ATLANTIC CENTRALI wonder what Mike knows about GRAVELY G series rear engine riders.......
I am on the edge of my seat waiting to find out.
I ran out of popcorn on the last page about 1/3 of the way down.
-Kevin
Living the dream.
ATLANTIC CENTRAL I was reminded of this discussion Sunday as I cut the grass on my GRAVELY tractor. I wonder what Mike knows about GRAVELY G series rear engine riders.......
I was reminded of this discussion Sunday as I cut the grass on my GRAVELY tractor.
I wonder what Mike knows about GRAVELY G series rear engine riders.......
Bayfield Transfer Railway Everything, of course.
Everything, of course.
Lastspikemike I have zero interest in "being right" and I am always right... On the occasions where a poster shows that I may be wrong I simply change my own opinion to accord with the correct information... Posting incorrect information to a board like this leads to posts that correct that information not just for the original poster but everyone who reads it... My ego is unassailable, in case you missed that... There are some very authoritative people posting to this board and I've learned a lot already, becoming "righter" myself in the process... I spent a lot of time reading this and several other related forums before choosing this one to join.
I have zero interest in "being right" and I am always right...
On the occasions where a poster shows that I may be wrong I simply change my own opinion to accord with the correct information...
Posting incorrect information to a board like this leads to posts that correct that information not just for the original poster but everyone who reads it...
My ego is unassailable, in case you missed that...
There are some very authoritative people posting to this board and I've learned a lot already, becoming "righter" myself in the process...
I spent a lot of time reading this and several other related forums before choosing this one to join.
Alton Junction
Disclaimer: This post may contain humor, sarcasm, and/or flatulence.
Michael Mornard
Bringing the North Woods to South Dakota!
I had to go buy more popcorn, but there is still more Coke and Mountain Dew in the train room frig.
It has a throttle and a governor, it responds to changes in load up to the selected throttle "notch". Because of the recent heavy rains, the governor was doing lots of load adjustments........
In fact, after 24 years of service I just replaced the original Kohler M18 engine with a new Kohler Command Pro 730 a few months ago.
While different from a railroad locomotive, it is a unique and interesting piece of engineering, not like other garden tractors.
Sheldon
LastspikemikeHP is defined in ft lbs (in itself a silly unit being 12 inches moving 16 oz ...)
I cheerfully grant you the silliness of the way we learned this unit. There has been a fairly determined amount of trying to get this unit expressed as 'lb-ft' or whatever; the problem is that I learned foot-pounds of torque and no matter how I try, that's where it stays. (I'm a cgs man, so newton-meters squared is impossibly coarse without decimals, and gram-centimeters as hopeless as pascals; I won't even go where SI tells me and use gram-millimeters. THOSE are sillier units, at least if you want to do coherent design without constantly checking magnitudes...)
While I will not argue that the units are silly other than having a certain haptic facility, they're really no sillier than, say, one ninety-millionth of an erroneous measurement of the circumference of the Earth at Paris, or a fractional number of wavelengths of a monochromatic emission line of a krypton isotope.
I would argue, only partly tongue-in-cheek, that standardizing the meter around the length of a pendulum beating one second at the equator is the least 'silly' of any of these length measurements. If you accept that something scientifically based and common-sense reproduceable is less silly.
550 ft lbs per second is a silly unit for power. The fact that it is arbitrary and not related in any way to the real world establishes that beyond argument.
Of course for more fun we can go into how silly 'pounds-force' as distinct from 'pounds-mass' is in the English system. I was learning physics during the era when folks tried using 'poundals' to make a stab at distinction. Didn't really help. And we still do need a better separation of the two senses.
Fuel burned = Watts out to drive the generator = Watts delivered to the traction motors = speed of the train ... "You forgot something. See if you can figure out what that is..." ... Hmmm, just what might that be and why might I choose to omit it? Any schoolboy understands that equations are not directional and any permutation of the elements said to be equal is equally valid. Therefore, your attempt at critique falls somewhat flat.
The context makes my meaning very clear. Any added factors would defeat the purpose of the "equation". Reverse the equations if you doubt that.
