Diesel/Electric Tractors

[sparc]

I see that Caterpillar has the D7E diesel/electric drive dozer and I couldn't help wonder if the same drive system had been considered for tractors and if it would work or not. Doesn't seem to be much different than hydrostatic drive in the end but then why did they convert the D7 over to electric. Don't most heavy earth moving machines (dozers, excavators, etc.) have hydraulically driven tracks today?

I'm sure there is something I'm not seeing that explains why this has not happened yet. Maybe it just doesn't scale down to smaller equipment. But I was thinking with the air quality requirements if this might be a way to reduce emissions as they did with the D7E.

 

[crazyal]

It would be interesting to know which way is more efficient and reliable. I'm guessing that the electric generator and motor would not be cheap compared to a hydraulic pump and motor.

 

[bcp]

An electric system will allow much more computer control than mechanical or hydraulic. Maybe allow a constant engine speed, too.

Caterpillar has been getting into locomotive power systems. Maybe they learned something useful for tractors.

Bruce

 

[crazyal]

I'm wondering which would be better, using the engine RPM to change the output of the generator to change tractor speed or using electronics to adjust the power levels. A CUT would also need an electric motor for the PTO. But it could be set up to use the on board generator so it could act like a portable generator, say for back up power for a house.

 

[Arc weld]

Letourneau has used diesel electric drive since the 60's, maybe even the 50's. Cat claims their haul trucks are more efficient than electric drive, while Liebherr claims their diesel electric drive is more efficient. A modern hydrostatic drive is not cheaper by any means. Crawler loaders and a lot of smaller dozers use hydrostatic drive and some large dozers do but the majority of larger dozers use conventional drive.

 

[sparc]

Well the technology has been used as we all know in locomotives for many years, GE has built hundreds. In power plants large variable speed pumps (85k GPM) are driven with M/G sets, now VFDs which have also been around a while are coming into vouge.

I've seen some videos on YT of homebrew D/E tractors. I expect to see more such BIY when parts from hybrid electric cars start to hit the junk yards.

I wonder who will be the first to offer a D/E tractor from among the major manufacturers. Maybe Cat will enter the tractor market, doesn't seem like such a jump from their current line.

 

[Arc weld]

Cat did enter the tractor market but the whole Challenger line went to Agco and now even the Cat Challenger track tractors are marketed as Massey Ferguson I think.

 

[nspec]

John Deere has fully embraced diesel-electric technology. In February they introduced the 644k front end loader that is fully diesel electric. The 944 is next and the plan is to have the entire lineup d.e. at some point. I first heard of this in 2011 by the way, so I'm sure it's been in the works for quite some time. They are also testing d.e. technology in the large farm tractors and sprayers currently. Much more efficient, excellent control over speed/power, and easier to meet emissions.

As a GENERAL rule of thumb, when comparing a d.e. piece of equipment to a conventional unit of the same platform, the d.e. unit will typically run a smaller diesel engine due to design efficiencies. Think - no loss of power through any sort of a transmission. In addition to railroad locomotives and Letourneau mining equipment, the marine industry has also fully embraced this technology for fuel efficiency, space/weight savings, and overall mechanical simplification.

It's actually old technology folks. What makes it so relevant now is that our electronics technology has come so far that the whole package works that much better.

 

[TerryR]

Think - no loss of power through any sort of a transmission.

What? Neither the generator nor the electric motors is 100% efficient, so there is clearly loss of power being transferred from the engine to the wheels. It's hard to find any numbers, but in one IEEE paper I found the highest generator and motor efficiencies shown are about 90% each, or 81% for a pair. Some systems were substantially less.

The question is whether electrical transmission loss is more or less loss than with mechanical or hydraulic systems. On that I have no clue.

Terry

 

[nspec]

On a D.E. setup, the horsepower of the diesel engine is not the important number. You size the engine to the needed generator output. The horsepower can be taken at each of the drive motors individually at each wheel. The horsepower is measured easily right at the end point - where the power meets the ground - not at the main engine where it then has to go through a transmission. Basically looking at drawbar horsepower. It's been proven that it is more efficient many times over, so I won't start the debate here. There is a reason why Cat and Deere and others are spending millions on R&D - it works. Infinite speed control, instant direction change, and you only generate the power needed at any given point in time. Cat claims 10-30% less fuel than conventional machine. The D7 electric dozer uses the same size engine as the D6.

I work in the marine industry. Shipowners are widely building d.e. setups now for these same reasons. You can size much smaller diesel engines than you could with a conventional powertrain. The electric motors are tremendously efficient, reliable, and put out amazing amounts of instant power and torque. As far as electrical transmission loss, that is extremely minimal - another benefit. Basically it all boils down to fuel savings.