Lars Loco is it safe to assume that modern engines will always deliver ~90% of the prime movers output into drawbar-force over their entire speed-range ?
GP40-2 JayPotterif I were going to apply a tractive-effort formula to an AC6000CW in notch eight at a speed of around 11 or more miles per hour, it would be (TE in pounds) equals (6000) times (factor X) divided by (speed in miles per hour), with factor X being a number somewhere between around 329 and around 337. Again, I'm not sure how useful the result of that calculation would be. Very good assumption. The 6000's "x-factor" ranges from 329 on a hard, slow speed pull to 348 at higher speeds.
JayPotterif I were going to apply a tractive-effort formula to an AC6000CW in notch eight at a speed of around 11 or more miles per hour, it would be (TE in pounds) equals (6000) times (factor X) divided by (speed in miles per hour), with factor X being a number somewhere between around 329 and around 337. Again, I'm not sure how useful the result of that calculation would be.
timzLars Loco is it safe to assume that modern engines will always deliver ~90% of the prime movers output into drawbar-force over their entire speed-range ? If an AC6000 produced 5400 dbhp at 1 mph that would be 2,000,000 lb.
Thanx Tim for the calculations,
Ok, 90% may not apply to extreme conditions (speeds down to zero), as this should result in spinning wheels, how about 10mph (cont. pull.) to 75mph?
For me, It would be interesting to know how much efficient the transmission-system over the speed range works, and how much it was improved over the last 20 years. Of course, still hoping to gain some results from real field tests...is the rail industrie really so shy
Cheers
lars
Lars LocoOk, 90% may not apply to extreme conditions (speeds down to zero), as this should result in spinning wheels.
The units' standard adhesion-management software prevents any traction motor from producing more than 30,000 pounds of tractive effort. In other words, once speed drops below about 11 mph, the unit will not produce more than 180,000 pounds of tractive effort regardless of how much further the speed drops. Advanced versions of the software set the limit higher, up to a maximum of 36,000 pounds per motor or 200,000 pounds per unit.
JayPotterLars LocoOk, 90% may not apply to extreme conditions (speeds down to zero), as this should result in spinning wheels. The units' standard adhesion-management software prevents any traction motor from producing more than 30,000 pounds of tractive effort. In other words, once speed drops below about 11 mph, the unit will not produce more than 180,000 pounds of tractive effort regardless of how much further the speed drops. Advanced versions of the software set the limit higher, up to a maximum of 36,000 pounds per motor or 200,000 pounds per unit.
10% increased tractive effort, not bad doing this just adjusting the software...
Lars Locois it safe to assume that modern engines will always deliver ~90% of the prime movers output into drawbar-force over their entire speed-range ?
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Lars Loco10% increased tractive effort, not bad doing this just adjusting the software...
The 180,000- and 200,000-pound figures are the maximum traction-effort levels that the software allows the units to produce. The extent to which a unit actually produces 200,000 pounds of tractive effort is a function not only of its software, but also of factors such as weight, rail conditions, and truck design.
People need to think of tractive effort for what it is which is available torque at the wheels. It has nothing to do with traction. That is called adhesion. You can have all the TE in the world but if your wheels slip at half of that, it's worthless which is where the factor of adhesion comes into play.
TE looks higher on modern engines over steam engines for a number of reasons but a very often overlooked one is wheel diameter. Let's say we have any generic steam engine. Let's also say that the only thing we changed was wheel diameter, assuming of course we could. If the wheels were made smaller, we'd have more TE. If the wheels were larger we'd have less TE. This applies with no other changes whatsoever including boiler pressure. In the case of a diesel, it would apply with no change in generated electrical horsepower.
I think of horsepower as what does the work and torque as the amount of leverage to do it. That's not quite accurate but gets the point across. Our smaller wheeled engine of the same power level has more TE because we have slowed it down. It takes more revolutions of the wheels to go the same distance. Basically the smaller wheels put it in a lower gear. This increases torque (TE) however it does nothing for power. If we have a low factor of adhesion, we'll just spin and all this TE does nothing. We could add more weight to cure this but we add to rail stress. At some point we need to add wheels. You get the idea.
While we generally think of only logging locomotives as geared, the reality is that all steam engines are always stuck in only 1 gear. The faster the engine was designed to move, the larger the drivers which is equal to a higher gear. Of course then you lower your TE but these were designed for lighter faster trains. Some of these trains needed helpers over certain grades just for passenger duty as a result even though their rated horsepower level may have seemed adequate. You try starting your car at slow speeds on a hill in high gear! If you only needed slow speed operation but needed the leverage to move trains, you built an engine with small wheels. These are basically low gear engines. They weren't fast but they could pull well. Give me a lever long enough and I will move the world! A little amount of power can move a lot of weight if given enough leverage and time .
There were many things that affected TE of course but wheel size was definitely important. Don't think that just because 1 engine has a higher TE than another that it is necessarily better. You need to see the big picture. What is the adhesion of each engine? At what speed is TE rated for each?