The Diesel engine must always waste a lot of fuel increasing its own power before the train speed can increase ... you may take it as given that I read very carefully. It is surprising how often people do not write what they mean and still read their own words as if they had. I am quite familiar with driving vehicles equipped with internal combustion engines and manual gearboxes. The topic at hand is the characteristics of transmissions for these massive Diesel engines.
Slippage has several meanings. The meaning clear from the context I was using is the difference between engine rpm and wheel speed. Accommodating that, especially from rest, is why a transmission is required in the first place.
I repeat, diesel electric engines use generator/traction motors as an automatic transmission with infinitely variable ratios. And no need for a separate clutch device. They are inefficient compared to a purely mechanical or purely electric transmission ...
... the curious "stepped" CVT automotive transmission [...] I am left wondering just how much of this human interface problem led to the otherwise entirely arbitrary 8 step throttle ... "An interesting analogy" ... Yes it is, and very useful since the engineering idea behind both is exactiy the same. A steam engine as implemented solved the problem of the requirement for slippage between the fire and the wheels by introducing a fairly simple heat storage device: boiler, creating a handy and powerful working fluid that could exert force without moving.
If you take the Karman transmission as an example, there is no 'slip' because the combustion engine drives nothing but a hydraulic pump, and the pump can be regulated in its load to suit the characteristics of the engine at any practical commencement of load. This pump essentially compresses hydraulic fluid against dry nitrogen at tens of thousands of psi behind a diaphragm, and builds up a reserve of high-pressure oil. This is then metered to the traction motors as desired to produce torque -- and while the pressure can be sustained, effective horsepower can be in the Ludicrous+ range, adhesion and rotational-speed limited only. Were this storage not available, all you'd have would be a hydrostatic transmission, and we all know how wasteful those usually are.
Likewise as soon as you introduce a hybrid battery into a motor-generator-traction motor system, all sorts of advantages related to motor operation come into effect, based on asynchronous loading and demand.
In the case of the external-combustion engine, even the very short 'reserve' in a flash-boiler setup with good load following, like Abner Doble's, has the quality you mention (that the pressure is assumed to be 'available at suitable mass flow' to produce power in the engine). This is the principal reason people claim 'a steam motor produces much more horsepower than even a good IC motor' -- the steam engine burns its fuel externally, in a better configuration with what can be a longer time, and is not limited to efficient combustion to heat-expanding dry gases inside the 'reaction vessel'. There have been, here and there, attempts to burn larger amounts of fuel in IC engines (twin and triple staged turbos being one example) or conversely to mimick the more efficient combustion in a diesel cycle in a continuous burner (Velox and a couple of forced-draft fired powerplants being examples, although not particularly high-compression-ratio as you might imagine). This volumetric limitation is really the thing you're discussing when you say "an internal combustion engine cannot do this" . But it isn't quite the same thing as discussing inefficiencies of a relatively small generating plant, distribution architecture, and geared motors on a self-contained locomotive. Note that third rail and catenary are energized by some greater source of power, which (coincidentally) usually happens to have higher net thermal efficiency due to lack of restrictions on packaging size, complexity, and weight (to name but a few considerations) and, usually, a very careful implementation of the Rankine cycle. Note also that EPRI found that in a number of part-load turndown situations a compression-ignition engine genset could be more efficient than the 'best' alternatives.
Where this comes up out of semantics is when a more capable locomotive has to be MUed with something, probably based on a diesel, that uses the 8-notch convention. You will note that straight electrics, designed as such, use a very different kind of MU control, and have a very different way of controlling 'notches'. The sorts of control-signal synthesis needed to adapt a typical straight electric to "MU" to control trailing diesels effectively look suspiciously like what the topic of this thread is asking.
"I tend to think of it as somewhat analogous to the synthesized or piped-in exhaust roar in some modern cars that would otherwise be Dustbuster-quiet." ... Well, that would be misleading. Piped in intake noise (exhaust isn't usually piped in, btw) has no engineering drawbacks, it's just a silly thing to want.
