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Caterpillar® has launched a microsite dedicated to the innovative D7E Track-Type Tractor with electric drive

6/2/2009

Caterpillar's D7E crawler dozer is the first electrically driven dozer using modern alternating-current (AC) technology, and Cat claims it will move up to 25 percent more material per gallon of fuel than the D7R Series II. The drive system takes advantage of today's small, less-costly semiconductors that can rectify heavy-duty-drive voltage to AC, eliminating brushes. The drive is developed by Caterpillar specifically for crawler tractors.

A 235-horsepower Cat C9.3 diesel drives a generator to produce electricity that runs to a power module where it is inverted to AC current. The current powers two AC drive motors arranged in series, which drives a differential steering system much like that used on other Caterpillar dozers.

The electric drive train has 60 percent fewer moving parts than the drive in previous D7s. And because power flows from the generator to the electric drives through cables, rather than a hard drive shaft, the tractor's heaviest components can be positioned optimally in the frame for ideal machine balance.

The C9.3 engine is smaller and achieves rated power at 1,700 rpm, compared to the D7R's 240-horsepower Cat 3176. Smaller displacement is responsible for some of the up-to-20-percent fuel savings, but the biggest efficiency gains come from eliminating the torque converter and keeping the engine running in a much more narrow range of speeds.

The 3176 diesel coupled to a powershift transmission in the D7R normally operates in a speed range from 1,200 to 2,100 rpm, whereas the C9 and electric drive operates more efficiently near peak torque, staying between 1,450 and 1,700 rpm, according to Mike Betz, Caterpillar engineering manager for track-type tractors.

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