How is a locomotive able to pull so many train cars?

Question

I saw a train pass today and it seemed like forever until the train completely crossed my path. There must have been about 100+ cars that it was connected to. How is it that 1 locomotive is able to pull that much weight without engine failure?

Thanks

Answer 1

Modern locomotives are mostly diesel-electric, meaning the diesel prime mover generates electricity, which supplies traction motors on each axle. This form produces much more torque and low end pulling power than the traditional transmission.

Modern locomotives also develop tremendous amounts of horsepower. Tractor-trailers usually develop around 300-500hp, whereas modern road locomotives routinely produce 4,000+hp per locomotive (strap a few together, you've got quite a few ponies working for you).

Something else to consider is what you specifically saw. I've pulled 7,000+ feet of train with one locomotive, but we stayed on mostly flat land, and the train was all empties. Other times, I've struggled up moderate grades with only 4,000 feet and two engines.

Answer 2

Mostly it's low rolling resistance. However the rolling resistance isn't really provided by friction. It's instead provided by deformation in this case deformation of the wheel and rail. For example a car with a flat tire is a lot harder to push than one with all four tires inflated even though the flat tire actually has less friction with the road. This is, I believe, the main reason why the mainline railroad tracks that get the most use and will be used by the heaviest, fully loaded trains are made from heavier, sturdier rail than are the sidings and yard tracks. It's so that the rails will flex or deform less as the train rolls over them deceasing the rolling resistance and making it easier for the locomotive(s) to pull the train. If a 100 car train had absolutely no rolling resistance and was on perfectly level rail then you could get the whole train moving by your self without even pulling very hard. However it would take you a very long time to get the train moving even a couple of miles per hour. Wow! Some really crazy answers come after mine. I just want to say a few more things here. The engines don't have gears like a car. Just one gear ratio in the final drive which is fixed. You can do this because the electric motors used to move the locomotive have a really flat torque curve compared to the diesel engine that ultimately powers them, and they'll still produce torgue even when completely stopped. This eliminates the need for a limited-slip device i.e. a clutch which would dissipate a lot of energy and wear out really fast due to the fact that it takes so long to get the train moving a decent speed. There's other advantages too such as being able to simply and accurately guage your power output without any loss of power.

Answer 3

I live in train country, coal country and the trains come through here loaded with coal. They have three engines on the front most of the way. They are very powerful, I do not know how many horse power each engine has but I'm sure it's a lot. Then when they get near where I live a team of2 or 3 engines come up behind the caboose and push it up and over a couple of mountains. They get it over the hump and then return. This happens several times each day and during the night. So, the power is awesome and they chug a lug like the Little Engine That Could! It gets done and it's amazing. Not so to hear at night since we have several crossings and they have to lay on those air horns three short and 1 long blow each time they near a crossing. Some engineers let you sleep others make sure you are awake. Some stick to the 3 and 1, some give one real long loud one. Very disturbing when you aren't sleeping well.

Answer 4

Most of the above is accurate. Horsepower converted to tractive effort on a large scale. Consider an SD45 develops about 105,000 f/lbs. of tractive effort, or torque. By comparison, the automobile production engine that developed into the 429 Hemi was the strongest puller at 492 f/lbs. of torque off the showroom floor.

Low friction is also a benefactor, as pointed out.

But, the train is not a solid chunk of dead weight. There is slack between the cars where they couple together. This allows the locomotive to start one car, which starts the next car, and the next and so on. The law of inertia states a body in motion tends to stay in motion unless acted on by external forces. Without the slack, nobody is going anywhere.

Answer 5

a locomotive has a diesel engine that powers an electric generator. the wheels under the locomotive are powered by electricity not by the engines torque. the more throttle the more electricity produced and that means more tractive effort for the wheels (traction motor). most trains have 2 or more locomotives (units) to prodice more tractive effort and engine braking (dynamic braking). its all about the electricity

Answer 6

The Diesel engines serve only as generators for the electric motors that actually do the pulling. It's like the worlds biggest hybrid. Electric motors have their max torque at zero RPM. and can be maxed out without excessive wear. Which makes them the most efficient for pulling massive loads. On top of the fact they have very low gears and can spin at high RPMs.

Answer 7

it's called tractive force the weight of the locomotive with a huge amouont of traction and sand shooting under the wheels when starting from a dead stop and power is made from diesel engine going to electric motors that are coupled to a huge gear that is on the inside of the wheels

Answer 8

Diesel electric. The diesel engine turns a generator that supplies an electric motor. Electric motors develop enormous amounts of torque at start-up, much more than you could ever get from an internal combustion engine.

Answer 9

Loads n Loads of torque bro n about 6000 horses of DIESEL power so its a childs play for the Locomotive

Answer 10

Besides the aforementioned about diesel/electric drives, the rolling resistance is very low (solid steel wheels riding on steel tracks). Also, railroad beds and rails are very close to level, slight in incline, unlike the hills and valleys trucks must maneuver on rubber tired vehicles.