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Control of Multiple Engines

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Metroman62

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As I am not very technically minded, I was wondering how multiple engines on trains are controlled to ensure they are all providing power and not being dragged or pshed by another. What I mean by this is when a train is being doubled headed by locomotives, or the various different engines on a multiple unit, how is it ensured that they are providing the correct power to stop the front one pulling the one behind if that is not in sync, or the one behind pushing the one in front if they are out of synce. I can imagine with modern trains there could be a computerised system to monitor such things,but on older units how do all the engines stay in synce so that non are pushign or pulling the others?
 
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Taunton

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The magic words are "multiple unit", which you can find many references to on the web. It's been around for more than a century on electric multiple units, and got onto diesel locos and then diesel railcars pretty much from the start.

In the USA where it was universal from the earliest diesel times the Association of American railroads (AAR) have long published technical standards which have ensured you can multiple pretty much anything with anything over there, regardless of age or manufacturer. The US have got much cleverer with this in recent times and can actually have unmanned freight locomotives mid-train under remote command from the front, using a combination of radio signals and measuring the pull through the couplings.

Most multiple unit controls have used electrical signals but there have been some which use compressed air pressure instead.

If the train is double headed by two (or more) locomotives the one is front is always pulling the one behind when they are under power, of course, and this is just how it's been since steam locomotive days, when of course there was no synchronisation but it all worked fine.
 

The Crab

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I did read somewhere that on the old dmus it was actually possible for vehicles to be under power going forward but another one could be under power in reverse. Fire!
 

AM9

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The magic words are "multiple unit", which you can find many references to on the web. It's been around for more than a century on electric multiple units, and got onto diesel locos and then diesel railcars pretty much from the start.

In the USA where it was universal from the earliest diesel times the Association of American railroads (AAR) have long published technical standards which have ensured you can multiple pretty much anything with anything over there, regardless of age or manufacturer. The US have got much cleverer with this in recent times and can actually have unmanned freight locomotives mid-train under remote command from the front, using a combination of radio signals and measuring the pull through the couplings.

Most multiple unit controls have used electrical signals but there have been some which use compressed air pressure instead.

If the train is double headed by two (or more) locomotives the one is front is always pulling the one behind when they are under power, of course, and this is just how it's been since steam locomotive days, when of course there was no synchronisation but it all worked fine.

I think the OP is asking something that I've often wondered, i.e. how is tractive effort controlled from a common control setting. Take a 150 and a 170 coupled together, (I think that combination is possible). I presume that the 170 has a lot more TE available at a given control setting, so to avoid the 170 doing all the work, how are they regulated?
The same problem exists on EMUs, can a 75mph geared Electrostar (378 or 376) be coupled to a 100mph geared one (375 or 377)?
 

DownSouth

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In the USA where it was universal from the earliest diesel times the Association of American railroads (AAR) have long published technical standards which have ensured you can multiple pretty much anything with anything over there, regardless of age or manufacturer.
Indeed. In Australia all of the freight world uses AAR standard multiple working equipment as a result of the decision being made to start modernising before the UK did with the result being lots of locally-built EMD, Alco and GE locomotives - due to economic issues at the time, we probably would have gone down the track of copying UK practice if they had gotten off to an earlier start.

It's incredible to see GM Class locomotives from 55-60 years ago getting put into traffic during the grain harvest season each year, where they quite happily operate in multiple with brand new C44ACi or GT46ACe locos that have all the modern tech like self-steering bogies and AC traction motors.

The US have got much cleverer with this in recent times and can actually have unmanned freight locomotives mid-train under remote command from the front, using a combination of radio signals and measuring the pull through the couplings
The state of the art has moved on from Locotrol II already - something the Marathon consortium in Europe should consider before pressing on with their attempts, motivated by Not Invented Here Syndrome, to create a copy of it.

With the successful entry to service of electronically controlled pneumatic brakes (ECP brakes) on new freight cars, the most modern freight trains now have digital data cables running the length of the train to control the brakes on each car (or more commonly, permanently coupled sets of between two and five cars) and give them braking performance more like a passenger DMU than a traditional freight train. These cables have plenty of bandwidth left to give a far greater level of control over the DP units than Locotrol II offers - even to the point of startup/shutdown control of the DP units while on the move, which is handy on a bulk freight route where a long train with two locos at the front and two at the back might head out empty and come back loaded up to five times as heavy when loaded.
 

