Data on "brake loss" (aka "sudden acceleration") after bump

Discussion in 'Gen 2 Prius Technical Discussion' started by 2009Prius, Apr 27, 2011.

  1. liskipper

    liskipper Member

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    I believe that you are absolutely correct in your observation. There is no loss of traction, just the fact that a bump will turn off regen. I have also noticed that regen will not cut in again until the car comes to a complete stop, or the brakes are released completely. Toyota continually claims that this is "normal ABS behavior". BS!
     
  2. 2k1Toaster

    2k1Toaster HID Guru

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    It is normal. Normal for a vehicle with 2 different types of brakes. 3 different types in some markets.

    If you want a "solution" shift to neutral before you decelerate. 100% friction braking, nothing to lag or switch over unless you actually lose traction.

    You can't have your cake and eat it too. Regen braking is what it is, and this is it. Come up with a different solution and more than likely there will be scenarios that doesn't "work" for either or are physically/technologically impossible to implement.
     
  3. jayman

    jayman Senior Member

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    I would agree with that except the FJ Cruiser has the same problem, and it doesn't have regen braking. It does have electric assist brakes, like the Prius

    Could be the nature of electric assist - as opposed to conventional vacuum assist - and the software algorithm all result in momentary reduction or even loss of braking
     
  4. moresee11

    moresee11 New Member

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    sorry did not notice that this was Gen II thread. I will hop over to the correct threads, but to answer your question- yes it is less than 5 mph, I was within 5 feet of the cross walk. and there no bumps or any reason for loss of traction. others think this is a feeling that I can't get use to but like I said this is the ABS kicking in releasing my brakes thinking that I am skidding. I reason I say ABS is that I feel and hear the cycling of my brakes by the ABS, the switchover does not make any rapid noises. This is not an every day occurrance so I know that this is not a mechanical issue. thanks for responding



     
  5. fuzzy1

    fuzzy1 Senior Member

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    I see two items here that don't match up with the event I am feeling, so yours is something different.

    The event I am describing is a transition from regeneration to pure friction braking that happens at 7 mph, not 'under 5'. It is a single release, with no ABS cycling.

    On some cars, including mine, this is not perfectly seamless, with the new friction braking force not perfectly matching the prior regen braking force. I notice it only some of the time, as a feeling of the brakes releasing. It is most noticeable on the smoothest dry pavement, and with the lightest braking.

    As braking force increases, the mismatch becomes a smaller fraction of the total force, so the difference becomes less perceptible. With moderate and hard braking, friction is already engaged, so there is no real transition.

    I don't regard this as a problem because it appears only with the lightest braking. Any time braking distance matters, the driver will be using harder braking, outside this mismatch zone. Drivers trying to use long light braking to stop just a foot from a pedestrian or other car are playing a dangerous game even with regular brakes.

    But again, your symptoms are describing something else.
     
  6. duffasaurus

    duffasaurus Senior Member

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    You say you feel and hear the cycling of your brakes, but I have driven many vehicles with ABS over the years and when ABS is actuated on a slippery surface; the cycling of the brakes is so rapid that it does not reduce your braking ability. Something does not make sense here. It seems that you are braking too late and not hard enough when approaching the cross walk?
     
  7. qbee42

    qbee42 My other car is a boat

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    ABS on the Prius does not feel like the old ABS, where there was a noticeable pulsing. Living where I do I frequently trigger ABS. The indicator light is the only indication.

    Tom
     
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