I know Diesels have throttle settings from 1-8. Why do they have this instead of just having a continuous slider from idle to max power? Also, what happens if you want to maintain a certain speed, say 60 mph? Do you notch it up and down all the time if the power needed to maintain that speed was an intermediate setting between two of the throttle notches?
Just like a car when you come to a hill you have to put more gas into it and when going down hill you have to just let off the gas. There really is no in between two notches. Yes you need to regulate speed with throttle and some sort of braking.
Pete
I know that happens a lot in MSTS, but track in the real world is rarely that consistent…if you have a notch that will maintain your speed perfectly, chances are it won’t be too long before you suddenly find your train slowing down or speeding up due to a curve or minor grade or other factor!
The response of the train to changes in power settings is very slow compared to a motor vehicle on a road. And train speeds tend to be more consistent than what is required of highway vehicles. So there is no need to be feathering small changes in the power for trains other than just changing notches. But beyond that, the power output of locomotives is controlled ultimately by the load regulator as the load of pulling the train varies. The throttle establishes a constant prime mover RPM, and then the load regulator sets the power output for that RPM. The load regulator changes lag behind the throttle setting changes.
But having said all that, I suppose there is no fundamental reason why a locomotive needs specific physical notches in the throttle control, especially considering that this feedback for throttle position could be displayed on a screen, if that is not the case already.
The governor that controls diesel speed runs balancing a hydraulic pressure due to the output of a hydraulic pump against the pressure of springs activated by 4 solenoids. The 4 solenoids are activated by the throttle in steps to successively add more and more spring force to a lever. That lever then moves down to inject more fuel into each cylinder as the pressure increases in the fuel supply line. When the engine speeds up the hydraulic pressure of the pump increases to push that lever the other way and reduce fuel flow. There are some diesels that activate the fuel injection using a rod thru the top of the engine that increases flow to all the injectors. This requires significant alignment of all the injectors and is hard to operate for a large diesel. Our diesels just increase the fuel pressure to the injectors, adding more fuel per spirt as the injector opens.
The other advantage of the 8 position throttle is that the Multiple Unit cable that connects all the diesels has 4 pins for these solenoids. These pins are labeled A, B, C and D governor solenoid. All locomotives in the consist throttle up (proportional to their horsepower) when the throttle is moved. These are the first digitally controlled machines. Long ago they discovered that digital signals were far easier to handle than a smoothly changing analog signal.
And yes, you have to modulate the throttle from 3 to 4 to go up a hill at 10 mph, for example. Later models have cruise control, but that takes all the fun out of driving.
I wasunder the impression that the notches were Part of the EMD system. You can only have the generator operating correctly at very fixed revolutions which produce a very consistant amount of power. Ergo the 8 steps are the only 8 steps at which the EMD transmission will provide correct power.
I think of it like a household gas generator, the engine is at a constant speed. You can mess with the governor to increase the RPMs of the motor, but the generator will no longer produce 110V AC it will produce something different and devices plugged in will not work correctly.
The diesel could provide a continuously increasing RPM if there were a way to linearly move the pressure on the governor lever using the throttle control. The 8 notches are just so the governor can be controlled easily with on/off electrical signals. There is a separate system called the load regulator. This increases the excitation (field current) on the generator as the RPM increases. This keeps the generator’s output current and voltage going up as the RPM increases. This matches the generator’s output to the voltage/current of the traction motors. That maximizes energy transmission from the generator to the motors. That is a linear system that is also controlled by the RPM of the prime mover.
I believe the early GE’s had 16-notch throttles, and one of the minority diesel builders - like Baldwin - also had many more notches, again at least 16 and maybe more. For comparison, note that straight electrics also often had more notches - the GG1’s had 22-notch throttles, I believe.