As I think I noted at some length, the 'steps' are introduced into a CVT primarily for marketing and 'feel-good' reasons, not engineering ones. Part of this is that CVTs for performance applications remain relatively 'too expensive' compared to fundamentally inferior hydrokinetic or mechanical transmissions that can transmit more torque or handle abrupt power transitions more effectively, so some drivers likely come to equate CVT with relatively tiny little engines and relative restrictions on hard acceleration, and gear selection with higher performance.
The irony is the planetary gearbox is being designed to achieve constant velocity effects by adding ratios, in order to converge on the ideal infinite ratio gearbox.
We hear similar complaints from drivers about those, the most comical to me being drivers who complain about not being able to tell which gear the car is in, presumably from engine noise. This in a car equipped with an 8 speed AUTOMATIC.
Wow, you do realize the first person in an argument to make an ad hominem attack loses automatically eh? Good job I'm not having an argument much less trying to win it.
... all of this can be automated although only by exiting the generator. ... "I am not sure, again, what this sentence is meant to express. Do you mean accelerating the engine? Accelerating the train with the least fuel consumption? "Exiting the generator" (probably an alternator) meaning what, exactly, and by what means for what purpose?" ... Ah, that may be because you have difficulty seeing a joke...
gregc tstage This has gone waaaay past decoders and well into prototype discussion. i've very interested in understanding how to simulate diesel notch settings, in a throttle, not decoder.
tstage This has gone waaaay past decoders and well into prototype discussion.
i've very interested in understanding how to simulate diesel notch settings, in a throttle, not decoder.
I agree with the moderator's decision to move this thread because you need to differentiate between scale model operations and prototype mechanics. If these two totally different forms of discussion become blurred, the forum becomes chaotic where anything goes.
Rich
If you max out the current and the wheels aren;t slipping, the train stalls. The model equivalent is a loco with traction ties trying to pull too many cars. It stalls, and the motor starts heating up. Don't reduce the current, and the motor burns out.
It is possible to stall a prototype locomotive. In the various stories published in Trains and Classic Trains over the years, there have been some where this has happened. Throttle is in the highest notch it can be without exceeding the maximum amps to the traction motors, the wheels aren't slipping, but not enough tractive effort is being produced to move the train.
Modern stuff just adds a whole other layer of complications, with the true microprocessor control, using wheel slip and ground speed radar to deliever the absolute maximum power to the rails without slipping or overloading the motors. In the good old days, it was the engineer watching that ammeter, and notice how they have time limits above the green range, so it was ok to momentarily run higher loads but exceeding that time at the higher current would likely cause damage to something. And the AC traction locos have even more complex control systems, since regulating the speed of an AC motor.
Some interesting information from Republic Locomotive:
http://www.republiclocomotive.com/ac-traction-vs-dc-traction.html#:~:text=The%20AC%20drive%20works%20by,which%20powers%20AC%20traction%20motors.&text=AC%20traction%20for%20locomotives%20is,over%20the%20old%20DC%20systems.
Note the AC systems work like a switch mode power supply - AC in, rectified to DC, then converted back to AC. (minus the final step of converting back to DC) This may sound horribly inefficient to the average person, but in truth, a switchmode power supply is generally way more efficient for a given current output than a monolithic transformer and rectifier.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
glad to see that we're converging. Overmod, thanks for your patience
OvermodI had thought the governor 'reaching a limit' was in fact one of the inputs to the load regulator, perhaps having priority over some others.
after becoming aware of the "load regulator", i'm now puzzled by what "proportional" means on the wiki page. (i had thought it might be like a series wound motor)
i'm guessing the load regulator normally maximizes field current and generator output power, but reduces it if the govenor reaches a limit. i'm guessing it won't increase the field current above that max value.
it seems there are two options for handling an overloaded motor/gen. reducing rpm doesn't seem practical since it would require changes to the govenor which has a fixed mechanical relationship between those four solenoids controlling target rpm.
so reducing field current seems practical
i think this gets back to your "speedband" where the motor/gen will operate at at a target rpm or some amount less if the motor/gen is overloaded until the traction motors increase speed (you said "accelerate"), reducing the current drawn and allowing the load regulator to restore field current.
