NHTSA Tracking Braking Loss on Prius Hybrids

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

  1. brad_rules_man

    brad_rules_man Hybrid electric revolutionizer

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    You don't really loose braking. If you REALLY needed to stop and were applying enough force because of a situation where you were STOPPING and not just slowing down, then your friction brakes would already be engaged. What you guys are feeling is when you are slowing down and loose 1 of the 2 wheels braking with regeneration.

    I admit, it makes your heart skip a beat, but it's absolutely positively nothing new. It's just slightly more noticeable on the gen 3 because it has more efficient regenerative braking. You will notice the same thing on any electric car with regenerative brakes, you will notice it on the Volt. It's just how it is.

    The only thing Toyota could do is change the behavior of the regenerative brakes, or the friction brakes which would undoubtedly result in a loss in efficiency.
     
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  2. Rokeby

    Rokeby Member

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    Although it is little mentioned, the Prius is a "High Performance"
    vehicle. I'm not talking back breaking acceleration, white knuckle
    handling, or eye popping braking. I'm talking the highest out-of-the-
    showroom fuel efficiency and MPGs. But, like back in the day, high
    performance comes with its share of special conditions.

    To realize the potential of the special equipment in a Prius, you have
    to adopt a high performance mindset. In the Prius, part of the high
    performance mindset is to slow down and pay attention. Not just to
    whats going on under the hood, but by sharpened awareness of
    what's going on outside, on the road. To get the most of the HSD
    you need distance ahead of you to adjust your speed whether to hit
    various "sweet spots" or to try to time a glide up to stops. Driving
    with your hood up against the car in front's bumper is counter
    productive. Driving with a little extra in front is also driving safely.

    An essential part of the high performance package is regenerative
    braking, "regen," capturing energy when the car is slowing down
    that would otherwise be lost foever in the form of heat. To get the
    high FE performance in a Prius, there has to be regen. Maybe new
    driver's didn't know this. Maybe they want a Prius to act just like a
    non-hybrid. If so they have unrealistic expectations. With the Prius'
    high FE performance comes regen and its little oddities and
    quirkiness.

    Back-in-the day, go-fast high performance meant all the subtlety of
    a football linebacker. Today's high performance means the
    smoothness, subtlety, and grace of a ballet dancer. Getting to know
    how a Prius operates around the regen dropout at about 8 MPH, and
    learning to adapt your driving to accomodate any road surface
    caused regen dropout is also part of learning the newest dance in
    town.

    It is truely unfortunate that this discussion is being conducted in an
    atmosphere of contention. Rather than bickering like children;
    "It is!"
    "It isn't!"
    "IT IS!"
    "IT ISN'T!"
    we ought to be dicussiong how to identify potential regen dropout
    situations and conditions and how to minimize their impact, if any,
    on our driving.

    There ought to be some learning happening here, instead of this
    food fight. :mad:
     
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  3. moresee11

    moresee11 New Member

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    here is my two cents, I have experienced this when I hit bumps while braking, it is not a failure in my mind since what is happening is the loss of regenerative braking. Additional brake pedal pressure should engage the friction brakes The loss of brake control sensation is probably most frightening at low speeds since you are expecting to stop then suddenly a loss of brake. However the Prius engineers can decide to tune the regenerative brake system to be only active above a certain MPH. This of course will hurt your MPG if do alot of stop and go driving. I would rather lose a few MPG and then to worry about my stopping distance over rough roads. As always defensive driving is always the best bet.
     
  4. Rhino

    Rhino New Member

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    I am no Toyota fan but I tend to agree now. You have people like hydrogenistheanswer posting telling everyone to complain and have disinformation like letting up on the brakes. Then they disappear and never post again.
     
  5. fuzzy1

    fuzzy1 Senior Member

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    Could PGPRIUS be referring to a 'washboard' surface, not to hydroplaning conditions?
     
  6. RobertMBecker

    RobertMBecker New Member

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    Silliness. This isn't about perception, evidence, engineering knowledge, or driver capability - and it's clearly not about money or a campaign against Toyota, albeit, considering you sell Toyotas for a living, I can understand your sensitivity to the issue.