Wyvern

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WE should point out that, with trains that are simply top and tailed to avoid running round the rearmost loco is usually dead in tow since there's no control cabling along the train.
 

Taunton

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I did read somewhere that on the old dmus it was actually possible for vehicles to be under power going forward but another one could be under power in reverse. Fire!
This was, and possibly still is, an occasional issue where errors in assembly of the control gear didn't show up in individual trials, but do when multipled. I believe it happened to the first pair of Class 20s when new, when they were first tried in multiple.

The same problem exists on EMUs, can a 75mph geared Electrostar (378 or 376) be coupled to a 100mph geared one (375 or 377)?
I don't know about this particular combination, but you do need to handle the situation where the train is driven from the 100mph end and the driver overlooks that there is a lesser-speed unit in the consist.

A comparable issue with old DMUs happened where the St Pancras-Bedford line had most units with automatic transmission, but they got some transferred with manual gearboxes (the standard). The automatics were retrofitted with an extra control (rarely used) to operate the change gear should there be a manual unit on the back, as the control was otherwise compatible, but the inevitable happened quite quickly, a driver forgot there was such a unit on the rear and accelerated with no indication that the rear unit's transmission was being grossly overspeeded, and indeed it eventually seized, and either caught fire or derailed (I can't remember).

The nearest we got to a universal mu system was the old Southern Region, which developed one which allowed their emus, dmus, diesel and electric locomotives, and hauled stock with driving trailers, to all operate in multiple, driven from any of these units, and a number of services did operate with mixed combinations (there was a thread here about this a while back). It required 27 circuits in the mu connections.
 

Metroman62

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I think the OP is asking something that I've often wondered, i.e. how is tractive effort controlled from a common control setting. Take a 150 and a 170 coupled together, (I think that combination is possible). I presume that the 170 has a lot more TE available at a given control setting, so to avoid the 170 doing all the work, how are they regulated?

Yes, that is what I meant to ask!
 

Taunton

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Indeed. In Australia all of the freight world uses AAR standard multiple working equipment ... locally-built EMD, Alco and GE locomotives ... It's incredible to see GM Class locomotives from 55-60 years ago getting put into traffic during the grain harvest season each year, where they quite happily operate in multiple with brand new C44ACi or GT46ACe locos.
How did you handle the quite substantial number of English Electric locos that were shipped out to Oz in the 1950s-70s? Did they get fitted with AAR or are they orphans that only work with themselves?
 

DownSouth

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I think the OP is asking something that I've often wondered, i.e. how is tractive effort controlled from a common control setting. Take a 150 and a 170 coupled together, (I think that combination is possible). I presume that the 170 has a lot more TE available at a given control setting, so to avoid the 170 doing all the work, how are they regulated?
Have a think about it - does it actually matter? How is it different from having powered cars and trailing cars in the same unit?

Unlike a long freight train, a passenger multiple unit consist effectively handles as a single vehicle with a larger number of powered axles thanks to the fairly rigid couplings. If some cars are producing more traction than the others, that traction gets equalised by passing it along through the couplings.

That's a good thing, not something to be 'fixed.' If the output is to be equalised, that would mean the lower-powered unit would be screaming away at full power (drinking lots of fuel and sustaining lots of wear and tear on everything from engines to wheelsets) while the higher-powered unit would be efficiently cruising at maybe 70% of its capacity. You'd be better off having all the engines operating at around 75-80% to get the same total power while getting a greater level of efficiency - and having the option where necessary to take all the engines to 100% for maximum performance when tackling a hill or accelerating to line speed after a stop.

Another thing to remember is that in practice, the condition of the various components will often produce a significant difference in the output of any two given drivetrains of the same specification, and in extreme cases this could get to be an even larger difference than the 18% difference in power:weight ratio from a 150 to a 170.
The same problem exists on EMUs, can a 75mph geared Electrostar (378 or 376) be coupled to a 100mph geared one (375 or 377)?
Again, it's not a problem. The force being transmitted through the coupling between the units would be far less than the force being transmitted through the permanent coupling between motor cars and trailing cars within the same unit.

The only problem with third-generation EMUs (from the last 20 years or so) would be the question of whether the software is compatible - even between those built by the same manufacturer and especially so when that manufacturer is Bombardier. Just because the couplers may be mechanically compatible doesn't mean they can actually be used in normal service while coupled together.
 

