NHTSA Tracking Braking Loss on Prius Hybrids

Discussion in 'Gen 3 Prius Main Forum' started by RobertMBecker, Dec 24, 2009.

  1. gail54

    gail54 Gail

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    NHTSA Braking Loss-opinions please-supposed to purchase december 31

    Hi

    I am sorry for everyone having this braking issue.

    For those of you experiencing this problem - Can you please tell
    me if you had not yet purchased the car would you still do so?

    & would you be able to tell me the build date on your cars that have experienced this issue?

    I have not yet purchased - I was supposed to purchase this
    Thursday - I have everything in order to do so.

    Thank you for your help!
     
  2. bighouse

    bighouse Active Member

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    I would still purchase. I have no intention of getting rid of my Prius. I love it but do drive it with that braking issue in mind and if/when it happens again I'm better prepared for it and it won't come as a shock to me.

    My car was built in July of 09 and it's a IV/SR.
     
  3. usbseawolf2000

    usbseawolf2000 HSD PhD

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    If you feel this behavior is dangerous, please follow Toyota recommended tire pressure.

    Over-inflating the tire would just make the situation worse.
     
  4. nooaah

    nooaah New Member

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    FWIW this happens to me only during regenerative braking/coasting, not when I have my foot on the brake pedal itself.
     
  5. Darwood

    Darwood Senior Member

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    True. Better milage comes at the expense of traction. I still prefer to keep my tires a bit overinflated for mileage reasons, as the brake thing doesn't bother my one iota.

    The brake issue is an overblown/trumped up concern, much like the concern over the lack of noise from the car creating "danger" for blind pedestrians.
     
  6. risingsun

    risingsun seeker of the way

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    Gail,

    I have experienced it once or twice on ours with a build date of 10/09. If you know there is a chance of this occuring, it will not take you by surprise and cause panic when it occurs. Just press down a bit harder on the brake pedal and everything comes to a stop as it should. If Toyota makes a change to resolve the problem or lessen the liklihood of this occuring, then I will accept the update, but to me it is not a reason to avoid purchasing the car or to be disappointed with it after purchase.

    Just my 2 cents...
     
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  7. gail54

    gail54 Gail

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    Thank you very much . Your right about knowing what might happen.
     
  8. DetPrius

    DetPrius Active Member

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    Gail54, I would still buy knowing about this issue. I don't know the build date offhand but I took delivery on 7/8/09.

    Bighouse, I share your attitude on this issue completely. I love the car, enjoy every minute I get to drive it, would buy another, and won't get rid of it because of this issue. I do want to support what Toyota has done with the technology in this car and really want to see this get addressed. Toyota does not need something like this to become an issue at this point in time.

    I have a rhetorical question for those that don't see this as a safety issue. If this same thing was happening on a GM, Ford, or Chrysler product, what would you be saying? I for one would say the same thing I am saying about it on a Toyota and that is that any time the brakes become unpredictable, due to the car and not nature such as ice, there is an issue and it needs to be looked at.

    I cannot believe that with Toyota's engineering prowess, they can't solve this without sacrificing the regen braking system in any way.
     
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  9. Darwood

    Darwood Senior Member

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    They could change it so the regenerative breaking ends at 15 or 20 MPH instead of 11. But I for one don't want that to happen. If you floor the brakes in an emergency, it locks up the mechanical brakes. If you are lightly braking (in order to produce the effect) you are not going to hit something via the extra foot of braking distance, else you'd be slamming the brakes to begin with.
     
  10. bighouse

    bighouse Active Member

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    I would not presume to know what they can do to fix it. As an architect I'm smart enough to know I'm outside my discipline and will let those who know mechanical engineering figure out what's really wrong and figure out the fix; Just as in my industry regarding engineering, I'd defer to the right engineers to figure that out.

    But, engineering aside, from a performance/user experience angle what they do need to do is make the transition from regen braking to friction braking totally seamless and invisible and it should NEVER result in loss of braking as sometimes currently experienced by the user.

    I do not feel, however, that a fix need NOT result in lesser FE as some seem to imply.
     
  11. Darwood

    Darwood Senior Member

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    That would be... an EV!
     
  12. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    there is a few threads that basically discuss the same issue,

    http://priuschat.com/forums/gen-iii.../73946-perfect-storm-doubt-5.html#post1029402

    as far as not buying a car due to an issue perceived by the user to be dangerous enough to cause an accident when at the same time there are a quarter million of them on the road today and we have yet to verify any accidents caused by this issue tells me that we might simply be covering all our bases to see if a possibly better option or adjustment is available which means there is nothing really wrong with the vehicle.

    now this investigation will hopefully shed more light on the subject and that is a good thing. but to not buy the Pri based on what might happen if you were to get into a low speed accident is simply beyond my comprehension considering all the other upsides to the car
     
  13. yardman 49

    yardman 49 Active Member

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    Not to muddy the waters here, but FWIW, on my new 2010 Toyota Sienna minivan, for the first several hundred miles it would seem to "speed up" whenever I took my foot off the accelerator and gently applied the brakes. I know that it was not really acceleration, but like the Prius, a temporary "loss of deceleration". Like those that have experienced this on the Prius, it was a little un-nerving at first.

    Now either the van has finally broken in, or maybe I just have grown so used to it so I don't notice it any longer. I'm really mistified as to what caused this on the minivan, since it is not a hybrid. It would happen almost constantly with light braking on perfect road surfaces, so it would not have been ABS.

