How do trains generate enough torque to pull so much weight?


I understand basic mechanics, but I’m still curious how a train engine could generate enough torque to pull that much weight. Also, how do they not snap/sheer a bunch of parts in the process of applying that much torque?

In: 69

I guess the most simple way is very slowly, and everything is made of metal.

Just like a train takes forever to stop, it takes a lot of time to start and after the initial movement, the train can ride off a lot of momentum over a whole bunch of different cogs, wheels, suspensions, all sorts of stuff

Like a vehicle towing a trailer, boat, whatever. They won’t just speed into motion, you move slowly to minimize the stress put on all the parts impacted by tension

Big electric motors

Modern trains all use large electric motors connected to their drive wheels. These are able to produce the crazy levels of torque needed while also being able to get up to high speed

Diesel alone can’t get the torque or speed required, the gears needed would be too big to work, so instead we’ve had diesel electric trains for about a century where the diesel spins a generator that feeds some batteries and the big electric motors

A big part of the answer is that pulling all that mass requires only a tiny force … as long as the rails are level. Steel wheels on steel rails have very low rolling resistance, smaller than that of road trucks by a factor of more than 10.

Railway tracks obviously do often have a slope but these are generally kept much more gentle than for roads. Tracks with a gradient steeper than 1 in 40 (2.5%) are very rare for heavy freight trains.

They start pulling one car at a time. If the train cars were held together without any travel in the connections the engines couldn’t start pulling the entire mass at once.

Because the train cars are attached with some play in the connections the engine only has to add momentum to one car at a time.

The engine starts moving, then it gets the next car moving, then those two moving cars get the third moving, etc. It doesn’t have to pull the entire mass at once to get moving, but is able to incrementally add momentum to its load one train car at a time

Edit: for the nay-sayers, read up

Diesel locomotives are the best example of a first-generation hybrid powertrain. The engines spin generators, and by varying the excitation of the field windings of the generators (basically making an electromagnet inside stronger or weaker), an engineer can produce an immense amount of torque at a very low speed to get it started, and back it off to a lesser amount once the train is up to speed and doesn’t need as much to keep going. The trains can operate over a wide variety of speeds and terrain with nothing more than a simple gear drive between the traction motor and drive wheels.

Like a hybrid car, they can also reverse the process going downhill, turning the traction motors into generators, though currently they divert the power produced into giant heating elements to dynamically slow the train while creating oodles of waste heat.

The nature of the system lends itself perfectly to include battery banks, which will store the energy from a downhill run for the next uphill, and next-generation locos are being developed that will function much like gigantic Priuses! They are also developing mains-rechargable full battery locos for railyard work such as making up the trains.