Good evening all! I was earlier this very evening talking with a visionary person and discussing the future of propulsion. After a time we started talking about diesel-electric propulsion. As I understand things, this is a fair bit more efficient way to transmit power as compared to mechanical or hydrostatically. So my curiosity has been peaked and I guess I need to add this to the list of things to use up my free time. There is of course the prominence of this is the rail and mining industry and a few other notable examples such as the newer Cat D7E and Letourneau’s many fine examples. Is there anyone with firsthand experience with any of these machines? Is there anyone who has any thoughts about the practical problems involved with diesel-electric drive propelling off highway equipment? What is the main factor in the limited use or acceptance of this in midsized equipment (-1000HP) application? Weight? Initiatial cost? Is this going to be a viable option in the future. I understand technology has overcome some of the burdens of years ago, such as smoothly controlling DC drives. Thanks for any thoughts on the matter.
I don't know much about the Cat D7Electric but was there for the rollout at the dealer level. Cat was claiming all the benefits, more efficient fuel use, cooler running components, longer service life, easier repair and so on and so forth. In my area of the country, I don't know of any of them being purchased and used. Initial cost I think was a big issue. They were about the same price as a D8T. I have worked on old Letourneau scrapers where all the controls for the implements were electric. If I remember correctly, the generator was AC as were all the motors. Control of the motors was DC. A stack of rectifiers were used to change the type of current. The rectifiers were getting scarce when I worked on a couple of them and hugely expensive if you could find one. The motors had incredible power though. The ejector cables I think were 5/8 or 3/4 wire rope and when the limit switch failed, the motor would part that line like it was a piece of cheap cotton thread. What I understand is that all the drives now days are AC. The initial issues with AC was that start up current is huge so they had problems on the big machines getting stuck in mud or trying to start moving on steep hills and burning out the motors. Apparently this issue was solved some years ago. What I have observed is that the components are very expensive. The run time is not much better if at all. The service ability is also no better. I know the dealer used mechanics to work on the dozers but some places require a licensed electrician. Now you have to have two highly trained and experienced people to take care of one machine. What might change the industry perceptions of diesel electric drives will be full integration of computer technology in driverless machinery. For the small stuff though, I believe the technology is just too expensive at this point.
Deere now has a couple of "hybrid" wheel loaders. The engine is running a 480V generator which in turn runs an electric motor mounted on a standard transmission. As far as I know the trans and drive axles are the same on the standard and the hybrid. They run a smaller engine in the hybrid therefore they are getting better fuel usage rates. I have a customer who just bought a 644K hybrid so I guess I will be finding out more about these.
I did not know Deere had a hybrid wheel loader! Wheel loaders are enough off the radar I have never looked at new I guess. This is all great information! Please keep it coming!
I've worked on the old LeTourneau and Wabco stuff, the control circuits for the contactors were AC from 2 legs of the 3phase system, the rectifiers were only for the battery charging system and boosting the generator (alternator) rotor field when the load increased, I have replaced many of those old selenium plate rectifiers with full wave bridges using 6 diodes. In fact for the battery charging rectifier I've used a bridge from a big Delco alternator to simplify things. Even though the best charging fix was to add an alternator to the engine to feed batteries.
I still want to know why most cars aren't diesel electric hybrids.
I wasn't smart enough to come up with a fix like that. Still not now either. Nice work. I knew it was something about those monsters. The owners had no stomach for buying parts so as soon as the spares they had were gone, that was the end of the scrapers. That was OK to me. Changing stranded wire rope and pulling engines to put new used clutches in them got old real fast. Sounds like Deere is trading in torque converters and hydraulic pumps for gen sets. I wonder what the weight difference is between the two? I don't see that being a big difference in fuel used though. Moving X amount of weight takes X amount of power which eats X amount of fuel. Generators create heat, wiring is heavy and copper is a lot more expensive than oil. It will be interesting to watch from the side lines this time. Diesel cars are a dirty word in this country.
I haven't looked into it to much yet but like I said it looks like I will be.
What I've been hearing about the new AC powered locomotives, is that they are using an AC generator with diodes to feed DC to an invertor that makes AC with a controllable frequency at full voltage to run the traction motors. The full voltage keeps the heat down and the variable frequency controls the speed output of the motor. even at full stall you cant burn up the motors unlike the old DC motors that went up in smoke at the least amount of low speed abuse. I think Deere is working along the same lines. So I think the trade to an electric "torque convertor" might be pretty accurate.
Do you know what sort of voltage the locomotives currently use?
