Technical Innovations
Hybrid-electrics join the Army
 Allison has worked with NAC on implementing its hybrid EP System into military vehicles. According to Allison, the EP System is flexible and easy-to-scale to a braod range of commercial applications. |
Hybrid-electric propulsion systems are especially attractive to the U.S. Army because the technology contributes to improved fuel consumption and reduced exhaust emissions. "The Army spends $1 billion annually buying new vehicles and $2 billion per year to operate and maintain them, with fuel accounting for 70% of the bulk tonnage transported by Army vehicles when our military forces are in combat," said Paul Skalny, Deputy Director of the U.S. Army's National Automotive Center (NAC).
According to Skalny and other industry experts, heavy-duty hybrid-electric trucks will be the cornerstone of the U.S. military's future fleet of commercial, heavy-duty trucks by the middle of the decade. "Right now, the Army fleet of vehicles needs to reduce fuel consumption 75% by the year 2010, while integrating more advanced technologies and lighter-weight materials," said Skalny. "The only way we're going to accomplish these ambitious goals is to accelerate emerging hybrid-electric drivetrain systems in heavy-duty vehicles. These systems are already demonstrating fuel economy improvements of 25% and hold out the promise of up to a 50% improvement. The Army needs to tap into industry if we are going to accelerate the infusion of advanced materials and technologies."
At the SAE Truck & Bus Exhibition last November, NAC displayed its hybrid-electric Command and Control Vehicle chassis, what its describes as the "poster child of dual-use technology." Ninety percent of its components were originally developed for a city bus application. The Class 8 motor home chassis is powered by a 205-kW (275-hp) Cummins diesel engine and two 75-kW electric motors driving the rear axles through a planetary gearbox. Electric energy is stored in two 250-kW lead-acid battery packs, though NiMH batteries are being considered for future use.
One of the hybrid-electric powertrains that NAC has experimented with is the EP System from Allison Transmission. The EP System extends the functionality of Allison's ES System to a broader range of applications. Both systems employ PowerCache ultracapacitors from Maxwell Technologies, an advanced super capacitor technology that delivers extended life compared to conventional batteries. The super capacitors offer a reliable and durable energy source that is about one-third the weight of batteries and one-half the volume.
Allison's EVDRIVE proprietary hybrid-drive unit makes possible a conventional component "packaging" that facilitates integration of the EP System into existing vehicle designs. This component configuration combines electrical machines and mechanical torque transfer. The split torque, continuously variable transmission design of the EVDRIVE enables the use of smaller engines and enhances efficiency by transferring power to the wheels via a combination of mechanical and electric means.
- Jean L. Broge
OMG controls emissions
According to OMG, its HPT-X5 emissions-control-catalyst technology reduces precious metal requirements by approximately 20% and raises efficiency by up to 50% compared to other state-of-the-art catalysts. The emissions-control catalysts contain two separate washcoat layers that are tailored to the catalytic function of the specific precious metals, in this case, platinum and rhodium. The first, lower layer is optimized with respect to the oxidation of hydrocarbons (HC) and carbon monoxide (CO). The top, second layer takes on the task of NOx reduction, but also contributes to the conversion of HC and CO, particularly in the cold-start phase.
Conventional three-way catalysts are less efficient during acceleration and deceleration testing, causing either too little or too much oxygen in the exhaust mix. HPT-X5 enables the rapid adsorption of excess oxygen under oxidizing exhaust-gas conditions. Accompanied by the simultaneous oxidation of CO and HC (and reversible release of oxygen under decreasing exhaust-gas conditions), HPT-X5 enables catalysts to operate close to their optimum in extreme driving situations.
The HPT-X5 catalysts have proven during lab tests to have a high temperature resistance. This feature allows them to be installed close to the engine and contributes to obtaining a quicker light-off temperature. The high temperature resistance also improves the aging characteristics of the catalyst through the use of high-temperature-resistant carrier oxides coupled with a reduction of the sintering behavior of precious metals on the catalyst surface.
The migration of the precious metals is significantly reduced by optimizing the carrier oxide/precious metal interaction, controlling the size and dispersion of the precious metal particles through the manufacturing process, and by modifying the carrier oxide surfaces and the related adhesion of the precious metals to the surface. Doping the carrier oxide with foreign atoms improves the lean stability of the catalyst at high temperatures, particularly in the case of rhodium.
- Jean L. Broge
