Overmod Former Car Maintainer yet the road vehicle has discrete steps in the transmission..... ... which correspond to transition or stages of field weakening, not throttle control. In the bad old days of motor-electrics, the function of the load regulator was separate from the motor throttle. It was therefore possible to select the engine screaming away with minimal field, the engine lugging down and skunk-stinking with too much load or at too low rpm, or the engine finding a critical speed or resonance and experiencing damage. Meanwhile, proportional systems do exist -- the standard Baldwin-Westinghouse throttle was a proportional air throttle without notches and, within its limits, worked reasonably well. See the early posts (necromanced from 2008) for why Dilworth et al. settled on eight Run speeds and AAR chose to standardize around them.
Former Car Maintainer yet the road vehicle has discrete steps in the transmission.....
... which correspond to transition or stages of field weakening, not throttle control.
In the bad old days of motor-electrics, the function of the load regulator was separate from the motor throttle. It was therefore possible to select the engine screaming away with minimal field, the engine lugging down and skunk-stinking with too much load or at too low rpm, or the engine finding a critical speed or resonance and experiencing damage.
Meanwhile, proportional systems do exist -- the standard Baldwin-Westinghouse throttle was a proportional air throttle without notches and, within its limits, worked reasonably well.
See the early posts (necromanced from 2008) for why Dilworth et al. settled on eight Run speeds and AAR chose to standardize around them.
Former Car Maintaineryet the road vehicle has discrete steps in the transmission.....
See the early posts (necromanced from 2008) for why Dileorth et al. settled on eight Run speeds.
Ulrich 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?
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?
SD70Dude Overmod a deranged locomotive. I guess you'd have to be pretty crazy to want to railroad up in Alaska...
Overmod a deranged locomotive.
a deranged locomotive.
I guess you'd have to be pretty crazy to want to railroad up in Alaska...
I typed 'derated' but crApple knew better. Who am I to say they were wrong?
I guess you'd have to be pretty crazy to want to railroad up in Alaska.....
Greetings from Alberta
-an Articulate Malcontent
rdamonDidn't the Alaska RR SD70-MACs do something like that with one of the traction motors?
As I heard the story lo! these many years ago, all the motors 'switched out' were on the trailing truck. Since ARR usually ran two of these units on summer trains this was supposed to leave ample horsepower for traction.
rdamon Didn't the Alaska RR SD70-MACs do something like that with one of the traction motors?
Didn't the Alaska RR SD70-MACs do something like that with one of the traction motors?
Yes. They use one of the traction inverters to supply HEP.
When operating in HEP mode only three or four traction motors are powered. I'm not sure which is correct, there is conflicting information floating around online, but I suspect Dave Goding will know the correct answer.
bogie_engineerThe opposite is the common arrangement; a failed HEP inverter can be "fixed" by switchgear that substitutes a traction inverter for the HEP inverter since the HEP is considered the highest priority load and the remaining traction inverters will get the train over the road.
Overmod As I recall, the Siemens Charger has the best of both worlds: they use a static inverter identical to the type used in AC-synthesis traction to generate the HEP AC off the existing DC-link, and I believe that can be reconfigured 'in the field' to stand in for a failed traction inverter. (I believe the ACS-64 electric uses a similar arrangement.)
As I recall, the Siemens Charger has the best of both worlds: they use a static inverter identical to the type used in AC-synthesis traction to generate the HEP AC off the existing DC-link, and I believe that can be reconfigured 'in the field' to stand in for a failed traction inverter. (I believe the ACS-64 electric uses a similar arrangement.)
The opposite is the common arrangement; a failed HEP inverter can be "fixed" by switchgear that substitutes a traction inverter for the HEP inverter since the HEP is considered the highest priority load and the remaining traction inverters will get the train over the road. This is how the LIRR DE and DM30AC's were set up and I am sure Siemens is following this practice on the Chargers.
Dave
Overmod'All' passenger diesels do not use the traction alternator for HEP;
One of our F units, originally an F3, now an F10, came to us from, I believe, MBTA. It has a genset located at the rear of the unit. We use undercar gensets for "HEP." so it sits idle.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
'All' passenger diesels do not use the traction alternator for HEP; in fact in my experience very few older locomotives do, and when used in lieu of gensets it has always been a cost-cutting expedient (trading the present value of the future excess fuel burn against the added capital costs and anticipated maintenance cost of gensets). My introduction to this was less of a compromise than F40s; it was the original order of U34CH-equipped 'Comet 1' trains for EL in the early '70s, where HEP only amounted to 200hp of a large available total, and the engine was designed to be used on freight when not actually needed on duty for commuter service.
