groundrules wrote >>
pez wrote >>
What do they consider 'train manufacturing'? General Electric makes locomotives in Erie, PA. The interesting thing about trains is that the diesel engine just runs a generator, the actual wheels are propelled by electric motors fed from the generator.
I think the "only manufacturer" is in reference to the DMU type trains, not regular freight trains.
and yeah, while I have no proof in the railroad world, my theory is that the advantage of electric power (via diesel generation) is that an electric motor has very different power delivery properties versus an internal combustion engine. For instance, you can get very near maximum torque (which is nice for hauling a big-ass load) at almost zero RPM, where as an internal combustion engine has an incremental power delivery that increases with engine speed. This requires that you have a transmission so that you can rev the engine to a torque producing speed but still allow the train wheels to turn slowly. An electric motor doesn't require that, and in fact doesn't care if it's running fast or slow or forward or backward.
that is more or less correct
using diesel electric eliminates the need for a clutch which with a locomotive with 4000hp would be enormous and hard to control to begin with
plus with locos weight is not an issue, they are typically ballasted up to their max weight which is 70,000lbs per axle
tractive force is coefficient of friction times weight, that can be anywhere from .1 up to around .65 depending on track conditions
a 6 axle loco will come in up around 420,000 lbs with a tractive force up around 140,000 lbs, friction coefficient runs around .33 or so normally and they have sand for when its slick that gets squirted in front of the wheels
they have other physical limits like drawbar strength, it will snap at around 250,000 lbs of pull---so with multiple locos jamming the throttle to max is a no no and the modern locos won't let that happen anyway, the power is very tightly controlled and wheel slip is limited otherwise the loco will literally rip the track to shreds
using electric also allows the motors to be used as brakes, they call that dynamic braking where the motors act in reverse as generators shunted across a resistive load