Why was diesel electric transmission chosen over Diesel mechanical where the diesel engine power the traction motors directly or diesel hydraulic where Diesel engine’s power is turned in turned into hydraulic motion?
It could be a “QWERTY” effect (after the first letters on the top row of your keyboard) where the first typewriters had that strange arrangement of keys, supposedly to slow typists down not to jam the typing keys, and people stuck with it since.
For example, hydraulic drive was more popular in Germany, and Rio Grande and Southern Pacific tried out those imported Diesel hydraulic locomotives, and they may have been unsuccessful because they were subject to lugging heavy freights in the US rather than the lighter trains on flatter lines in Germany. I heard there were problems with them that may not have been with the hydraulic drive. Maybe the German maker didn’t do their “homework” – think of the troubled history of GE Diesel electrics in the U.S. and how GE and their railroad customers stuck with the GE locomotive design until after many years they got it right.
For a scientific answer, any transmission that trades off torque for speed as do both the hydraulic and electric drives, that transmission has losses and hence must dissipate heat. For the lugging that U.S. locomotives are called upon to do, the electric drive with its traction motor and generator blowers may dissipate heat more effectively than a hydraulic transmission with its oil cooler.
The other thing is that an electric drive, in its fundamental form, is a piece of wire through which current flows, which in turn develops the tractive force. Electric drives are more forgiving of mechanical wear and precision of alignment. Hydraulic drives depend on pumping hydraulic fluid, which depends on close mechanical tolerances for efficiency, tolerances that are subject to wear if there is the least bit of contamination of the hydraulic fluid. A piece of wire can’t suffer from the “wrong kind of electrons” getting mixed into the current.
For example, aircraft have long been an application of hydraulic actuators of varying kinds, to lower and raise the landing wheels, to move control surfac
The RTL Turboliners, as well as the French RTG’s. had gas turbine hydraulic drive. The Voith 411 bru Transmission was designed specically to make optimum use of the gas turbine’s characteristics. In addition to being very reliable, they had the added advantages of simplicity and immunity from the problems of flying snow. The RTL’s provided 25 years of good service and were very popular with the riding public and the staff at Rennselaer if not with diesel electric tribe at headquarters.
Straight electrics were first, such as trolleys and some a bit bigger. The thought was to add a power plant to an electric. It worked, quite well.
The diesel-hydraulics take a lot more maintenance to keep going, The wheels have to be real close to the same size, as they are geared together. The transmissions themselves also required a lot of maintenance.
A diesel-electric with individual traction motors doesn’t really have to deal with this. If the wheels are different sizes, it doesn’t matter as much, as each wheel and motor will go the speed needed.
The hydraulic transmission requiring high levels of maintenance is a speculation I had offered, but Jerry Pier just told us that the hydraulic transmissions on the Empire Corridor Turboliners gave years of reliable service in that particular application (a lightweight, high-speed train).
With respect to the wheels needing to be matched, I read that criticism, don’t remember if it was in Trains for in Railway Age with respect to the imported German K-M (Krauss-Maffie) locomotives used by Rio Grande and Southern Pacific in the 1960’s. Somehow I got the impression that there were other problems with those locomotives beyond matching wheels and not directly related to the hydraulic transmissions. Rio Grande seemed to have serious problems with the cooling systems, especially in tunnels and snow sheds, with the ingestion of heated air triggering automatic shut downs.
Also with respect to matching wheel diameters, they had to do that with steam locomotives, rod or gear driven. Nowadays, they have to do that with the EMD AC locomotives that have one inverter system per truck. For all of the fuss “the Diesel hydraulics needed shop work to keep the wheels the same diameter to sub-millimeter levels”, people seem to accept the same restriction on a particular new generation of Diesel electric
Mechanical transmissions cannot match the efficiency of the best electrical transmissions. Except when direct coupled and operating at the ideal engine speed with no slippage through the transmission, the diesel electric is more efficient, because it allow the diesel to operate at the most efficient speed for a particular horsepower output, instead of the speed determined by the transmission and the speed of the train (rotation of the wheels). Using the gen-set approach, a diesel electric is even more efficient, since only enough engines to supply the needed horsepower need operate at a particular time.
The mechanical transmission diesels tried by SP and D&RGW were about the most powerfull of diesel mechanicals built. Generally, wordwide, they are used in lighter applications, such as branchline railcars and switchers. Some attemtps at high-speed diesel-mechanicals have been tried, but generally have been replaced by diesel electrics. One of the New Haven’sthree experminental high speeds was an adaption of the RDC diesel mechanical railcar design. Of course Turbos are a different matter.
TRAINS covered the importation of the cab-Krauts, the first built for SP. Check it out.
When the three got to Roseville from Houston, they were called out immediately; the manufacturer’s reps said that they needed maintenance, servicing and inspections. Going with tonnage merely from coastal Texas to central California was supposed to be a walk out to the mailbox, not an event requiring rest similar to between the Preakness and the Belmont.
Another factor: white haired engrs. then weren’t about to endorse products that came from this country’s WWII combatant.
Another factor: tracking on our jointed rail, I didn’t experience it, caused thrill ride rock and roll—"this SOB is gonna turn over! "!
