I know the proper term for a “diesel” is “diesel-electric”. I know there is a honkin’ great diesel engine inside the hood, followed up by an electrical generator, which provides power to traction motors, which then turn, by gears, the axles of the locomotive.
Is the diesel engine connected to the main generator by a crankshaft, or does the rotary motion of the diesel go through a transmission, first?
When a modern engineer puts his locomotive into motion, are the notches on the throttle controlling just the diesel engine, or controlling the amount of power the generator sends to the traction motors?
The throttle directly controls engine speed on pre-microprecessor locomotives to give a fixed engine rpm. Exact power output at any Rpm. will be determined by engine condition, and the fuel rack setting done by the shop. Modern microprocessor locomotives are set up one of two ways, based on the choice made by the Mechanical Dept of the railroad. Either the diesel will operate like older power and the engine will run at a fixed Rpm for each throttle setting, or it can be setup to produce a fixed amount of tractive effort at a particular throttle setting. Of course the TE rating for each throttle setting must be somewhat proportional to the engine speed. For example you cannot have the throttle setting Run 1 try to have the locomotive put out 95 percent of its maximum TE.
Depending on the unit, an auxiliary drive shaft also runs the air compressor, although a few GE’s had an electric compressor.
From GP 38s and up, EMD has used an alternator, not a generator, and the current is run through a rectifier to convert it from AC to DC for the traction motors.
Same concept as your automobile, a DC system powered by an alternator, producing AC that is then changed to DC for use.
Alternators have less moving parts, are more hardy and reliable, dont have brushes and are not as affected by dirt, moisture and such.
Engine RMP determines alternator output, which is the same, no matter if it is a GE or EMD, both at notch 4 will give you the same alternator output, so you can MU different makes.
Newer units, with the “computers” can limit wheel slip, monitor traction on a motor by motor basis, apply the sander when needed, fun stuff like that.
No. Generator is directly coupled to the diesel engine.
For most older locomotives:
The throttle controls the diesel engine speed (RPM) via a fly-ball governor. The governor also has control of the fuel rack and generator excitation. It will increase the fuel and load (load regulator - a hydraulic motor controlled rheostat) until it reaches a preset maximum fuel rack setting for that notch.
If you wipe the throttle on an SD40-2, the throttle will energize the A, B and C solenoids in the governor. That tells the governor to make the engine run at 904 RPM. The gov. will increase the fuel and load until the engine reaches 904 RPM and the fuel rack is at 0.87.
There are exceptions, like Amtrak’s F40PH. The F40PH provided head end power to the train by tapping some juice off of the main alternator. But in doing this the prime mover needs to run at a constant speed when in HEP mode. Therefore the amount of power delivered to the wheels could not be controlled by varying the prime mover speed. In that case the throttle controlls the excitation field in the alternator. This effects the coupleing efficiency between the mechanical input and electrical output. Kind of like the clutch in a car (actually more like a variable pitch torque converter). When the F40PH is NOT in HEP mode it works like a normal freight loco and the throttle changes the RPM of the prime mover.
Is it true that on some modern engines, throttle Run 8 doesn’t always use maximum engine RPM, depending on locomotive speed? If so, just GEs, or EMDs too?
The AC4400AC-CTE (CTE= Controlled Tractive Effort) units can derate themselves. I believe this is a feature to prevent rear helpers from shoveing too hard on the train as tractive effort increases (speed decreases)
I didn’t make myself clear. I think I read that some (GE?) locomotives will (in some circumstances – maybe high train speed? or low train speed?) drop the engine RPM a bit when the throttle is in Run 8, with increased excitation to maintain full rated power.
Only in standby. No power is tapped off the AR-10 in normal , that power comes from the HEP alternator, 4 pole 1800 rpm, 60 hz 480 vac. The AR-10 has 12 poles… can anyone tell me the diesel RPM in standby ?
If I may…a slight possible correction. I believe the F40PH that Metra used had a seperate mechanism attached to the rear of the main crankshaft; this device is what generated the electricity for the coaches.
When the locomotive was in “standby” mode (meaning the unit was generating electricity for the train but none was available to the motors) the unit would rev up to the rpm equivalent to about the 4th or 5th notch.