[darwins]

For around a hundred years from about 1895 to about 1995 most electric multiple units and trams had a throttle with some kind of electrical or mechanical automatic acceleration.
Typically this would be controlled by current sensitive relays. The driver would move the controller to maximum and the unit would start in the 'first notch' and 'notch up' automatically as the speed increased (or more accurately as the traction current decreased).

This type of throttle was never represented in MSTS and can not be accurately represented in OpenRails.

A good 'work around' for the acceleration can be made in OpenRails by using ORTSMaxTractiveForceCurves in this case changes in 'notch' are set according to speed and can be calculated to change at a fixed value of Tractive Force (which is more or less equivalent to a fixed current value in OR).

This 'work around' is fairly good for inner suburban trains and trams - where running is accelerate / coast / brake. The limitations make it less suitable for faster non-stopping trains. This is because the real throttle only provided for 'notching up' and not for 'running down'. In order to reduce power the driver would have to return the controller to OFF and then notch up again.

Two variations of this were common in UK from the 1950s to the 1990s.


British Railways:

Five position controller 0 - OFF / 1 - Shunt or Inch / 2 - SERIES / 3 - PARALLEL / 4 - WEAK FIELD

Normally the train would 'notch up' until it reached the selected power.

However if the controller was moved back to a lower setting then notching was halted.
This allowed the train to remain for a short time in a resistance notch before either continuing to notch up or shutting off power to coast.
On d.c. units running for any length of time in that way would cause resistances to overheat, but it could be used to slow down acceleration in low adhesion conditions.


London Transport:

Four position controller 0 - OFF / 1 - Shunt or Inch / 2 - SERIES / 3 - PARALLEL

In this case there was no means of halting 'notching' at intermediate values, acceleration would continue until the highest running notch selected was reached.

There were generally three other switches in the cab that affected the behaviour of the throttle.

Rate Switch - allowed either normal rate of notching up or slower acceleration for conditions of low adhesion.

Weak Field Switch - when OFF position 3 on the controller was full parallel, but when ON notching continued to the weak field setting(s).

Coasting Control - limited maximum speed generally to 30 mph if the weak field switch was off.

I believe the additional switches could only be changed when the train was stationary.


Trello card

[MMax]

A similar behavior is found on modern locomotives like the IORE too where, as long as the lever is in the forward position, the power and brake logic automatically increases the power and, if the lever is moved to "hold", holds the notch in the position.
More about this can be read here: https://library.e.ab...rmer-Kiruna.pdf

[ATW]

Some modern diesel-electrics of today use the same method. But some also give a Throttle delay even though you put it in a higher position quicker that some impatient engineers don't like it but its built in the locomotives software per company. There is even some software that optimize fuel where if you are a light train with too much power or even a heavy it won't let the projected speed exceed a certain point if in power. Lets change projected speed to acceleration control where pulling Force an HP is automatically reduced to keep at parameter set value of no more then 10MPH gained per minute.

That method even sometimes reduces chances of string lining depending on Degree of Curve vs how much force the Railhead/Wheels/Draft can take, if stock is legal to negotiate the given curve and what are its limits from straight line over or breaking the rail.

I can tell you I don't like how Gensets 3GS4B are programed in remote operation that do this that they can't pull even in packs vs a single GP15 pulling hard an faster.

[dajones]

"Electric Railway Engineering" by Francis Doane has wiring diagrams for two automatic M.U. controllers that use relay logic. The first is for two DC motors with three resistors in series with each motor. The relays provide seven series steps and four parallel steps. The controller has four forward positions: series hold, series advance, parallel hold and parallel advance. When the controller is in an advance position the cars automatically advance between steps when the current drops below a pre-set threshold. Moving the controller to a hold position stops the advance. This controller does not have the ability to step down. To do that you need to shut off and then use series advance.

The other controller is for AC power. It uses a step down transformer with three voltage taps. Each voltage tap has a resistor that can be cut out, so there are a total of six steps. The controller has three positions that correspond to the different voltages. The logic automatically steps through the voltages with and without resistors until the selected voltage is reach. This controller has the ability to step down to a lower voltage without the resistor.

Doug

[darwins]

dajones, on 04 January 2020 - 10:57 AM, said:

"Electric Railway Engineering" by Francis Doane has wiring diagrams for two automatic M.U. controllers that use relay logic. The first is for two DC motors with three resistors in series with each motor. The relays provide seven series steps and four parallel steps. The controller has four forward positions: series hold, series advance, parallel hold and parallel advance. When the controller is in an advance position the cars automatically advance between steps when the current drops below a pre-set threshold. Moving the controller to a hold position stops the advance. This controller does not have the ability to step down. To do that you need to shut off and then use series advance.

