On the way to a demonstration of Caterpillar's first hybrid dozer, I was expecting it would be one of the little ones, the kind used to dig pools and landscape suburban back yards. But looming up in the middle of Holt of California, a Caterpillar dealer outside Sacramento, Calif., was a huge beast, a massive yellow earth mover, the metal tracks of which came up to my waist. The Caterpillar D7E was a lot bigger than the little hybrid I was expecting.
A Caterpillar representative jumped in the cab and, metal tracks scraping up the clean concrete floor, pivoted the big dozer around and drove it out to the demonstration area, a field of dirt with one big hill, and strategically placed holes and trenches--not to mention a slalom course marked by orange pylons. As a dramatic start to the demonstration, the driver took the 56,669 pound D7E over the steepest section of the hill, the dozer's blade pointing up toward the sky. At the top, it neatly balanced on the crest before making its descent, demonstrating how easily it maintained control on this loose ground.
The D7E differs from traditional earth-moving equipment in that it uses a locomotive-style series hybrid drivetrain. It still has a big diesel engine in front of the cab, but it merely serves as a generator, powering two electric motors. The 9-liter diesel engine runs at a steady 1,500rpm to 1,800rpm, its most efficient power band. That engine is smaller by a liter than the D7R, Caterpillar's comparable diesel dozer. Net power output from the electric drive is 235 horsepower, and the D7E has almost 100,000 pounds of pulling power. As one of Caterpillar's engineers pointed out, the fact that it only weighs 56,669 pounds, it will exceed its grip before it maxes out on pulling power. … Read more