Understanding your braking system

Discussion in 'Gen 3 Prius Main Forum' started by hobbit, Feb 3, 2010.

  1. hobbit

    hobbit Senior Member

    Joined:
    Mar 23, 2005
    4,089
    457
    0
    Location:
    Bahstahn
    Vehicle:
    2004 Prius
    Model:
    N/A
    I really hate to start yet another thread about Prius brakes,
    but I need to call specific attention to a few clarifying points.
    The babble has risen to unmanageable levels and there are far too
    many other threads to keep track of, but I see a common trend across
    pretty much all the ones on braking [here and on other forums].
    .
    Integrated regenerative and hydraulic braking systems are unique,
    and still a young science. To Toyota's credit they've done a
    really nice integration job with the Prius in general, with almost
    seamless balancing of the braking force provided by the separate
    parts of the system. It requires tight computer communication,
    and does its job in very short timeframes under wildly varying
    conditions and high mechanical stress conditions. There are
    certain unavoidable limits on batteries and inverters that
    restrict regenerative braking to a certain "operating envelope",
    which the car will not let the driver exceed. Such systems are
    bound to have a few quirks in their early stages, and trust me,
    even the 2010 Prius is an "early stage" for a lot of this science.
    It's not perfect and may never be. Maybe the 2010 system is more
    squirrely than the second-gen or maybe it isn't -- I don't know, all
    I know is that it's fairly different but the principles of operation
    AND LIMITING FACTORS are exactly the same.
    .
    Fact is, the braking "sag" over bumps is a quirk that has existed
    from the 2004 Prius right on down. The "old guard" owners know all
    about it and know how to respond and in some cases even prevent it
    from happening with sufficiently skillful driving. I see that
    virtually all of the recent complaints and new threads on the topic
    have come from NEW OWNERS, who have not researched what has, uh,
    gone before.
    .
    Therefore I would urge all new owners to go read my detailed
    discussion on the braking system -- you can skip the techie stuff but the
    operational observations are near the end, and have been well-documented
    even before that article was written in *2005*. Learn your vehicle and
    how to control it. It is generically unsafe in any car to try and do
    all your braking right at the end of a stop, and much more efficient in
    a regenerative system to spread it long and slow over as much distance
    as you can predict and make available. The shift between regenerative
    and hydraulic is not "acceleration" as so many confused posters have
    called it, it is simply a momentary diminishment of overall braking
    force *per given pedal demand* as the system compensates for some
    limits being exceeded. One is battery current; another is low speed
    under which regen isn't practical anymore.
    .
    New owners have also probably not gone off and read all about the
    "B" shift setting, either, still believing some dreck from their
    dealers about how it's for "charging your battery". Well, that is
    partially right in that "B" does tend to increase regen current,
    but also throws away a lot more energy elsewhere. However, it also
    offers a way to partially make up for regen loss. If you get the
    "sag" over a bump and have already compensated for it with your foot
    but want some of your regen back on that stop, whack the shifter down
    into "B". You will then feel that you need *less* pedal force to
    decelerate at the same rate, as the car sort of falls on its face.
    You'll hear the engine spin a bit, you'll see your HSI slam toward
    the left, and after the car gets down to around 5 MPH you can just
    go back into D since you're on full hydraulics at that point anyway.
    [Don't leave it in B or your engine might keep idling if was on.]
    .
    That's it. Your best means of compensating for regen loss is to
    first expect it, and then try to get a little bit of it back with
    "B" if you have time. Whether or not you GIVE yourself that leisure
    time to decide and act is up to you, and that's where I'd put my
    energy rather than whining about the NHTSA. This has been a solved
    problem for six years.
    .
    It was not really an issue on the first-gen Prius because that system
    always brings in about half hydraulics anyway giving much less ground
    to cover in a "transition". One of the nicest aspects of the PII and
    the PIII is that it tries its best to stay *completely* off the
    energy-squandering hydraulics until you need them. The rest is up
    to the loose nut behind the wheel.
    .
    _H*
     
    29 people like this.
  2. KK6PD

    KK6PD _ . _ . / _ _ . _

    Joined:
    Mar 24, 2008
    4,003
    934
    118
    Location:
    Los Angeles Foothills
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Yep!!!
    Nicely summed up!!!
     
  3. mitch672

    mitch672 Technology Geek

    Joined:
    Mar 10, 2004
    1,077
    197
    0
    Location:
    Randolph, MA
    Vehicle:
    Other Electric Vehicle
    Model:
    N/A
    Yes, hobbit, you are exactly correct, and I also posted a short version of what you said in the "Toyota may recall the 2010 Prius" thread. Most new owners are not really aware of the unique differences of the braking systems between the Prius and EVERY other traditional car. Thanks for the eloquent explantion for the newbies.

