Executives showed off a heavy HybriDrive at last year's Work Truck Show in Indianapolis, sponsored by the National Truck Equipment Association. Since then BAE has announced long-term contracts with key suppliers. One is Caterpillar, which makes the CX31 automatic transmission that's part of the setup in this 2011-model Kenworth T800 dump truck. It was available for sampling in the Green Truck Ride and Drive at this year's show, also in Indy.
Here's why I found this truck interesting: During the construction season in central Ohio, where I live, I see a lot of dump and concrete mixer trucks rumbling along county roads. They brake often for arterial stop signs at intersections, and I have to believe that these would make excellent applications for hybrid-drive systems, whether electric or hydraulic. These are heavy trucks that require considerable braking force to make these frequent stops; couldn't a lot of that energy be captured and used to launch the trucks each time?
Most people who design hybrids say no, that the stops aren't frequent enough to justify the extra cost of the hybrid apparatus. Yet BAE chose a dump truck to demonstrate its system, so I felt vindicated, and made it a point to drive it. I came away impressed.
Smooth and quick are the words I'll use to describe the HybriDrive. Its electric components blended well with the truck's 425-horsepower Cummins ISM, boosting power to the driveline, while the Cat six-speed automatic tranny shifted smartly every time. The truck was fast off the line, but its bed was empty so of course it should've been. This is a parallel system so both power sources can work at the same time, and did during my short drive. With a more intense workout the HybriDrive should sometimes have enough electricity stored up to launch the truck by itself.
Regeneration during braking was noticeable but rather unobtrusive except for some faint whining. During deceleration, the 145-horsepower electric motor behind the engine acts as a generator, sending electricity to a 5-kilowatt lithium-ion battery pack. Foundation brakes come into play when the truck nears a complete stop, or in emergencies, which I never faced. Overall the brakes see far less wear, so maintenance on them is also less, as is the case with most hybrids.
When the driver steps on the accelerator, electric power from the batteries is then sent back to the motor, which propels the truck as it moves away from a stop. The motor makes as much as 590 pounds-feet right from the start; that lessens the amount of torque and horsepower needed from the engine, which saves fuel. The motor-generator is also the diesel's starter, and an automatic clutch decouples it from the engine when the electric device is not needed for any of its three duties.
Track tests last year showed that HybriDrive saves about 30% in fuel compared to a diesel-only powertrain, BAE says. That's exactly in line with what other hybrid manufacturers are claiming, even if some users say they're saving even more. Then again, others get less, but it depends a great deal on how the truck is used.
Would a dump truck's regular duties present enough stopping and starting to generate the savings that would pay back the cost of the system in three to five years, as BAE claims? Is that time short enough for the average small-fleet operator? Maybe not. But progressive minds managing larger fleets might think so. And I hope one of these hybrids soon comes whining down a road near my house, 'cause then I can say, "Told ya so!"