455driver

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I think the OP is asking something that I've often wondered, i.e. how is tractive effort controlled from a common control setting. Take a 150 and a 170 coupled together, (I think that combination is possible). I presume that the 170 has a lot more TE available at a given control setting, so to avoid the 170 doing all the work, how are they regulated?
The same problem exists on EMUs, can a 75mph geared Electrostar (378 or 376) be coupled to a 100mph geared one (375 or 377)?

You are overthinking it!
They will be allowed to run at the maximum speed of the slowest unit.

If the rear unit is providing more power then it will (gently) push the one in front, there wont be that much difference that it would be a problem, I have driven units where the front one is dead and the rear doing all the work, it isnt a problem, just a bit slow getting going.

How do you think 90s and 91s do when they are pushing their 10 coach trains along from a standing start to 100mph or more?
The climb out of London Liverpool St (with the 90 pushing) is very steep for a mainline.
--- old post above --- --- new post below ---
This was, and possibly still is, an occasional issue where errors in assembly of the control gear didn't show up in individual trials, but do when multipled. I believe it happened to the first pair of Class 20s when new, when they were first tried in multiple.
This is correct, or at least a very strong tale!

I don't know about this particular combination, but you do need to handle the situation where the train is driven from the 100mph end and the driver overlooks that there is a lesser-speed unit in the consist.
This has happened a few times! :oops:

A comparable issue with old DMUs happened where the St Pancras-Bedford line had most units with automatic transmission, but they got some transferred with manual gearboxes (the standard). The automatics were retrofitted with an extra control (rarely used) to operate the change gear should there be a manual unit on the back, as the control was otherwise compatible, but the inevitable happened quite quickly, a driver forgot there was such a unit on the rear and accelerated with no indication that the rear unit's transmission was being grossly overspeeded, and indeed it eventually seized, and either caught fire or derailed (I can't remember).
It (actually there were a few) caught fire and was the reason the 127s were reclassified from blue square (the 'standard' system) to red diamond, to prevent it happening.

The nearest we got to a universal mu system was the old Southern Region, which developed one which allowed their emus, dmus, diesel and electric locomotives, and hauled stock with driving trailers, to all operate in multiple, driven from any of these units, and a number of services did operate with mixed combinations (there was a thread here about this a while back). It required 27 circuits in the mu connections.
The 73/0s could actually work as a brake converter where-as the lead loco and stock could be air braked, then the 73/0 and the rear stock could be vaccuum braked.
A 73 is a very versatile loco!
 
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edwin_m

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Slightly off-topic but a colleague used to tell a story (which might have been true) about the Tyseley DMU fleet. For those that don't remember it, there were a vast number of different types, probably just about every combination of cab/centre, brake or not, powered and trailing, and the formations were pretty random too.

There was a diagram which was formed up of two sets at Tyseley and was due to split up somewhere during the day. The portions were duly uncoupled and the first one disappeared off, only for the driver of the second to find it was formed entirely of trailers.
 

455driver

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There was a diagram which was formed up of two sets at Tyseley and was due to split up somewhere during the day. The portions were duly uncoupled and the first one disappeared off, only for the driver of the second to find it was formed entirely of trailers.

That absolutely never, ever happened and there is no truth in the rumour that a friend of mine (Chris) couldnt get his engines to start on 2 coach 108 when prepping them for service, mainly because they were both trailers! Nope absolutely no truth whatsoever! ;)
 

SprinterJedi

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In Scotland, a 170 may occasionally be coupled in front of a 156, more commonly a 158 but will rarely/never "push".
The control system is the same, a simple 3 wire method controlling fuel relays and valves. The sprinter engines will output depending on throttle selection from the driving vehicle and the resultant output is transmitted to the Voith. Multiple Sprinter engines will put out the same power (slight variation from 158 to 156).
 

AM9

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You are overthinking it!
They will be allowed to run at the maximum speed of the slowest unit.

If the rear unit is providing more power then it will (gently) push the one in front, there wont be that much difference that it would be a problem, I have driven units where the front one is dead and the rear doing all the work, it isnt a problem, just a bit slow getting going.

How do you think 90s and 91s do when they are pushing their 10 coach trains along from a standing start to 100mph or more?
The climb out of London Liverpool St (with the 90 pushing) is very steep for a mainline.
--- old post above --- --- new post below ---

This is correct, or at least a very strong tale!


This has happened a few times! :oops:


It (actually there were a few) caught fire and was the reason the 127s were reclassified from blue square (the 'standard' system) to red diamond, to prevent it happening.


The 73/0s could actually work as a brake converter where-as the lead loco and stock could be air braked, then the 73/0 and the rear stock could be vaccuum braked.
A 73 is a very versatile loco!

