[Lamplighter]

Hi!
UIC (International union of railways) has the rule UIC 544-1 (Brakes - Braking performance) with Annex B.1 for verifying the effect of the brakes.
The brake performance is evaluated in a graph by plotting the calculated net brake ratio od car (or sum of the net brake ratio cars of train) on the speed curve. The intersection then shows the required distance to stop.

Usually I check the correct setting of the brakes on my vehicles (.eng, .wag) - especially the MaxBrakeForce parameter.
In the OR on a straight track, the tested train will start at the required speed. Then I reset the odometer at the same time and apply the full brake. I'll wait for the train to stop completely and read the distance traveled from the odometer.
I then compare this distance with the calculated distance from the UIC 544-1 graph. The result shows how well my brakes are set (braking force, brake reaction time - brake distributors, valves, equipment etc.).

Because I'm also interested in American locomotives and cars, I know that there is an AAR (Association of American Railroads) instead of UIC. I can't find a similar rule or graph for AAR (Verification of the effect of the brakes using the net brake ratio and stopping distance at different speeds).
Has anyone seen anything like this?

Attached File(s)

•  Nomograms.zip (819.56K)
  Number of downloads: 365

[sim-al2]

So in short, the US doesn't have explicit stopping distance requirements (or those nice UIC-style performance charts), either by law or as far as I can tell, from the AAR. However, the AAR does have its own brake ratio requirements (explicitly for high friction composition brake shoes, as cast iron brake shoes are now extremely rare here). I think the Coals to Newcastle site explains the implications of this better than I could, and includes the current AAR brake ratio chart. I *believe* that both sets of requirements give similar results for empty cars, but obviously the UIC standards require much greater performance for loaded cars than the AAR standards. The UIC standards also seem to be aligned to cast iron brake performance (or composition shoes with similar characteristics), while the US moved away from cast iron shoes as car weights increased rather substantially in the 1960s and onward. If you want to read more about how the US diverged from European practice, this old US DOT publication titled "BRAKE SYSTEM DESIGN OPTIMIZATION" is helpful too.

I think the biggest difference in OR practice is that fewer US cars have empty-load devices (i.e. the 2-stage brake cylinder found in European practice for over a century now, or more modern versions). The heaviest US cars (i.e. 125 ton cars) should have empty-load devices, these usually work on the principle of reducing the brake cylinder pressure when the car is empty by a certain percentage, often to 55 or 65% of the loaded brake cylinder pressure. I believe that changeover is automatic (i.e. controlled by a device mounted on the car's bogies and not a manual control like many older European cars).

As a side note, that DOT report also mentions that electro-pneumatic brakes for freight trains were proposed as far back as 1887.

[Lamplighter]

Thank you for the detailed description.
I would look for an explanation of the situation in the dense railway network on the European continent.
Therefore, more detailed regulations for braking, shorter trains, less loads and short braking distances.

[darwins]

The interesting thing here is that most trains in Europe also no longer have cast iron brake blocks. However all the standards are set out using the equivalent cast iron brake blocks - and braking% (braked mass) and so on is always stated as what the equivalent would be for cast iron brakes.
So if we set the friction for cast iron (as given on CTN) then it is fairly easy to set the correct brake force from wagon data.
For more modern composite brake blocks and brake discs it can be challenging because a variety of different materials are used and it seems impossible to find the speed-friction data curves for most of them.

If we can get the material data though, the curves provided will be an excellent resource for checking that brake forces are correctly set.

[Lamplighter]

Here are examples of CoF (Coefficient of Friction) curves for three types of composite shoes and cast iron shoes up to 120 km/h.
The curves come from some measurement. For the purpose of determining OR the ORTSBrakeShoeFriction parameter, the curves would have to be interpolated. But that is not a major problem.
I am more surprised by the difference in the coefficient for the same materials. US sources for cast iron state CoF 0.5, European sources around 0.32. And it's similar for composite materials.

Attached File(s)

•  CoF.zip (243.73K)
  Number of downloads: 353

[Coolhand101]

Lamplighter, on 01 September 2020 - 12:29 AM, said:

I am more surprised by the difference in the coefficient for the same materials. US sources for cast iron state CoF 0.5, European sources around 0.32. And it's similar for composite materials.

When this feature was first implemented in OR, I was using a Cof of 0.35 for UK trains with cast-iron brakes. However, OR defaults to 0.50 and manual charts show 0.50. So I updated my trainsets accordingly!

So which CoF to use for UK trains with cast-iron brake blocks?

Thanks

[Lamplighter]

I create settings for rail vehicles of Czech and Slovak railways (including the predecessor of Czechoslovak railways - before 1992).
I am therefore based on the operating regulations used for these railways.
Specifically from the official regulation "Service handle - Description of brakes of railway vehicles".
Here is the chapter on the coefficient of shear friction:
Fig. 2 shows the dependence of the coefficient of friction on the vehicle speed. In this figure, the individual curves mean:
1a) coefficient of friction of cast iron brake shoe at a specific force of 0.4 MPa in the friction surface.
1b) coefficient of friction of cast iron brake shoe at a specific force of 1.0 MPa in the friction surface.
1c) coefficient of friction of cast iron brake shoe at a specific force of 2.0 MPa in the friction surface.
2) coefficient of friction of brake linings (drum brakes, disc brakes),
3) coefficient of shear friction of wheels on rails.



fig. 2 Dependence of the coefficient of friction on the vehicle speed
f - coefficient of friction between the brake shoe and the wheel
The course of individual curves shows the influence of speed and specific force on the coefficient of friction f.
With speed and increasing specific force, the magnitude of the coefficient of friction between the brake shoe and the wheel decreases.
For composite materials, the coefficient is lower - 0.20 and the course is more uniform.

For a standard braking force of 1.0 MPa (145 psi) per brake shoe I use a coefficient f = 0.31 and for a disc brake a coefficient f = 0.42

ORTSBrakeShoeFriction ( 0 0.31 1 0.30 2 0.28 3 0.27 4 0.26 5 0.25 7 0.24 8 0.23 9 0.22 12 0.21 14 0.20 17 0.19 20 0.18 24 0.17 29 0.16 34 0.15 40 0.14 47 0.13 55 0.12 66 0.11 84 0.10 115 0.09 160 0.09 )
or
ORTSBrakeShoeFriction ( 0 0.42 1 0.40 2 0.39 3 0.38 4 0.37 5 0.37 7 0.36 8 0.35 9 0.34 12 0.33 14 0.32 16 0.31 20 0.30 24 0.30 30 0.29 34 0.28 40 0.27 48 0.26 56 0.26 68 0.25 84 0.24 120 0.23 160 0.23 )

In the case of British Railways, a similar local regulation or standard would have to be followed. However, national regulations are based on UIC regulations, so the values ​​will be very similar.

[Robo_TR]

Hello,

I made some test with parameter BrakePipeVolume. At first start of the game, ORTS accepts parameter, but after save and load, I have suspicion, BrakePipeVolume is ignored. Time during the releasing brakes is too quick also on a long freight trains. Can somebody check it ?

Thank you.

[darwins]

There are indeed strange things going on somewhere. It seems almost as if the laws of physics in USA may be different to those in Europe.

The Bremskerl brochure for Europe and the Bremskerl 176 brochure for USA appear to give different CoF curves for the same material.

https://i.imgur.com/Vc0h7Rd.jpg

https://www.bremsker...6-lf-brake-shoe

https://www.bremsker...vehicles-german

[Lamplighter]

Probably because sliding speed is not the same as velocity.
In brochures, both graphs represent something different.The US version is the correct one. And it is interesting that the material almost copies the cast iron.