FedEx Goes Hybrid?
From a truck perspective, the knock against hybrid/electric drivetrains is that trucks have to work for a living and therefore need all their power available all the time, not like typical hybrids that only need occasional bursts of energy for acceleration.
FedEx is testing OptiFleet diesel/electric hybrids, which have the same payload and performance of standard work trucks, but slurp down 57-percent-less diesel fuel. Because the hybrid is part of a larger experiment in conjunction with Environmental Defense aimed at cleaning up exhaust emissions, each truck also carries a diesel catalyst, which contributes to a 65 percent reduction in smog-forming emissions and a particulate trap that eliminates 96 percent of sooty particulates from the truck's diesel exhaust.
The basic FedEx delivery truck is a Utilimaster W700 step van built on a Freightliner MT45 chassis, powered by the familiar Cummins 5.9-liter inline-six turbodiesel that drives through an Allison AT542FE automatic. The OptiFleet hybrid trucks substitute a 170-horsepower, 420-pound-foot, 4.3-liter, four-cylinder Mercedes-Benz OM904 turbodiesel internal-combustion engine combined with an electric motor to provide extra oomph as needed. The transmission is an automatically shifted six-speed manual transmission provided by Eaton, the company that designed, built, and installed the hybrid system in the trucks. The transmission uses the same computer-controlled paddle-shift concept pioneered by Ferrari. As with a regular manual trans, better gas mileage is a benefit because there's no torque converter. A taller 3.31:1 final drive replaces the regular 4.10:1 rearend for maximum fuel economy while exploiting the electric motor's high starting torque.
The trucks don't drive much differently from today's conventional delivery trucks, other than noticeable deceleration when the driver lifts off the gas as the electric motor switches to generator mode. This is expected to save the company money on brake wear, which, considering the stop-and-go nature of the business, is a big expense.
Unlike other hybrids, the OptiFleet trucks don't automatically stop the diesel engine when idling at stoplights. That's because FedEx drivers always switch the engine off whenever they stop for a delivery, so the only benefit of such a system would be at traffic lights.
With luck, the technology pioneered for commercial fleets will soon find its way to consumer trucks and SUVs, giving us the option of thrifty hybrids that can still pull trailers and haul loads.-Dan Carney
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