The other controller is for AC power. It uses a step down transformer with three voltage taps. Each voltage tap has a resistor that can be cut out, so there are a total of six steps. The controller has three positions that correspond to the different voltages. The logic automatically steps through the voltages with and without resistors until the selected voltage is reach. This controller has the ability to step down to a lower voltage without the resistor.

AGNEW, W. A. "Electric Trains - Their Equipment and Operation" is a very detailed work from 1937 dealing with several controllers then in use in Britain, ( all d.c. )

Quote

A similar behavior is found on modern locomotives like the IORE too where, as long as the lever is in the forward position, the power and brake logic automatically increases the power and, if the lever is moved to "hold", holds the notch in the position.

The idea of "power up" hold and "power down" was very common throughout Europe for a.c. electric locomotives.


There was a good description of it in an earlier thread and a link to a video of a Hungarian loco.

For example British class 81 a.c. locos had 38 transformer taps for full field, plus two steps of field weakening. The controller was
OFFRUN DOWN - automatically goes down through the notches until it either reaches OFF or is moved to HOLD
NOTCH DOWN - moves manually one notch downHOLDNOTCH UP - moves manually one notch upRUN - automatically goes up through the 38+2 notches until it either reaches the maximum or is moved to HOLD
As I understand it this kind of controller does not use a current sensitive relay to decide when to notch up or down but simply takes about 1.5 seconds in each notch before changing up or down. So it is a little different from automatic acceleration in a multiple unit train.
There is also a Trello card for that.
As stated there the idea of an ADVANCE - HOLD - REDUCE type of control can be applied to steam reversers on steam locos as well.
So far OR has not had the ability to include controls of this general type.

[ATW]

NickonWheels, on 04 January 2020 - 01:16 AM, said:

Do you mean an engine could have the same efficiency at 50% than at 100% throttle; sounds not very realistic but maybe it´s possible (the way of electric locomotive traction)?

Sort of, its just automatic governor systems on modern freight trains removing unnecessary acceleration to save fuel and emission standards... Its like the accelerometer governing the Engine or Traction to not exceed its set limit where for example your train can't gain the set limit of no more then 15MPH every 60 seconds. The engines wont rev up traction any faster but you will still get power and speed climbing slowly just not any faster then set. Its like running ORTS in autopilot trying to make AI not be so impatient or too fast heavy on the throttle. Doesn't really have to do with slowing down deceleration.

PTC (Positive Train Control) has similar future in some units that are automated with the click of a button.

[AlanColey]

darwins, on 04 January 2020 - 12:06 PM, said:

There is also a Trello card for that.

https://trello.com/c...pe-of-throttles
(This controller can be faked in OR by the work around of changing power according to speed depending - but of course it should change power with time.)

Please let me know where to find the work around mentioned in the Trello card. For example, on a class 40, the field changes at approx. 24mph increasing the amps at that speed.

Useful topic: https://www.railforu...-divert.119164/

This post has been edited by AlanColey: 01 February 2020 - 02:51 PM

[darwins]

AlanColey, on 01 February 2020 - 02:46 PM, said:

https://trello.com/c...pe-of-throttles
(This controller can be faked in OR by the work around of changing power according to speed depending - but of course it should change power with time.)

Please let me know where to find the work around mentioned in the Trello card. For example, on a class 40, the field changes at approx. 24mph increasing the amps at that speed.

Useful topic: https://www.railforu...-divert.119164/

Hi Alan
The workaround that I was referring to above was one that I had applied to British Electric Multiple Units that have resistance notches.
The same can be used to fake the performance of diesel electric locomotives - including field weakening steps.
To do this you do need to know at what speeds the changes such as field weakening and offloading occur.

Graphs like chart 9 and chart 12 in the BR test report for 10203 should help.
Although I note in the charts a smooth curve is given for tractive effort versus speed - so current change would appear smooth in OR - fortunately the relevant speeds are highlighted so it may be possible to "saw tooth" the changes in force in order to model the changes in current.
BR 10203 (direct ancestor of Class 40) is modelled on CTN using tractive force curves - you might like to have a look at this and see what could be done to highlight the changes due to field weakening.
I am shortly going to try to make some replacement OR files for British diesel electric locos.
One problem for me with trying to include field weakening and offloading points would be getting the relevant prototype information.
I think that it may be possible for me to find the relevant information for classes 08, 15, 20, 24, 28, 31, 40, 45, 47, 50, 55 and 56 at the NRM - with curves for other classes being assumed similar.
If you have prototype information for any others (including HST) please let me know.