Believe it or not, they are often more efficient than diesel-electric. Most DMUs are diesel-hydraulic, to boot, due to this. Pay Google a visit if you really want to learn more about them.
Another advantage that they may have (someone please confirm this) is one that was lost when US railroads converted from steam to diesel-electric, that being the ability to run through flooded sections of track that would be under relatively deep water. (Diesel-electrics cannot do this; their traction motors would short out.)
The main reason that the D&RGW and SP werelooking at hydraulics was to get more continuous tractive effort fom a single carbody. The hydraulic transmission was supposed be happier running at low speeds than the current DC traction motors and the fact that all three axles on a truck were turning in unison helped with adhesion. Nowadays, those advantages are provided by AC traction motors plus improved slip control (e.g. EMD's super series technology).
Reasons why the hydraulics didn't catch on is that the engine reliability on the KM's was poor, and the Alco's weren't hugely better. Seem to recall that the hydraulic transmissions weren't as rugged as expected from European service - there's noting in Europe quite like "The Hill" (Donner Pass route).
Added note: The hydraulic transmissions used torque converters (not hydrostatic) obviously on a larger scale than the ones used in automotive tranny's. The KM's were equipped with three torque converters per engine/truck each with a different gear ratio, transitions were accomplished by draining one converter and filling another.
Yet another advantage of the DH's were that hydrodynamic braking was effective at lower speeds than with the then available dynamic braking on diesel electrics.
JT22CW wrote:Another advantage that they may have (someone please confirm this) is one that was lost when US railroads converted from steam to diesel-electric, that being the ability to run through flooded sections of track that would be under relatively deep water. (Diesel-electrics cannot do this; their traction motors would short out.)
....Wonder if price might have been a factor....Example: Our last automobile had 2 hydraulic motor driven radiator fans and now our current automoblle {same brand}, has in the same place...2 electric motors to do that job. My guess is simply the electric motors are less expensive and it was a cost cutting move. Perhaps same reason in the locomotive. {At least as one of the reasons}.
Quentin
Pop-off-valves would be hard to control so the pressure would get lower as the spring got weeker. Thus the horsepower from the engine would drop. It took a mechanic that knew his job at seting the pressure. To high and the oil lines would blow.
If you blew a line then the oil would be all over and one heck of a mess to clean up. Hot oil in an engine compartment set the stage for a fire. Nothing like stoping a train like an oil fire.
As I recall, erikem hit the main reason - we ask different tasks of locomotives here than they do in Europe (where the design was, and may still be, popular). I believe trains there are generally shorter, and the runs are definitely shorter. Plenty of opportunity for tweaking.
On of the K-M's ended up as a camera platform for SP - pushed by Diesels.
Aside - one nickname of the ALCo DH's was "Alcohaulics."
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
As mentioned there would be some efficiency advantages with diesel hydrolic locomotives, if you can make them reliable that is.
West Germany was the biggest successfull use of diesel hydrolics. My theory is that Germany in the post war period had plenty of cheap and skillfull labour to tap from. So the cost of low tolerance regular maintance wasn't so high as compared to most everywhere else including the US. Now the cost of skilled labour in Germany is astronomical and not as readily available and this has reduced the use of diesel hydrolic locomtives in mainline service. More diesel electrics.
So when skilled labour is more plentifull then fuel oils, then go hydrolic. When properly maintained they should work great.
Western England used Diesel hydrolics extensively for a while too, but suffered from lack of skilled mechanics.
To go back to the question WHY, British Railways' Western Region's reason for opting for Diesel Hydraulics for main line power was the significant weight saving on the then equivalent Diesel Electrics available.
The difference in the weight of the D800 class and its variants and the D200 class (later Class 40) offered by English Electric was the equivalent to around a carriage and a half (perhaps someone with a better personal library can quote the exact weights).
Their thinking was that either less fuel would be used to haul similar trains, or the popular trains could accommodate rather more fare paying customers.
The downside was that being lighter, the D800s would be totally unsuited and highly unpopular for anything other than passenger and parcel trains and the fully braked freights of that time. So no chance of seeing them on a typical South Wales Valleys coal train.
Hwyl,
Martin.
I undrestand that what doomed the Warships after all the mechanical issues were dealt with that 2000 hp was not realy enough for mainline passenger work when steam engines had delivered higher hp.