i'll suggest field current is controlled using relays to connect a different numbers of field windings. these relays are what i assumed you and others were referring to as solenoids
tstageThis has gone waaaay past decoders and well into prototype discussion.
i've very interested in understanding how to simulate diesel notch settings, in a throttle, not decoder. to do so, the throttle needs to know drawbar force and the tonnage (see ProtoThrottle) which determines mass as well as wheel bearing friction.
drawbar force is basically HP / speed (feet/sec).
and i need to understand the relationship between notch and HP. thanks to Overmod, i now understand that while there may be a target HP for each notch, that HP may be derated if the motor/gen is overloaded because the traction motor current excedes the motor/gen capability in a particular notch.
i need to think if/how to simulate this derating
i'm sure there are not so insignificant details i don't yet understand
2281
greg - Philadelphia & Reading / Reading
LastspikemikeSeems we now have an exceptionally detailed explanation of what I wrote early on in this thread. Essentially, it is impossible to duplicate in our models what the notch throttle does in the prototype.
Just for clarity horsepower and watts are the same thing. Slightly ironic that Watts himself ...
...didn't name the power unit after himself but after a horse ... and horsepower is a pretty silly unit in reality, which horse are you talking about today?
Fuel burned = Watts out to drive the generator = Watts delivered to the traction motors = speed of the train.
The Diesel engine must always waste a lot of fuel increasing its own power before the train speed can increase...
Slippage occurs with all acceleration which explains the varying sounds of rpm and load changes, not the same thing at all.
... the closest analogy seems to be the curious "stepped" CVT automotive transmission. For purely cosmetic reasons (even modern humans can't seem to get their head around driving a car with a properly engineered CVT) automotive engineers applied weird software controls to a CVT to mimic the steps in a geared transmission. There is no sound engineering reason to do so. I am left wondering just how much of this human interface problem led to the otherwise entirely arbitrary 8 step throttle.
I note that the heavily accented Indian text book (and apparently all Indian train engineer instructors always look as if they see the oncoming train at the end of every tunnel, judging purely from their bio photos you understand) ...
... points out that all of this can be automated although only by exiting the generator.
This has gone waaaay past decoders and well into prototype discussion. With that being the case, I'm moving it to the Prototype forum...
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
gregc ... if the governor is unable to maintain rpm, the load regulator reduces excitation to reduce the load on the motor so that the governor can maintain rpm.
Now if this occurs in a Run lower than 8, there might be the moral equivalent of an 'upshift light' prompting to increase throttle to prevent reduced excitation.
... it's not obvious if the load regulator is the only thing controlling excitation or if the governor reaching a limit is the only input
Not to confuse or complicate the issue, but earlier versions of motor-electric control usually involved throttled (gasolene or distillate) engines, which ran without notch control. An early problem was that it was possible to regulate 'output power' either with throttle adjustment or generator excitation ... leading to problems like engine overspeed with excessively light excitation for the throttle setting, or engine lugging if the excitation were too high at low rpm. Great ingenuity in the form of modified Ward-Leonard and later Lemp control was exercised over combining the throttle and excitation automagically so the engineman didn't have to use the kind of skills that, say, a mecanicien on a de Glehn compound had to have.
In a sense the eight-notch system was a step backward from stepless proportional control using a system like Lemp control, and some of the modern designs implementing 8-notch MU on EFI engines do, in fact, control the engine for maximum practical fuel savings. (I'm not going to start explaining that here!)
after watching the video posted by randy, it seems the load regulator works opposite the way i described above. the video suggested that if the govenor is unable to maintain rpm, the load regulator reduces excitation to reduce the load on the motor so that the govenor can maintain rpm.
it's not obvious if the load regulator is the only thing controlling excitation or if the govenor reaching a limit is the only input
2140
Overmod i understand that the excitation (field current) is increased. i don't understand what it is proportional to. Fuel flow rate? Proportional to the increased horsepower that the governor can deliver by increasing the fuel flow rate. Bet that's no clearer, though.
i understand that the excitation (field current) is increased. i don't understand what it is proportional to. Fuel flow rate?
