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.

 

[brain55]

I know in large ship applications they are using super-conductor motors and generators which can be a third of the size and weight of conventional copper wound, not to mention their 99% efficiency. With various rare-earth conductors super-conduction can be acheived with industrial refrigerants no need for liguid nitrogen or oxygen anymore. One just has to weigh the cost versus weight and efficiency.

Brian

 

[nspec]

I'm not even going that far. Awesome technology, but I'm just talking run of the mill setups on supply boats, tugs, ferries, etc... It may cost more, but on a dozer, think of all that you eliminate - no torque converter, no reduction gears, no steering clutches, etc.... Plus, you eliminate probably 30-50 gallons of hydraulic and gear oil on the dozer.

Once battery technology improves, you'll also be able to store excess energy that you create as well. I know one of the companies was playing around with a diesel electric excavator. They had a generator that produced energy every time the thing would swing and then send it to the storage bank to be used in the next cycle. Really neat stuff.

 

[Birdhunter1]

Allis Chalmers in the 1950's had a hydrogen fuel cell tractor that would pull a 2 bottom plow, there used to be a video of it on youtube but it is gone now. My guess is the oil companies and government saw it and pulled it so we don't start some sort of trend to a greener tractor, but I am kinda a conspiracy nut anyway (actually the guy that had the video's is no longer a youtube user, maybe he was bought off I don't know). Go to youtube and search 'Allis Chalmers Electric Tractor' and there are several videos where guys have taken G model AC's and converted them to battery powered electric drive.

 

[SPYDERLK]

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

Youre right. At the simplistic level at which claims are promugated it is perfectly valid to attribute no advantage ... essentially 1:1. As brought out later youll see that there is MUCH more relatively straightforward optimization that can be done with electrical drive and electronics so that even 1:1 at a specific task will win out overall. ... And you can push above 90% with well designed electrical main components. -- And to near 100% with superconducting as mentioned. But there goes simplism again. What about the cost of keeping it cold? And what about the mechanical parts? All considered, as things advance to the limits of Physics we may reach 95% in a mobile system.
larry

 

[CobyRupert]

Hint: Look at the speed torque curve of a DC or variable speed AC motor versus trying to get that through a burning clutch or a hydro pump. Hydro is probably pretty good, but a still a lot more wear and heat.

 

[Sysop]

Trains on average haul more weight than any construction equipment or tractors and they have used diesel electric generation to power their locomotives for years. It is the most efficient use of the fuel once you get above a certain amount of weight.

 

[houstonscott]

It's the lack of rolling resistance that make trains efficient, not the diesel electric configuration. That configuration eliminates a transmission and its weight too.

HS

 

[Sysop]

It's the lack of rolling resistance that make trains efficient, not the diesel electric configuration. That configuration eliminates a transmission and its weight too.

HS

They had diesel gear and hydraulic drive between the current generation diesel electric and the older steam engines of which there were even diesel variants). They opted for the diesel electric because it was most efficient of all other forms of power transmission from the engine to the ground, rolling resistance wasn't a factor in in the progress of locomotive locomotion since all used the same tracks. I guess you could say newer tracks have less rolling resistance due to better manufacturing and installation processes, but I don't think that would have enough influence on the situation to matter. All the stuff that makes up the generators and drive motors actually outweighs what a geared transmission would. Freight train engines are heavier now than ever before.

 

[GManBart]

Trains on average haul more weight than any construction equipment or tractors and they have used diesel electric generation to power their locomotives for years. It is the most efficient use of the fuel once you get above a certain amount of weight.

Absolutely....because you can adjust the engine/generator parameters to maximize fuel efficiency (and electrical generating efficiency), and leave them there, rather than change in response to speed, elevation, and load changes. Maximize those two things, then store essentially all of the power you generate, rather than blow a lot of it out the exhaust stack.

 

[Sysop]

I think eventually we may see similar systems on smaller tractors, but it is still many years off.