Like mentioned above the Warships were not suitable for freights because of their low weight to horse power, but I heard it wasn't because of pulling power, it was more about braking power. Diesel hydrolics don't slip as easy as the contemerary diesel electrics but you wouln't want to lock the wheels when braking. Freight trains had no brakes exept a hand brake in the brake van and what the locomotive and tender has. No bakes on freight cars?! I guess the technoligy of the Warship was foiled by outdated technoligy and operations for freight traffic.
The German equivilant was the V200, wich were used on heavy coal and freight trains for a long time, wich were heavier then British freights at the time.
They are still building and rebuilding a lot of diesel-hydraulics in Germany. Vosloh of Kiel, Germany under the brandname Mak, is the main diesel builder in Western Europe. They even supply quite a few locomotives to France See the website www.loks-aus.kiel.de. They may get competition at the high horsepower end from Voith, one of the hydraulic suppliers.
Alstom is rebuilding former East German V100's (very popular with private railroads!) and to a lesser extend West German V100's as well
Main competition is the EMD class 66.
greetings,
Marc Immeker
Dan
Bucyrus wrote:Can someone describe the power train between the engine and the wheels of the KM diesel-hydraulic locomotives tested in the U.S? Did the Alco diesel-hydraulic of the same era use the same power train as the KMs?
A good description of the operation of the power train is on pages 36-37 of the November 1962 issue of Trains. The Alco DH-643's also used Voith transmissions, presumably with the same operating mode as the Voith transmission used in the KM's if not exactly the same unit.
The engines were coupled to the transmissions by a Cardan shaft - essentially the same design as a typical driveshaft on a rear drive car. Another cardan shaft connects the tranny to a dropbox mounted in the bogie/truck of the locomotive, the lower part pf the dropbox is connected by driveshafts to gearboxes mounted on each axle, the gearbox contains a bevel gear to couple the longitudinal driveshafts with the axle.
The Voith L 830 RU transmissions used in the KM's had three torque converters optimized for maximum efficiency at 27, 41 and 59 MPH (85, 88 and 82.5% respectively), as I wrote earlier, 'shifting' is accomplished by draining one converter and filling another. The only time that gears are actually shifted is when reversing direction of the locomotive. The transmissions have provisions for hydrodynamic braking with a larger speed range than what was then available with electric transmissions. Also recall that torque converters can multiply torque when the impeller is turning faster than the turbine (which is why the Chevy PowerDive -er- PowerGlide transmission could get by with two forward gears).
The overall peak efficiency of the hydraulic drivetrain was about 86% (there were losses of about 2% involved with the truck's gearing and driveshafts), roughly comparable to the 85% efficiency figure quoted for electric transmissions of that era. AC transmissions are being quoted as having better than 90% efficiency.
My understanding is that the hydraulic transmissions used on RDC's and DMU's are essentially beefier versions of the automatic transmissions used in cars - though set up to have the same number of gear ratios in both directions. The advantage in this application is reduced size and weight compared to electric transmissions - but a lot of progress has been made recently on reducing the weight of the components used in electric transmissions.
Contemplating today's world, as contrasted to the then (and I recall basically the same thing about the KMs and Alcos -- maintenance issues, and a rather poor fit with US service).
Diesel hydraulics make, seems to me, good sense in a DMU type application (and indeed, they are used there): the power requirements are relatively small in relation to the size of the vehicle, and control (particularly slip) isn't a really big issue.
However... I would hate to see what hydrodyamic drives for a 6,000 hp diesel would look like! Further, the modern electronic controls for diesel electrics provide near-instantaneous variation of the torque going to the axles, and thus very very high adhesion factors. Maybe I'm missing something, but I doubt that one could modulate a torque converter as fast as one can modulate an electric motor -- and that's the one of the big secrets to the very high adhesions.
Anybody else out there remember the original Buick Dynaflow? The ultimate slushbox -- didn't shift at all; did it all with a very fancy torque converter. Worked fine, except the efficiency wan't much to write home about!
I also don't think a torque converter can be modulated as rapidly as an electric motor. The DH's did get a boost in adhesion due to having all of the axles on one truck turning in unison compared to problems with slip control when the DC motors were operated in series at low speeds (to match the amp rating for the DC generators) - much the same way a locking differential gives better traction than an open differential. The disadvantage for the DH is that all the wheels on a truck need to be almost exactly the same diameter.
Another disadvantage to the hydrodynamic transmissions is that they almost require a separate engine for each truck - both the KM's and the Alco DH643's were dual engine.
I've heard stories about the Dynaflow - often referred to as the Dynaflush. Amusing to consider when I have a 5-speed Allison automatic in my pickup truck. Also interesting/amusing to consider is that many hybrid vehicles (e.g. Prius and GMC Yukon hybrid) use a combination of electric and mechanical means to get a continuously variable transmission.