Proportional to the increased horsepower that the governor can deliver by increasing the fuel flow rate. Bet that's no clearer, though.
"Fuel flow rate?" i think that's a yes, unless there's a direct measure of motor HP (torque and rpm)?
Overmod i'm guessing that notch setting "targets" a field current and a target rpm.
i'm guessing that notch setting "targets" a field current and a target rpm.
Overmod —miserable 80-second-to-wiped-response GEs as described by Don Oltmann: dashpotting on the fuel rack, and delays and modulation on the excitation.
As the saying went among engineers about the early GEs "Eight-and-wait" they would seemingly take forever to load.
An aside to all this talk about current being supplied to the traction motors, the engineer still had to rely on the ammeter (or power meter in later, dynamic equipped models) to avoid flashover, overheating and melted windings.
F3_Ammeter by Edmund, on Flickr
In the Penn-Central days you were lucky if 50% of your engines were still running once you got out on the road. Many photos of early P-C operations show six or eight engines on the head end (usually a few Alcos and GEs interspersed with the more reliable EMDs) — the "power desk" was hedging their bets.
Chances are at least two or three of those engines would have been "off-line" by the time the trip was over, if the crew didn't outlaw because of failure to maintain track-speed.
Regards, Ed
gregci could have said this clearer.
Look: in any given Run notch, the engine can produce more horsepower than the one before it, but only by feeding more fuel to it at the notch-determined rpm. If we were just to feed that fuel past the governor, it would make the engine increase speed just as if pushing down the accelerator in a diesel truck. What we do instead is increase the excitation to load down the engine while the governor is turning it at the notch range of speed. That makes the engine tend to slow down, the governor reacts by feeding more fuel, and so the combination produces more output horsepower at the same shaft rpm, the notch-determined governed rpm.
it's clear to me that increasing the field current (excitation) increases the generator output (i.e. voltage).
... the increased current load on the generator requires a greater torque from the diesel motor requiring more fuel flow.
... seems there's two mechanisms affecting output power: motor/generator rpm and field current.
Imagine for a moment that you have two robots, independent robots, running things. One (corresponding to the MU governor) takes a binary combination of control 1 to control 8 and sets the engine governor to a corresponding target speed (see Don Oltmann's post for the particular solenoids corresponding to each Run, and the description of the Woodward PG for what happens in the hydraulics for each combination. The other adjusts the excitation of the traction generator/alternator to get peak load out of what the motor can produce at the speed determined by the first one -- but without necessarily 'talking to it'. As the excitation increases, and more power is created by the generator, the engine is physically slowed and the 'other half' of the governor, like a cruise-control for motor rotational speed, feeds more fuel to recover the commanded speed. Note that there is a limit to how much fuel it can feed to make power at that rpm, and this will represent the balancing speed under the given conditions for that notch.
If the engineer wants more horsepower, e.g. for higher balancing speed, he will select a higher notch. The engine will spin up to that higher speed, at which point more fuel can be used to make more horsepower at the higher constant rpm by increasing the excitation...
... a computer (microprocessor) based system can easily juggle these parameters to optimally transition to an equilibrium (target) state when the notch is changed, as well as changes in drawbar load.
... I think this transition is what you're referring to when you say "accelerated to match the notch". i'm sure mechanical systems did so much more crudely.
i wish you could state things clearer
Overmod not sure what "proportionally increased" means: rpm or notch setting. Here, neither.
not sure what "proportionally increased" means: rpm or notch setting.
Here, neither.
i could have said this clearer. i understand that the excitation (field current) is increased. i don't understand what it is proportional to. fuel flow rate?
OvermodThe horsepower goes up, and the 'amount of electricity' produced by the generator goes up, ...
HP of motor ~= Watts produced by the generator?
Overmod... even though the shaft rpm does not, and the notch setting once the engine has accelerated to match the notch does not.