If all passenger diesels need to run at a fixed RPM because of HEP requirements than all passenger diesel locomotives are technologically obsolete. Possibly the "Charger" is more technologically current.
Just as traction motor inverters operate off of a DC bus after rectificstion of the 3-phase AC from the main generator, so too, whether drawn from the main generator or an auxiliary one, the Hotel Power can and should get the same kind of treatment-- to enable the prime mover to operate at the most efficient RPM for the total load, as is done on freight power. The savings in fuel costs would pay for the added electronics quickly.
On an F40 the alternator needs to run at a constant fixed high speed not to make lots of power, but to keep the frequency of the AC HEP correct. That is a function of the Woodward governor in a non-EFI engine, and the logical thing to do would be to have Run 8 adjusted for 900rpm so that at all times, including maximum acceleration at the same time peak HEP is demanded, the engine will have adequate performance.
As load, including amp draw of the HEP system, changes, the Woodward governor, virtually steplessly, adjusts the fuel rack to hold the engine stable at 900rpm. It will do that faithfully, and mechanically, even if there is no actual electrical load on the engine crankshaft. The device connected to the notch throttle only controls engine rotational speed.
The colossal fuel burn at 900rpm is an artifact of how diesels work: just as jet engines require a large share of their turbine power just to turn the compressor, a Diesel engine uses a great deal of its fuel to keep itself turning through all the required compression. It is not a measure of increased "power" from the alternator that causes the added fuel burn. (In all probability if the fixed frequency were not mandatory, the engine could be run at a lower speed notch, for example when the 'output for traction' from the alternator would just match the HEP load (whatever that happens to be at the moment) and the engine could be thought to be producing comparable horsepower to a separate smaller HEP genset in one of the F40s that was so equipped at that point. That won't work, though, if stable AC frequency is a design requirement (and you can't use modern AC-synthesis transversion, as you can for example in some of the modern Siemens passenger locomotives...)
The load regulator, or alternator field (the thing 'generator field switch' drops out in three-step) is what is varied to change the electrical output of the alternator, and this could be given a switch to change it. But this is not 'increasing the amperage' -- if you have a HEP equivalent of a loadmeter it shows the amps drawn by the load, not output 'forced' in some way out of the alternator.
So there would be doubly no point in 'undetenting' the 8-notch detent to give continuous engine-speed control, triply when you consider the wealth of critical speeds that could damage various parts of the engine and which the notch system is 'tuned' to avoid sustaining.
What this implies is that he had some kind of stepless load control for the HEP, but isn't much of that load likewise systems that don't like running at undervoltage, like HVAC or fluorescent ballasts.
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AAUGH! Family friendly... must... keep... comments... about... IT resetting pages... family... friendly...
So I got curious and looked up the differences between the VIA and Amtrak HEP systems. I also didn't know that GO or any other commuter operators still used the 575v system that originated on CN's Tempo equipment back in the 1960s.
http://www.nwrail.com/HEP_config.html
http://www.gntrains.com/Documents/ViaHEP.pdf
mvlandsw Only one unit on a train was allowed to supply HEP .
Only one unit on a train was allowed to supply HEP .
That one is new to me, but perhaps VIA sets things up differently than Amtrak, due to the high power draw from the 30 car 'Canadian' consists that are run during summer tourist season.
Is one HEP unit really enough to power a long consist like the Auto Train?
bogie_engineer mvlandsw Amtrak's F40PH's had a notchless throttle when the diesel was running at high speed to generate the head end power. When not generating head end power they used the usual 8 notch throttle. Mark Vinski As far as I remember, they still had 8 traction power steps with the same notched handle, just that the engine ran at a fixed 900 rpm to hold HEP frequency steady. Dave
mvlandsw Amtrak's F40PH's had a notchless throttle when the diesel was running at high speed to generate the head end power. When not generating head end power they used the usual 8 notch throttle. Mark Vinski
Amtrak's F40PH's had a notchless throttle when the diesel was running at high speed to generate the head end power. When not generating head end power they used the usual 8 notch throttle.
Mark Vinski
As far as I remember, they still had 8 traction power steps with the same notched handle, just that the engine ran at a fixed 900 rpm to hold HEP frequency steady.
My memory is that the throttle could vary the amperage smoothly without any steps just like the dynamic brake. It has been around 40 years since I ran one of those though. The physical throttle notches on the control stand definitely went away when the HEP was engaged.
