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?
Railroad to Freedom
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 surfaces. Hydraulic systems allow high levels of force and power in compact sizes with light weight. When you look out the window during the approach to landing and see this motor turning a lead screw to crank down the flaps, I am told that this is a hydraulic and not an electric motor.
There is a movement in the aviation industry to replace as much of the hydraulics as they can with electric motors, newer more lightweight and powerful kinds of electric motors. Again, hydraulic systems require seals that can leak, filters that can clog -- they just seem to require more expensive maintenance than electric systems. Even on an automobile, they are replacing hydraulic power steering with electric power steering.
This is not to say that someone could not build a successful hydraulic locomotive for US conditions. It is just as with everything else, there are various advantages and disadvantages, various engineering trades. You would also be competing with the electric drives, where they now have really rugged AC systems.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
WSOR 3801 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.
As I said, even GE or maybe especially GE perservered for years to come up with a (reliable) competing brand to EMD dominance, and that is with another Diesel electric, and maybe it wasn't a matter of GE's deserving their unreliable reputation but in training the railroad mechanics in the correct procedures. Think of the K-M Diesel hydraulic locomotives as odd beasts (with metric bolts back before mechanics had those tools) back in the day that confounded shop foremen.
The hypothesis that electric locomotives had been around before Diesel electrics, and that the Diesel electric was the "obvious next step" of adding a Diesel engine and generator to power an electric locomotive without the overhead wire, that is probably the most logical reason for the widespread adoption of Diesel-electric locomotives. Hydraulic drive has been successful is some railroad applications, and if people had the patience and development money, perhaps it could be made to work in others.
The other thing is for lugging a train up a mountain grade, I am thinking that European railroads are pretty much straight-electric for that application and they reserve Diesels for lighter-duty applications. An electric drive probably can't be beat for allowing max power and RPM from the prime mover while creeping up hill at the thermal limits of the traction motors. The Voith hydraulic transmissions have both torque converters and speed ranges ("gear shifts", but I heard they were done hydraulically by selectively filling different passages with fluid), but you never get the flat torque curve of an electric motor.
People need to remember that you can wreck a hydraulic transmission by lugging, although you can burn up a traction motor too. I have a friend, a mechanical engineer running a company supplying hydraulic gear, who as much as bragged about how he wrecked the automatic transmission on his pickup truck lugging trailer loads of telephone poles up a hill to his canyon house so as to build a retaining wall. Maybe the multi-thousand dollar repair on the truck was a "good engineering trade" given the multi-thousand dollar expense to hire out that kind of heavy landscaping work. But the automatic transmission in a car or light truck is easily ruined by overloading it.
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?
Paul Milenkovic 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.
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.
efftenxrfe 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?
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. I got a sense that they were highly modified for heavy haulage for the US freight application, and from the amount of troubles, that they were prototypes rather than production models. I get the sense that D&RGW and later SP said "thanks, but no thanks, we are sticking with our Diesel electrics" in that the tried them (the hydraulics) out and didn't want to put the effort of doing Kraus-Maffei's test engineering for them and decided to move on.
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
http://www.trem.org.br/lista01/iglvm02.htm
Jerry Pier 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.
The RTL Turboliners weren't attempting to pull 18,000 trailing tons on a daily basis with a 92 day service schedule either.
CSSHEGEWISCH 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 http://www.trem.org.br/lista01/iglvm02.htm
The caption from the first link indicates the engines were less than a rousing success in Brazil also.
Never too old to have a happy childhood!
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.
samfp1943 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 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..
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
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.
Farmer John 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.
In Kirkland's "Dawn of the Diesel Age" he discusses and shows photos of most of the various methods tried to transmit the output from the diesel engine to the running gear. The methods tried included
Hydraulic - still used.
Direct Drive - where the crankshaft of the engine is one of the drive wheel axles. Starting and stopping was a big problem as was breakage of the crankshaft.
Pneumatic - The diesel runs an air compressor and the air is used in a steam locomotive chassis.