    Mitch
     
  4. tpfun

    tpfun New Member

    Joined:
    Oct 4, 2009
    791
    53
    1
    Location:
    Oh Never Mind,CA
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
  5. xpcman

    xpcman Senior Member

    Joined:
    Jun 11, 2009
    1,302
    292
    0
    Location:
    California - SF Bay area
    Vehicle:
    2008 Prius
    I own both a 2008 and 2010 Prius. I would have to say the the braking problem in the 2010 is MUCH more pronounced. If there is no problem then why did Toyota admit that there IS a problem (read the above USATODAY story). We have to stop being "fanboys" for Toyota and be objective. I expect the car to stop when I need it to stop not when it wants to stop.
     
    1 person likes this.
  6. GrumpyCabbie

    GrumpyCabbie Senior Member

    Joined:
    Dec 14, 2009
    6,723
    2,117
    45
    Location:
    North Yorkshire, UK
    Vehicle:
    2010 Prius
    Model:
    III
    Maybe there is a problem with SOME cars but not all. That is why your brakes appear to be safe and seamless and others appear to have issues.
     
  7. PaJa

    PaJa Senior member

    Joined:
    Sep 3, 2009
    678
    113
    92
    Location:
    Czech republic
    Vehicle:
    2017 Prius
    Model:
    N/A
    It is fresh news based on AP agency. I don't know about any other reference/source stating the same.
     
  8. The Electric Me

    The Electric Me Go Speed Go!

    Joined:
    May 22, 2009
    9,083
    5,768
    0
    Location:
    Undisclosed Location
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A

    Horrific Blunder. Absolutley terrible news.

    How could Toyota recognize that there were design problems to the extent that they "secretly" correct the design for models sold since late January BUT not tell owners that had purchased previously?!!!

    I guess I just need to step back and let the news unfold but this is HUGE.

    I think the public can be forgiving and understanding about a gas pedal that Toyota openly recalls and repairs A.S.A.P. but I don't know how it's going to sit with most of the public if it is revealed Toyota knew about a problem with the design of Prius Brakes, actually made changes to the model being produced in January but did NOT mention it to owners and buyers that purchased earlier.

    You just don't do that. PERIOD.

    Still investigating how to inform people who had bought them earlier? Are you kidding me? That's total BS.

    Note to Toyota: You know how you inform people who bought them earlier? You inform them! You inform them any way and every way you can!

    What was Toyota thinking? Did they hope they could just quietly "fix" the problem and then "moving forward" complaints would decrease and they could just ignore the fact that everyone that purchased a Prius before January had a "design problem"?

    I've been optimistic. I really believed Toyota would emerge. I still want to hear more about how this happened and what Toyota intended. But this is horrible news.

    Makes you kind of wonder about the timing of the Prius price increase. Wonder if Toyota wanted to secretly correct the design and make new owners pay the price as well.

    Tell me it isn't so Toyota, Tell me it isn't so!
     
  9. PaJa

    PaJa Senior member

    Joined:
    Sep 3, 2009
    678
    113
    92
    Location:
    Czech republic
    Vehicle:
    2017 Prius
    Model:
    N/A
    Electric,
    stay calm - you are very safe with your current, non-prius, non-hybrid car :)
    Why are you waiting for Prius if you have so bad feeling about TMC? Choose the other car, other manfacturer which will suit to you.
    I'm sorry for my reply, but your posts in each other thread look like as from 'Chevy' PR agency.
     
  10. GrumpyCabbie

    GrumpyCabbie Senior Member

    Joined:
    Dec 14, 2009
    6,723
    2,117
    45
    Location:
    North Yorkshire, UK
    Vehicle:
    2010 Prius
    Model:
    III
    It would appear it is so!

    There was a post on this forum recently from a guy in Japan who said that the latest January models in Japan had been given a software upgrade to solve the braking problem.

    One wonders why that wasn't made available to all previous owners. I use my car for my business and if it gets pulled off road for safety reasons I'll be not very happy at all (and that's an understatement).

    I am hearing the words class action :mad:
     
  11. The Electric Me

    The Electric Me Go Speed Go!

    Joined:
    May 22, 2009
    9,083
    5,768
    0
    Location:
    Undisclosed Location
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Bull! Pure Bull! I've been in here most of the day defending Toyota. .....and I still will wait for more details...BUT if this new story is valid and Toyota did make design changes to The Prius Brake System in the 2010 and NOT inform previous purchasers...then IMO Toyota blew it.

    I will await further details and clarification but as the story stands now, there is no way I can think it isn't anything but horrible.

    Yeh, if this turns out to be true? I'm going to have a very bad feeling about Toyota.
     
  12. The Electric Me

    The Electric Me Go Speed Go!

    Joined:
    May 22, 2009
    9,083
    5,768
    0
    Location:
    Undisclosed Location
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Hmm...I guess that's why we all have to wait for more details. Why would it be referred to as a "design change" if it was a software update?

