of hybrid truck technology in the longer term. Project opportunities should be pursued to evaluate cost-effective vehicle electrification configurations for trucks, including hybrid
drives with optimized component ratings to minimize their payback periods in different vehicle classes and applications. This future work should take advantage of technology advances originally made and commercialized for light-duty vehicles, including new battery technologies as well as opportunities for integrated microelectrification of truck functions such as start/stop operation, idle reduction, waste heat recovery, engine starting, and accessory electrification.
Finding 4-3. Although EPA and NHTSA have made considerable progress toward defining the certification procedures for fuel consumption and emissions in hybrid MHDVs, these procedures are still incomplete and imprecise in some important areas, particularly with regard to chassis dynamometer testing of complete hybrid MHDVs, and dynamometer testing of hybrid drivetrain power packs to determine their emissions and fuel consumption performance.
Recommendation 4-3. 21CTP should make it a priority to encourage EPA and NHTSA to accelerate their efforts to strengthen and finalize procedures for certifying the fuel consumption and emissions of hybrid MHDVs, including procedures for chassis dynamomenter testing of complete hybrid vehicles and dynamometer testing of hybrid propulsion drivetrains alone. The 21CTP leadership is encouraged to work together with EPA and NHTSA to inform and educate the 21CTP stakeholders and the broader MHDV manufacturing community about the details of these procedures when they become available.
Finding 4-4. The 21CTP has articulated its strategy of depending on investments by DOE in the development of key components—that is, batteries, motors, and power electronics—in light-duty hybrid vehicles, based on the argument that this technology will be applicable to hybrid MHDV drivetrains as well. However, statements in the 2013 21CTP roadmap and technical white papers document pointedly note the limitations of this approach because of key differences between the performance and lifetime requirements for the two types of vehicles, as well as differences in their operating environments.
Recommendation 4-4. The 21CTP should acknowledge that there are substantive differences between the hybrid drive requirements of LDVs and MHDVs, making it sensible to focus future hybrid MHDV investments on those components and subsystems where these differences exist and have the highest impact on the performance and cost of hybrid drives in MHDVs. This strategy should be combined whenever possible with efforts to design the hybridization equipment to accomplish multiple functions in the integrated drivetrains of future hybrid MHDVs.
21CTP (21st Century Truck Partnership). 2013. Roadmap and Technical White Papers. Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. https://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/21ctp_roadmap_white_papers_2013.pdf.
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ANL (Argonne National Laboratory). 2013. Autonomie web page. http://www.autonomie.net.
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Birky, A.K. 2014. Modeling for Market Analysis: HTEB, TRUCK, and LVChoice. TA Engineering, Inc. DOE Annual Merit Review VAN012, Washington, D.C., June 18.
CALSTART. n.d. HTUF: High-Efficiency Truck Users Forum. http://www.calstart.org/Projects/htuf.aspx.
CALSTART. 2010. Saving Fuel, Saving Money: An Assessment of Fleet Cost Savings from High Efficiency Trucks, Pasadena, Cal. http://www.calstart.org/Libraries/Publications/Saving_Fuel_Saving_Money_-_Final_Fleet_Report.sflb.ashx.
Carr, A., and N. Williams. 2014. Hydrogen Fuel-Cell Electric Hybrid Truck and Zero Emission Delivery Vehicle Deployment. Houston-Galveston Area Council. DOE Annual Merit Review VSS116, Washington, D.C., June 19.
Choe, B. 2014. Zero-Emission Heavy-Duty Drayage Truck Demonstration. Principal Investigator: M. Miyasato, South Coast Air Quality Management District. DOE Annual Merit Review VSS115, Washington, D.C., June 19.
Cox, J. 2014. Plug-in Hybrid Electric Commercial Fleet Demonstration and Evaluation. Principle Investigator: M. Miyasato. South Coast Air Quality Management District. DOE Annual Merit Review ARRAVT083, Washington, D.C., June 19.
Deter, D. 2014. Cummins MD & HD Accessory Hybridization CRADA. Center for Transportation Analysis and ORNL. DOE Annual Merit Review VSS133, Washington, D.C., June 16-20.
DeVoto, D. 2014. Performance and Reliability of Bonded Interfaces for High-Temperature Packaging. National Renewable Energy Laboratory. DOE Annual Merit Review APE063, Washington, D.C., June 17.
