U.S. Military Considers Green Vehicles

Photo: Lance Cpl. J. Agg

Today, the U.S. military’s mission to go “green” involves much more than the familiar camouflage paint of its vehicles. Like the civilian world, the military is excited about the potential of hybrid and fuel cell vehicles because of their high fuel economy, something that’s more important to national defense than most of us realize.

Why would that be? If you think that $2.50-a-gallon gasoline is outrageous, look at it from a strategic perspective where a gallon of military diesel can cost $400 to $600 by the time it reaches the field. According to Paul Skalny, deputy director of the U.S. military’s National Automotive Center (NAC), the importance of this is obvious when you consider that some 70% of the bulk tonnage the military takes to war is fuel. The NAC, part of the Army’s Tank Automotive Research and Development Engineering Center (TARDEC), is responsible for the nation’s advanced military automotive technology and is the organization responsible for technology transfer between the military and civilian worlds.

The Army is interested in three types of hybrid systems – hybrid hydraulic, hybrid electric, and hybrid fuel cell – all technologies that also have civilian applications such as trucks and buses.

Permo-Drive's hydraulic hybrid unit

A hybrid hydraulic example is the Permo-Drive Hydraulic Regenerative Drive System (RDS) from Australia. The RDS recoups energy normally wasted during deceleration by pressurizing hydraulic fluid stored in accumulators. This energy is released back into the driveshaft as required such as when accelerating, climbing grades, or shifting gears. Besides gaining up to 30 percent better fuel economy with associated reductions in emissions, RDS can decrease wear on brake and driveline parts. Dana Corp. and Permo-Drive Technologies are jointly working to incorporate Permo-Drive into the U.S. military’s FMTV (Family of Medium Tactical Vehicles). Dana would supply the RDS to FMTV supplier Stewart and Stevenson for use in new vehicles with the potential for retrofitting existing ones in the future.

Ford has proposed a hybrid hydraulic version for the Army’s COMBATT (Commercially Based Tactical Truck) program, which militarizes Ford F-350, Dodge Ram 2500/3500, and Chevrolet Silverado pickups. Ford’s hybrid hydraulic concept features the Eaton-built Hydraulic Launch Assist (HLA) system installed in an F-350 Super Duty Crew Cab pickup. Like the Permo-Drive RDS, this hydraulic recovery system supplements the vehicle’s 7.3-liter diesel engine. HLA debuted in the F-350 Mighty Tonka concept vehicle.

Ford's hydraulic hybrid system

As shown above, the HLA system captures kinetic energy during deceleration, driving a combination pump/motor as a pump to transfer oil from a reservoir to an accumulator. This oil compresses nitrogen in the accumulator bladder to pressurize the accumulator. Pressure released during acceleration drives the pump/motor as a motor, transferring torque to the driveshaft and helping propel the vehicle.

The Army is additionally interested in hybrid electric designs like the Oshkosh ProPulse. In this series hybrid, a diesel engine powers a 400-kilowatt electric alternator, which in turn provides power to electric motors for each differential. The alternator also charges ultracapacitors that store energy for use when a surge of additional power is needed for quick accelerating or climbing. Besides improving fuel economy by up to 40 percent, ProPulse reduces emissions to meet new stricter EPA standards. The alternator can also generate up to 400 kilowatts of AC power to replace cumbersome generator sets that could be used to supply power for an airfield, hospital, command center, or for that matter an entire city block. An initial commercial application for ProPulse could be in the company’s line of aircraft rescue and fire fighting vehicles.

BAE Systems has installed its HybriDrive system, which the company acquired when it purchased HybriDrive developer Lockheed Martin, in a 5-ton M1086 FMTV cargo truck. HybriDrive features an auxiliary power unit (APU) mated directly to the standard FMTV diesel engine. The truck is driven by two AC induction motors using energy supplied by the APU and a traction battery system. The motors, one at the front axle and one at the rear tandem axle, also act as generators in a regenerative braking mode. The battery system stores energy to supplement APU output during peak power demands such as when accelerating. It also stores regenerative braking energy. This large battery pack can supply up to 200 kilowatts of continuous electric power during a “silent watch” mode, allowing stealth operations. The dual-function engine/generator powerpack can eliminate the need for towed generators that would normally provide service for mobile or stationary battlefield electrical requirements. An FMTV with HybriDrive could cut fuel consumption by 25-50 percent to reduce logistics requirements and increase vehicle range. On the civilian side, HybriDrive has been installed in several buses now being used in revenue service in California and New York. These have been so successful in New York that another 325 have been ordered.