So does the controller send a signal corresponding to whatever proportion of full throttle is set and that is interpreted by all slave units as the same proportion of their full throttle?
 

Taunton

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.... the Tyseley DMU fleet. For those that don't remember it, there were a vast number of different types, probably just about every combination of cab/centre, brake or not, powered and trailing, and the formations were pretty random too.
What a mess. Would never have happened if the Western hadn't been made to give the depot to the Midland lot :) The western even kept their cars in the set order they were delivered in for much of their life.

Actually, Haymarket seemed worse, they would turn out cars, in service, coupled at the gangway end to another cab so the unwitting passenger tugging on the handle had just the little pin between them and falling onto the ballast.

455driver said:
This [the Class 20s] is correct, or at least a very strong tale!
It was reported in a train mag at the time. MU is of course an engineering challenge because the units can be coupled up any way round and yet still need to set off in the same direction, including if you take one and turn it on the turntable and then connect up again.

Traditional DMUs had engine/gearbox from contemporary buses/trucks of the period. Actually the gearboxes were different, because instead of 5 forward and one low reverse you need to do the same speeds in both directions, so there were 5 gears in the gearbox and another component for changing direction. This needed some thought, especially should one transmission not respond to the direction signal in the controls. The basic concepts were worked out by AEC, the old bus/truck manufacturer, on the old GWR railcars of the 1930s which had two AEC engines and transmissions, and formed the prototypes for this form of control, and was then perfected (and in all truth it stood the railway in good stead for a couple of generations - Southern Region excepted) by a company called Walker Brothers of Wigan, who did various adaptations like starting all the engines from the front control desk using the batteries on each car (one of the differences between Yellow Diamond and Blue Square cars I understand).

London Underground for a long time didn't get involved in this complexity, and for their trains having to be a certain way round is easier technically, fine as long as there aren't loops or triangles on the line which allow trains to get turned around; I believe some lines still have this type of train, and someone will probably be along soon to list them all.

So does the controller send a signal corresponding to whatever proportion of full throttle is set and that is interpreted by all slave units as the same proportion of their full throttle?
Simplistically yes, which is (part of) why the controller has a fixed number of "notches" rather than being infinitely variable like the accelerator pedal of a car. Incidentally, all units are "slaves" in this system, including the power units on the leading car, they all respond in the same way. There will indeed be some balancing point of power along the train, maybe some couplings will be in tension and others in compression, but trains have always handled this without difficulty.

The St Pancras automatic transmission dmus I spoke about earlier had a synchronising arrangement through the control wires so that all cars in the set changed gear together rather than each doing their own thing, which would have been jerky. I believe similar transmissions in Northern Ireland didn't have this and you could find trains ascending gradients with different power cars in different gears.
 
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IanM

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That absolutely never, ever happened and there is no truth in the rumour that a friend of mine (Chris) couldnt get his engines to start on 2 coach 108 when prepping them for service, mainly because they were both trailers! Nope absolutely no truth whatsoever! ;)

Surely not! I did manage to put 5 bubble cars and a drive end trailer out for the 0740 from Dorridge one morning. That was the wackiest formation I ever managed to create. :D
 

455driver

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So does the controller send a signal corresponding to whatever proportion of full throttle is set and that is interpreted by all slave units as the same proportion of their full throttle?

A DMU has 7 power notches so notch 1 will be roughly one seventh power, notch 2 will be roughly two sevenths etc etc until notch 7 is full power, whatever that may be whether its 200hp (Pacer) or 400hp (159).
--- old post above --- --- new post below ---
Surely not! I did manage to put 5 bubble cars and a drive end trailer out for the 0740 from Dorridge one morning. That was the wackiest formation I ever managed to create. :D

You planners always seemed to come up with some weird and wonderful formations, an art sadly lost.
 

cjmillsnun

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As I am not very technically minded, I was wondering how multiple engines on trains are controlled to ensure they are all providing power and not being dragged or pshed by another. What I mean by this is when a train is being doubled headed by locomotives, or the various different engines on a multiple unit, how is it ensured that they are providing the correct power to stop the front one pulling the one behind if that is not in sync, or the one behind pushing the one in front if they are out of synce. I can imagine with modern trains there could be a computerised system to monitor such things,but on older units how do all the engines stay in synce so that non are pushign or pulling the others?

As far as double heading goes, it depends...