I don't know how the control of trailing units was handled. Only one unit on a train was allowed to supply HEP .
timzIf two F40s are MUed, the MU cables don't know how to transmit notchless throttle commands, do they?
Older push-pull control trainlined through dedicated consists to dedicated power with 567/645/710 might not use stepless control, either. The last time I rode MN service on the Hudson Line, they were still using the rebuilt FL9s and the 'bumps' corresponding to throttle positions were very noticeable at the head end.
It would be theoretically possible to get somewhat more 'stepless' control of an F40 refitted with EFI by using one of the extended RF protocols for the engine control. However the microprocessor would still be programmed primarily to avoid the critical speeds in the EMD engine, and might still have to be arranged to use speeds corresponding to HEP frequency if using main-engine-driven alternator supply without transversion, so there might be some extended version of a 'notch' system in proprietary control.
PsychotI know we've had this discussion many times, but I'll say it again: I can't imagine a time when freight trains run autonomously without any human involvement.
Why can't you imagine it?
timz If two F40s are MUed, the MU cables don't know how to transmit notchless throttle commands, do they?
If two F40s are MUed, the MU cables don't know how to transmit notchless throttle commands, do they?
As noted, for traction power, they still use the same 8 notch setup. Thus, the can MU with any other power.
Lol, I was reading the "cruise control" posts on this thread and saying to myself "don't you guys know about EMS?" Then I noticed the posts were from 2008.
I know we've had this discussion many times, but I'll say it again: I can't imagine a time when freight trains run autonomously without any human involvement. Maybe we will reach a point some day where EMS can manage in-train forces as well as an experienced engineer, but there are so many other factors involved in getting a train safely over the road...
erikem enr2099 Interesting discussion. BTW, not all locomotives had an 8-notch 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. IIRC, the old GE's only had 8 engine speed settings, but had two generator excitation levels for each speed setting.
enr2099 Interesting discussion. BTW, not all locomotives had an 8-notch 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.
IIRC, the old GE's only had 8 engine speed settings, but had two generator excitation levels for each speed setting.
The Budds didn't really need notches as they only had two 'speeds' -- converter unlocked and direct-drive. Presumably one of the 'notches' corresponded to idle with the converter empty or slipped, and the others giving simple two-relay 'binary' engine-governor command using the same principle of seven-power-notch '8-notch' system with one fewer solenoid and no fancy triangle plate setup...
The basic Baldwin system was a stepless air throttle for engine governing, and to my knowledge this was analog between units (which again IIRC imposed limits on how many could be in one consist, etc. as noted... the response time and positive authority being reasons as noted.) I do not remember how critical speeds were handled. When they had to offer "electric MU compatibility" as an option, I think most examples, certainly those I have read about, were standard 8-notch compatible. It is possible they would have a 22-notch 'compatible' with two steps between each eight-notch 'required' position, but the advantage is dubious: remember that a 608-engined Baldwin could accelerate to somewhere in the mid-20mph range just on idle power as the engine governor held rpm...
Perhaps this was something intended for PRR that would MU with some of the straight electrics? Somebody ask Bill Volkmer!
Building self-driving aircraft is far easier than building self-driving cars, which in turn are more difficult to do than self-driving trains. In the tested range of conditions or in the lab, with only predicted failures of maintenance, for the predicted operations. All with "perfect safety" and without requiring the engine an to stay ready to leap to fix a computer mistake ... perhaps an insidious or complex one ... within a few seconds with little warning or indeed no warning.
Crews often appreciate these things better than systems architects. They also don't trust the motives of those paying for the systems they get.
I find it interesting how the mentality towards "self-driving" trains has shifted in the 12 years since ths thread has started. We've gone from a "wouldn't that be great? The crew can just put their feet up on the windowsill and snooze" philosophy, to where... now that automating trains is possible, it's the crews themselves who are the strategy's greatest critics.
"Be careful what one wishes for", perhaps?
Even in early thyristor controlled DC motor rail cars, speed controlled relays would kick in automatically, ie 0-10 mph series 1, 10-25 mph series 2, 25-35 mph series 3, 35-50mph shunt 1, 50+ mph shunt 2. In effect this 5 notch system gave good acceleration at 2mphps....Even later IGBT controlled AC motor rail cars using VFVV would step through different modes of waveform generation as speed increases, similar to a three notch system, ie six step, quasi six step, pwm, etc....
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