[Csantucci]

Blended braking is one of the very few MSTS features that aren't yet available in OR. I got a request for addition of such feature. Are there other people missing it (although I wouldn't volunteer for that, as I'm not the expert on brakes)? Is it worth implementing it?

[ATW]

Yep I say it's very worth implementing since out here in North America trains like Amtrak use it. Some braking parameters like the default Acela use it along with protections to the brake shoes from power braking with a limit as to where power is cut out.

BrakesEngineControllers( "Train, Dynamic, Blended" )

DoesBrakeCutPower( 1 )
BrakeCutsPowerAtBrakeCylinderPressure( 15 )

[gpz]

I would implement it if needed, but I don't know how it is supposed to work. I would like to implement it in a way that works both in Europe and America.

[EricF]

Mimicking the MSTS blended braking might be a good start; it ought to work fairly well for passenger train implementations across the board as a means of gentle, controlled braking -- even if it isn't the prototypical method in every case. That would at least help meet the stated 1.0 goal of matching MSTS behavior.

Branching out beyond that is probably best left to releases beyond 1.0 -- and opens up a wider variety of braking systems. There are electro-pneumatic systems and the anti-locking varieties (Usually referred to as anti-slide or anti-skid in railway terminology, but functionally similar in principle to anti-lock brakes on cars that use a servo system to modulate brake application at the wheels regardless of brake pipe pressure).

I run mostly US prototypes in OR which uses the single-pipe air system. Forgive my ignorance, but is the twin-pipe system often used in the rest of the world being fully modeled in OR? If not, that would certainly be welcomed.

[markus_GE]

EricF, on 21 January 2015 - 04:50 AM, said:

[...]

I run mostly US prototypes in OR which uses the single-pipe air system. Forgive my ignorance, but is the twin-pipe system often used in the rest of the world being fully modeled in OR? If not, that would certainly be welcomed.

At least here in Europe, twin pipe brakes are standard.

Cheers, Markus

[Csantucci]

I also agree that starting mimicking MSTS (but how does MSTS manage blended braking exactly?) is a good idea. However to take into account different locos from different countries, one idea that I suggest is to implement support for double-interpolated braking curves, that can be structured like the curves already available in OR for the tractive force (see e.g. paragraph 8.14 of the manual).
There could be two tables, organized as follows:
- for the dynamic/electric brake:
ORTSDynamicBrakeBlending(
brakecontroller%value_0 (
speed_value0 dynamicbrakecontroller%value0
speed_value1 dynamicbrakecontroller%value1
...
speed_valuen dynamicbrakecontroller%valuen
)
brakecontroller%value_a (
speed_value0 dynamicbrakecontroller%value0
speed_value1 dynamicbrakecontroller%value1
...
speed_valuen dynamicbrakecontroller%valuen
)

....
brakecontroller%value_100 (
speed_value0 dynamicbrakecontroller%value0
speed_value1 dynamicbrakecontroller%value1
...
speed_valuen dynamicbrakecontroller%valuen
)
)

for the train brake:
ORTSTrainBrakeBlending()
organized as the above table.
The double interpolation functions should be already available within the OR code.
It has also to be evaluated if putting outside of the internal parentheses the speed values and inside the brake controller values were be a better solution.

When such tables are not there, the standard MSTS approach is used.

[Csantucci]

As a contribution to this theme, I write here how blending is implemented in some Italian locos and EMUs, by translating some info I got.
- in the most part of the Italian trains with electric braking (with the exception of the TAF EMU and of the E464 single-cab loco for push-pull trains) the brake lever has a first position where only the electric braking is active with maximum electric braking force, and from the second position in addition to the electric braking also the pneumatic braking begins to be active.
- in the TAF in the first three positions of the brake lever only the electric braking is inserted ( 25-50-75kN), with the 4th position the electric braking is inserted to 100kN and also the pneumatic braking begins to be inserted
- in the E464 in the first position of the brake lever the electric braking is inserted at 50% of the full value, and with the next positions the electric braking increases intensity and together also the pneumatic brake is inserted more and more.
- all locos themselves that have electric braking have a device that manages the braking of their motorized axles; if at a certain moment on such axles the electric braking is active, on such axles at the same moment the pneumatic braking is disabled
- the electric braking is enabled from max speed down to 35 km/h; if at the same time also the pneumatic is active, that lower threshold is reduced down to 5-10km/h.

I hope this can provide some idea. With some table and some threshold a good parametrization is possible.

I add another point: the same person let me notice that
"BrakeCutsPowerAtBrakeCylinderPressure( 30 )"
is not implemented in OR. I think it would not be a big job to add this to the braking management.

[disc]

As i know, in europe the dynamic brake blending is not depending on speed, but the target, and achievable braking force. Which means if you drive an EMU, it will use they dynamic brake as primary brake, and in normal conditions the airbrakes only applied at very low speeds to make the train completely stop, and keep it stopped. But if the line voltage drops(or other failure) so the regenerative braking is impossible, then the computer automatically applies the airbrakes to reach the target brake force.

On modern electric locomotives also the regenerative brake is the main brake, so the computer will use that even if you pull the train brake lever, and starts using the airbrake on the loco only if the maximal dynamic brake force is reached, and more braking force is needed.

So in short: dynamic brakes are used as main brakes both in modern EMU and locomotives, airbrakes applied only if the dynamic brake force is not enough. But there are locomotives around the world that have "fixed" dynamic brake/airbrake settings, where every trainbrake lever notch sets a certain percentage of dynamic and airbrake.
For this we need a working ORTSDynamicBrakeForceCurves, which is implemented, but actually works... parameters for setting limits (overall brake force, max/min speed), a working anti-slip/anti-lock wheel system is needed.