When the military services became interested in a hybrid version of the High Mobility Multipurpose Wheeled Vehicle (HMMWV) – the familiar Hummer – the Army contracted IDT-PEI electronics to build two proof-of-concept Hybrid HMMWVs followed by four hybrid Humvee test vehicles. The latter were fitted with a hybrid-electric drive consisting of a 75 kilowatt generator, two 75 kilowatt propulsion motors, and conventional lead-acid batteries.

A militarized Chevy Silverado hybrid is GM's COMBATT developmental vehicle.

DaimlerChrysler has developed a hybrid version of its COMBATT based on the Dodge Ram. This hybrid system is like the one used in the hybrid Dodge Ram variant it plans to sell commercially. General Motors has also developed a hybrid version of its COMBATT, but goes one step further by adding a fuel cell APU. Its COMBATT is a militarized version of the Chevrolet Silverado crew cab using a 6.6-liter Duramax Diesel V-8 engine mated to a parallel hybrid electric system, which uses a continuously variable transmission (CVT) with integral electric motors and a lightweight nickel-metal-hydride battery system for energy storage. The diesel-electric hybrid can operate as a self-contained generator to provide up to 30-kilowatts of DC and AC electricity. The APU is a Hydrogenics 5-kilowatt proton exchange membrane (PEM) regenerative fuel cell. While the COMBATT is driven, the PEM’s electrolyzer uses electricity generated by the diesel engine to break down water into oxygen and hydrogen. Since the regenerative APU produces its own hydrogen, a new logistics fuel (hydrogen) does not have to be added to the Army’s supply line.

Hydrogenics fuel cell APU

The GM effort highlights the military’s initial interest in fuel cells for power generation rather than vehicle propulsion. Skalny advises that initial efforts would focus on auxiliary power units that could remove the accessory load and allow the main engine to do what it does best – propelling the vehicle. Fuel cell APUs can deliver the same amount of power as a conventional generator, but stealthily. Due to hydrogen’s superior energy density and the inherent efficiency of fuel cells, fuel cell APUs provide the same capability as equal-sized batteries, but can operate six to ten times longer, a very important consideration during military missions.

When it comes to these new technologies, similar challenges face both military users and their civilian counterparts. These include lengthy and costly development, reliability and durability issues (in the military’s case, complicated by deployment in a combat environment), and for hydrogen fuel cells a required infrastructure. Today, the U.S. military has a “single fuel” policy, which means that everything from trucks and tanks to fighters and helicopters must run on JP-8, a fuel that can be used in both diesel and turbine engines. Hydrogen would complicate things so if hydrogen is used, it has to be produced in the field either by electrolyzing water or reforming JP-8.

Quantum Fuel Systems Technologies Worldwide, which is developing a high performance, light-duty fuel cell-powered off-road vehicle for the NAC, is also supplying a transportable hydrogen refueler called the HyHauler Plus. The HyHauler Plus is a lightweight, hydrogen fuel dispensing system specifically designed for fast fills that uses an onboard electrolyzer to generate hydrogen from water and electricity. This self-contained unit can be transported by a full-size pickup truck or sport utility vehicle rated for towing, and is anticipated to deliver enough fuel for up to 11 light-duty off-road vehicles. Hydrogen is stored in Quantum’s ultra-lightweight TriShield tanks.

The Marine Corps could be the first to have a hybrid electric combat vehicle. This would be the Shadow Reconnaissance, Surveillance, and Targeting Vehicle (RST-V) being developed by General Dynamics Land Systems under sponsorship of the Office of Naval Research and the Defense Advanced Research Projects Agency. The Shadow features a lightweight diesel engine coupled to an alternator that supplies electric power to four in-hub electric wheel motors and charging batteries. The RST-V’s lithium-ion battery pack enables engine-off silent travel for up to 20 miles with extremely low thermal and acoustic signatures for stealthy reconnaissance missions. The four-man RST-V is designed to be carried by the MV-22 Osprey and could replace both the M151-A2 Fast Attack Vehicle and HMMWV. Four prototype RST-Vs have been successfully tested and evaluated with the next step the System Design and Development phase of the acquisition process.

Ultimately, Skalny sees more than a transfer of technology between the Army and the civilian world, noting that there’s also a transfer of knowledge since many young soldiers will be working on systems that are certainly on the leading edge. This training could help assure there is a cadre of technicians with the knowledge and experience to maintain similar hybrid and fuel cell vehicle technologies in civilian life.