.....And the Powerglide and Turboglide....All had multiple turbine converters and were very inefficient.
....Am I missing something. I'm hearing mention of torque converters in these diesel hydraulic units....?? I must not be understanding the system that were being used.
Modelcar,
The KM's and Alco DH643's used hydrodynamic, not hydrostatic, transmissions. The KM's did use hydrostatic drives for the fans. I'm not sure if I want to be anywhere near a hydrostatic transmission capable of handling 2,000HP. OTOH, locomotives with a few hundred horsepower may likely be hydrostatic.
....I need to stop and see schematics of drive train components so I really understand what is being discussed here.
Diesel Hydraulics and or Diesel Hydrodynamics.....
There are "Powerwheel" units driven by hydraulics with pretty high horse power into running them and that application doesn't have torque convertors, and now this railroad application of hydraulics is something in a different direction, so must see what we're talking about.
The article in the November 1962 Trains specifically mentioned hydraulic torque converters and specifically mentioned impellers, guide wheels (reaction members) and turbine runners. The "hydraulic" presumably comes from the reaction fluid being a liquid as opposed to a gas (i.e. pneumatic). Without the torque converters, the KM's (and Alco DH's) would be diesel-mechanical as power transfer between the engine and transmission, the transmission and truck (bogie), the truck gearbox and axles were all handled by Cardan shafts (shafts with U-joints at each end). The "hydraulics" were only used to provide for a variable ratio between engine speed and axle speed. One huge advantage of a torque converter over a staright mechanical transmission is to allow a running engine to supply torque to a stalled load.
Hope this clears things up a bit.
There's a nice cutaway drawing of the KM in the October 1961 Trains which shows the locations of the engine, transmission and the numerous Cardan shafts.
erikem wrote:Modelcar, The article in the November 1962 Trains specifically mentioned hydraulic torque converters and specifically mentioned impellers, guide wheels (reaction members) and turbine runners. The "hydraulic" presumably comes from the reaction fluid being a liquid as opposed to a gas (i.e. pneumatic). Without the torque converters, the KM's (and Alco DH's) would be diesel-mechanical as power transfer between the engine and transmission, the transmission and truck (bogie), the truck gearbox and axles were all handled by Cardan shafts (shafts with U-joints at each end). The "hydraulics" were only used to provide for a variable ratio between engine speed and axle speed. One huge advantage of a torque converter over a staright mechanical transmission is to allow a running engine to supply torque to a stalled load.Hope this clears things up a bit.There's a nice cutaway drawing of the KM in the October 1961 Trains which shows the locations of the engine, transmission and the numerous Cardan shafts.
Voith is coming out with a competitor to the Vossloh/EMD Euro 4000 (European SD70M-2), called the Maxima 40C it will be a 4000hp Diesel-Hydraulic powered with a ABC 16-cyl. medium speed diesel. Voith decided to get into building their own complete locomotives when they saw the inroads EMD was making into the European market causing them a loss of sales. Vossloh has been kind of ambivilent about building locomotives, they own the former MaK factory in Kiel and bought the former Alstom (ex-Macosa) factory in Valencia, Spain. But the CEO who engineered these moves was forced out. The locomotive business is cyclical, and dissident shareholders want the company to sell the locomotive business and concentrated on building components for passenger equipment and track components. Vossloh has good sized subsidiaries in the US in these business lines. Because of this uncertainty, especially at the Kiel factory, some of the Engineering staff have left Vossloh, and gone to work for Voith across town. What is interesting to me is that these people convinced Voith to switch from high-speed diesels to medium-speed diesels for all the larger locomotives (similar operating speed to EMD and GE engines), based on their experience with the ABC engine used in the Vossloh built Belgian Class 7700 light roadswitchers.
....Erik: Thanks for your comments. I simply need to eyeball the power train components. Guess I really haven't looked at the layout of such a powertrain or if I have it's been too long ago.
I probably have those TRAIN's mag. and articles you mention, but you might know how it is with them stored in boxes, etc......
It sounds like you are saying mechanical power was brought to the truck area via the double cardan shafts and into an arrangement of torque convertors and then into a mechanical gear box and on to the axles....
If that is the case, those must have been some stout T C's to handle that job. Of course if that was the set up, the T C's assisted in starting the load by their capability of multiplying the engine torque into the gear set and into the axles....and on grades where the speed would get down to a point where the load and power would dip into the T C's uncoupling and start to once again multiply torque.