This Wikipedia page gives a good account of the different types that have been or are in use in Great Britain.

http://en.wikipedia.org/wiki/Multiple_working
 

edwin_m

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In steam days "multiple" working was achieved by having a crew on each loco, and the trailing engine crew were supposed to do the same as the one in front. I guess this was by a combination of route knowledge and looking/listening for signals, whistles and what the other loco was doing. It wasn't very scientific but seemed to work!

And before the pedants descend I'm aware this was and is known as "tandem" working, and can still happen if the trains being coupled don't have a compatible multiple working system. I remember a couple of times around 1980 witnessing this when a DMU with one engine out was assisted by a class 20. I was sat in the usual seat behind the driver, who drove the train pretty much as normal.
 

Taunton

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In steam days "multiple" working was achieved by having a crew on each loco, and the trailing engine crew were supposed to do the same as the one in front. I guess this was by a combination of route knowledge and looking/listening for signals, whistles and what the other loco was doing. It wasn't very scientific but seemed to work!.
It was quite straightforward. The loco in front acted as normal, did the brake, and such like. The second loco just assisted, it was basically steam on or steam off, depending on their judgement. Contrary to some opinion, there were no whistle signals between crews of a double header (though there were with a banker at the back), but there were gestures from the driver ahead.

"Other railways" would put the assisting engine in front, but the GWR/Western Region were, of course, the opposite, and inserted the assisting engine behind, to keep the main train driver in front.

From the USA. At the steam/diesel changeover the new diesel train loco (probably 3 or 4 units) was assisted in the rear up a major hill by the large steam loco always stationed at the bottom for that purpose. Obviously life on a diesel going up this hill was now very easy compared to the effort required in steam days. Train sets off, and is not really making much progress, little more than walking pace, diesel crew looked back but it's a big train and end is out of sight. Unknown to the steam banker crew the chief inspector (US = Road Foreman) is up on the new diesel. On the outside of a long curve he lets himself down the ladder onto the ballast. Another train length goes by and suddenly great noise breaks out at the rear, steam and smoke rise high, and a distinct increase in speed. At the top the road foreman walks forward, with a "that's one trick they won't do again" dusting of hands.

For what is undoubtedly the best written book ever on a railway with lots of double heading, David L Smith's "Tales of the Glasgow & South Western Railway" is a must. For example, he writes of a unbraked double-headed freight on a dark night which, as ever, got up some huge speed on the downhill to keep the couplings tight, the guard at the back having the van brake fully on, when the second loco suddenly found that all they had in front of them was a tender ... the coupling between first loco and its tender had broken with all the shocks up and down the train, and the crew had, most wisely (remember, no continuous brake), decided to keep going.
 

DownSouth

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How did you handle the quite substantial number of English Electric locos that were shipped out to Oz in the 1950s-70s? Did they get fitted with AAR or are they orphans that only work with themselves?
346 EE locomotives were used in Australia (48 imported, 298 built here) by five rail systems, which may sound like a lot to the average UK enthusiast but in actual fact is quite a small piece of the pie. The New South Wales Government Railways alone ordered enough AlCo locomotives to outnumber the whole country's total of EE locos by 80 - and they had a fairly even split of AlCo and EMD locos.

The multiple unit working issue was really quite simple - they almost never needed it apart from within their own classes. Most of the EE locos were small shunter-switcher locos (lots of them had a rough resemblance to the British Class 20) which just shunted or ran small trains as like-for-like replacements of steam locos. If a train was too heavy for a pair of EE locos, it deserved to use the bigger AlCo or EMD locos instead, which led to the EE locos starting to get withdrawn not long after the final withdrawal of steam in the 1960s allowed freight trains to get longer and heavier in the 1970s.

The South Australian Railways had 46 EE shunters/switchers in three classes and the ten unique SAR-designed 900 Class mainline locos which had EE components - all 56 were built in the SAR's own workshops. The mainline SAR fleet was otherwise all AlCo, 95 of them in four classes, with the 900 Class generally kept on the flatter routes north of Adelaide and promptly retired when the freight side of the SAR was transferred to Australian National.

The Western Australian Government Railways had 42 EE locos (all shunter/switchers) but most interestingly they were outnumbered in WA by the X Class which used the infamous Crossley engine! A private freight transport company experimentally had AAR multiple working equipment retro-fitted to three of the former WAGR K Class about a decade ago, without any great deal of success.

A few of the old EE locos are still sprinkled around the country working in freight yards, but they are dwindling in number as they get older.
 
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