In a road vehicle the throttle can be adjusted from zero to maximum throttle by simply varying the pressure on the gas peddle. Why aren’t locomotives designed this way…with a continuously variable throttle?.. i.e. why the eight settings?
I’ve wondered that for years. Does it have to do with the fact that the actual traction comes from an electric motor? Trolley cars have (used to have) notches on their throttles.
I don’t think its the electric motor…those 200 ton dump trucks used in mines are diesel-electric also…and they have a continuously variable foot throttle much like a car does.
Seems like we talked about this a while back.
I think part of it has to do with MU’ing locomotives together. Something like three or four wires can give you enough combinations to do all eight steps.
Searched “throttle settings”…found nothin
Because you don’t need the ability to vary the throttle.
As Tree pointed out, you have to MU locomotives, so they need to all have the same basic settings…in that a given RPM produces a set amp rate to the traction motors.
Notch 5 on a Dash 9 is the same as notch 5 on a SD70.
Also, you would be fatigued beyond any thing you have experienced if you used a foot throttle on a locomotive…driving a automobile or a large truck is totally different.
You have varying terrain or road surfaces, and the need to accelerate and decelerate quickly for turns and stops, neither of which really applies to what a train does.
Keep in mind that a Dash 9 weighs in around 440,000lbs…if you “stomped on the gas” in one, it would slip the wheels, and something that weighs that much needs a constant steady acceleration, just like what is provided by “notches” as opposed to a variable throttle.
But a constant setting works best for how trains handle…you don’t need to stop and start often, so why go through the mechanical additions to create a variable throttle that’s not needed.
That’s interesting…you mentioned “the same amp rate for a given rpm” for each power setting. So the power setting determines the rpm which in turn determines the current output of the generator.
Locomotives have to have a system to maintain speed of the engine regardless of load placed on the engine, a function which is provided by a governor. Automobiles do not need this system because they do not have an electrical transmission but have a mechanical transmission.
EMD began by designing its locomotives with eight throttle steps plus idle. It could have chosen 10, 16, 7, 9, or 25, but chose eight because (1) that was a sufficient level of “fineness” to meet users needs for the rather narrow rpm range capability of the engine without subjecting the user to needless complexity that would drive up purchase price and maintenance price, and (2) it was convenient to use 8 because of the electromechanical technology of the day. The Woodward governor applied to an EMD engine used four solenoids to effect speed control. Each throttle setting energized a different combination of solenoids, as follows (for a 16-567C):
|
Throttle Position |
Governor Speed RPM |
Solenoid Energized |
Governor Speed RPM |
Adjustment |
||||||
You nailed it, RWM! Now I understand how a diesel-electric throttle works (in principle, anyway). Hope you don’t mind if I cut and save your response for my personal RR info file. - a.s.
RWM has it right. I’ll just add that the number of notches is 8 instead of 7 of 9 or 10 because that’s how many unique combinations you can make from 3 solenoids. The 4th, “D” solenoid is in the governor to actuate an engine shutdown.
The governor is basically a flyball type and the three solenoid act on a triangular plate with a geometry such that each solenoid is “worth” either 1, 2 or 4 notches. (I think A is worth 1, B is worth 4 and C is worth 2) The plate pushes against a spring in the opposite direction from that of the flyball mechanism.
The D solenoid is woth -2 (it doesn’t act on the triangular plate directly) and is is picked up along with C in notches 5 and 6 to get it some exercise so it won’t be stuck when it’s called on for a shut down. It is also used for low idle (D + A = -1, not enough for a shut down)
If you added another solenoid, you could get 16 speed settings.
The fulcrum nut sets the speed.
Interesting discussion. BTW, not all locomotives had an 8-note throttle. Anyone remember the throttles on some old GE’s with 16 notches, or the Budd RDC’s that have 4 notch throttles? IIRC some Baldwins had 22-notch throttles.
Besides, “notch 8” wouldn’t mean anything any more (ie, full throttle).
Thanks everyone for your input… lots of very knowledgeable people on this site…
Didn’t the Fairbanks-Morse locomotives also have a 16-notch throttle ? (very vague recollection here)
If you can, find some Trains from the 1960’s and 1970’s when there was an annual “All-Diesel” issue, and experts such as Jerry A. Pinkepank (and others whom I can’t remember right now) contributed articles on such things, the MU (multiple-unit) hoses and pins, Herman Lemp’s development of the electrical transmission and control system, etc.
- Paul North.
Ulrich, it seems that you may have a valid point here, despite the negative comments above, although they may ultimately have more general and wider applicability. Here’s a quote from Al Krug’s great website, in the “Railroad Facts and Figures” section, on the page for the Dash 9 - 44CW or “C44” locomotive, at:
http://www.alkrug.vcn.com/rrfacts/dash9.htm
under the table for “C44 Fuel Use & Horsepower by Throttle Position”:
“Note 1: Notice that the Hp increases by 150% from throttle 1 to 2 [ 200 HP to 500 HP - PDN] and by 100% from 2 to 3 [ 500 HP to 1040 HP - PDN]. These huge increases make yarding trains at 10mph difficult. You must either constantly move the throttle up & down to maintain 10 mph or else apply independent brakes and work the power against the brakes making them hot. Perhaps GE had something with the 16 notch throttles on the 1960s era U25Cs.”
Oddly enough, though, Al doesn’t have a lot about throttle positions other than fairly extensive tables for fuel usage and horsepower output, etc., and commentary on same for each one for several different locomotives. Nevertheless, you might find some more useful information by just browsing through it at:
http://www.alkrug.vcn.com/rrfacts/rrfacts.htm
or his home page at: http://www.al
I think I read somewhere that early Baldwins had a throttle that was virtually continuous, so you could make very fine adjustments - didn’t really have notches (or at least had many notches). However the technology to do that was pushing the envelope in 1940’s electronics, and it apparently was a maintenance / reliability nightmare. Eight notches were cruder by comparison but easier to maintain and use.
IIRC, the old GE’s only had 8 engine speed settings, but had two generator excitation levels for each speed setting.
Most Baldwins were built with an air throttle which was continuous in theory. A separate air line rather than jumper cables was required to operate in multiple. A maximum of four units could be operated in multiple with an air throttle since response time faded beyond the fourth unit. Needless to say, a Baldwin with an air throttle could not MU with anything with an electric throttle (just about everything else).
[quote user=“Railway Man”]
Locomotives have to have a system to maintain speed of the engine regardless of load placed on the engine, a function which is provided by a governor. Automobiles do not need this system because they do not have an electrical transmission but have a mechanical transmission.
EMD began by designing its locomotives with eight throttle steps plus idle. It could have chosen 10, 16, 7, 9, or 25, but chose eight because (1) that was a sufficient level of “fineness” to meet users needs for the rather narrow rpm range capability of the engine without subjecting the user to needless complexity that would drive up purchase price and maintenance price, and (2) it was convenient to use 8 because of the electromechanical technology of the day. The Woodward governor applied to an EMD engine used four solenoids to effect speed control. Each throttle setting energized a different combination of solenoids, as follows (for a 16-567C):
|
Throttle Position |
Governor Speed RPM |
Solenoid Energized |
Governor Speed RPM |
Adjustment |
||||||