~constant rpm ... at target operating point?
it's clear to me that increasing the field current (excitation) increases the generator output (i.e. voltage). the increased voltage causes the traction motors to draw more current. the increased current load on the generator requires a greater torque from the diesel motor requiring more fuel flow.
seems there's two mechanisms affecting output power: motor/generator rpm and field current.
i'm guessing that notch setting "targets" a field current and a target rpm. a computer (microprocessor) based system can easily juggle these parameters to optimally transition to an equilibrium (target) state when the notch is changed, as well as changes in drawbar load.
i think this transition is what you're referring to when you say "accelerated to match the notch". i'm sure mechanical systems did so much more crudely.
gregcthanks randy. looks like "excitation" is referring to the field current.
As the throttle is moved to higher power notches, the fuel rate to the prime mover will increase, resulting in a corresponding increase in RPM and horsepower output.
At the same time, main generator field excitation will be proportionally increased to absorb the higher power...
I wouldn't have said 'at the same time', I'd have said 'when the engine is done accelerating to the new speed and has settled on the governor' (as with some diesel engines, like the 244s and 251s, excess fueling into 'too much load' is what produces the smoke shows.) But it is certainly possible for the load regulator to control the rate of engine acceleration, in part, by modulating (which is just a fancy way of proportional increasing here) the traction-alternator excitation.
...nor what "absorb the higher power" means.
SeeYou190 Lastspikemike Nope, a Roots blower is not a compressor. A centrifugal turbine is. Period. I know I said I tapped out, but... -Kevin
Lastspikemike Nope, a Roots blower is not a compressor. A centrifugal turbine is. Period.
I know I said I tapped out, but...
Kevin,
You have to think of this as something you bring popcorn and coke to.......
This, and the flangeway disccussion over on the Trains forum.
You know how a diesel engine works, I know how a diesel engine works, and Overmod knows how a diesel engine works, and he has the patience of a saint.
I know this, I'm happy the sound of all my EMD and ALCO prime movers are carefully operating in my imagination, so that I can also hear John Prine on the stereo as my four trains, each pulled by four locos, make their way around the layout.
I can't even fathom the sound of 16 of those squawky little sound systems playing at the same time, even in 1500 sq ft.
LastspikemikeNope, a Roots blower is not a compressor. A centrifugal turbine is. Period.
rrinker There's one more component in the engine control - the load regulator. This alters the main generator excitation under control of the governor.
thanks randy. looks like "excitation" is referring to the field current.
As the throttle is moved to higher power notches, the fuel rate to the prime mover will increase, resulting in a corresponding increase in RPM and horsepower output. At the same time, main generator field excitation will be proportionally increased to absorb the higher power.
not sure what "proportionally increased" means: rpm or notch setting. nor what "aborb the higher power" means.
looking forward to wathcing the video, thank again
There's one more component in the engine control - the load regulator. This alters the main generator excitation under control of the governor.
Here is a very good video, done by a guy who not only ran the things, but repaired them. Specifically goes over a DD40X, but similar era other EMD locos would be similar. Skip ahead to about the 50 minute mark to see the governor and load regulator, but there is quite a bit before that on operating the loco.
https://www.youtube.com/watch?v=ERNezIjd-GE
1:06 shows the clutch pack for the supercharger/turbocharger
Interesting this display loco, they removed all the power assemblies. Probably were still good, or had some life left in them when the loco was retiured and donated.
richhotrain Lastspikemike Trying to fit in but it's a tough audience In that case, you are going about it in the wrong way.
Lastspikemike Trying to fit in but it's a tough audience
Trying to fit in but it's a tough audience
In that case, you are going about it in the wrong way.
every forum has That Guy.
OvermodHere is a cross-section of a Woodward locomotive governor.
ok, i see that solenoids are used to control a speed adjustment mechanism in the govenor and there are two different types (ABC vs D)
and i now understand that notches control the target speed or speedband to determine output power (i.e. higher rpm, higher output power) not field connections
the text in the image of a govenor you posted says "functions to maintain a constant engine speed". don't understand your emphasis on speedband. i doubt it is perfect. a common problem with any feedback loop is the need for a error to make an adjustment. microprcessors can certainly avoid this limitation
OvermodAgain, I'm not sure where this comes from, but it certainly isn't how real locomotives manage MU control.
please explain how is does work?