Thanks Erik. So the KM transmission used three separate torque converters. I assume that they each produced a different speed/torque multiplication. So then shifting from one torque converter to another was equivalent to shifting gears in a mechanical transmission. I can understand the problem of the wheels needing to be the exact same diameter.
My understanding is that a hydrostatic transmission uses a variable displacement, engine-driven pump, which pumps oil to a fixed displacement motor. So by mechanically controlling the rate of output flow from the pump, the motor speed can be changed. I have heard that the motor can also be variable displacement, thus adding to the speed change capability of the pump.
This type of drive would seem to be quite analogous to the diesel-electric drive of locomotives if the hydraulic motors were hung on the axles like electric traction motors, and the hydraulic pump were directly coupled to the engine. Is there any fundamental engineering reason why this hydrostatic drive cannot be applied to a locomotive? One problem I can see is the need for hoses connecting to the motors in order to accommodate the movement of the axles relative to the rest of the locomotive.
An electric traction motor requires flexible leads for the same reason. Anything that routinely flexes is heading for eventual breakage. It may not be an issue with electric leads as they may be easy enough to monitor and replace if necessary. But the flexing of hydraulic hoses occurs when the hoses are already under the physical pressure loading of operation. Whereas, with electric leads there is no physical aspect to the electric load (I guess). The consequence of a broken hose would not only be locomotive failure, but also a serious oil spill. Perhaps, however, a 100% reliable hose connection could be developed for such a hydraulic traction motor application.
Quentin,
Glad I was able clear things up. I can understand your confusion as "hydraulic" is usually associated with high pressure and relatively low flow.
Bucyrus,
Making a long lasting flexible electrical connection is relatively easy, just use lots of very fine strands of wire in the cable, the key issue in fatigue is the ratio of overall bend radius to the individual strand radius. Making a high pressure hose that can take a lot of flexing is a 'bit' more of a challenge. I think you're on the right track with the comment about electrical connections not needing physical strength compared to high pressure hose.
- Erik
Ulrich wrote:Back in the 60s and 70s...possibly earlier, several builders and carriers experiemented with diesel hydraulics. Why? What were they trying to accomplish...what advantage would a diesel hydraulic have over a diesel electric?
There's some really interesting discussion above (thanks for the info on Vossloh, beaulieu) but to return to the original question.
I assume you are talking about the U.S. only. The only significant experiment with hydraulic transmission took place 1960-63 with the design, construction, and commissioning of Krauss-Maffei A.G. locomotives for Southern Pacific and Rio Grande, followed by a valiant but ultimately futile effort to obtain value by moving freight. The rationale of the railroads in question was to have a locomotive that could:
1) deliver full prime-mover horsepower to the rail at very low speeds in drag-freight, heavy-grade service -- diesel-electrics with D.C. transmissions cannot deliver full horsepower to the rail for more than a few minutes below their minimum continuous speed (typically 11-12 mph) without experiencing permanent damage to the traction motors.
2) obtain higher horsepower in a single unit than what was then currently available from EMD -- nominally 2500 hp for EMD vs. 4,000 hp for the K-M, thereby obtaining unit reductions for the equivalent drawbar tonnage.
3) dispense with traction motors, a high-maintenance component and the least-reliable major item on the locomotive.
4) a general dissatisfaction with the lack of innovation at EMD, and desire for the viable strong competitor to EMD that Alco wasn't. Recall that in 1959-60, when this idea had genesis, that EMD had 85% or better market share (testimony to Alco's weakness), and for 10 years had been upgrading the GP7 only incrementally. Granted the GP9 was a much better iteration of the GP7, but from an operating department point of view there wasn't any meaningful difference, and the GP18/GP20, also from an operating department perspective, was warmed-over more of the same (Note that the operating department runs the railroad -- sometime they are subordinate to traffic, but more often not. Mechanical is almost always in a secondary role. And operating departments weren't happy because they weren't getting a continual increase in train-mile productivity.)
In theory the K-M could deliver, in reality it did not. The locomotive was slippery at low speeds in drag-freight service (this was very disappointing), unreliable, overheated in tunnels and snowsheds, and froze up in cold weather.
Anyway, GE came along at about that time and EMD made the big leap from 567 and D.C. main generators to 645 and A.C. main generators, and the D77 traction motor was a big improvement over previous models.
H.F. Cavanaugh, mechanical officer for NYC, wrote an excellent survey of the K-Ms and their foibles in the June 1976 Trains.
