I really can't wrap my head around this, google is no help. Can someone who knows the answer please explain?
if diesels have half the horsepower, why do they need more axles to put half the power on the rail ?!?!?!
Like most people, you haven't figured out what power is.
It's force times speed.
For a locomotive, that might mean 50000 pounds of pulling force (at the wheelrims, on the rail) times 45 miles per hour (if the locomotive happens to be running at that speed) is 2,250,000 units of power. Nothing wrong with those "units of power", but as it happens no one uses them; instead, we say 2,250,000 units of power equals 6000 horsepower, an arbitrary definition.
The point is, at constant power, pulling force must double if speed is halved. If that locomotive is producing a constant 6000 hp at the wheelrims as its speed drops, it has 100000 lb of tractive effort at 22.5 mph, and 200000 lb at 11.25 mph, and 1000000 lb at 2.25 mph.
You can see the problem-- no locomotive can maintain constant power down to a standstill. The wheels will eventually slip.
Unless you pile more weight on the wheels, which is what diesel locomotives do. To reliably exert, say, 150000 lb of tractive effort, a locomotive needs to weigh more than 400000 lb. So it needs more wheels.
In other words, the four-axle electric puts out more power than the six-axle diesel at 60 mph, but much less power at 10 mph.
I have seen 6-axle electrics -- I rode behind one once on the OBB (Austrian Federal Railway).
Amtrak famously purchased 6-axle electrics from GE, and they seemed to fall off the tracks at the speeds Amtrak wanted to operate them.
The reason for 4-axles on an electric locomotive may have to do with the only demand for them being Amtrak in high-speed passenger service and that 2-axle trucks of current designs may be more stable at high speeds than 3-axle trucks.
As to the horsepower, what the electric wire gives you is the ability to tap into nearly limitless power (if you are willing to pay the electric bill) whereas a Diesel-electric incurs the weight penalty of the the Diesel engine and its alternator to power the traction motors. Yes, electrics typically require transformers and other electric gear, but there has been technological progress making that lighter in weight.
The faster you go, the more HP you need for the same tractive effort and also the more tractive effort you need to overcome aerodynamic drag. Electric locomotives are offered as the solution to getting enough HP without a high weight penalty to power high-speed trains.
You do give up starting tractive effort -- one is from the axle-load restrictions so high-speed operation doesn't pound up the track, another is that your traction motors need "tall" gearing to run at 150 MPH+ without "birdnesting" the traction motors (that is, having them fly apart into a messy mass of copper and iron parts). AC traction may help with that because the rotating part is much simpler and rugged.
The other thing is that "back in the day" it was thought you needed all axles powered for HSR, which is what the Bullet train does. Part of that is that the Japanese HSR is a mountain railroad, but part of that was the thinking that adhesion, or the adhesion you could rely upon diminished with speed. The newer fast-acting wheel slip controls, apparently, allow the use of locomotives for HSR, or it least in European practice.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul Milenkovic Amtrak famously purchased 6-axle electrics from GE, and they seemed to fall off the tracks at the speeds Amtrak wanted to operate them. The reason for 4-axles on an electric locomotive may have to do with the only demand for them being Amtrak in high-speed passenger service and that 2-axle trucks of current designs may be more stable at high speeds than 3-axle trucks.
Those E60's were a poorly adapted freight design, and weighed over 190 tons (about the same as a U30C or SD40-2) so it's no wonder they didn't do well at high speeds. More weight means more stress on the track.
I don't know enough to say which truck design is more stable, but EMD's E-units (3 axle A1A trucks) were known to have a smooth ride at speed.
Greetings from Alberta
-an Articulate Malcontent
The quick answer is the very different service they are used in. Having 6 axles instead of 4 allows additional weight and increases tractive effort significantly. Tractive effort is what is required to haul heavy loads.
Passenger trains, on the other hand, are comparatively light, say 800 tons instead of a 17,000 ton coal train. Tractive effort is rarely a limiting factor. But they do need to go fast, and speed requires horsepower, lots of it. If you have ever ridden a bicycle against a strong wind you will know what air resistance can do, and it rises exponentially with speed.