    Let's hope the Toyota technicians take a closer look, find a potential resolution, if there is one, and ease the anxieties of those who are trying to get to the bottom of the issue. I'm pretty confident that those who have experienced the issue and have received no resolution are pretty happy that something may be done about it. :)
     
  7. DeadPhish

    DeadPhish Senior Member

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    Your prior statements belie your milder words here. You don't like the feel of your vehicle and you complained. They said it's perfectly normal and you got a burr in your saddle and now you don't want your vehicle. You stated that you looked at selling it but the loss would be too much. What you want is for Toyota to stroke you and give you back your money so that you don't have to keep the car and so that you don't have to take a loss. It's about money.

    No one is guaranteed to like every purchase they make, cars included. But you live with your decisions. You simply made a bad decision because you didn't do enough investigation to determine if you'd like the 'feel' of the vehicle in every case imaginable. However categorically stating that there is a safety issue when there is no evidence or data to support your position is simply your opinion. 10 yrs of data and evidence over hundreds of millions of miles point in exactly the opposite direction.

    Why anyone should pay attention to you and your sensitive driving needs is what galls me the most. You simply aren't familiar with the vehicle, you made a mistake, the vehicle is not for you. So sell it and move on. Take personal responsibility for making a bad personal decision. But NO you want to be made whole, your own words, you don't want to take a financial loss. Money.
     
  8. john1701a

    john1701a Prius Guru

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    Here's a new twist adding fuel to the growing fire of deception:

    full article here

    In reality, if you don't react at all braking resumes as before a split-second later, the friction brakes slow at a higher rate, and there is no need to press harder.
    .
     
  9. jim256

    jim256 Member

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    removed my post on second thought--this thread no longer seems to be for the exchange of info or education.
     
  10. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I don't have 2010 Prius so I don't know the difference in behavior. This is just food for discussion.

    2010 Prius switched the rear brakes from drum to disc.

    1) The contact gap (distance) between the shoe/pad to the drum/rotor may be different.
    2) Drum brakes are sealed and therefore the friction should be more predictable. Disc brake rotor can rust and calcualting the friction (especially the initial contact) will be more difficult.
     
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  11. john1701a

    john1701a Prius Guru

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    I had both and can most definitely say the effect is more pronounced with the older model. With that one, I did feel it from time to time, so it happened more often too.

    In the 2010, it took me riding the brakes over a set of train tracks before even noticing the brief pulse.
    .
     
  12. john1701a

    john1701a Prius Guru

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    That's just here. Other countries have had discs in back for years.

    Also, the 2010 captures more with regen, in part due to the larger electric motor.
    .
     
  13. usbseawolf2000

    usbseawolf2000 HSD PhD

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    John,

    Great points. If it was improved in 2010, I guess it is just a matter of new owner issue. I do agree that the manual should mention about it, if it has not already.

    New owners need to realize that the brake is a friction-electric hybrid. The transition between the two can be sometimes felt like when the gas engine shut off.

    My opinion is... if you want a more refined / upscaled hybrid, get a Lexus (also at an expense of less MPG).

    I also think Toyota can improve it... maybe come up with a new compound for the rotor? Aluminum disc rotor... lighter, dissipate heat faster and it does not rust.
     
  14. dogfriend

    dogfriend Human - Animal Hybrid

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    Hardness and strength would be lower than steel. Even with hard anodize layer, it would probably wear much faster than a steel rotor. Also, aluminum does corrode given the right environment - chlorides (road salt, seawater mist) are bad for aluminum.
     
  15. Lewie

    Lewie Junior Member

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    Just out of curiosity, what needs to be improved with the disk brake system? Disk brakes with steel rotors are rather common these days, what Prius requirement would call for a different rotor? Wouldn't aluminum be more susceptible to warping too?

    I'd think that the only way to improve the existing system would be to shorten the time interval between the dropout of regenerative braking and the friction brakes kicking in. But even this lag is not a big thing in my book. I even navigated my favorite bump today a few times at different speeds and different stopping rates to get a better understanding of the process. During a hard stop you don't notice the transition at all, the frictions are already in play. The short delay during a moderate stop seems to be less than 1/2 second and doesn't significantly affect the stopping distance, in my opinion. Further, my favorite bump, besides being my favorite, is the only bump I've found so far that triggers the switch. Even bumping across railroad tracks doesn't trigger it for me. This whole topic is a tempest in a teapot! We'd all be frosted if Toyota was forced to reduce the efficiency of the regenerative braking system to make a few people feel better in an edge case! Of course, accident statistics will quickly show if there is a real safety issue here, and I'm sure that Toyota will be on the problem like white on rice if there is.
     
