Electric drive isn't this Cat's only meow

  • 10-Jul-2008 03:14 EDT
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A Cat scan shows the inner workings of the D7E. The attachment on the back of the cab is the separate electric A/C unit.

The entirely new Caterpillar D7E contains more advances than just a new electric drivetrain (see "Cat sets plan of attack on ac electric drive," May/June 08). The ability to engineer from scratch eliminated some common annoyances that plague older designs.

The cab offers better visibility by utilizing a central pillar at the front. “Our engineers have come up with an industry-exclusive design, what we call center-post cab. The view is really quite something. You line up that center post of the cab, the pre-cleaner, the exhaust stack, and also that single lift cylinder right on down the line,” said David Nicoll, Commercial Manager for track-type tractors. “This cab is larger, it's more comfortable, and there's a 50% reduction in sound. We've redesigned controls that are more ergonomic, and we've reduced vibration on this machine.”

A single, large blade lift cylinder is mounted centrally and allows for better visibility as well as half the parts for reduced costs and maintenance. It is large enough to provide the same power as the traditional twin-cylinder setup.

The 235 hp (175 kW) comes from a Cat C9 straight six diesel, which in turn powers a generator. No belts are needed, and all auxiliary systems are powered by the generator. This electric drive system is claimed to move 25% more material per gallon of fuel, while returning 10% more productivity and 10% lower lifetime costs. The electric motors eliminate the traditional transmission, making the Cat easier to use as there are no gear changes.

Usability of the D7E has been dealt with as it offers advanced side-slope performance and has been designed to work with many implements. The midsize D7E competes in the 60,000-lb (27,000-kg) class and is designed for heavy moving and finishing applications in construction, waste management, forestry, mining, and site development.

The D7E rides on a Cat SystemOne undercarriage designed for long service. The track joints are cartridges, rather than pins and bushings, and are sealed and lubricated for life. The center tread idler does not come in contact with the tracks, only the cartridges, thus eliminating scalloping on the link rails. Other components of the track system are also designed with long life in mind. 

The electrohydraulic steering setup has long been used by Cat but now claims 50% better performance.

Having an electric drivetrain allows for longer service intervals, but when servicing is necessary Cat engineers have grouped service points together and allowed the cab to tilt sideways for easy access.

“We doubled the hydraulic oil life from 1000 hours to 2000 hours. And we quadrupled the drivetrain oil life from 1000 hours to 4000 hours,” said Nicoll. “So that means two things. One, the service technician is going to visit the machine less to do these oil changes. Secondly, this machine is environmentally friendly. Because we have to change the oil less often, we are using less oil.”

The Cat Accugrade GPS Grade Control System allows dozer operators to grade with increased accuracy without the need for survey stakes. Although it is optional, every D7E will have the infrastructure to allow easy retrofitting if desired.

Environmentally, the engine meets Tier 3 standards with a view to Tier 4, while the rest of the D7E is designed with more lifetime parts and fewer fluids required. Major components are engineered to be rebuilt/reused. The machine is expected to come to market in 2009.

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