With the announcement of the first dozer-specific electric drive on its D7E tract-type tractor and an industry-exclusive single post cab, Caterpillar has started off ConExpo with a bang.
The D7E, with more than 100 patents, is “innovative from the inside out,” says David Nicoll, Cat’s commercial manager for track-type tractors. The net effect for users, according to the company:
- 10 percent more material moved per hour
- 25 percent more material moved per gallon of fuel
- Up to 20 percent less fuel consumption
How does the D7E electric drive work? In the D7E power train, the diesel engine drives a generator to produce electricity that ultimately powers two AC electric drive motors, which are connected to a differential steering system. A traditional mechanical transmission is not needed, because the variable speed electric motors serve the function of a continuously variable transmission. The electric drive train has 60 percent fewer moving parts compared to previous D7s. The electric system also provides power to auxiliary components so that no engine belts are needed. And cables have replaced the hard drive shaft.
By comparison, in the D7R – which the D7E will eventually replace – engine power goes through a torque divider and a powershift transmission.
Although electric dives have been in off-highway trucks and locomotives for years now, they use DC technology, which Cat says is harder to maintain. With advances in AC power semiconductors, larger and more reliable power flows can be achieved with lower costs, says Amy Moore-McKee, new product manager for track-type tractors. “This offers a very efficient method of converting power to the job,” she says.
Cat says the electric drive – with its sealed, liquid-cooled components – works in all environments. Eliminated are what Moore-McKee calls the “nuisance items:” engine belts, alternators and electric water pumps.