Steam & Diesel - A steam locomotive is equipped with both steam cylinders and with double acting diesel cylinders. Both are tied to a steam locomotive chassis. The steam cylinders start the train and when a certain speed is met the engineer shuts off the steam supply and starts the oil supply to the diesel cylinders.
Mechanical Drive - the diesel is connected to the axles with a multi speed gear box. Shifting gears on a 1000 + horsepower locomotive must have been an experience.
All of these drives were tried and had some success but the electric drive proved superior and became the standard.
DS4-4-1000Direct Drive - where the crankshaft of the engine is one of the drive wheel axles. Starting and stopping was a big problem as was breakage of the crankshaft.
Can you point me to an example where the crankshaft was incorporated in the axle (or the drive was taken directly from pistons onto a cranked axle)?
I had thought that the 'direct drive' on the early Diesel experiments was rod drive, like that on the original "Thermolokomotive" of circa 1912 (which had crank breakage as an explicit issue). Any of the other things I've seen with mechanical IC motor drive had the crankshaft distinctly separate from the axle, for a number of very good reasons. The Kitson-Still had the final drive through gears, although the drivers were then connected with side rods. (See the article in Backtrack v.23 n1 (Jan 2009) for more on steam/diesel hybrids.) Are you somehow conflating this with Batchelder-style motors with armatures directly on the axle, as on the MILW bipolars (or the Heilmann locomotives)?
WizlishDS4-4-1000Direct Drive - where the crankshaft of the engine is one of the drive wheel axles. Starting and stopping was a big problem as was breakage of the crankshaft. Can you point me to an example where the crankshaft was incorporated in the axle (or the drive was taken directly from pistons onto a cranked axle)? I had thought that the 'direct drive' on the early Diesel experiments was rod drive, like that on the original "Thermolokomotive" of circa 1912 (which had crank breakage as an explicit issue). Any of the other things I've seen with mechanical IC motor drive had the crankshaft distinctly separate from the axle, for a number of very good reasons. The Kitson-Still had the final drive through gears, although the drivers were then connected with side rods. (See the article in Backtrack v.23 n1 (Jan 2009) for more on steam/diesel hybrids.) Are you somehow conflating this with Batchelder-style motors with armatures directly on the axle, as on the MILW bipolars (or the Heilmann locomotives)?
I was thinking of the 4 cylinder Sulzer diesel locomotive of 1913 which, when I was able to access my copy of Kirkland, was as you say; a separate crankshaft from the axles. I had remembered it as a 4-6-4 rather than the 4-4-4 it really was, with a separate crankshaft wheel between the drivers.
However, I do not equate rods on the drivers with direct drive. The Steam - Diesel locomotives obviously had rods and they are certainly different technology than was the Sulzer. Also, quite a few diesel electric locomotives had side rods, such as the GE 45 tonner, and numerous models by Porter, Whitcomb, Atlas and the like. That was simply a way of reducing the cost of the locomotive by reducing the number of traction motors.
DS4-4-1000I was thinking of the 4 cylinder Sulzer diesel locomotive of 1913
timz DS4-4-1000 I was thinking of the 4 cylinder Sulzer diesel locomotive of 1913 Wasn't it a 2-cyl?
DS4-4-1000
I was thinking of the 4 cylinder Sulzer diesel locomotive of 1913
Wasn't it a 2-cyl?
If you are thinking of the Diesel-Klose-Sulzer Thermolokomotive, the 'direct=drive' engine is 4-cylinder, 4LV38. The accessory engine (used for, among other things, acceleration with the main engine on compressed air up to about 7mph) was 2-cylinder.
A central factor in diesel locomotive concepts is conversion of motor torque – it’s only by finding a sound design solution to this aspect diesel locomotives were able to rise to such tremendous starting tractive efforts as they did while the diesel motor itself never had a toque over rpm diagram but anywhere near that of a steam locomotive , in contrast as we all know it can’t even start from standstill under load. Thus , any efforts at retaining something like a direct drive somehow more or less elegantly adapted from steam loco classic concept – rather less – were bound to fail . For simplicity I will herein also file the ‘tongue-in-cheek’ compressed air quasi ‘steam’ loco with a diesel motor and compressor replacing a boiler .