The DC models I worked on were 600V, the AC models, I'm not sure. I think 480V would be a fair guess. I should quantify this statement by saying the DC models were 600V at full engine RPM, at lower throttle settings, voltages were lower.
I don't know about locos but what I was referring to were the big electric drive haul trucks. For years the big dogs were DC but didn't catch on well because of the start ups. Cat came on with the big mechanicals and about the same time the AC drives seemed to come on line. I didn't work on any of the big Haulpaks at the time but they were brought in for the Centralia coal mine. I got sent to school for the smaller mechanical drive units and saw a bunch of the training cells put together for the two hundred ton trucks. I was happy to dodge that bullet.
I worked at a sand mine that has a CAT 988K XE hybrid-electric wheel loader. I never ran it, was just on the various 980s at that site. While it seemed to work well enough aside from minor teething trouble, it didn't accrue enough hours to be significant before I moved on to greener pastures. They demoed a Deere 944K for about a month before going with the CAT machine - guessing it was due to dealer support since they didn't have any other Deere equipment in the state. That same company had another Deere 944K at a mine in Arizona - don't remember if it was purchased, leased, or on demo.
A couple of years ago I read an article about the future of AG tractors. In it was a fairly detailed report of John Deere's prototype diesel electric, 200 HP equivalent row crop tractors that were then being tested on European farms. They had all electric implements to use with them. Switching implements included switching the computer program to enable the controls to operate the different attachments. It also had a welding outlet built in to the tractor generator. They touted the advantage of no more blown hydraulic hoses and no oil spills. I have occasionally wondered when we were going to here more about how they were turning out but have not seen anything more on them. In fairness, I have not searched for info either.
Letourneau log stackers were fairly popular in the PNW. Not sure how many are still operating. There were still some working in Longview in 2007. The Alaska Railroad just retired a couple of them in Anchorage. To expensive to operate and downtime for parts was crazy. They were used for unloading intermodal. AllPro Alaska delivered a giant Toyota lift truck as a replacement.
In my lifetime things have done a 180. Early on Cat couldn't say enough bad things about diesel electric drive and now have reversed their position which IMHO makes them total hypocrites. Le Tourneau has always been ahead in this field not only scrapers but also dump trucks and wheel loaders and are still the leaders in diesel electric drive today under the Komatsu brand. Stuff that Le TourneU designed 50 years ago has still not been matched in size by Caterpillar which makes Johnny come latelys. I won't deny there weren't problems with WABCO scrapers, most were minor but with serious consequences but on the whole it ran rings around Caterpillar equipment and still does
CAT bought out Terex/Bucyrus so now they have both mechanical and electric haul trucks. Go figure.
And I bet they'll butcher that by adding computers and electronic gizmos.
LMAO! No doubt!
Support for the forner Unit-Rig electric drive trucks continues. I don't think they're actively pushing sales of new units at this time. The newest Specalog I can find online is 7 years old.
The Cat/Bucyrus/Terex deal was a strange one to follow. Cat decides to get out of the mining shovel game and sells the 5000 series to Terex, but spends 8.6B for Bucyrus and then doesn’t sell any shovels.
I see working letourneau log loaders every day. Those things always impressed me, they were built for the job.
IMHO Cat wanted O&K (which was what the 5000-series shovel range ought to have been from the start - but wasn't), the rest of the Bucyrus deal was collateral damage as far as they were concerned.
Nige, I see. You have a good global perspective of the mine biz. How is the O&K excavator market doing nowadays, with the Cat dealer relationship? Speaking of Cat and diesel-electric, I haven’t heard much about Progress Rail, EMD or the Caterpillar locomotive business, lately.
TBH I have no idea. The areas where I've been over the past few years have been 100% Hitachi on big shovels for a considerable time. I know that Cat tendered for the shovel that I just put together, but with Hitachi already on site it was going to be an uphill battle. I've kinda lost track with what's going on further South. Haven't been down that way for over 10 years now.
I had quite a few hours on a Wabco 111A paddle scraper. This was back in the late '70's/early '80's. Electric steer and electric chain drive, hydraulic bowl lift and eject. Biggest problem was the electric steering contactors dropping out from low voltage as you slowed for a turn. It didn't take long to figure out you slowed before a turn, and turned at full rack. IIRC, the electric system was 240V 3 phase. However, it was a 120 Hz system, which allowed more power for a given size motor. The contactors had silver alloy contact buttons, and were expensive enough I just redressed them, never replaced any. I was a youngster then and it was always interesting talking to old hands, as any mention of LeTourneau or electrics always brought out stories, ranging from scary to roll on the floor funny. With the capabilities of modern day variable frequency drives and large scale experience from Tesla and other electric vehicle manufacturers I expect more tries at electric. Like any new venture, you can always tell the pioneers, they are the ones full of arrows.
