As governments around the globe get serious about shrinking carbon footprints, they’re focusing regulatory attention on the heavy-duty road transport sector, which accounts for roughly a quarter of transportation emissions. Our own EPA/NHTSA is targeting a 24 percent reduction in tractor/trailer fuel consumption between 2021 and 2027. Toward that end, Eaton Corporation devised a diesel/battery-electric hybrid drivetrain for heavy-duty trucks, which it sells primarily in Europe. Fleet testing with Coca-Cola suggests it can slash consumption by 30 percent on congested urban routes, but Coke’s 13-month fleet average savings was just 13.7 percent. Wal-Mart has tested a similar setup on Peterbilt long-haul trucks, measuring a 5-7 percent fuel savings.
Recouping the $40,000-$45,000 cost of such systems is easiest for businesses that run stop-and-go routes (and qualify for tax incentives). Coke bought 120 medium-duty hybrid trucks, and UPS bought 200 hybrid delivery vans. It’s harder to make the math work out for long-haul truckers. But Strasbourg, France-based Adgero thinks there may be a better way: Hybridize the trailer.
Adgero’s lower-cost idea replaces one of the trailer’s axles with a driven axle employing a differential to which a compact, axial-flow Yokeless and Segmented Armature electric machine producing 268 hp and 553 lb-ft of torque from YASA Motors is attached. The energy flowing to and from this oil-cooled motor resides in an 800-volt bank of ultracapacitors capable of storing 880 watt-hours of energy. It reportedly offers double the energy density and five times the power density of the next best ultracapacitors.
Skeleton Technologies, an Estonian company, developed these SkelCap ultracaps. They leverage the improved conductivity and higher surface area of patented nanoporous carbide-derived carbon (CDC). This high-tech carbon also lowers internal resistance, so energy lost to heat is five times less than with competing ultracaps. (The SkelCap pack is air-cooled.) Unlike batteries, they work great at -40 degrees and can be charged and discharged roughly a million times. (The $5,000 Eaton battery packs need replacement after “tens of thousands” of cycles.) Target system weight is less than 1,100 pounds, 500 of which is the ultracap pack.
Adgero’s hybrid trailer takes orders from a small, inexpensive (around $50) controller that mounts to the tractor. Like cars, today’s semi-tractor trucks communicate vital information over a CAN data bus, sharing this info with the trailer via a standardized 15-pin connector. Adgero’s controller taps into this CAN bus to determine when the driver is accelerating or braking—either by the friction-brake pedal or the diesel engine retarder—and communicates with the trailer via the connector to order up regenerative braking, acceleration assistance, or neither if the rig is experiencing an ABS or stability-control event or if powering the trailer risks jackknifing the rig. Just as with the hybrid tractors, the aim here is to add electric power to fill in where the diesel’s operating efficiency is lowest—low-rpm, off-boost, below the torque peak.
Adgero founder Mack Murray sees his hybrid trailer as ideally suited for multimodal transit applications, where a trailer is loaded in one country, driven to a railhead, and shipped to another where it is routed to the end user. Shipping companies would equip all their tractors with the cheap controllers then add trailers as the budget allows. Under these conditions the system should deliver 15-25 percent fuel savings, recouping the expected price premium of $27,500 in three years at European fuel prices. A bonus: Trailer equipment includes a 4G connection, GPS, and axle-weight sensors, so it can monitor and report progress every step of the way.
After extensive testing in the U.K., Murray expects to market the system on new trailers and as retrofit kits starting in 2018. Low diesel prices in the U.S. should extend the payoff period here, but a lot can happen between now and 2018 (or 2027).