See also Al Krug’s “Railroad Facts and Figures” webpage on the “Dash 9 - 44CW”, at -
http://www.alkrug.vcn.com/rrfacts/dash9.htm
Note his comments in Note 1. below the table under the heading of “C44 Fuel Use & Horsepower by Throttle Position” at about the middle of this webpage regarding the GE 1960’s U25C’s throttles, and cycling back and forth between 2 notches when yarding a train at low speed because of the huge increase in power that results when going from a ‘low’ throttle notch to the next, etc.
- Paul North.
Baldwins were equipped with an air throttle, which theoretically had infinitely many settings but were equipped with 4 notches for convenience. The air throttle also precluded Baldwins from being operated in multiple with locomotives from other builders that had electric throttles.
Basically it’s like driving a car or pick-up with a standard transmission. . . .each gear (notch) has a specific speed and torque range for certain situations. Drop a notch for more torque (power) to pull an uphill grade or to maintain speed down a grade. Go up a notch to increase speed for flat running.
An automotive transmission is a poor comparison. If you want to talk about transition and how the traction motors are connected to the generator (series, series-parallel, parallel, etc), you’ll be a lot closer. Unless you’re running an old locomotive with manual transition, you don’t really worry about it. If you want to pull harder (go faster), advance the throttle. If you want to go slower, back it down.
That’s DC. From what I gather, the AC’s are a different breed altogether. I’ve read accounts of AC’s doing .5 MPH in notch 8. It’s all in how the solid state controllers deliver the electricity to the traction motors.
Or to use a phrase from an old steam locomotive engineer that I always liked:
“Lifting and Drifting”
With not too much emphasis on the “g’s”
Bruce
Sorry, this is just plain wrong on so many levels. The traction motors are infinitely variable rate transmissions regardless of the notch settings. The notch setting will control the maximum power available to the traction motors for that setting, but the motors can vary the torque infinitely within that power range. That’s the beauty of using electric motors vs. a fixed gear mechanical transmission.
Also, AC traction motor locomotives are completely different animals than DC motored locomotives. What ever historical information you have on DC traction, you can just throw out the door at this point. Frequency drive AC motors have completely taken over DC designs in heavy industry, and they will take over the locomotive market in the near future too. From a technical prospective, there is simply no reason to build new DC traction motor locomotives at this point.
I’m fairly sure that the throttle control was the first digitally controlled machine, but it was certainly and early use of binary for machine control.
I have no disagreement with your comment about the benefits of digital control over some form of analog control for this application.
- Erik
Sorry, I’m still a little new to railroading and there are things I have not yet figured out and things that I’m still learning. So the purpose of the notches are not like I thought then? The notches are just for certain ranges of power and speed?
Someone refresh my memory. Were some AMTRAK motors set up to use an analog type control? (maybe called “P control”?) I know a couple trips on an AEM-7DC the engineer could set the maximum speed dial and then uses any notch to maintain that exact speed? I believe these motors could not be controlled remotely from a cab car??
Because 2^3 = 8. As others have mentioned, there are 4 solenoids to control the setting of the fly-ball governor. Three are for diesel engine speed control, the 4th for shut down. The three act on an triangular plate such that the distance between the solenoid location and the governor shaft center provides unequal leverage. The governor is set up to deliver roughly equal spacing in engine RPM between the notches. Each solenoid is “worth” an increment of engine speed. Solenoid A is worth 1 increment, B is worth 4 and C is worth 2. D, the shutdown solenoid is worth -2. The power output available from 8 notches provides enough resolution for most operating circumstances. Locomotives spend more about half their non-idle time in notch 8 as it is.
The solenoid schedule works like this:
idle and N1 - no solenoids
N2 - A
N3 - C
N4 - A&C
N5 - B&C&D
N6 - A&B&C&D
N7 - B&C
N8 - A&B&C
Low idle is A&D Technically, you don’t need to use D in N5 and N6, but they do this to keep the D solenoid exercised.
While U25B&C did have a 16 notch throttle, the diesel engine speed changes were handled with the A, B, C, D solenoids the same as other locomotives. When the throttle was placed in a
“Half” notch there was an excitation change and a slight movement of the ammeter, but no diesel engine speed change.