DOD (U.S. Department of Defense). 2014. Response to TARDEC-Specific Questions from the National Academies Committee on Review of the 21st Century Truck Partnership, Phase 3, Advanced Starter Generator (DOD006), November.
DOE (U.S. Department of Energy). 2011. Hybrid Propulsion White Paper, Submitted by the DOE Office of Vehicle Technologies to the NRC Committee for Review of the 21st Century Truck Partnership, Phase 2, February 28.
DOE. 2014. Alternative Fuel and Advanced Vehicle Search: Hybrid Systems. Alternative Fuels Data Center, DOE Clean Cities program. http://www.afdc.energy.gov/vehicles/search/hybrid/?¤t=true&display_length=50&all_fuels=y&all_manufacturers=y.
Drive Clean Chicago. 2014. Drive Clean Truck–Eligible Vehicles. Drive Clean Chicago, LLC. http://www.drivecleanchicago.com/HowToParticipate/EligibleVehicles.aspx.
Eaton. 2013. Eaton Drops Hydraulic Hybrid System, HDT Truckinginfo, September 3. http://www.truckinginfo.com/news/story/2013/09/eatondrops-hydraulic-hybrid-system.aspx.
Eaton. 2014. Eaton drops hybrids in North America, Fleets & Fuels, June 26. http://www.fleetsandfuels.com/fuels/hybrids/2014/06/eaton-dropshybrids-in-north-america/.
EPA (U.S. Environmental Protection Agency). 2011. EPA and NHTSA Adopt First-Ever Program to Reduce Greenhouse Gas Emissions and Improve Fuel Efficiency of Medium- and Heavy-Duty Vehicles. Office of Transportation and Air Quality. EPA-420-F-11-031. http://www.epa.gov/otaq/////climate/documents/420f11031.pdf.
EPA. 2013. Heavy-Duty Engine and Vehicle, and Nonroad Technical Amendments. Federal Register, vol. 78, no. 116, June 17.
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Heavy-duty Class 8 transit buses are particularly good candidates for hybrid technology owing to their frequent starts and stops for passenger pickups and drop-offs, combined with occasional longer-distance trips to return to a terminal. In addition, their typical use in densely urban areas that often fail to comply with air quality standards increases their attractiveness because of the emissions reductions they can offer.
Since the transit bus application is so well suited to hybridization, it has received considerable attention and growth. The 21CTP roadmap and white papers (21CTP, 2013) provide details of some of the prior accomplishments and support for this hybrid vehicle application area. Important past programs that have provided financial support in recent years include the National Fuel Cell Bus Program, from 2006 to 2010, the Transit Investments for Greenhouse Gas and Energy Reduction (TIGGER) in fiscal year 2011,9 and emissions certification support for hybrid buses. For the latter effort, a final report was issued by the Federal Transit Administration in August 2013 on the emissions testing done at West Virginia University’s Center for Alternative Fuels, Engines and Emissions (Wayne, 2013). Data gathered during this program on emissions and fuel economy of hybrid transit buses up to model year 2009 are available at the Integrated Bus Information Systems (IBIS) website.10
Unlike the case for many of the other medium- and heavy-duty truck classes, the technology of hybrid transit buses has matured to the point that significant numbers of buses with hybrid propulsion systems have been manufactured by several companies and are now in daily use in many urban bus fleets in the United States and around the world. For example, the total number of BAE Systems transit bus hybrid electric propulsion systems manufactured and installed globally to date exceeds 4,500 units.11 The corresponding total number of hybrid electric propulsion systems manufactured for transit buses by Allison Transmission over the past 11 years is greater than 6,500 (Allison, 2015).
However, there continue to be significant rebates and incentives available to purchasers of HD hybrid transit buses even today. The cost of a transit bus is paid 80 percent by the Federal Transit Authority in the United States. If the vehicle is a hybrid, the amount is 82 percent, or 90 percent of the differential, as stated by Bart Mancini, senior principal systems engineer at BAE Systems, in his presentation to the committee on December 4, 2014. Other countries are known to offer incentives as well. Yan Zhou and Thomas Stephens reported in the 2014 Annual Merit Review for DOE project VAN011 that China provides financial incentives of 420,000 to 500,000 yuan for hybrid and battery-electric buses longer than 10 meters. They also reported significant volumes for hybrid and battery-electric bus production of 4,000 units in 2010, growing to >10,000 units in 2013.