Also , the quite simple solution used in automobiles , using a friction transmission clutch in combination with a stick shift was way out of consideration where 1000s of tonnes of train load were to be started day in day out .
What was mandatory was a transmission that would allow for an uninterrupted flow of power from a standing start to top speed and at the same time would allow for torque conversion , that is amplifying the motor’s limited torque *significantly* at start and all through lower speed range , speeds at which to go up-hill under continuous high tractive effort demands .
Left in the end were those two concepts mentioned , namely electric or hydraulic transmission . While both provide ample torque levering at low speeds , there are some important differences :
a) Transmission efficiency of a torque converter – and that already is a more sophisticated device than a mere hydraulic clutch , mind it – is subject to a curve of it’s own , with an optimum around lower differences between input and output torque in the 1960 reaching some 80 % and considerably lower efficiency notably at the low speed output end , to the effect that the diesel motor has to run at near full output to build up torque to be amplified for starting tractive effort . To be sure : demanded tractive effort will thus be fully attained , however only by high load on the diesel motor – it is not that a properly designed diesel-hydraulic would lack maximum tractive effort as such .
To really cut the effects of reduced degrees of efficiency of the torque converter at extreme ends of in and out torque modern automatic transmissions in cars and trucks have come to be built with more and more gear speeds , to the extent where they now have more speeds than anyone would want to have in a stick shift . This development to perfection has gone a long way from the days of the Krauss-Maffei diesel-hydraulics – engines that had indeed been especially concepted and designed for heavy duty US freight service – the way it had been understood in Munich ( understood to some extent obviously , certainly not in all of its implications and hard tribulations ) with locos tested on the Austrian Semmering mountain line with long 1 in 50 and even 1 in 40 ramps , including tunnels which again were no ways as long and hot and choking as those on some of the renown passes of their envisaged US customers ( road testing had only been possible by special permit by the Austrian railways in view of axle overload , in spite of it being low in relation to contemporary US diesels – keeping load acceptable for testing probably had been another factor limiting design scope ) . Inevitable by concept , the KM diesels had to suffer from the same inefficiency at very low speed / maximum tractive effort pulling as did all the rest of the European diesel-hydraulics – only , in Europe such extreme conditions of running usually didn’t last long , could rather be considered transient efforts . Where in fact such high tractive effort running was prolonged , such as on the long steep ramps of the Schwarzwald line , 2700 motor hp diesel-hydraulics , series V200.1 although built with demands in view , did initially fail while 1800 ihp class 39 three cylinder Mikados for some years continued to serve the line as they had done for three decades and without much trouble . On a lighter level , V100.1 ( point one for series improved and power upgraded ) had to be ‘service hardened’ over years to come until they could be called a worthy replacement of the ageing Prussian P8 4-6-0 and T18 4-6-4 tank . What had been largely underestimated was the ability of steam locomotives to regularly rise above nominal output when fully extended during acceleration or on tightly timed schedules : while the V200 and light V100 tended to be ailing when only asked full motor output over a certain extended degree of running time , the old Prussian steamers in spite of their nominal 1180 ( P8 ) and 1050 ( T18 tank ) ihp in actual service could shake up some 1600 / 1400 cylinder hp and struggled through with overload consists or made up time where the diesels succumbed and fell short of scheduled speeds . Since main focus of power demand lay in fast acceleration of generally rather lighter trains ( 7 to 9 times adhesion mass ) , the diesels could not but for an initial transient moment play off their superior starting tractive effort while their lack of power reserve in the upper speed range meant they were forever ‘hung’ at wanting speeds when with the old steamers the driver had already linked up and eased throttle just to keep from speeding .