  16. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I thought there was an issue with the brakes grabbing too much and this going over a bump forward (at slow speed with regen) does not provide enough brakes.

    This leads me to believe this may be a calibration issue. Going along that line of thought, a frictional surface that gives consistant braking force would make it no-brainer for the programming.

    John confirmed that the friction brake delay was improved (after regen stops abruptly). I also think the delay should be cut down further if possible. I do remember reading from 2010 new car feature (NCF) document that the function of traction control was moved from ECU to the ABS. The idea was to apply friction brakes to allow tires to spin yet control the RPM to protect MG1.

    Could this change of decoupling the integration of the powertrain and traction control (as well as regen brake) introduced a new scenario? I am not perfectly clear on the change so therefore putting this out here to discuss.
     
  17. john1701a

    john1701a Prius Guru

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    Remember the credibility attack on Prius when the newest generation became available, 6 years ago?

    We were absolutely inundated with claims of MPG disappointment, none of which took the effects of winter efficiency into account. They just relentlessly slammed the new Prius as a failure, not delivering as promised. It was sickening to witness such undermining take place. It was blatant greenwashing. But back then, few were aware of what factors affected MPG.

    Then the warm weather finally arrived... after 6 months of Prius attacks. MPG shot way up, vindicating our explanations of seasonal effect. All of those who had made those terrible accusations vanished. None offered an apology for misleading consumers so much. Annual MPG averages revealed the efficiency was indeed an improvement over the previous generation.

    We'll never know the extent of the damage those attacks caused... just like the ones taking place now.
    .
     
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  18. wfolta

    wfolta Active Member

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    It is most likely ALL ABOUT perception. Your perception.

    I'll say it again, I've driven almost 7000 miles now and have never even once experienced any scary braking. I live in a city and commute to the suburbs, so every single day I drive in all kinds of conditions from interstates to stoplight-every-block city, and I've never once experienced the horrible, heart-stopping danger you complain so loudly about.

    How likely is it that I have not experienced the conditions you drive in? Absolutely, spectacularly unlikely. So, to be honest, I have probably experienced what you have multiple times, and it hasn't even registered.

    So it boils down to either: 1) Your perceptions, 2) Your Prius is defective, 3) An incomprehensibly unlikely possibility that I've simply not hit the right conditions, or 4) You have bad driving habits that create particular circumstances.

    I think choice #1 is the most likely, though #4 seems increasingly likely based on your rants.
     
  19. rachaelseven

    rachaelseven New Member

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    If there were one or two loud complainers, then perhaps you would have a point. But given the large number of people that have experienced this, I think you are (perhaps without realizing) making an unfounded personal attack here. I have definitely experienced this same thing and can recreate it at will. It does not even take a bump - a manhole cover or drain grate will do it quite easily - and it is extremely heart stopping, nerve wracking, and down right unusual. And yes, it is unusual even for cars with ABS - I've driven plenty of them among the hundreds of cars I've driven in my 24 years of licensed driving. So of your 4 choices there, I think #2 is much more likely - although I would not say defect so much as perhaps a difference in behavior among different cars.
     
  20. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Sounds like a suggestion for a three element poll:

    • 2010 Prius - not experienced
    • 2010 Prius - about once per month
    • 2010 Prius - about once per week
    • 2010 Prius - about once per day
    • 2010 Prius - scary, safety issue
    • 2010 Prius - can live with it
    • 2010 Prius - no big deal, not a risk
    • 2004-09 Prius - not experienced
    • 2004-09 Prius - about once per month
    • 2004-09 Prius - about once per week
    • 2004-09 Prius - about once per day
    • 2004-09 Prius - scary, safety issue
    • 2004-09 Prius - can live with it
    • 2004-09 Prius - no big deal, not a risk
    The elements are:

    1. 2010 Prius vs 2004-09 Prius
    2. Frequency: never, monthly, weekly, daily
    3. Risk: scary, can live with it, not a risk
    Can you think of anything else to include? Run it for a couple of weeks?

    Bob Wilson
     
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