PC Afb Don't Hold The Speed(brakes Problem)

Discussion in 'Technical Reports' started by PseudoStalker, Oct 1, 2021.

  1. PseudoStalker

    PseudoStalker New Member

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    BR146 & BR185 from Dresden don't hold the speed in AFB mode. The train continues to accelerate when driving downhill. Visually brakes are applied but have almost no effect. At high gradients, speeding can reach 10+ km/h.
     
  2. solicitr

    solicitr Well-Known Member

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    That's realistic. AFB can hold speed on the flat or a slight downgrade, but a significant downhill requires one to (a) set AFB to a lower speed, or (b) go to manual brakes. Older TSW implementations made it a Magic Speed Regulator.
     
  3. PseudoStalker

    PseudoStalker New Member

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    So, AFB on ICE3 is broken, because it can hold speed on any downhill?
     
  4. solicitr

    solicitr Well-Known Member

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    Not necessarily. The ICE 3 has a signal advantage over loco-hauled trains in that the traction motors are spaced along the entire consist (two driven axles on each car, total of 16), which means that you get more effective acceleration and especially deceleration* than if you have just 4 motors, all up front. (it also has a whopping 11,000 horsepower, double a TRAXX')

    *Under dynamic/eddy braking alone, which AFB uses, the wagons behind a loco are not braked in any way, and so are shoving against the locomotive.
     
    Last edited: Oct 1, 2021
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  5. Monder

    Monder Well-Known Member

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    To add to what solicitr mentioned - ICE3 AFB is also usually used is higher speeds, where you have more air resistance and need to apply more power just to keep the speed. So on a downhill, you can still slow down and AFB using the little amount of brakeforce it does is enough.
     
  6. OpenMinded

    OpenMinded Well-Known Member

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    Yes, this is what was modelled, however, it is not very realistic. The real AFB does use air as well. Check the TSW BR101 out, there you can see how it should be.

    The way the AFB works is that it actually commands breaks to achieve a certain deceleration, hence, it would use more air on a slope down. For cargo trains, this is actually quite a difficult task, as brakes are somewhat slower to react.

    In modern locos you can disable the air brake part of the AFB, which may be beneficial, especially on cargo trains. Also, the AFB is actually quite regulated on cargo trains and not used on steep descents, as solicitr has already said. Manual braking is always superior to the AFB.
     
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