but if the traction motors are directly connected to the generator output, the only way I can imagine to push more current into the traction motor is to increase the potential, the voltage. They don't work this way?
the patents with only diagram and claims without the explaination aren't helpful. Is there a particular chapter you were refering to in the book from india?
again, don't understand why this can't be explained simply. not asking for details, just basic principles
1850
LastspikemikeUsing a "supercharger" also doesn't necessarily result in actual supercharging of the cylinder. I'm pretty sure the cylinders in the FM opposed piston engine were not pressurized by the Roots blower. That was a scavenger air pump as far as I can tell. A Roots blower needs a closed end system to generate pressure, otherwise it just pumps. It was in fact invented only to move air, not as a "compressor" .
A Roots blower is perfectly happy as a positive-displacement compressor, and anyone who claims it has no use as a supercharger is woefully uninformed on that great American pastime, drag racing. It is not as suited as a centrifugal compressor to be driven by an exhaust-gas turbine, which is a principal reason you don't see it used in turbocharging.
Roots on a 567 is used for scavenge (not "scavenging" air); if you look at a cross-section of an EMD power assembly you can see how the arrangement works and how it can be used for a certain amount of supercharging. Basically the pressurized scavenge air enters through the transfer ports near BDC, and the four exhaust valves are timed to open as this occurs. The products of combustion are swept (with some dispatch!) through the exhaust valves before the piston closes the transfer ports in its subsequent compression stroke (and then of course compresses the charge air from the initial pressure when the transfer port is occluded -- which can be above atmospheric pressure, hence producing supercharging effect -- to the temperature and pressure that will give effective compression ignition upon fuel injection.
Note that the arrangement on a FM OP engine is different, as there is obviously no place to put exhaust valves at the 'tops' of the cylinders. In case you were wondering about the asymmetrical timing of the two crankshafts, it is so scavenge air through one set of transfer ports will sweep through to the other set of transfer ports, one of the 'genius' design points of this engine family.
All a supercharger of any kind does is increase the amount of oxygen available for combustion in a given stroke, which allows more fuel to be burned. This is why the somewhat counterproductive-sounding use of intercooling on diesel engines is practiced: while it is more thermodynamically efficient to keep the charge air hot, both the pressure and temperature begin to get wildly high for the gains involved. Some of the work in the '70s involved staged turbocharging (twins) to reach pressures of ~60psi with various kinds of thermal barrier coating in the engine -- this could achieve wild mileage levels but equally wild nitrogen-oxide generation and interesting kinds of engine failure.
gregcare you suggesting the solenoids are used to directly control fuel flow into the diesel motor?
Here is a cross-section of a Woodward locomotive governor. The solenoids and their actuator plate are visible at upper left.
There are plenty of sources for a Woodward 36703 manual; here is one that gives you a PDF download:
https://www.pmcontrol.com.au/attachments/PMControl/products/7/36703_NEW_PGEV-PGE.pdf
If you still have issues with what this does and the logic behind it, you can email the Woodward tech support at EngineHelpDesk@woodward.com and they can explain it more patiently than I probably can.
thought the solenoid switches are controlling the connections of field coils of the generator, reconfiguring it to generate power in discrete (1 of 8) amounts.
... the [diesel] motor is intended to operate at constant target rpm maintained by a govenor controlling fuel flow that depends on notch setting to obtain peak output power at that notch setting
You just won't give it up, will you? The Woodward locomotive governor uses notch setting to set a SPEEDBAND; the rest of the not-inconsiderable stuff (as described for example in US patent 2,039,507) handles accommodation for the engine to produce the proportional output horsepower THAT KEEPS THE ENGINE IN THAT SPEEDBAND.
... changing a notch, reconfigures the generator resulting in more power (greater voltage) to the traction motors. at first, low BEMF in the traction motors cause them to draw more current, loading down the generator causing a decrease in rpm and fuel is increased to maintain target rpm. As the traction motors increase speed, BEMF increases, they draw less current, reducing the load (current) on the generator and requiring less fuel to maintain rpm
An example of a more complicated modern (that is, '80s modern!) control system can be seen in EP0151570B1, which is chosen as an example with particularly well-described detail. This uses the 8-notch (or intermediate-notch with one extra wire) signal as one of a multiplicity of inputs for microprocessor control. Note that one of the references cited there, US patent 3263142A, is an example of the sort of electrical modulation that helps the engine operate effectively in any particular notch commanded by the MU system signal.
