PC Br423/br425 Discrepancy In Brake Force

Discussion in 'Technical Reports' started by cwf.green, Mar 17, 2021.

  1. cwf.green

    cwf.green Well-Known Member

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    I've noticed that the BR425 in Munich-Augsburg (via HRR) brakes much more strongly than the BR423 that comes with the route.

    For example: When braking at 80% of max brake from 120 km/h it takes about 700m to stop with the BR423 but only about 450m to stop with the BR425.

    This implies that the maximum deceleration for the BR423 is about 1.0 m/s^2 but almost 1.6m/s^2 with the BR425. According to Wikipedia (and the source it sites) the deceleration should be about the same for both EMUs: 0.9m/s^2. Assuming that the deceleration is from 140 km/h (or whatever max speed of the EMU) then the brakes on the BR423 seems to be acting realistically but the brakes on the BR425 are almost 60% too strong.

    Iirc Maik Goltz, who is behind many of the most realistic German addons for Railworks was involved in the design of the BR425 HRR, so perhaps this is either prototypical (the sources are wrong) or maybe something is bugged.

    Does anyone have any thoughts/input?
     
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  2. Coastway trainspotter

    Coastway trainspotter Well-Known Member

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    The brakes on the 423 are quite weak irl so this is realistic in the game
     
  3. cwf.green

    cwf.green Well-Known Member

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    I may have worded my post in a confusing way, I do think the 423 have realistic brakes (at least according to what I've read) but I'm wondering whether the 425 should really have such strong brakes in comparison, they seem to be very similar trains.
     
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  4. solicitr

    solicitr Well-Known Member

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    AIUI, the 425 has such notably weak brakes that DB have put restrictions on it (no more than 140 except under LZB, and just 120 in autumn with wet leaves on the rails)
     
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  5. cwf.green

    cwf.green Well-Known Member

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    I read that some of the BR425 had magnetic track brakes installed to improve braking performance during autumn (the conditions solicitr mentioned above).

    It could be that the TSW2 BR425 is based on one of these variants of the BR425 which *could* explain the much higher brake force.

    BUT, you don't normally brake with track brakes, they only lower during an emergency brake application. It seems like DTG/whoever doesn't want to actually model magnetic track brakes but instead simply bumps up the air brake so that at full service it is the same as the real counterpart with magnetic track brakes applied. This is wrong.

    If F_ab is the maximum brake force (at full service) of the air brakes and F_mg is the brake force just from the magnetic track brake, then the braking scheme would look like this:

    Brake force goes up linearly and smoothly toward F_ab at full service, and then if the emergency brake is activated the brake force instantly increases to F_ab + F_mg.
     
  6. solicitr

    solicitr Well-Known Member

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    More than that, actually, because the emergency reservoirs feed the brake cylinders in addition to the service reservoirs. Or at least, that's the way US brake systems are set up.
     
  7. cwf.green

    cwf.green Well-Known Member

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    On most European trains I don't think is very common, although on some UK EMU/DMUs they have "enhanced emergency brakes" that do give (iirc) 30% or so extra air brake force.

    On most German/main land EU trains the emergency brake will just apply faster than a full service application, without having higher brake force.

    Interestingly enough, almost all trains (ICE3 might be an exception) that have electrical brakes (rheostatic or regenerative) will cut off this mechanism during an emergency brake application which could actually make the emergency brakes less effective than full service, unless track brakes are installed.
     
  8. solicitr

    solicitr Well-Known Member

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    That used to be the case (as a matter of Federal regulations) with US trains. It was a major contributing factor in the San Bernardino disaster, which is why soon thereafter the regulation was flipped and now forbids emergency brakes to kill the dynamics.
     

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