If intended for passenger service, four powered axles are more than enough to provide tractive effort so there is no need to create a much heavier and more expensive locomotive with 6 motors. The later North American examples built for freight service, on the other hand, were built with 6 axles. The horsepower ratings were still higher than contemporary diesel electrics but that was mostly because they were no longer limited by the capacity of the on-board generator.
Although don't usually use this example. Say an electric passenger train running at a constant 60 MPH needs 3000HP to maintain its tractive effort. If it runs at 120 MPH it will need 6000 HP since to cover the same distance but it will use the previous example of the force exerted to cover the same distance. So total HP minutes same at both speeds.
Covering the distance twice as fast means wheel slip not a problem with just 4 axels. The ACS-64s maximum HP is ~ 8400 so each axel produces 2100 HP max. DC motors of 2100 way too big but the AC motors no problem.
This of course does not take into wind resistance or F=MV squared..
It is all about intended service. Shorter faster trains such as those common in Europe will use four axle electrics (even for freight) because it is cheaper than using axles they don't need. This also allows one platform from each builder to serve both freight and passenger trains.
For greater tractive effort, six axles are also used on electrics. Most of China's electrics are six axles.
On some modern diesels, AC traction and wheel slip control, have made them practical to run efficently on 4 powered axels, however they must retain the 5th and 6th axels to carry the weight of the diesel loco.
Paul Milenkovicpart of that was the thinking that adhesion, or the adhesion you could rely upon diminished with speed.
I think there is more to it, and between you and a historian of PDN's quality we can quickly develop it.
My father said that when he was a boy it was 'common knowledge'* that no wheel-driven train could exceed about 320 mph, as that was the speed where adhesion for the necessary hp transfer went to zero. Also, somewhat unsurprisingly, a nominally-voltage-controlled electric motor rotating at high speed that is also producing high torque (for high horsepower) is going to demonstrate substantial acceleration in a slip (think of the T1 high-speed slipping with more teeth) so a risk of birdsnesting is greatly magnified. These were supposed to be major reasons for use of maglev or TACV (driven externally in a modern analogue of Kruckenberg's Schienenzeppelin) for things going that fast... in the Sixties.
I thought the 'all-axles-powered' idea hadn't been current since around the time of the Metroliners. It applies much more to trains that need reliable (and relatively frequent) quick acceleration rate than those that reach "normal" historical HSR speeds (and run as much as possible on 'momentum' with a minimum of actual speed change once on their special LGV or whatever; there are also electrical considerations about getting power to axles in the train at the required power density when you can't or don't want to 'distribute' 25kV (or higher!) electricity supply to the passenger cars, as was the case for 'power cars' in the original TGV and some other European trains.
At very high speed, unsprung mass in the suspension, and particularly lateral forces, become more significant than power transfer though the contact patch. So does vehicle weight, including the mass of transformers, cables, and all the paraphernalia in the trucks -- body-mounted motors taking up too much space if 'distributed' in the carbodies. Unsurprisingly to me it turned out to be cheaper to use 'top and tail' (or centralized) power in the equivalent of 'locomotives', or to go to one high-powered locomotive with relatively-sophisticated power technology and slip management with a 'driving trailer' at the other end.
*Not quite with the same arrogance as 'bumblebees don't have the aerodynamics to fly' situation... but note the current wheel-driven rail speed records and the stated reasons for their practical limitation...
If you are talking about real high speed, there is an advantage to taking electric power through only one pantograph/contact shoe. If you have multiple pantographs, especially with EMUs, you have the problem of the first one in the consist jangling the overhead wire and bouncing the "downstream" contact shoes, creating arcing and all manner of bad things in the electric gear.
The Metroliner had this problem, especially with the tall overhead wire. On the purpose-built Japan Shinkansen line allowing a very restrictive height of the trains, the wire is really low to the train, and the pantographs are these low-mass little-bitty things. I remember standing on the (high-level) platform in Tokyo station and thinking how this 25 kV line was almost at face level.
