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When using brakes how do you know

Discussion in 'Gen 3 Prius Main Forum' started by Oskar, Jul 31, 2015.

  1. Oskar

    Oskar Member

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    at what point you are using the actual brakes as opposed to the regenerative braking? I know when I come to a stop light/sign I coast and then gently apply the brakes. I may be wrong, but I don't thing I'm actually using the brakes to slow down, unless I really hit them hard.

    I'm wondering if there is a certain point on pressing the brake pedal when it goes from regenerative to the actual wheel brakes.
     
  2. bisco

    bisco cookie crumbler

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    yes, around 6 mph i think. also, if you watch the hsi when braking, the harder you press, the further the line moves to the left. if it goes all the way, you're friction braking.
     
  3. cproaudio

    cproaudio Speedlock Overrider

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    If you want to know for sure, get a scangauge and use xgauge and set one to monitor mechanical brakes and one for battery amp. The HSI is not completely accurate. When the battery gets too hot, the regen cuts out and mechanical brakes kick in even though the regen bar is half way.
     
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  4. RRxing

    RRxing Senior Member

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    Close enough. ;)
    The transition from regenerative to friction brakes occurs at 7 mph, assuming you are using the regen brakes when slowing down.
     
  5. Oskar

    Oskar Member

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    Thanks for the responses. Funny I would have thought that regen braking would kick in at a faster speed than 6 or 7 mph.
     
  6. bisco

    bisco cookie crumbler

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    i know, it's amazing, isn't it?
     
  7. DoubleDAZ

    DoubleDAZ Senior Member

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    I think you misread. Regen braking basically kicks as soon as you hit the brakes. It's "friction" braking that kicks in at 6-7 mph for the last few feet of stopping distance. And this assumes you slowed down by pressing the brake pedal a little and didn't wait until the last minute. Obviously, if you hit the pedal hard, friction braking kicks in right away. If you watch the display as you press the brake pedal, you'll see the indicator start moving to the left. This is regen braking. When you get to 6-7 mph, the friction brakes kick in even though the display might still only be at the halfway point. At least that's how I understand things.
     
  8. fuzzy1

    fuzzy1 Senior Member

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    Regen is available at all speeds above 7 mph, unavailable below.

    Are you using the HSI display so that you can see the CHG portion of the bar? If so, a reasonable first approximation is that you are using all regen when the bar is not pegged to the left. The available regen braking force varies considerably with speed, producing moderate braking force at low speed but only light force at highway speed. (Battery power limit sets the regen braking limit. Force equals power divided by speed.)

    But as Cproaudio mentioned, this is not the whole story, you need added instrumentation to see the rest of it.
     
    #8 fuzzy1, Aug 1, 2015
    Last edited: Aug 1, 2015
  9. DoubleDAZ

    DoubleDAZ Senior Member

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    Oh, and AFAIK, when you're going downhill, the car is regen braking even if you don't press the brake pedal. This is why the Prius can navigate down a lot of hills without ever having to use the brake pedal, unlike most other cars.
     
  10. bisco

    bisco cookie crumbler

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    when i post a question, and come back to find a bunch of responses, i only read the last one.
     
  11. RRxing

    RRxing Senior Member

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    You are actually using regen braking anytime your foot is off the accelerator (up hill, down hill, no hill) and not on the brake. It is designed to simulate a regular engine's braking effect. With your foot off of the gas, you can see a small line on the CHG indicator - that's the regen kicking in, unless, as mentioned, the traction battery is at or near full charge and other variables (Temperatures, etc.) are in play.
     
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    I'm not sure it's all-or-nothing with the brakes. If I've washed the car,and it's sat a day or two, built up some rust on the rotors: I'll hear some noise from the brakes regardless of speed.
     
  13. cproaudio

    cproaudio Speedlock Overrider

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    Here's proof that friction brake kicks on even though the HSI shows regen only. I believe this is done to protect the battery during extreme temperature. It didn't show on the video but it was 108f that day. I've seen this issue when the outside temp as low as 95f. This only happens when I parked the car in direct sunlight for longer than an hour. Look at the lower left scangauge. BRK monitors the friction brake. Normally, the BRK shows 0.00 when no friction brakes. During extreme temperatures, it shows 655. Not sure if it's the scangauge's fault or OBD-II's fault. When friction brakes is activated no matter how small, it'll show above 0.01. This is how I know the friction brakes have activated during supposed regen only braking. Typical moderate braking shows about 0.3-0.5. Hill start assist takes 1.5 to kick on.
    Amp monitors amperage gain or loss. - means regen. During regen, you'll see somewhere between -99 amps and -20 amps depending on how hard you pressing the brake pedal. At cool temperature, during full regen but just shy of friction brakes activating will generate -70 to -99 amps.
    In this video I never pegged the CHG bar while braking. The Amp meter showed less than -16.1 amps of gain at the most. This is the same as lifting the foot off the gas pedal without applying the brakes. When I did apply the brakes, the regen never engaged. Friction brake is what slowed down the car.
     
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  14. bisco

    bisco cookie crumbler

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    did you have the software flash?
     
  15. Mendel Leisk

    Mendel Leisk Senior Member

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  16. RRxing

    RRxing Senior Member

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    I have Scangauge envy... ;)
     
  17. bisco

    bisco cookie crumbler

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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    My uneducated take is it uses a blend of the two, maybe in varying proportions.
     
  19. Ali Terzian

    Ali Terzian New Member

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    From what I have read when you apply the brakes and it goes into the charge area on the indicator scale for about the first half of that is is using the braking motor and the very end half of the charge indicator is actually when the brakes kick in and recharge.
     
  20. David Beale

    David Beale Senior Member

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    According to the Toyota description the friction brake pads are moved "to the discs" but no pressure is applied. This is to "get ready to brake if needed".

    So it sounds like we have advantages AND disadvantages living where it actually gets -cold- in winter.

    Advantage - battery will probably not have overheating issues -ever- (max. summer temps of around 30C or about 80F).
    Disadvantage - warmup can take awhile in winter. Oh yeah, and then there is the ice (solid water type) and snow.