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Afb - What's The Correct Way To Slow Down And Stop

Discussion in 'PC Discussion' started by tbaac, Sep 18, 2021.

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  1. tbaac

    tbaac Active Member

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    Hi. Been trying to get used to AFB. From what I can work out, if for example I am doing 110 km/h using AFB, and a station is coming up in 1 km, then I need to slow down and stop. What's the best way of doing that?

    What I've been doing is to set the AFB to about 50 km/h, which will trigger the electric brakes and then supplement it with some train brakes. It seems like if you do this then this triggers the throttle lock and AFB can't apply power again until you move the power lever to zero and then increase it again (this wouldn't be a problem if slowing down at the right time but it is possible to slow down a bit early and then needing to add a bit of speed near the end).

    Then I'd reduce AFB again to about 20 km/h, etc.

    It sometimes feels like it would be easier to turn AFB off when slowing down, but that could be a pain and probably isn't the right way anyway.

    Thanks
     
  2. HaibaraHariko

    HaibaraHariko Active Member

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    Leave the AFB level, set power to zero and apply brake manually. I don't think you are supposed to use AFB to slow down in this case.
     
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  3. tbaac

    tbaac Active Member

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    Okay thanks, although it does give you added breaking (maybe not as the wheels presumably can only handle so much friction). Thanks.
     
  4. FD1003

    FD1003 Well-Known Member

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    It doesn't, on all german locos if you operate the train brake you will also automatically use the dynamic/electric brake.

    In fact AFB shouldn't even really be used to hold speed, but more as a safeguard, I usually set it to the speed limit and manually hold 3 to 5 km/h below the set speed.

    Braking action from AFB should be avoided whenever possible, human intervention will always be preferable.

    If you use the BR143 or 112 you can set the "power" and dynamic braking using R and F
     
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  5. tbaac

    tbaac Active Member

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    Thanks for the replies. I've got a Raildriver and the RD Ind Brake lever is mapped to the AFB lever, and that works really well (with the Throttle part of the combined RD Throttle/Brake lever used for applying power) so I don't need the key combinations although they may be useful for others obviously :)

    Thanks though, it is good to have an idea of what I should be doing.
     
  6. Crosstie

    Crosstie Well-Known Member

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    Actually, I didn't know that. Thanks for the tip. I must admit I have been using the AFB like the OP. I adjust it to slow the train, then just before reaching the station, I put it to zero and use the train brake to stop. If this is incorrect, I'll try doing it the proper way as described by HaibaraHariko.
     
  7. davidh0501

    davidh0501 Well-Known Member

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    I just leave it at the line speed and juggle the brakes.
    Whether thats prototypical I have no idea.
     
  8. conniethunder

    conniethunder Active Member

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    Thanks to the OP for what I too was wondering.
    AFB is great for 'cruising' with heavy goods, but commuter runs always baffled me when it came to stopping.
    I too will try leaving AFB set and reducing throttle/using brakes. :)
    Thanks HaibaraHariko
     
  9. OpenMinded

    OpenMinded Active Member

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    I think the way you are supposed to use the AFB is pretty much dependant in what type loco you are, what kind of train you have at the back, what Stretch of track you are at and in what country you are. Austria and Swiss are much more restrictive on the AFB use then DB in Germany, no idea about other countries.

    Technically there shouldn’t be a problem using the AFB to hold your speed, as long as you don’t have liquid cargo at the back in tanker Waggons, are on steep gradients, your train is on G (not quite sure on this one, though) or, and I think this is what you are referring to (?), it is not economical (ie you climb a hill, loose speed but would be able to build it up again without power when you drive down the hill on the other side, the AFB would unnecessarily burn energy in this example), hence you would only use the AFB as a „safeguard“.

    Braking is a different beast. AFB on its own (if not under LZB guidance) will not guarantee braking in the required braking curves, hence you should do it yourself. Braking by 10kmh or 20kmh is no problem, AFB can do it easily, the question is, is it beneficial. Usually you know the speed restriction is coming and start your brake process much earlier. This way is usually more economical and also more comfortable for your passengers.

    Never use the AFB to stop your train. Not even under LZB guidance. You should always stay before your braking curve.
     
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  10. FD1003

    FD1003 Well-Known Member

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    Completely agree, there are situations where using AFB as cruise control is completely fine, but generally you will do a better job if you do it yourself (I.e. on the avoiding line in BRD there are some up and downs, and if you just let AFB to its thing it will just end up accelerating and braking, which is quite inefficient, it would make more sense to let the speed drop as you go uphill and regain a bit of speed while going downhill).

    In other cases, like for example in Rapid Transit where there is a never ending 120 km/h flat section without too many stops it's not a problem just letting AFB hold your speed.

    I also usually use Tempomat more frequently (but again on BRD it tends to do a lot of little useless acceleration/braking thing instead of just coasting, so I usually switch it on, and then switch it off and coast if there is a small downhill section).

    That's why I said that human intervention is better, the driver knows more than AFB/PZB, it's a different story for LZB or ETCS, which has informations about the line km ahead and gradients. Unless the conditions are perfect AFB it will not do the best/most efficient/more comfortable for passenger action, and that's why, AFAIK it's not used extensively.
     
    Last edited: Sep 19, 2021
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