These questions apply to typical freight locomotives.
How is the generator/alternator linked to the prime mover?
What real difference is gained by modest increases in horsepower, such as the 4000 hp of a -9 40CW as compared to the 4400 hp of a -9 44CW?
I recall the “horsepower wars” of the 1960’s where it seemed like the manufacturers were boosting the horsepower of the prime movers in each successive model. Were higher capacity generators part of the higher horsepower package or was the more powerful diesel engine turning the same type generator used in a previous model, only at a higher rpm?
In a given diesel engine series, such as an EMD 567 or a 645, how were these horsepower increases achieved?
I guess it would be a fair assessment to say that I’m clueless about exactly what happens between the engine and the traction motors.
These questions apply to typical freight locomotives.
How is the generator/alternator linked to the prime mover?
Typically it is a “hard” coupling, i.e., there is no flex coupling. In an EMD, the flywheel is bolted directly to the input shaft of the main generator.
What real difference is gained by modest increases in horsepower, such as the 4000 hp of a -9 40CW as compared to the 4400 hp of a -9 44CW?
10% more work output for essentially the same purchase price, maintenance price, and dispatching cost – there might be slightly more purchase price and maintenance price, but if it’s not overwhelmed by the difference in work output, there’s no ability by the manufacturer to successfully market the higher output locomotive.
I recall the “horsepower wars” of the 1960’s where it seemed like the manufacturers were boosting the horsepower of the prime movers in each successive model. Were higher capacity generators part of the higher horsepower package or was the more powerful diesel engine turning the same type generator used in a previous model, only at a higher rpm?
Yes, and in fact limits on D.C. generators that would still fit within a carbody were a greater limit than the limits at that time on prime mover design. Limits on the D.C. main generator were resolved by the A.C. main generator, which EMD introduced with the 40-series in 1965-66.
In a given diesel engine series, such as an EMD 567 or a 645, how were these horsepower increases achieved?
Turbocharging, increase in rpm, and increase in displacement have been the primary solutions to achieving greater horsepower within the same basic physical envelope that the engine may occupy. Each in turn requires substantial strengthening of the locomotive crankcase (EMD) or block (GE or Alco) and rotating and reciprocating components, increase in cooling capa
Thanks for taking the time to respond to my questions. I was kind of surprised with the answer to question #1- I had envisioned some sort of gearbox arrangement. Thanks again!
To extend what RWM wrote on locos with DC traction motors:
The traction generator/alternator controls are set up so that the output voltage droops with increasing output current (more or less constant power). When combined with the characteristics of the DC series motor, this gives an equivalent to a continuously variable transmission. One consequence is that the electrical gear in a locomotive is tied intimately with the characteristics of the traction generator/alternator - which means that putting a different engine into a locomotive (e.g. replacing an EMD prime mover with a Cat) will be a very involved process.
With AC traction motors, the grunt work in providing the continuously variable transmission is done by the inverter. The traction alternator is simply called on to produce a c