How do Diesel train engines keep same power?

[Lakeslad]

I catch the train quite often and today thought: <p>On a train of 4 carriages, if each has an engine, how does each know how much power to exert? i.e. if the second carriage was putting out less power than the first carriage then the first carriage would in fact be pulling the second?

[Loosehead]

Usually they are deisel electric which means the engines do not drive the train, they are generators that charge batteries that run electric motors and they can easily be kept in sync.

[Catso]

I disagree, loosehead. The 'little' railbus/sprinter type things nearly all have diesel engines with automatic mechanical transmission.

With modern electronics, it's much better controlled than it was on earlier trains.

In the old days, it all worked because even though the engines were throttled all together, the inevitable minor differences in speed and power got balanced out because internal combustion engines slow down as they are asked to produce more power (your car slows when it comes to climb a hill). So if one engine was being asked to do more work, it would be slowed down a bit by this, enabling the other(s) to 'catch up'.

[Loosehead]

I know there are direct drive diesels but I always thought they where mostly diesel electric.

[Lakeslad]

That makes scense, thanks very much.

[Catso]

The locomotive-type engines are always diesel-electric, yes.