Another factor: the limitation of waiting for the torque converters to fill when going from neutral to either forward or reverse or just changing direction.
Another factor: In the cab you’re on top of 1800 horse power of metal stuff which if it freezes or blows up is directed at your shoes and hip pocket.
Another factor: D&RGW’s were modified with water spraying on the radiators, then cool air ducting… T-2 inspiration?
The diesel-electric locomotive in the US are descendents of the gas electric cars and the Dan Patch line gas electric locomotives with a lot of electric locomotive experience thrown in. The gas electrics generally had a better record than the gas mechanicals (e.g. the McKeen’s) and electric locomotives were well understood by the 1930’s. In addition, large traction generators had been developed in the 1920’s for the M-G sets used on the DT&I and GN electrics, so the necessary components were in production when suitable diesel engines became available.
Another factor: It is much easier to install flexible motor leads to a swiveling truck than a drive shaft.
I remember reading an article in TRAINS some years back covering tests involving two KM’s on NYC’s Boston & Albany line. NYC found that the improvement in adhesion came from coupled axles rather than the torque-converter drive.
I am wondering if I read the story about the gripe about grind the wheels all the same size in Railway Age, because that one article seemed to suggest that this was the only problem with those locomotives. Trade mags also tend to put a positive spin on everything so as to not offend advertisers and industry people.
I am thinking I read a more realistic account of the KMs in Trains, but these “other factors” you mention seem new to me and may reflect your personal connection to those machines.
But from the Trains article, I got a kind of sense that the KM’s were not off-the-shelf-German locomotives and let’s-try-them-out-in-America.&nb
The KM’s may have not been off-the-shelf models, but they did turn up in Brazil on EFVM:
http://www.pell.portland.or.us/~efbrazil/km.html
http://www.pell.portland.or.us/~efbrazil/efvm_krauss.html
http://www.pell.portland.or.us/~efbrazil/ml_4000_draw_b.html
The RTL Turboliners weren’t attempting to pull 18,000 trailing tons on a daily basis with a 92 day service schedule either.
The caption from the first link indicates the engines were less than a rousing success in Brazil also.
Since we are discussing the types of why a specific drive, and the topic has come around to the Diesel-Hydraulic. It seems only fair to look at the American-built Diesel Hydraulics of the Southern Pacific.
http://espee.railfan.net/spdh-643.html
The fol;lowing quote from the above website might help to explain why Southern Pacific had some problematic performances from their K-M D/H’s:
FTL: “…Unlike the KM’s, which were built in metric dimensions and with German parts; the Alco (DH643’s) delivered in a “Hood” style configuration; used mostly all American components so was familiar to shop forces unlike the KM’s which were serviced by many German fitters employed by SP from Germany and with metric tools…”
THe ALCO’s lasted from 1964 to 1972 on the SP. There were 37 models built of K-M ML4000. They went of course to the SP, DRG&W(21 units) The first delivered were “Cab” Units, while the second order was for “Hood” units and EFVM. (16) were sort of a modified “Hood Style” with a “Cab” style front end.
I was not aware of these ALCO diesel hydraulics. A real shame that the great builder who was willing to go head to head with Krauss- Maffei did not survive.
I question the second to last paragraph as the Alco’s had German built Voith hydraulic transmissions…in fact it seems likely that they had both metric and standard components and so may have been an even bigger maintenance headache than the KM’s.
IIRC, they spent a good bit of their time on Espee in storage…
In the late 30’s when the first production Diesels were being developed electric transmission was really the only practical option for handling over 1000 HP in a non-direct connected drive (analogous to a direct manual transmission in a car vs a non direct automatic with torque converter). Electric locomotives were mature technology so the rail end was covered. Diesel engines and generators were also mature technology, and marrying the two together as EMC/EMD did was a natural.
Both technologies had lots of room for growth.
I can’t speak directly to locomotives, but there were parallel developments in large mining trucks. The torque converter and planetary auto transmission came of age during WWII. At the end of the war, this combination was limited to about 200 HP. This was later developed to about 450 HP by 1960. In 1964 or so a competing truck came out with a 1000 HP diesel electric drive and stole the market. Electric drive using locomotive technology for the electrical part, dominated until about 15 years ago when Cat came out with a 3000 HP single engine mechanical drive.
Diesel electric started the revolution and won. The technology may not have been the best or most elegant solution, but it was a quantum improvement over steam. It was good enough. The technology with improvements carries to this day.
By the way, as someone once said, steam didn’t necessarily loose to diesel on the road, it lost in the shops.
And to some extent, so did the mechanical transmission.
International Harvester tried adapting diesel hydrolic (hydro) ttransmissions to its larger farm tractors in the '70s. It turned out to be an inefficient system and wasted horsepower. I think a whole new approch involving turbin engineering is in the future of locomotive propulsion. Efficiency in turning fuel into motion needs to be addressed. Diesel fuel isn’t 20 cents a gallon like it was when todays technology was addapted.
What are you suggesting burning in those gas turbines?
Although gas turbine technology has come a long way in improving fuel efficiency, the diesel still has an edge in fuel efficiency in applications like locomotives.