Note that these braking systems can be controlled by automatic train controlling systems too, like AFB which is controlled either by the driver, or the LZB.

[gpz]

Yes, I think disc is right: The thing with curves can be handled with ORTSDynamicBrakeForceCurves, of course with the exception currently, that train brake lever cannot be locked to move in pair with dynamic brake lever. This makes me wonder what would be the better approach: take the train brake lever position and blend the dynamic brake into it, or take the dynamic brake position and blend the train brake into it. I tend to the latter, since it is a common configuration of having a separate train brake only controller on locomotives (at least there is on MÁV's Stadler Flirt EMUs), and maybe not so common of having a separate dyn.brake controller beside the combined one.

I don't know how much the MSTS implementation is useful. Reading on forums, I understand it that MSTS-way doesn't match any real-world locomotive... If it is true, it would be a waste of time implementing that one...

[Csantucci]

As I wrote, here it is the opposite, that is with the train brake lever you command both dynamic brake and train brake. The dynamic brake lever does not have effect on the train brake.

[gpz]

So on these locomotives there is an additional, separated dyn-brake controller? Does that set different dyn-brake forces at different speeds and controller positions, than the blended brake controller? So are there two different ORTSDynamicBrakeForceCurves needed to handle these?

[Csantucci]

Peter, I will ask for detail.

[Csantucci]

gpz, on 22 January 2015 - 03:34 AM, said:

So on these locomotives there is an additional, separated dyn-brake controller? Does that set different dyn-brake forces at different speeds and controller positions, than the blended brake controller? So are there two different ORTSDynamicBrakeForceCurves needed to handle these?

I got a reply.
Trainsets like the TAF that I mentioned in my above post, and that already can command different electric braking levels with the train brake lever, don't have another way to command the electric brakes.
Trainsets like the E464, built by Bombardier in 688 exemplars, that is the backbone of regional and interregional trains in Italy ( http://en.wikipedia..../FS_Class_E.464 ), and that have only one possible electric braking level commanded with the train brake lever, have also a classical traction-electric brake combined control lever. (In the case of the E464 there are two further levers that are used when automatic speed control is selected: one is used to set speed, and the other is used to set max tractive - electric braking effort to achieve the speed target, but that's another story :) ).

In the meantime Eugen R. reminded me that also SBB locos like the SBB460 have blended braking, at least looking at their parameters in the MSTS .eng file...

[gpz]

After some thinking on it, maybe only two additional information is needed for the train brake (TB) notch controller, for the dynamic brake (DB) is to be blended:

• the correspondence from TB to DB notch positions,
  
• a TB notch position to desired braking force interpolator,
  
• additionally, a DB notch position to desired braking force interpolator might be needed, see below.

The effective DB force in function of speed and notch position is already available in ORTSDynamicBrakeForceCurves, as implemented by Matej. As the force will decrease by the decreasing speed, we will have to know how much it is below the desired force, if at all, so that the necessary amount of air can be let in or bailed off the cylinder.

Certainly, some specialities are to be defined here:

• In (1) the corresponding DB notch position could be -1, to indicate the DB is to be disengaged. Explicit disengaging command must be possible, because re-engaging takes time on Diesels.
  
• There must be a way to blend TB into a combined throttle-DB controller. For this case a separate (3) must be defined. Using this one only instead of (2) above might not be adequate, since there could be a configuration, where e.g. tha max. DB force is assigned to multiple TB notch positions, but with different desired total brake forces.

[Matej Pacha]

Well,
first of all, OR code is not ready for such features. You need to create "levers" independent from "controllers". In modern traction, some important modules are allowed to command the controllers and the driver's levers are "untouched". For older locomotives, it is very easy to bind a lever with a controller to act like the one.
Second, a dynamic brake is not a safe brake, if it is line-voltage dependent. Based on this, you cannot make the system act like described in some previous posts. If you would command the dynamic brake as the main brake, in the case of failure, the air brake would start to act with some delay, what is not desirable. You need to command them at the same time to ensure the braking effect. If the dynamic brake response is OK, then you can bail-off the air brake.

Usually the dynamic brake is controlled by the locomotive brake pressure and bails-off the locomotive brake if the dynamic brake works fine. Level of the bail-off can be controlled by the dynamic brake feedback to replace the dynamic brake fade-effect at low or high speeds.
The first command usually comes from the train brake or the combined throttle lever. It can be an electric signal, but it is converted to a pneumatic signal (pressure) to ensure the train brake will always play a role. This pressure signal is converted back to an electric signal to command the dynamic brake controller. Based on the dynamic brake response, the bail-off command is executed to save the friction brake material. If the dynamic brake fades due to low or high speeds, the pneumatic brake replaces the brake effect. In case of the dynamic brake failure, the feedback is lost and the air brake covers whole brake effect. The description above is a brake system of Skoda and CKD locomotives since 1975 (more than 2000 locomotives with a dynamic brake).

In fact, it doesn't matter who or what commands the brake controller. It can be a driver or e.g. an automatic speed (cruise) controller.

And about the brake effect - the brake system must not cause the train to skid when braking. Thus, the dynamic brake must be marked as "safe" to be used with emergency braking. If it is not marked as "safe", it must be switched off when the emergency brake is engaged. The brake effect of the dynamic brake must not be higher than the pneumatic brake according to the latest TSI specifications (TSI - technical specifications for interoperability in EU). The brake effect mentioned in TSI must not be higher than adheasion factor 0.12, what means 0.12*9.81*85t = 100 kN for 85 ton locomotive. I'm not sure if we need to care about this, but definitelly it should be considered at least.

Matej