About twin engine diesel locomotives

Good day to all,
I was wondering how diesel locomotives with two prime movers were built and operated. I am from Italy and may not know something that you in the US may take for granted.
I am referring for example to E series, DD40 etc...
First of all: did they have separate generators, or were fitted to a single one?
Then, a single engine was able to give current to all traction motors, or was wired just to one of the trucks.
Operationally wise, was it possible to have only one engine operating (and the other one idling or shut down completely) in case full power is not needed (descending slopes or failure of one engine).

Thank you very much

 

Each diesel had a generator mounted. That saved Baldwin and Lima the trouble of running shafts through the cabs of their center cab transfer switchers.

More importantly, it allowed the locomotive to operate on one diesel if the other failed. It would kind of spoil things if the working diesel had to turn the failed diesel in order to turn the generator.

One engine powered all traction motors. While those locomotives would run with one diesel shut off, I don't think one could be revved up while the other one stayed at idle. If they were both running, they both responded to the throttle.

 

Thank you guys,
That more or less covers all, I got an operatorm manual for the E9, and looks like each engine was wired to the 2 motors of the respective truck. The hydraulics are the same, also because the engines are connected to the wheels vith the transmission.
That said, as acptulsa said, makes sense that the two engines respond as one to the throttle.

 

Operator's manuals tend to be oversimplified. Remember that the wheels had to be able to drive both directions, but the diesels only spun one direction. There was a control box in the circuit. Some very early units, often gas-electric motorcars, had manual transition.

Having multiple control circuits and trucks isolated from each other would have disadvantages. Motors receiving no power at all are a big drag. Even giving motors just a little electricity makes them spin much more easily.

While running big cables from one end of the engine to the other wasn't easy, it was much, much easier than running shafts to transfer and equalize power from torque converters. And the advantages are undeniable. Diesel-hydraulics would use only one reversing gearbox, if that could be done more easily and cheaply. I can't imagine they didn't centralize electrical control.

I've seen diagrams of the layout of E units. Control circuitry was centralized behind the cabs. These were oversimplified, too. They certainly weren't wiring diagrams. But that suggests power was routed to a single place, and distributed from there. That would have been cheaper, too, at a time when control circuits were far more complex, costly and harder to keep cool and dust-free than today.

Torque converter drive was undeniably more efficient than any diesel-electric system. But the latter has ruled the U.S. locomotive market all along for good reasons. It isn't just the challenge of developing converters that can handle 3000+ horsepower. There's also dynamic braking, which takes power from all wheel motors.

Diesel electrics are different animals. Their complexity is not an advantage in itself, but that complexity makes certain advantages possible.

 

HEre in Europe, the only one fans of hydraulics were the Germans, almost all other diesels of non german design were electrics.
In Italy we had a batch of 30 first gen hydraulics being tested with another 30 electrics, and in spite of the electrics being heavier, the reduced maintenance and fuel consumption got them to score a win. Italian companies never built other hydraulics.
Nevertheless the German built some impressive and reliable hydraulics fro more than 30 yrs, the class 218 has some 3500 HP, and is just now being replaced by electrics after almost 50 years of service.
There is still a good number of 218, and older twin engined 220s and other german hydraulics sold as used and working now all over europe for private companies (mostly MOW trains).