ANUFACTURERS are grappling with the impact their equipment has on the looming double whammy of reducing oil supplies and global warming. The release of the D7E electric drive bulldozer is one of the first alternative energy powered pieces of earthmoving equipment other than mega large dump trucks and loaders.

Cat chose ConExpo to release this radical new machine which will go into production in 2009. Cat says “it will be the most fuel efficient and productive track type tractor in its class with the lowest overall operating costs”.

On-board generator

A C9 Tier 3 compliant engine producing 235 horsepower delivers power to “an on-board generator to efficiently convert engine power into ac electrical current that drives the tractor. This electrical drive train configuration has 60 per cent fewer moving parts, requiring less service and replacement than conventional transmissions, enabling the D7E to extend drive train component life and reduce lifetime operating costs by an average 10 per cent.

“The electric drive system also enables the customer to move up to 25 per cent more material per gallon consumed and reduce the accompanying greenhouse gas emissions by similar amounts – improvements that wouldn’t be possible with conventional drive systems.

Also with visibility increases of 35 per cent and improved access and egress the D7E is safe on the job site.”

This machine has variable speed electric motors which presumably, will provide infinitely variable drive to each track through the massive planetary final drives. This machine is a “flat track” as opposed to the “high track” concept which Cat introduced in 1978 and has characterised the Cat range of dozers.

Elevated sprocket

Cat says (and has done since inception) that the “elevated sprocket increases productivity, simplifies maintenance, reduces downtime with modular components, and raises final drives and associated power train components out of the work environment”.

But Cat has still stuck with and developed a range of “flat tracks” at the smaller end of their range up to their D6K which is the equivalent of, say, an older D5B. The D4 and D5 “high tracks” no longer appear on the Cat list of crawlers.

Moving into the heavier end of the range I was surprised to find that there is a model designated D7G Series 2 which looked remarkably like the D7G introduced (I seem to recall) in the late 70s and still popular in the Asian market according to a Cat distributor sales manager mate who has had the Cat yellow blood coursing through his veins for so long that withdrawal from the yellow drip would surely mean death.

In fact, when I mentioned I was doing some research on the D7E he asked, “would that be the 160 hp or the 180 hp model Doug?” To which I replied, “No Stuart, the 235 hp model”.

It was though, the model numbering that caught my eye for it was a 180 hp D7E (the 160 hp model was released in 1961 and the 180 hp in 1966) that I first operated as a logging contractor. Direct drive, pilot motor start, manual Hyster winch – 180 hp at 1,275 rpm from four large cylinders. The most beautiful sound with pronounced turbo whistle when the clutch was disengaged – when you could almost count the revs. Talk about low down torque! If the big numbers ever come up I will have one restored and in my shed.

Enough of the nostalgia

My CAT friends say the “high drive” is here to say. I suggest that the new D7E is a mid-sized machine which, if it does everything Cat suggests in the Cat statements above, it could be duplicated in the larger models – as happened with the “high drives”.

And I have nothing against “high drives” having operated a number across the range – including the original D10. It is sometimes frustrating though, because you can look across a paddock and depending on the distance would not be able to tell which model dozer it was – they all look the same.

I also had to tell my Cat friends that the new D7E had a resemblance to a late model D85 Komatsu with a 1970s Terex 82-20 front end with a single blade lift cylinder mounted in the centre. They were not amused.

Whatever, I like its claimed credentials and would love to have a play around with one when they are released next year.

Doug Huett was National Executive Director of the Civil Contractors Federation from 1988-2002. He is now an industry commentator.

Source: Construction Contractor