    And if it is just a software update why the hesitation about informing previous purchasers?
     
  13. PaJa

    PaJa Senior member

    Joined:
    Sep 3, 2009
    678
    113
    92
    Location:
    Czech republic
    Vehicle:
    2017 Prius
    Model:
    N/A
    The software is designed as well.
    But, for now, there is a just one sentence from spokewomen without any other details. Everybody who have an experience with journalists or spokepersons will know what I mean.....:)
     
  14. cwerdna

    cwerdna Senior Member

    Joined:
    Sep 4, 2005
    12,544
    2,113
    1
    Location:
    SF Bay Area, CA
    Vehicle:
    2006 Prius
    FWIW, design changes, improvements, changes to parts and firmware updates happen to cars (not just Toyotas), all the time. There isn't necessarily any notification nor obligation to do anything for previous owners, let alone notify them.

    Sometimes, they're mentioned in TSBs and if an owner comes in and cites the problem and/or shows/mentions the TSB, the dealer will fix it/make change, depending on the nature of what it is.

    That said, I don't off the top of my head know of any similar case relating to braking relating firmware, esp. a "design problem". (One can split hairs as to the definition of that.)

    Example:
    Here's one that I did have done to my 02 Maxima: http://maxima.theowensfamily.com/tsb/NTB03-023.pdf. It was a 255 hp car that was a virtual rocket ship, but I recall two problems and don't remember if this was the fix one or both issues.

    One was pinging even w/the recommended premium gas. The other was a very intermittent and almost impossible to repro step on the gas and nothing seems to happen, as if your foot slipped off the pedal. Let go, press it again and it accelerates. I think I probably hit it <10x before I had the TSB done.

    Nissan never notified me nor anyone of this TSB. I only knew about it from being a maxima.org user.
     
    1 person likes this.
  15. Rhino

    Rhino New Member

    Joined:
    Oct 5, 2009
    460
    40
    0
    Location:
    U.S.A.
    Vehicle:
    2010 Prius
    Model:
    III
    I totally agree with you on this one but I would also like to defend the average driver.

    1. The fact that people are not getting into accidents even with this braking characteristic is testament that just about all of us leave enough of a safety margin when stopping just about all of the time. Let me say this again - we are all doing it already and that's why we haven't crashed.

    2. People are not doing all of their braking at the end of a stop because they rely on (2.1) a safety margin in distance, see point 1 above and (2.2) excess capacity in the brakes. Regarding excess braking capacity, people are not using all their braking power. They know that if something unexpected happens, they can stop even faster, by slamming on the brakes. Of course, when the brakes becomes momentarily unresponsive, you lose both the safety margin in distance and the safety margin in using additional braking force [during the momentary part. It comes back and is generally sufficient to stop the car in time since most people who experience it do not crash. The temporary feel of losing braking is what's causes people to be concerned. And rightly so. They don't know if it is the beginning of a slow decline (a bad problem going to get worse), a malfunction, or just normal. Silence on the part of the manufacturer until recently did not help.] (correction added)

    3. The reason why this appears to be happening at the end, near a stop, is not because of operator error. Most sensible people have bled off all the excess speed before coming close to an intersection. This characteristic only happens at low speed. And low speed is encountered near the end. Once again, since we are all not crashing or running into intersections, we are being safe already.

    4. And, while I respectfully agree that all people should endeavor to know how the car works, this is not even in the manual.

    I love my Prius . . . still . . . but the luster has come off a bit.
     
    1 person likes this.
  16. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,210
    6,574
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Poor Hobbit wants to deal in facts, Chicken Little wants to scream the sky is falling. No one will hear our Hobbit.
     
  17. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
    18,059
    3,043
    7
    Location:
    Northern Michigan
    Vehicle:
    2006 Prius
    "BURN THE HOBBIT, I SAY!"

    ;)

    Tom
     
  18. spwolf

    spwolf Senior Member

    Joined:
    Sep 16, 2005
    3,156
    440
    0
    Location:
    Eastern Europe
    dont the brakes respond right away if you "slam" them?
     
  19. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
    18,059
    3,043
    7
    Location:
    Northern Michigan
    Vehicle:
    2006 Prius
    This post hits the nail on the head. At issue is whether a design change is a simple improvement or a safety fix. Toyota did not see this brake drop-out issue as a safety problem, or if they did, chose not to treat it as such. Not being a safety issue, the improvement was installed only on new cars, starting in January. Small running improvements are made all of the time.

    The real issue, then, is whether Toyota was remiss or sinister in not considering this as a safety issue.

    Tom
     
  20. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
    18,059
    3,043
    7
    Location:
    Northern Michigan
    Vehicle:
    2006 Prius
    Yes they do.

    Tom
     
Loading...