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The Perfect Stop?

Discussion in 'Gen 2 Prius Main Forum' started by Anonymous, Apr 21, 2005.

  1. Anonymous

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    When my dad was teaching me to drive he used an approach that stays with me till this day.
    "Any idiot can go fast and jam on the brakes. It takes a skillful driver to have such great control over the vehicle that a blindfolded passenger would not be able to tell when the car started and stopped." Rising to that challenge made me value a smooth ride.

    Every car I have owned, I have mastered the "perfect stop" but I am having a little trouble with my new Prius. The brakes seem a little grabby right at the end of the stop. Are there any techniques that could help me in my quest? I did get really close today, but I don't know exactly what I did. I didn't try shifting to neutral. That would be cheating anyhow.

    BTW, my son mastered the perfect Start/Stop with his Prism, Manual Transmission, when he learned to drive. Family traditions are wonderful.
     
    #1 Anonymous, Apr 21, 2005
  2. efusco

    efusco Moderator Emeritus
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    It takes some time, and there's always going to be a palpable transition at the drop from 8mph-7mph when the regen braking kickes out, but with time your foot will get used to the sensitivity of the braking and it'll probably be as smooth or smoother than anything you've driven before.
     
    #2 efusco, Apr 21, 2005
  3. gschoen

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    Try letting up on brake pressure as you come closer and closer to a stop, the goal at the final stop to have just enough pressure on the brake to keep from moving. This helps get rid of that final jerk (on all cars). Once completely stopped, I mash the brake to prevent creep.

    This can increase your stopping distance somewhat, especially if this is new for the driver.
     
    #3 gschoen, Apr 21, 2005
  4. Devil's Advocate

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    try this,
    "be the ball Danny"
    NA NA NA NA NA NA NA NA NA NA NA NA NA
     
    #4 Devil's Advocate, Apr 21, 2005
  5. Dr.Jay

    Dr.Jay New Member

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    You will (or should) notice that 'The perfect stop' depends a lot on the state of charge on the battery.
    I've had many occasions during braking, as I slowed down to 3-2 MPH, just when the car should have stopped, the car then picked up speed again to around 3-4 MPH (no I was not on a down slope).
    After this happened several times, that's when I noticed the battery at 7 green and no charge being generated (so no regenerative braking) but I guess not quite enough pressure to activate conventional braking.
     
    #5 Dr.Jay, Apr 21, 2005
  6. Anonymous

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    After this happened several times, that's when I noticed the battery at 7 green and no charge being generated (so no regenerative braking) but I guess not quite enough pressure to activate conventional braking.
    [/quote]

    I see what you mean about the shift from Regen to friction brake. I have not experienced the speed up but the shift of braking modes is noticeable to an experienced Prius drive like myself (almost 300 miles!) <ha ha>. I am still pursueing the perfect stop, but not with the wife as a passenger. It is annoying to the passenger; I can't imagine why??

    Here's an idea: In industrial machinery it is common to take regenerated current and channel it through big old hairy resistors in order to dissapate the kinetic energy as heat. Could the Prius do something similar when the battery is fully charged and there is still energy to dump? It would save wear and tear on the brake pads. The Toyota engineers probably thought of that one and rejected it. Too much extra weight, another fan to cool the resistors, fire hazard, etc.
    Cheers
     
    #6 Anonymous, Apr 24, 2005
  7. DanMan32

    DanMan32 Senior Member

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    You all mean 8 green bars, right? With 7 green bars, you still have one bar left.
     
    #7 DanMan32, Apr 24, 2005
  8. gschoen

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    It's rare for 8 bars to appear, let alone stick around very long. Many have NEVER seen 8 bars (myself included) and the people who do regularily (like going down a really steep hill on way home) don't have it very long.

    My Prius is happiest at 6 bars. 7 bars, it LOVES to use the battery, 3 bars, not so eager. Since most would never need resistors to burn off regen braking energy, and the regular brakes are up for the task, probably not cost effective. BUT if you're at 8 bars and want a "poor man" resistor, turn all your accessories on, especially rear DF and AC on High and pull big time current, try to hit that 100A limit for 12V. Kidding, but it would be (up to) a 1200W resistor (AC could make it higher since it's outside 12V limit)

    Dr Jay - if I don't step hard on the brake, it seems to think I want to "creep." I'm not sure the friction brakes are even working, more like it's trying to simulate the movement from an Auto trans. When I get to a stop I mash the brake since it seems sensitive around the stop point.

    It did take awhile to re-learn to stop without making everyone sick. Thankfully I haven't heard any complaints in awhile, but def. "different" feel than used to.
     
    #8 gschoen, Apr 25, 2005
  9. Dr.Jay

    Dr.Jay New Member

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    Tinman32, 7 bars was correct.
    I rarely hit 7 bars and have never hit 8.
    At 7 bars, when coming to a stop, there are no arrows showing so no load on motor.
    So (in my case) If SOC goes from 6 bars to 7 bars, while applying brakes and speed is below 5 MPH, car goes from light braking to coasting.
     
    #9 Dr.Jay, Apr 25, 2005
  10. Anonymous

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    I remember hearing a Car Talk show with
    Tom and Ray Magliozzi where someone called in with a question something like, "Does it make sense to use engine braking by down shifting to save wear and tear on the brakes" I guess this is similar to using a brake resistor or increasing the electrical load to dump energy. Their answer?
    "You are saving wear and tear on relatively inexpensive, easy to change parts like brake pads by wearing out relatively expensive, hard to change engine parts. Just use the engine braking if you think the brakes will overheat and cause a safety problem."
    My brake pads on the old Camry lasted around 40K due to my Dr. Fusco-like driving habits and Delaware being so flat. It would be hard to justify protecting the brake pads on the Prius with regen if I'm not charging the batterie.
     
    #10 Anonymous, Apr 26, 2005
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