The engine can generate enough power in 4.5 minutes to run the A/C for 50 minutes when the outside temperature is 95 degrees F and humidity is at 50 percent, Kahn said. The stop-start engine operation allows the truck to stay legal even in places where laws limit idling; often that limit is five minutes, so the 4.5-minute running time complies under those circumstances. More engine use would be needed under hotter and/or more humid conditions.
This 386 Hybrid is unique in the Wal-Mart fleet. Disney said the tractor will not go into regular service, but instead is used for presentations (such as to the company's board of directors the day after I drove it) and to benchmark it against standard tractors. Meanwhile, another diesel-electric hybrid is in the works. It's being prepared by International, Cummins and ArvinMeritor, and will be based on International's new ProStar tractor. ArvinMeritor says it's due out in January 2009.
The green 386 also serves to familiarize drivers with the hybrid concept. "Guys that have driven it really like it," Disney said. "It's a paradigm change for them - there's no noise. They're used to noise when a truck takes off, and there isn't any" with the hybrid.
There's no noise at first because the motor silently begins moving the truck from a standstill, and the engine begins revving as its idle speed matches road speed and more power is needed to accelerate. Then revs rise and fall as the transmission changes gears and road speed builds. To my ears, engine noise after launch is pretty much normal, and was made worse because the 10-speed UltraShift tended to hang in each gear and didn't upshift until 1,900 or so rpm. This should be alterable by reprogramming the transmission's electronic controls, but in the meantime, I began prompting progressive upshifts by punching the M (for manual) button and then the Up arrow at lower revs.
The electric motor-generator makes as much as 60 horsepower and 340 pounds-feet. With a really light foot you can make the motor work longer on launch, but acceleration then would be really slow. Once I was able to use electric-only power while backing up, and the motor emitted a slight whine while the engine stayed at idle. Otherwise I never heard the motor, and while I could feel it work on launch, it was imperceptible while under way.
A really useful feature is the motor-generator's "hill-holder" ability. Kahn pointed it out when he noticed I was using the trailer brake to keep us in place on a slight upgrade as we waited to venture onto a busy street - from a Wal-Mart Super Center, appropriately enough. "You can use the hill holder here," he said. "The motor produces torque at zero rpm, so it can keep the truck from rolling backward. Just put your foot on the accelerator and release the brake." I did, and it worked. During this activity the clutch is disengaged from the still-idling engine so its facings aren't burned, and there's no harm to the motor-generator, either.
The Eaton UltraShift, with its automatically operated clutch, takes away much of the work of driving a heavy truck. It lets its driver concentrate on traffic and maneuvering through it, and seeing to his/her deliveries. Tests and fleet experience show it saves fuel because it makes everybody an economical driver.
Not so at Wal-Mart. "Our drivers are seasoned with many miles behind them, so the automatic doesn't do as well with us," Disney said. "We know it's part of the hybrid system and we have to accept it, but the manual transmission does better with our drivers for fuel economy," which of course is the point of the hybrid.
"At this point it's not cost-effective, and there's no return on investment," he said of the hybrid. "It's very costly" - how much neither he nor Kahn would say - "but it's doing what we want it to at this point. We're trying to understand what it can and cannot do, and seeing who (among suppliers) can provide best efficiency with the best return on investment. We want a production truck; we don't want a one-off vehicle."
The current high cost of the hybrid's "lithium-ion battery modules," as Kahn calls them, is primarily what makes the hybrid truck unaffordable for now, and its efficiency gains don't qualify it for any federal subsidies at this time. But he believes cost will come down as more of the batteries are used in other diesel- and gasoline-electric hybrids and volume production of the batteries gets under way. That might be two or three years away, which would jibe with Peterbilt's and Eaton's prediction of 2010 production for hybrid road tractors.
Much closer are other Peterbilt hybrids: a medium-duty public-utility bucket truck, with eight Model 335-based units now built and being outfitted with bodies for test; and a midrange delivery truck, with four 330 chassis with van bodies entering limited service. These use Cummins-made Paccar PX diesels with Eaton electric hybrid systems.
There's also a heavy trash-truck hybrid using a Model 320 low-cabover chassis; it has a Cummins ISL and Eaton's Hydraulic Launch Assist. Twelve of these are now being tested in fleets, and production could start next year. So watch down the street to see if a big green truck shows up to fetch your garbage.