How do helper railroad engines coordinate their speed with the front engines pulling the train?

Question

if the engines push too fast, the cars may leave the rails, if they push too slowly, they may drag and slow the train down. so how does this work?

Answer 1

I beleive your talking about an engine at the rear of the train. ITs called distributive power. Such locomotives in the rear are in contact by radio with the controls of the front locomotive.

Answer 2

Helper engines on the front of a train are linked by electric and pneumatic jumper cables. Provided they are compatible multiple unit wise, the controls in the lead unit control those in the following units -- such as throttle, sanders, headlight, etc..

A train with additional units in the middle and/or end are DPU's or distributed power units. This is done, as Mr. TropicSon stated, by electronic control (not familiar with it enough to call it remote or radio). At any rate, per this system, the additional units are controlled electronically.

On modern diesel-electric locomotives (and most all of them for that matter, except maybe an old ALCO on a shortline somewhere), loco's have a 9 position throttle - IDLE and Run 1-8. Whatever notch the controlling unit is in, the trailing units will also go - advancing or decreasing the throttle in the controlling unit instantaneously controls the helpers.

That may sound easy enough, but for the longest time, front and rear end helpers were run by feel and whistle signal. I've heard some mind boggling stories about helpers in the steam days, more from the days of dieselization, passed on from the old heads.

Answer 3

The two or more engins ar linked together via computer esentially making them one. The diference in power output between the two is not more than you pushing on a wall as hard as you can.