    Maybe it was just a loss of drag from the automatic transmission as it changed gearing, or came out of overdrive? Never did figure it out. Just plain weird. :confused:
     
  14. KieferSkunk

    KieferSkunk Technogeek

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    Yanno, I'm really surprised that NOBODY in this thread has thought to ask whether someone in a Gen-3 Prius experiencing this issue has heard any unusual noises coming from the front of the car or seen any lights flashing on dashboard when they experience this temporary loss of braking. I've owned a 2005 Gen-2 and currently own a 2007 Gen-2, and in BOTH cars, whenever this has happened to me, I can usually hear a whirring noise from the brake system and often also see the Traction Control light flash once or twice - same behavior as when the car is genuinely slipping on slick ground or ice. (If the car is also slipping sideways, then it starts beeping, but it will just flash the light without beeping if I'm just slipping straight forward.)

    If the Gen-3 Prius has any similar indicator for "loss of traction", does that ever light up when you're feeling the car surge? I won't deny the possibility that the issue is perhaps worse in a Gen-3 than a Gen-2, but I'd be willing to bet it's the same issue, and if so, it's just a quirk of the Prius's traction control and something drivers should get used to.

    And there are good technical reasons for the traction control working the way it does in the Prius, compared to most other cars. The Power Split Device, if you recall, is about the size of a Coke can, and that's what drives the entire car. Without traction control, you'd have a lot of cases where bumps and slips could put way too much torque on the gears in the PSD, and you'd run the risk of damaging the PSD any time you slipped on a train track. The TC has to be as aggressive as it is to protect the relatively delicate transmission - remember that most other cars have much larger, heavier transmissions that can handle a much greater degree of force without risk of damage.

    I'm reasonably sure that about the most Toyota could do to address this issue would be to adjust the timings a little bit, but short of completely redesigning core components of the hybrid system, I'm not sure there's much they can do. And to my knowledge, the most this issue has ever caused has been a small amount of discomfort or panic on the part of people who weren't expecting it.

    For the record, my 2005 Prius engaged its traction control a lot more often than my 2007 does. Braking experience was about the same in both cars, but the 2005 tended to cut acceleration more often when it thought the tires were slipping, like on painted lines at an intersection when it's raining. Both cars do it, though, and as I understand it, it's for the same reasons as I explained above.

    Does this help at all?
     
  15. sj_ted

    sj_ted New Member

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    I've experienced this too. The point that I didn't see mentioned is this. If this .5 sec lapse occurs at the transition between regen and friction brakes, then, if it was normal, it would happen all the time. But the fact that it happens when hitting bumps or other challenging road conditions does point to a defect of some kind. Why would a braking lapse need to occur with a bump and not a normal road condition. I love my Prius, but Toyota needs to address this.
     
  16. KieferSkunk

    KieferSkunk Technogeek

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    As several people mentioned, if the system thinks you've lost traction for any reason, the traction control system engages both to ensure that you KEEP traction and to prevent damage to critical parts in the system. It might be more aggressive than it really needs to be, but I don't see it as a defect - just a quirk. This issue has never caused me or anyone I know to be in danger of crashing into anyone.
     
  17. spwolf

    spwolf Senior Member

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    thats like saying why does the VSC engages only when you lose traction and not otherwise and hence it could be an issue and should be fixed ;-).
     
  18. efusco

    efusco Moderator Emeritus
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    I don't think it was "fair enough" at all, where was the explaination of what occurs, the test drive by a professional who could experience it and make a remark on to the safety or lack thereof?

    But I do agree with the last part, I think Toyota should attempt to make the regen to friction transition more smooth. I don't want people to decide not to buy a Prius b/c they experience this on a test drive or read a bias article and become afraid that the car is somehow unsafe. Whether it is a safety issue or not is almost irrelevant b/c if it is perceived to be a safety issue people will be less likely to buy.

    I think what the whole thing boils down to is a trade-off b/w maximizing regenerative braking sensitivity of the transition (ie, what is the threshold to jump from regen to friction--higher threshold means delay in emergency braking, lower threshold means a smaller bump will kick off regen), and finally the comfort of the driver. Right now I think safety is actually at a maximum which is why such a minor bump kicks out regen and why everyone feels that transition so much. But people will trade off that margin of safety for the sensation of a smoother transition.
     
  19. Tom183

    Tom183 New Member

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    As a new Prius owner, I hope Toyota comes up with a fix but don't see it as a true safety issue since any serious braking maneuver would be unaffected.

    Part of the "problem" is similar to ABS - when you feel it happen, you need to push harder. Often (esp. for someone new), the instinctive reaction is to pull away.
     
  20. efusco

    efusco Moderator Emeritus
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    I'm not saying Toyota should ignore it, but I completely disagree with the suggestion that there is a safety issue. Those are two different things. And the transition takes nowhere near 2 seconds, or even one second. It's a split second and resolves with a slight increase in brake pressure.
    I just don't want to see a situation that is simply unfamiliar and frightening construed as dangerous or unsafe. I would like to see Toyota fix it in any case b/c I don't want anyone turned off by the unfamiliar sensation.

    Not agreeing and trying to educate are very different things. And when people claim that it is a huge safety issue without facts and want/expect Toyota to buy their car back and go to independent "news" sources to publish their vendetta and then take that "source" to a legitimate news agency and propagate their fear and vendetta there then I do have an issue with that. An unfamiliar sensation does NOT equate to a safety issue.

    Report away to NHTSA--I think that's great. I'd love to see this investigated to determine if there is a safety issue. I don't feel there is, but perhaps I'm wrong...but let's let the facts come forward.
     
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