But what to do when you have to power an electric locomotive at each end of the consist? It looks like at least some of the European trains are "trainlining" the 25 kV at rooftop level?
As to the benefits of more traction motors, don't some of the TGV train sets have proper locomotives at each end, but they treat the intervening passenger cars as "slugs" by feeding low voltage power to at least some of the axles -- at least the passenger-car axles right next to the locomotive?
On HSRs on the DB, the ICE 2 & 3s have all axles in the trainset powered; on the first HSR, the ICE 1s, only the end units are powered. On the OBB their HSRs, the Raijets, are locomotive powered, with the end car acting as a control car. Their top speed is only 140 mph, while ICE 3s can manage 175.
C&NW, CA&E, MILW, CGW and IC fan
Am I correct that the horsepower rating of a diesel electric locomotive referes to the combined cumulated power of the electric motors?
Rio Grande Valley, CFI,CFII
schlimm On HSRs on the DB, the ICE 2 & 3s have all axles in the trainset powered; on the first HSR, the ICE 1s, only the end units are powered. On the OBB their HSRs, the Raijets, are locomotive powered, with the end car acting as a control car. Their top speed is only 140 mph, while ICE 3s can manage 175.
Thanks.
M636CThe ICE-T (Tilting) Classes 411 and 415 have half the axles on all the intermediate cars powered.
That statement is true for the 415 (two unpowered end cars and four powered intermediate cars), the 411 consists of one additional powered and unpowered car each.
The reason for this arrangement is that you have the heavy transformers in the unpowered cars: one trafo-car can support up to two powered cars. Because of the tilting mechanisme the traction motors are not suspended in the bogies: they are hanging under the longitudinal car bodies (that is why there is only one powered axle per powered bogie).
Note that modern constant-tension catenary is less likely to get into trouble with multiple pantographs than the 83-year old material still on much of the NEC south of New York. A pan on each end of the train is also less likely to get into troiuble then multiple pans, say on every other coach in a seven or nine-car train. If the pans and power are train-lined, the front and rear combination can save arcing and reduce wear on both the pan and the wire. And, of course, more than one pan is really desirable with ice storms and wet weather in general.
Note also that the most successful electrio locomotives of all time, the GG-1 and its mates the EP-3, EP-4. and EF-3, on the New Haven, all were 4-6-6-4 locomotives, hardly just four axles!
JPS1Am I correct that the horsepower rating of a diesel electric locomotive referes to the combined cumulated power of the electric motors?
EMD used to make the GP40, 3000 hp with four traction motors, and the SD40, 3000 hp with six of the same motors.
In the US, diesels are supposed to put their rated power into the main generator/alternator. So a "4400 hp" locomotive's V-16 actually produces around 4600? 4700? total horsepower, including the power to run the cooling fans etc.
Starting tractive effort is related to the weight on drivers, practical factor of adhesion, and.for a specific motor design and gear ratio and wheel diameter, the maximoum current the motor can handle. All other matters being equal, if the weight on each driving wheel remains the same, a six-motor locomotive should be able to start a 50% heavier train than a four-motored locomotive. Note that since the wieght on each driver remains the same, the six-motor locomotive will also weigth 50% more.
Cursator M636C That statement is true for the 415 (two unpowered end cars and four powered intermediate cars), the 411 consists of one additional powered and unpowered car each. The reason for this arrangement is that you have the heavy transformers in the unpowered cars: one 'trafo-car' can support up to two powered cars. Because of the tilting mechanism the traction motors are not suspended in the bogies: they are hanging under the longitudinal car bodies (that is why there is only one powered axle per powered bogie).
M636C
The reason for this arrangement is that you have the heavy transformers in the unpowered cars: one 'trafo-car' can support up to two powered cars. Because of the tilting mechanism the traction motors are not suspended in the bogies: they are hanging under the longitudinal car bodies (that is why there is only one powered axle per powered bogie).
