AVIATION WEEK | Hybrid Vehicles Are In U.S. Military's Future
May 11, 2011 § Leave a comment
By Paul McLeary, Kimberly Johnson
Washington, Greenville, S.C.
While the need to reduce the military’s fuel consumption has never been greater due to rising fuel prices and the budget crunch the Pentagon is facing, the path forward for acquisitions is littered with new technology slow to tempt the old guard. The mindset of the military regarding fuel efficiency is different than on the commercial side, says Mike Mekhiche, BAE Systems director of parallel drive systems. “There are cultural hurdles that need to be overcome.”
Commercial makers of hybrid vehicles, such as Oshkosh and BAE, want to persuade the services to make the switch for future acquisitions with up to 20% reduction in fuel consumption and a power-rich source of life for energy-hungry electronic warfare components. (For a story on sustainable battlefield energy initiatives, see p. 28.)
Hybrid benefits, however, carry major changes under the hood. Drive trains come in two basic versions: series and parallel. Unlike a traditional drivetrain where the engine is directly connected to a vehicle’s wheels, the engine in a series hybrid powers a generator, which supplies torque to the wheels through electric motors. In a parallel system, both the petroleum-fueled engine and battery-powered electric engine are connected to the transmission and can work at the same time to turn the wheels. Both architectures rack up fuel economy gains when leveling out changing demands on the engine, most dramatically in stop-and-go scenarios or mountainous terrain. Kinetic energy lost during braking and deceleration, which is the Achilles heel of a conventional vehicle’s fuel consumption, can be captured and stored, then reused to assist the next acceleration.
Significantly, for a ground force that increasingly relies on small electronics like night-vision equipment, handheld radios, biometric systems and metal detectors to sniff out buried roadside bombs, hybrid trucks carry their own generators and can export power. The ability to export power, makers say, creates a huge draw for hybrid technology, which is considered a force multiplier by being capable of generating enough power to run a forward operating base for 2-3 days.
Still, the image of the Army’s fleet of tactical vehicles running hybrid engines on the battlefield anytime soon might need to be put on hold, says Paul Skalny, director of the Army’s Tank Automotive Research, Development and Engineering Center’s (Tardec) National Automotive Center. “The fielding of hybrids will be in the non-tactical world” first, he says. “A fuel-cell hybrid in a tactical situation is something that may happen, but quite some time from now. You may see a fuel cell auxiliary power unit (APU) in a vehicle [but] it will be some time [before it is fielded on a battlefield], because we have issues” with exposing an APU to battlefield dirt, which “would kill an APU.”
Skalny says that from the Army’s perspective, investment in advanced propulsion systems in tactical situations is dependent first on any capability gaps that might need to be filled. It’s not only fuel efficiency that the service is looking for, but advances that bring in exportable power, such as incorporating a bank of lithium ion batteries that allows for silent watch or silent mobility, improved acceleration and extended range.
Trying to work through some of these issues, Oshkosh is testing its ProPulse series hybrid electric drivetrain design for the Heavy Expanded Mobility Tactical Truck (Hemtt A3), at Aberdeen Proving Ground, Md. Its system relies on an ultracapcitor for energy storage. Likewise, BAE is submitting a series hybrid system in its prototype bid for the Army’s planned Ground Combat Vehicle competition, but would look to batteries to retain the power.
Perhaps most daunting for the technology in gaining full acceptance by the military is concern over maintenance requirements, including the safety of working on the high-voltage systems in the field, and component life.
Oshkosh contends the ProPulse system’s use of ultracapacitors for energy storage in military applications instead of batteries heads off many of these worries. “With a battery system, there’s limited life,” says Nader Nasr, chief engineer at Oshkosh’s Advanced Battery Group. “Every few years you have to replace the battery system on the vehicle, versus the ultracapacitor where the number of cycles it withstands is in the millions, versus the thousands you get with lithium ion technology.”
Ultracapacitors offer quick power storage as opposed to the slower energy release of chemical batteries, and a burst of torque during heavy-truck acceleration, Nasr explains. He points to commercial vehicles as an example. “If you want a lot of energy, as in you want to be able to drive your vehicle with the engine off for a few miles, like with a Toyota Prius, you want more energy density” such as with a battery-powered hybrid.