RWM
I wonder if the hydraulic transmission might some day become victorious; as the ground shifts with respect to fuel efficiency, the use of copper, etc. I don't see any fundamental reason why fluid drive should take a back seat to electric drive. One reason we are doing it the electric way is that we have done it that way for so long.
It is interesting that the hydraulic transmission has evolved as the preferred method for the high power drive trains in bulldozers, yet one of the major pioneers in that area was R.J. Letourneau, advocating what he called the "electric-wheel," as he called the principle.
Letourneau coupled a diesel engine to a generator, and used the electricity to power traction motors. He was an electric drive advocate swimming upstream with those who were more enamored with the idea of replacing gears with hydraulics.
Bucyrus wrote:I wonder if the hydraulic transmission might some day become victorious; as the ground shifts with respect to fuel efficiency, the use of copper, etc. I don't see any fundamental reason why fluid drive should take a back seat to electric drive. One reason we are doing it the electric way is that we have done it that way for so long.It is interesting that the hydraulic transmission has evolved as the preferred method for the high power drive trains in bulldozers, yet one of the major pioneers in that area was R.J. Letourneau, advocating what he called the "electric-wheel," as he called the principle.Letourneau coupled a diesel engine to a generator, and used the electricity to power traction motors. He was an electric drive advocate swimming upstream with those who were more enamored with the idea of replacing gears with hydraulics.
Hydraulic transmissions for future locomotives? I am deeply doubtful.
Earthmoving machinery is quite a different application and only weakly comparable to locomotives. Machinery drive types have proliferated in order to optimize the machine's suitability for the the type of use, periodicity of use, and initial and operating costs. Three basic types are offered: diesel-electric, where the prime mover drives a main generator that supplies electricity to traction motors geared to each driven axle or wheel; hydrostatic, where the prime mover drives a hydraulic pump that supplies hydraulic fluid to hydraulic motors powering each driven wheel or axle; and mechanical drive, where the prime mover is directly geared to each driven wheel or axle via an intervening geared transmission connected to the prime mover via either a clutch or torque converter.
Earthmoving machines that have intermittent use with lots of idling time and are "entry level" such as loader-backhoes are mostly mechanical drive. Mid-size machines where flexibility and speed are much more important than initial cost and fuel cost, and where useage is intense for short periods of high production followed by long periods of down time, such as track loaders, are usually hydrostatic drive. Bulldozers are a mixed bag; Deere and Liebherr, which only compete for the small to mid-size applications (similar to the track loader) have gone to hydrostatic drive, whereas the high-production, high-use segments such as mining, where fuel cost, reliability, and availability are all important, and initial cost is not so much of an object, is dominated by Caterpillar and Komatsu, which have retained the "hard drive."
Off-road trucks are probably the most similar application to railroading, especially in the large (175-400 ton) sizes used in open-cast mining, where fuel consumption, maintenance cost, availability, and reliability are very important and the machine is expected to work around the clock 365 days a year. Euclid followed by Dart perfected the off-road mechanical-drive truck in the late 1930s and split the mining market until LeTourneau-Westinghouse (WABCO) introduced the diesel-electric Haulpak in sizes suitable for mining in 1960-63. Unit Rig, which had pioneered diesel-electric drive for oil rigs, introduced the LectraHaul in 1963, and it and WABCO quickly pushed Dart's and Euclid's mechanical-drive machines out of the mining truck segment of the market (Euclid retained a presence in smaller trucks in the quarry segment). Caterpillar first offered an off-road truck in 1963, the 35-ton mechanical drive 769, then, observing the success of Unit Rig and WABCO, tried its hand at a diesel-electric truck, the 779, introduced in 1967. It was a failure and all were repurchased by the manufacturer circa 1970 and scrapped. Cat then returned to mechanical drive with a vengeance and used its superior dealer network, immense R&D budget, and cash to seize more than 50% market share in the big trucks. However, now Cat has conceded that diesel-electric is the next step forward and is currently testing a 400-ton diesel-electric truck to compete with 400-ton diesel-electrics offered by Komatsu (the former HaulPak line), Liebherr (the former Wiseda line), and Terex (the former Unit Rig, Euclid, and Dart lines).
The K-M was a mechanical-drive locomotive with a torque converter. I think what you are suggesting is that there is opportunity to revisit such a concept (but not a hydrostatic concept). But I can't see why; the same old disadvantages of the K-M transmission haven't gone away in the meantime.
Our community is FREE to join. To participate you must either login or register for an account.