In November of 2014, Allison Transmission made announcements about its further development of hybrid bus products. These announcements included news of CARB’s approval for the pairing of the Allison H40/50 EP hybrid transmission with either the Cummins ISB6.7 or the Cummins ISL9 engines (Allison Transmission Holdings Inc., 2014a) and a total electrification option for powering air conditioning, air compressors, and power steering (Allison Transmission Holdings, Inc., 2014b).
In October 2014, BAE Systems announced that it would install four hybrid drive systems in buses for the City of Honolulu, where there are already 80 hybrid buses in the fleet of 525 (15 percent of the fleet). The buses are being paid for using American Recovery and Reinvestment Act funds (Cresenzo, 2014). The same announcement indicates that Hawaii is pushing to move more of its bus fleet to low-emissions energy sources, including hydrogen fuel cells and batteries.
The third manufacturer in the IBIS list that has a history of producing hybrid transit bus transmissions, ISE, filed for bankruptcy in 2010 and then sold its assets to Bluways USA, a subsidiary of Bluways International in Belgium. ISE had sold 300 hybrid systems. No information on Bluways USA products is available online.12
Some of the technical challenges that must be overcome in order for hybrid and battery-electric drives to achieve greater market penetration have much in common with those that face hybrid drives in other MD and HD truck applications. The most important of these is the challenge of building hybrid drives that cost much less than they do today in order to make them more economically attractive to cities and municipalities that face tightening budgets for future bus purchases. For battery-electric drives, improvements in the battery energy and power density characteristics are critical in order to extend the buses’ all-electric driving range and to improve their ability to absorb high peak regenerative braking power pulses without needing to use their mechanical brakes. Achieving these major battery performance improvements without increasing their cost (or, better yet, while decreasing their cost) is one of the biggest challenges facing hybrid- and battery-electric drive systems for virtually all truck, bus, and passenger vehicle applications.
11 B. Mancini, BAE Systems, “Electric-Hybrid Powertrains: Past, Present, and Future,” presentation to the NRC Committee on Assessment of Technologies and Approaches for Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, Phase 2, December 4, 2014.
21CTP (21st Century Truck Partnership). 2013. Roadmap and Technical White Papers. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. https://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/21ctp_roadmap_white_papers_2013.pdf.
Allison Transmission, Inc. 2011. Allison Hybrid H 40 EP/H 50 EP. http://www.allisontransmission.com/docs/default-source/marketingmaterials/sa5983en-h40-50-ep1BCB31AC06C2F2B94ACCEED0.pdf?sfvrsn=4. Accessed April 23, 2015.
Allison Transmission, Inc. 2015. H 3000TM Introduction and Hybrid Market Update for MD- and HD-Vehicles. Report provided to the committee by Allison Transmission, February.
Allison Transmission Holdings Inc. 2014a. Allison Transmission and Cummins receive ARB approval in California for the H 40/50 EP system paired with ISB6.7 and ISL9 engines. PR Newswire, November 13. http://www.prnewswire.com/news-releases/allison-transmission-andcummins-receive-arb-approval-in-california-for-the-h-4050-ep-system-paired-with-isb67-and-isl9-engines-282555441.html. Accessed April 23, 2015.
Allison Transmission Holdings Inc. 2014b. Allison Transmission announces total electrification option for components used with its H 40/50 EP™ system. PR Newswire, November 7. http://www.prnewswire.com/news-releases/allison-transmission-announces-total-electrification-option-for-components-used-with-its-h-4050-ep-system-281910791.html. Accessed April 23, 2015.
Cresenzo, B. 2014. BAE Systems to equip new Honolulu buses with hybrid system. Pacific Business News, October 16. http://www.bizjournals.com/pacific/news/2014/10/16/bae-systems-to-equip-new-honolulu-buses-with.html. Accessed April 23, 2015.
Wayne, W.S. 2013. Transit Vehicle Emissions Program Final Report. Federal Transit Administration Report No. 0048. U.S. Department of Transportation.