Some of you might find this 'textbook' from India useful in assessing how various parts of diesel-electric locomotives from different manufacturers work.
don't understand why this can't be explained more simply
OvermodThe solenoid arrangement calls for 'enough more fuel' to accelerate the engine TO THE SELECTED RPM GOVERNING RANGE regardless of imposed load
are you suggesting the solenoids are used to directly control fuel flow into the diesel motor?
i thought the solenoid switches are controlling the connections of field coils of the generator, reconfiguring it to generate power in discrete (1 of 8) amounts. (we used knife switches at school)
and the motor is intended to operate at constant target rpm maintained by a govenor controlling fuel flow that depends on notch setting to obtain peak output power at that notch setting
my understanding is changing a notch, reconfigures the generator resulting in more power (greater voltage) to the traction motors. at first, low BEMF in the traction motors cause them to draw more current, loading down the generator causing a decrease in rpm and fuel is increased to maintain target rpm. as the traction motors increase speed, BEMF increases, they draw less current, reducing the load (current) on the generator and requiring less fuel to maintain rpm
a link would be great?
gregci'm assuming "engine rpm" refers to the generator.
... notches configure solenoid switches resulting in different amounts of power (i.e. same rpm generates different power depending on solenoid configuration).
The governor does two basic things: it commands rack excursion to particular points -- which is what the solenoid actuation controls -- and then uses a servo device to 'govern' the commanded rpm within control limits, like the flyball governor on a steam engine.
Now remember that a diesel doesn't have a throttle; its speed will depend chiefly on the amount of fuel injected and burned, expanding against load and the need to develop compression for other pistons. The solenoid arrangement calls for 'enough more fuel' to accelerate the engine TO THE SELECTED RPM GOVERNING RANGE regardless of imposed load, and then the governor part does fine adjust of the fuel to KEEP the engine at that speed. "Power" is completely secondary, in the Woodward governor's 'mind', to keeping at the prescribed rotational speed. (I'll come back to how the "power" comes out in a bit.)
for a given solenoid configuration, power varies with rpm.
i'm guessing some regulator circuit (governor?) is adjusting fuel to achieve some desired rpm/hp.
... reduce fuel if > target rpm and increase fuel < target rpm.
There's no reason for the "engine rpm" to be simulated with a feedback from the throttle. The Proto Throttle works as well as it's going to get without actual physical momentum which you will NEVER get friom any scale model, unless we invent gravity fields and can build a layout in a room with 1:87 gravity and wear speace suits so the air density can be 1:87. And carefully weight each loco and car to preciesly 1:87 the real thing. Oh and ditch the worm gears, or at least use multiple spiral worms (which can be turned from the worm gear side). I suppse we also need 1:87 air brakes so there is a train brake in addition to the independent on the loco. At this point - just spend your money on those "you drive the loco" experiences. Or set up a short private railroad so you can run a full size train and not worry about FRA regulations.
The decoders commonly used with the Proto Throttle have quite a wide set of features to use BEMF to regulate the sound and momentum. As such, it seems to do about as well as you can with making the loco response and control prototypical without making it so complex that only someone with actual locomotive engineer experience can possibly use it. You cna sort of simulate much of it using a regular throttle, but operating the brakes by pressing function buttons is not nearly as easy as having a brake lever.
Re superchargers: ALL EMD diesels have a supercharger. It's REQUIRED for a 2 stroke diesel, with no exhaust stroke to force out burned gasses. The air box has to be pressurized to force out the combustion gases when the valves open. Exhaust-drive turbochargers were fitted to some to boost horsepower. On some models, these were one and the same - working as a shaft drive supercharger until speed were reached with sufficient exhaust flow to spin the turbine wheel, at which point an overrunning clutch allowed the turbo to spin faster than the shaft driving the impeller.