Ultracapacitors increase maintenance safety as voltage can be zeroed out, which eliminates the risk of explosion, electrocution or damaging components. Batteries, on the other hand, cannot be fully depleted without permanent damage.
Oshkosh, which has demonstrated the ProPulse system in the commercial market, has seen significant fuel savings in garbage truck applications. “In that sort of start-stop frequency, you can get fuel-efficiency gains in excess of 70%,” says Gary Schmiedel, executive vice president of technology at Oshkosh, who quickly cautioned that true gains need a macro lens. “It’s more traditional to get a day-long, week-long, month-long kind of average in the 10-30% range,” he notes.
For the military, even a small percentage of trucks that consume less fuel on a regular basis “moves that needle quite significantly,” Schmiedel adds.
By divorcing heavy trucks from a conventional linear engine layout, space is created through hybrid design. Oshkosh’s 700-lb. ultracapacitor for a Hemtt A3, for example, would fit inside the frame of a heavy truck. And with that reconfiguration comes new uses for space. The crew cab, for example, would have room for one more person; and there would also be room on the truck for materials-handling equipment that could unload a C-130. This in turn would create space in the aircraft that would otherwise have been used for the handling equipment.
BAE’s proposed hybrid variant of the Army Ground Combat Vehicle, unveiled earlier this year, incorporates a series system based on the technology used for the past 12 years to power its public buses. Addition of the 700-lb., 12-kw/hr. battery becomes weight-neutral with removal of the transmission and reduction in engine size, says Mekhiche.
Because the hybrid system is built as a series, maintainers are able to lock out and remove individual components safely, says BAE. Maintenance is simplified through the reduction of moving parts.
In the commercial arena, BAE recently launched the HybriDrive Parallel System for Class 6, 7 and 8 trucks, which unlike the series, is actually a blending of combustible engine power and electric power to drive the transmission. Included in the HybriDrive design is an electric machine sandwiched between the engine and transmission that behaves as a generator or a motor depending on what the vehicle is doing.
“Although the primary intent is to put the parallel system (and series) in commercial trucks, there are definitely advantages and unique characteristics that would make those two systems attractive to potential military vehicles, whether tactical or combat,” Mekhiche says. Starting with commercial technology also reduces front-end engineering costs for military applications, he adds.
Hybrid systems are becoming more affordable as the cost of energy storage systems comes down, says Mark Signorelli, vice president and general manager of the Ground Combat Vehicle at BAE. “The cost in a combat vehicle of a conventional propulsion system and a hybrid electric drive system are comparable. So while there’s no penalty in the production costs, there are huge benefits in life-cycle costs from fuel efficiency and increased reliability.”
Asked to look 15 years into the future, Skalny says that on the non-tactical side, every vehicle at military installations should be an advanced-propulsion vehicle. Tactically, “if we address the issues that we have to as a full community—looking at impacts from the maintenance standpoint, reliability, how we fill capability gaps in different systems—in 15 years you’ll have some type of advanced-propulsion system” on combat vehicles. He doesn’t know what these might be, since requirements will be driven by mission profiles and the vehicles involved.
Tardec is also working on hybrid prototypes such as the Clandestine Extended Range Vehicle (CERV). Built in partnership with Quantum Technology, CERV is designed to perform reconnaissance, surveillance and target designation in the field, incorporating an all-wheel-drive diesel hybrid-electric powertrain that reaches 80 mph, maneuvers over 60% grades and has a torque rating of 5,000 ft.-lb. The 3,000‑lb. vehicle reportedly slashes fuel consumption by 25% versus comparable vehicles.
Then there is the XM1124 hybrid-electric Humvee that operates in an all-electric or hybrid mode. Running in all-electric mode, the vehicle can run quietly for 10 mi., while hybrid mode uses fuel to power the generator, which recharges the batteries. The truck is also capable of exporting enough energy to run components such as air conditioning systems, while using 28% less fuel than the standard Humvee, with similar acceleration.
At a time when roadside bombs have killed hundreds of U.S. service members in Iraq and Afghanistan—and are one of the favorite low-cost weapons for insurgent and guerilla groups to use against vehicle convoys—Skalny calculates that only a 1% increase in fuel efficiency across the fleet would mean 6,444 fewer soldiers involved in convoy operations. While this is significant, many questions have to be answered before that many soldiers are pulled off the roads.