This turns out to be quite interesting. Yes, it's a bit like "RDC-II", with the Europeans now calling the idea of motors in the cars "distributed traction" (which is as good a term for the idea as there needs to be). M636C will doubtless provide additional technical information, but 'basically' the motors are mounted 'inline', under the floor of the car, with Cardan shaft drive to a gearbox on the axle. The tilting mechanism (derived from the British APT via Fiat Ferroviaire, and famous on some classes of Pendolino) does not permit a 'through shaft' to the outer axle, and so only the inner axles are driven - weight is apparently not 'equal' on the two truck axles, with the inner driven one given about twice the axle loading of the outer one.
As an introduction the general layout is shown in this PDF from Voith, which makes some of the drive components, showing some of the layout. (The relevant section is toward the end, and you will see some very interesting high-speed truck and drive designs before you get there...)
There is an interesting discussion of bogie design and suspension in this PDF reference (from the Railway Technical Encyclopedia, courtesy of SKF) which I think (almost right at the end) shows the general truck layout without reference to the tilting mechanism.
(Interesting how many problems the diesel version of the ICE-T reportedly had, including very high specific fuel consumption.)
EDIT - I found this article from 2011 (which I wish I'd read earlier!) that discusses some of the distributed-traction issues and why this approach has 'taken over' from the older idea of concentrating traction and power in special cars.
One thing, though: my understanding was that United States principles restricted passenger access to the nose of railcars, which may limit some of the 'incentive' to distributed traction (as putting all the powertrain 'underfloor' and thereby opening up more of the structure to usable seating or service space) in American HSR. I think we've discussed some aspects of this in earlier threads.
I have not 'run numbers' (there are some in the Voith material) on whether the gains in lightness and polar moment, etc. in the single-axle underfloor truck actually give higher-speed performance than the frame-mounted versions as for example seen directly above them. Are there observed problems with suspension and steering when one axle is more heavily loaded, and drive and 'dynamic braking' are limited to a lesser number of carrying axles than would be utilized in an all-axles-motored truck? (A peripheral question: Is part of the single-axle configuration necessitated by there being no way to conjugate the truck axles by shaft with the tilt mechanism 'in the way', or is it related to the known difficulty conjugating multiple high-speed axles with gearing and shafts... and solved with operational restrictions like a slower initial acceleration rate.)
A PDF from SKF?
What's a PDF -- is that kind of like an RDC or what we now call a DMU
Wizlishweight is apparently not 'equal' on the two truck axles, with the inner driven one given about twice the axle loading of the outer one.
Shades of the Brill Maximum-traction truck from 1911, notorious for, uh, wandering... Brill used an off-center bolster to distribute more of the car's weight onto the powered axle. On an RDC, the only additional weight on the inner axle was the Spicer drive and about half of the weight of the cardan shaft.
Paul MilenkovicWhat's a PDF -- is that kind of like an RDC or what we now call a DMU
No, although it is certainly portable.
I usually do use the abbreviation ".pdf" to make it clear that it's something fairly large that's going to be downloaded or inline-opened when I'm actually posting a link to one...
(Yes, I know this was 'in fun'...)
blue streak 1Say an electric passenger train running at a constant 60 MPH needs 3000HP to maintain its tractive effort. If it runs at 120 MPH it will need 6000 HP since to cover the same distance but it will use the previous example of the force exerted to cover the same distance. So total HP minutes same at both speeds
It isn't quite that simple. The portion of the horsepower that is needed to overcome air resistance goes up by the cube of speed. So if you double your speed you need 8 times the horsepower to overcome the air resistance. That is only part of the horsepower requirement for speed but it is certainly not linear.
Looking across the other ocean, a sizeable percentage of Japanese juice burners had six powered axles. The earliest box cabs ran 1-Co+Co-1 for freight, 2-Co+Co-2 for passenger service. Then there was the real oddity, Class EF55, which was a 2-Co+Co-1 with a streamlined cab at the four wheel truck end and a conventional box cab at the two-wheel truck end. Class EF58, 2-Co+Co-2, the last of the articulated-frame electrics, has a box body with nicely shaped semistreamlined ends. One, EF5861, remains available to pull the Imperial Train on lines which retain 1500VDC catenary.
