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Cat’s cool diesel-electric dozer: the D7E

Yesterday I was asking myself: “I wonder if Caterpillar’s making a hybrid?”

Yeah. This is old news for hard-core Cat-watchers: the D7E, Prius of earthmoving set. Instead of a diesel engine doing most of the work of turning the tracks — putting a lot more strain on the engine and burning a lot more fuel — the D7E engine delivers power to a pair of electric motors, which do most of the heavy lifting while the diesel-powered engine operates in a fairly narrow range (like switching from city driving to highway). From Caterpillar’s pitch:

This electric drive train configuration has 60 percent 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 of 10 percent. The electric drive system also enables the customer to move up to 25 percent more material per gallon of fuel consumed and reduce the accompanying greenhouse gas (GHG) emissions by similar amounts -– improvements that wouldn’t be possible with conventional drive systems. Also, with visibility increases of 35 percent and improved access /egress, the D7E is safe on the jobsite. … The D7E is scheduled for introduction in 2009.

This video with the editor of Construction Equipment magazine interviews a Cat engineer — who drones on a bit but does fill in some of the details on the D7E. This vid shows one turning on a dime.

The diesel engine is at the front left; electric motors turn the drive axles.

The diesel engine is at the front left; electric motors turn the drive axles. This is from a Las Vegas trade show in March 2008.

Various bulletin board postings from potential users seem pretty enthusiastic. This one notes that Volvo is hot on Cat’s tail with its own hybrid drive.

Diesel-electric is old technology: locomotives have been using it for decades. But there is a high-tech twist with the D7E: According to the Cat engineer interviewed in the video above, the advent of semiconductors that can withstand construction site torture tests has smoothed the transition of diesel-electric from trains to track-type tractors. So there’s even a Silicon Valley link for my geeky neighbors to appreciate.

More on the D7E at this Construction Equipment article.

2 comments | Permalink | Tags: ,
Tom Mangan posted at 10:29 am December 20th, 2008 |

2 Responses to 'Cat’s cool diesel-electric dozer: the D7E'

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  1. Larry Stewart says:


    Great job discerning how significant the D7E project is to Caterpillar’s future. Carrying diesel-electric drive over into construction-size dozers is a major development with significance throughout the industry, as you aptly note in pointing out Volvo’s work on the concept.

    It’s probably important to point out, though, that the D7E is not really a hybrid drive system, by most people’s definition of “hybrid drive.” ‘Course the definition itself is hardly absolute, but most agree that an electric drive system becomes a “hybrid” when it includes some sort of way to store energy that can be delivered later, when the engine needs a boost.

    Cat engineers made this distinction themselves during the press introduction of the D7E. It’s certainly not much of a stretch to imagine a drive like that used here with a battery or other energy-storage system added to it. But in that respect, the Volvo concept probably qualifies more as a hybrid than the D7E.

    I don’t know which — the D7E or the Volvo wheel loader — will be on a production line sooner. Both companies spoke of 2009 introductions, but the Volvo people suggested later in 2009, while Cat was speaking more in terms of early 2009. The coming quarter — Q1 2009 — will be an interesting time to be at construction equipment trade shows.

    Larry Stewart

    Permalink | Posted December 23rd, 2008, at 8:36 am
  2. Tom Mangan says:

    Thanks for clarifying … your knowledge of drive systems shown on the video interview was most impressive.

    I knew Priuses store energy in the batteries but I wasn’t aware that was the key signifier of “hybrid.” I figured it meant a combination of gas engine and electric motor. In that sense, though, the new Cat dozer wouldn’t qualify either, because the engine runs the electric motors directly rather than switching on and off.

    Permalink | Posted December 23rd, 2008, at 10:25 am

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