What made hydraulic transmission attractive in Europe mainly were two factors :
(1) It was a lightweight transmission in comparison with electric transmission which really consists of one unit converting motor power into electric energy and then individual units using that energy , in other words you may see a diesel-electric as a power plant with three energy generating and consuming units in contrast to but one plus a true trans in the diesel-hydraulic – disadvantage in extended low speed / high tractive effort efficiency was regarded secondary to considerations of restrained locomotive service mass .
(2) Coupling of axles via mechanical gear was seen as an adhesion advantage of diesels over electrics which back then were quite sensible to adhesion ( *at least* as sensible as the PRR T1 , rather more !)
b) With electric transmission on the other hand , transmission efficiency is much more evenly distributed over the range of speeds and efforts and although not perfect is significantly higher namely at high rates of torque conversion as in starting and low speed up-hill creeping . That has a very important effect that is notable at once when watching a diesel-electric start a heavy train as against a diesel-hydraulic : while the former starts out without much noise and seemingly easy at relatively low motor rpm , the latter revs up and raves at full cry from the very point it starts out .
I think it was largely that difference in power characteristics that closed the case for the Krauss-Maffei diesels , in long hot tunnels the diesel motors running at full cry just had to overheat – further it would appear KM did much as they were used to do with European diesels : they filled the power house pretty tightly and this certainly didn’t help to dissipate heat accumulating inside the locomotive .
So – who was to blame ? to some extent maybe both sides . Or , maybe the result of the trial just came fitting to some . In the end it wasn’t all wrong the way it turned out : the diesel-*electric* because of its superior efficiency over the diesel-*hydraulic* at low speed high tractive effort working *was* the right choice for American Railroads with their tremendous loads to be heaved over high mountain passes .
If mainline electrification would have offered an even larger margin of improvement to train traction and as the only mode of traction would have offered a complete solution of the tunnel heat and sulphuric acid and choking problem – this is my personal point of view .
Regards
Don't know about the rest of you gents but I just learned something.
Of couse, with a head like I've got just how much of it I'll retain is something else, but that's not Juniatha's fault.
As a follow on to my post from almost three years ago...
The US railroads in general were impressed by the performance of the early electrifications, though balked at the capital cost and other operational issues involved with an external power source. The early gas electrics and later diesel electrics were a way of gaining many of the advantages of electrification without the capital expenditures needed for electrification.
The greatest legacy of the Milwaukee's electrification was what regenerative (or dynamic braking) did for train handling on mountain roads. Before electrificaton, the Milwaukee noted that a third to a half of the brake shoe was worn off traversing the line between Harlowton and Avery, whereas wear was minimal afterwards.
The KM's built for the D&RGW and the Espee had hydrodynamic brakes, which were effective to a much lower speed than the electric dynamic brakes on contemporary US diesel-electrics. I do wonder what effect using the transmision fluid as a heat exchange mdium for the braking heat had on the fluid's lifetime. The braking resistors are designed to run at red heat for hours at a time.
Electric transmissions using AC motors have further widened the efficiency advantage ovr hydraulic transmissions. One headache with all of the axles on a truck moving at exactly the same speed is that the wheel diameters on a truck have to be matched much better than what is necessary with an inverter per axle AC transmission.
- Erik
D OwensAs I was reading your post it occurred to me that there is a locomotive that does (did) incorporate piston to axle direct drive. It is a steam locomotive and not either a diesel or an electric, as was the point of this thread, but on the side of interest in things that make you go "Huh?", I thought that I might point out the Shay Locomotive. It had direct drive to not only the engine but to it's attached tender as well. I it has universal joints that allow flexing of the drive-shaft in both dimensions.
To me a shay still has a mechanical transmission between the cylinders and the axles. I look at direct drive requiring crank pins on the wheels or an axle like this.
Of course this photo is for a 3 cylinder steam locomotive but a direct drive diesel would either have outside rods connected directly to the cylinders like the Soviet Steam - Diesel hybrids or inside rods connected from the cylinders to a crank axle like this. The 1913 German locomotive does not fit because the crank axle is separate from the drivers which is also true of the Shay.
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