Post-WWII the Bo-Bo-Bo design became popular, and continues so to the present. There were only two Co-Co classes, massively heavy machines designed to climb (and descend, as brake helpers) the 6.8% Usui grade at very modest speed. After the Usui grade was taken out of service they were tested elsewhere, but were unsafe at normal freight speed.
There were a number of classes of four-axle power in Bo+Bo, 1-Bo+Bo-1, Bo-Bo and, my very favorite, the ED72 class Bo-1-Bo. Yup, one laterally-moving unpowered axle amidships, needed to support the weight of a train heat boiler and its water tanks.
Note that all of these were/are 3'6" gauge, so even the 'high speed' locos aren't very fast by North American or European standards. There are good reasons why the Shinkansen network is standard gauge.
Chuck
tomikawaTTThere were a number of classes of four-axle power in Bo+Bo, 1-Bo+Bo-1, Bo-Bo and, my very favorite, the ED72 class Bo-1-Bo. Yup, one laterally-moving unpowered axle amidships, needed to support the weight of a train heat boiler and its water tanks.
Far from me to criticize someone who not only knows this subject better than I do, but was there -- but my understanding is that the ED72 class would be Bo-2-Bo in your system, with the 2 being axles (as in the German system) rather than wheels (as in Whyte coding):
Now it may well be that this class was originally built with a single axle in the middle; the early NYC third-rail locomotives had Bissel trucks, and the very talented man who designed those locomotives resigned when 'higher-ups' started shoehorning two-axle trucks into them without consulting him first...
If so, please let me see a picture or drawing that shows the underframe arrangement.
My apologies about the misidentification of the JNR Bo-1-Bo class. I shot from the hip [my key reference book is temporarily (I hope) AWOL] and scored a clean hit on my toe. The ED73 (and the later ED76-) is Bo-2-Bo.
Checking locos used on private electric railways, all but a handful were Bo-Bo or Bo+Bo. The oddballs, all Bo-Bo-Bo, were all withdrawn from service when their owners discontinued freight service.
tomikawaTT My apologies about the misidentification of the JNR Bo-1-Bo class. I shot from the hip [my key reference book is temporarily (I hope) AWOL] and scored a clean hit on my toe. The ED73 (and the later ED76-) is Bo-2-Bo. Checking locos used on private electric railways, all but a handful were Bo-Bo or Bo+Bo. The oddballs, all Bo-Bo-Bo, were all withdrawn from service when their owners discontinued freight service. Chuck
Having checked Japanese Wikipedia...
ED62, a rebuild of ED61...
So DC and not AC.
https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:ED6214b.jpg
(I wonder if that will work....)
M636CED62, a rebuild of ED61... So DC and not AC. https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:ED6214b.jpg (I wonder if that will work....)
It does for me ... nicely. Oddly enough, typing "Bo-1-Bo" into Google gives one hit on Wikipedia that mentions the ED62, and there are a number of English-language pages with information. The class is apparently covered in Inouye's JNR locomotive encyclopedia, if anyone here owns a copy or has access to one.
The conversion was done fairly recently (middle to late '70s) and was successful enough that the last example survived into the new millennium. Three, perhaps four, have been preserved.
Now can someone describe the details of the single-axle support? The necessary load reduction wasn't much (from 15 to 13 tons axle load) and it certainly seems easy to get a single axle in, which at the center point between the truck pivots is going to track well even on spiral-transition curves.
The key is the reduction to a 13 ton axle load - the maximum for a lot of rather lightly-built lines which received 1500VDC catenary in the immediate postwar period. There were several steam loco rebuilds (from 2-8-2 to 2-8-4) done for the same reason (and operated earlier on the same lines.)
I should have realized that the place to look was in 1500VDC-land. That's (part of) what I model in 1:80 scale.
Chuck (Modeling Central Japan in September, 1964)
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