It is hard to compare a diesel/electric to a steam engine as a result of these differences. An electric motor has max torque (TE) at 0 rpm. However at 0 rpm you aren't doing work as you can't have horsepower at 0 rpm. TE is so high because this is the point of max leverage.
fredswainPeople need to think of tractive effort for what it is which is available torque at the wheels. It has nothing to do with traction. That is called adhesion. You can have all the TE in the world but if your wheels slip at half of that, it's worthless which is where the factor of adhesion comes into play.
I'm afraid that I don't understand the concepts of (1) tractive effort having nothing to do with traction and (2) having a certain amount of tractive effort but having part of that be worthless.
I guess my question is if tractive effort is actually "available torque at the wheels" instead of whatever tractive effort a locomotive is actually producing, how is that actual tractive effort measured?
Thanks.
I thought tractive effort was measured at the coupler.
Anthony V.
You'll see people using the term that way, but far as I'm concerned "drawbar pull" (which is measured at the coupler) isn't the same as "tractive effort". The latter should be measured at the wheelrim/rail. In other words, drawbar pull = TE minus the force needed to move the engine itself.
In any case, yes, TE is a linear force, not a torque.
fredswainPeople need to think of tractive effort for what it is which is available torque at the wheels. It has nothing to do with traction. That is called adhesion. You can have all the TE in the world but if your wheels slip at half of that, it's worthless which is where the factor of adhesion comes into play. TE looks higher on modern engines over steam engines for a number of reasons but a very often overlooked one is wheel diameter. Let's say we have any generic steam engine. Let's also say that the only thing we changed was wheel diameter, assuming of course we could. If the wheels were made smaller, we'd have more TE. If the wheels were larger we'd have less TE. This applies with no other changes whatsoever including boiler pressure. In the case of a diesel, it would apply with no change in generated electrical horsepower.
Hogwash.This is wrong in the case of a steam locomotive, and it is wrong in the case of Diesel-electric locomotives too. A larger wheel increases leverage, and it also increases the size of the wheels contact patch which increases the potential force that can be applied without slipping. In the case of steam locomotives you may have noticed that all later "Super-power" steam locomotives had comparatively larger diameter drive wheels than the locomotives that they replaced. The larger diameter drivers on the NKP S class Berks (69" versus 63") on the Mikados they replaced allowed a longer stroke (34" versus 32"), in turn the crank pin was lengthened creating greater mechanical leverage, crankpin is further from the center of the wheel. In every late generation similar changes were made N&W Y6 compared to early Y3 and Y4, C&O H-8 Allegheny versus the predecessor H-7, DM&IR M3 Yellowstone versus the preceding MS rebuilds, in all cases the driver diameter was increased, and the reason wasn't to run faster.
With modern Diesel locomotives, driver size has increased from the 40" typical of the '40s through '70s era, to 44" or 45" found on today's SD70ACe and ES44AC locomotives. It is no coincidence that the EMD locomotives with the smallest drive wheel diameter were the E-units used in passenger service.
timz You'll see people using the term that way, but far as I'm concerned "drawbar pull" (which is measured at the coupler) isn't the same as "tractive effort". The latter should be measured at the wheelrim/rail. In other words, drawbar pull = TE minus the force needed to move the engine itself. In any case, yes, TE is a linear force, not a torque.
If that is the case then:
Drawbar pull = TE - Drag Force - Grade Force - Force to Accelerate Loco (any other forces acting on the locomotive?)
Drawbar pull = TE - Drag Force - Grade Force - Force to Accelerate Loco
(any other forces acting on the locomotive?)
On level track at constant speed:
Drawbar pull = TE - Drag Force
The drag force becomes smaller at lower and lower speeds. At low speeds only
Drawbar Pull = TE (approximately)
How is the TE measured? Or, is it back-calculated based on the drawbar pull measured with a dynomometer car? Or, is it measured using some gigantic dyno?
AnthonyVHow is the TE measured? Or, is it back-calculated
As for drawbar pull-- when you're measuring it with a dynamometer car you have to keep track of the grade and acceleration so you can correct the measured drawbar pull to what it would have been at constant speed on the level. (And I guess you'd have to keep track of the locomotive's fuel level. if you wanted to correct for acceleration really correctly.)
could TE be measured on a supplier dynamotor just as they do automobiles?
For a given electric motor and given gearing, smaller wheels do mean higher theoretical tractive effort. But the smaller wheel also means lower factor of adhesion because of a smaller contact patch.
A given motor can have the same theoretical tractive effort regardless of wheel size, simply by changing the gear ratio in proprotion to the wheel size.
A given motor can be used to optimize speed or tractive effort regardless of wheel size (within practical limits) simply by choosing the correct gearing.
This is why high speed steam locomotives needed large diameter drivers and high tractive effort freight locmotives needed smaller drivers (in general, although many other considerations including cylinder bore and stroke, etc apply).
But with diesel-electrics and straight electrics this rule is out the window because there is always a choice of gearing. (Wheel motors are the exception, but that is a whole new story.) Indeed larger drivers for higher effective tractive effort makes sense ---to provide a large contact patch.
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