Have you run a D or C Pull, had an electric motor for each bowl function as well. I never experienced malfunctions with the contacts but the limit switches could be a problem. When the steering ones failed, usually one side, lead to some interesting moments. A mate had one fail on a hilly haul road, rolled twice landing on its wheels. He was ko'd when the windscreen hit him on the noggin. The mechanic fitted a new switch, while I cut a track in and it was driven out, checked over and put back to work. No ROPS in those days.
I have some hours on C pulls. You forgot to mention the four speed manual transmission with the clutch. Never had a steering issue. The ejectors though tore through lots of wire rope when the limit switches didn't work.
You can never call yourself a scraper operator until the you break off the gear shift lever on C pull ! We used to weld them back on and keep on speed shiftin.
Yeah nah, I was to young for those. Everything was powershift when I started, suppose what the ole timers called "a spoilt brat".
from what I remember, Johndeere stuck a genny in the middle of the tractor to power implements of a moderate power requirements. Something like 30% of engine power and could be used to power tools ,welders,etc. What is the efficiency of diesel electric in optimum conditions? Do any powershift dozers or haul trucks have converter lockups? Think some volvo loaders do . The Fendt type CVT transmission doesnt seem to have made any inroads in construction equipment.
As I recall, all the rigid frame and articulated trucks that I worked on in the nineties had lock up torque converters. The bigger Komatsu dozers, D375 that I know of had a lockup converter. The current version on the Cat D9, 10 and 11 have what they call something like an optimized drive train that has been explained to me as a lock up converter setup. I don't know that I've seen a CVT in any yellow iron so far.
In the 70s i spent a year at Finning . They were big on the welding and fab side in the Port Hardy shop with Utah Mines Island Copper operation close by. There they ran Electrohaul trucks powered by 16V 149 s . We were tasked with rebuilding the boxes . They were loaded with electric P&H shovels ,thats a bucket we rebuilt with my pickup in it. Thats my experience with big electric machinery.
All mechanical drive rigid trucks & ADTs still have lockup converters, certaoinly at least the Cat products do. Lockup converters are useful in wheel loaders if they are used for load & carry operations of say 100m or more one way but a boat anchor for general loading operations. On larger loaders they are often an optional attachment but typically salesman don't know how or when to specify them. I've seen machines with lockup clutches truck loading, and machines doing load & carry that were crying out for a lockup clutch and didn't have one. The current generation of D9-11 tractors have a combined torque divider/torque converter setup. The divider sends about 25% of the torque from the crankshaft directly to the transmission input shaft bypassing the converter completely, the other 75% is modulated via the converter. I wouldn't call it a lockup setup because there is no one-way clutch in the converter. I seem to recall one of the larger komatsu tractors (D375?) being equipped with a lockup clutch in carrydozer configuration but never worked on one.
That torque divider sounds interesting. Had a quick look at Cat website . They seem to offer diesel electric and torque converter/powershift side by side . I would expect a lockup would be more economical than electric . When VME was put together the largest Euclid rigid truck was diesel eletric as per the volvo range catalog I had as a young fella . I always assumed they didnt make torque converters big enough to handle the power .
Put simply, the profile of the mine haul roads goes a long way in determining whether mechanical or electric drive is the way to go for the haul truck fleet. The 797 truck torque converter will handle 4000 HP.
working in the oil sands in Canada. there are talks of cat having a sale of there 794 electric drive. while in the mine im at has 2 test 798 haul trucks. as for the cat C175 motor not to much else is cat. the biggest complaint is ride quality from the operators. they do leave the Komatsu and Liebherr in the rear view mirrors pulling any hills or getting out of the shovel pit. that being said I was just apart of a 2 week shut down on one of the units. it had 11000hr on it and coming from cat mechanical truck background I thought the nosecone section they have on this electric truck is garbage instead of the dog bone set up they have with the 797 series trucks. also the steering and front suspension system is junk compared to the mechanical drive trucks. to many moving parts to wear out. Personaly I think if they take the frame work of the 797F truck and put in the electric drive system from the unit-rig it should be pretty bullet proof
Last time I had the chance of a close look at a Unit Rig truck in the field (when they were still badged as U-R) was many years ago, I think about 2005-ish. Compared to the Cat mechanical-drive line of haul trucks we were supporting at that time it looked as though it had been built by Fred Flintstone. I recall what the front struts & steering gear looked like and remember thinking hmmmmmmmmm.......