Why doesn't this car show when brakes are engaged?

Discussion in 'Gen 3 Prius Technical Discussion' started by Skoorbmax, Mar 23, 2010.

  1. Exponent

    Exponent New Member

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    From what I have picked up here and there on PriusChat, I don't think that the regen braking versus friction braking is a black & white situation that transitions over completely. When you go over the max charge bar, the regen braking still continues to brake as much as the generator/battery can handle, but friction braking starts to help out.

    My guess is that your squeaking brakes only squeak when you're using them somewhat strongly. If you're only barely using your friction brakes (which is the case when you've just barely gone over the max on the charge bar), they probably don't squeak at all.
     
  2. hobbit

    hobbit Senior Member

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    Actually, there's an Xgauge out now that tells you hydraulic
    pressure to the brake lines. Between that, a battery-current
    Xgauge, and the HSI, you should be able to pretty much nail where
    you fall off regen to physical brakes in your 2010. With the
    second-gens it's harder but the pressure sensors are more
    accessible to feed analog readouts.
    .
    _H*
     
  3. Prius42

    Prius42 New Member

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    Thank you all for the great explanations! I guess it makes sense that the friction brakes are actuated along with the regenerative braking and there is no black/white cross over. After all, the friction braking is still direct coupled hydraulic (w/power assist) and not fly-by-wire. I think you-all have finally sold me on the scangauge II. It really appeals to my inner-geek. Can you read the tiny screen without driving off the road? I really need the HUD shown in this post:

    http://priuschat.com/forums/gen-iii...hat-changes-will-2011-prius-2.html#post903269
     
  4. qbee42

    qbee42 My other car is a boat

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    Not quite right. Friction braking *is* fly by wire, unless you have a failure in the control system, at which point it will fail over to a direct hydraulic system.

    Tom
     
  5. Prius42

    Prius42 New Member

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    Really? It actually switches from only using an encoder to directly engaging the hydraulic system? Is there actually a mechanism that does this? It must engage every time the power is off. Cool!
     
  6. qbee42

    qbee42 My other car is a boat

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    Yes. During normal braking, as you press the brake you actuate the master cylinder. Instead of sending hydraulic fluid to the brake pistons, the hydraulic fluid presses against a "stroke simulator", which is really a piston with a big spring. The stroke simulator gives the brake pedal a normal feel, even though it isn't doing anything.

    Two pressure sensors in the hydraulic lines tell the ECU how much braking you want. That ECU talks to another ECU to see how regenerative braking is available. If more braking is needed, the ECU sends commands to open the ports to the hydraulic brakes, sending pressure from the power brake system to the friction brakes (brake by wire).

    In the event of a power failure or other major failure, power is removed from several solenoid valves. When powered, these valves normally route the hydraulic pressure to the stroke simulator. Without power these valves direct the hydraulic pressure from the master cylinder directly to the friction brakes.

    It's a pretty slick system. There are some differences between the Gen II brakes and the Gen III brakes, but the concept is the same.

    Tom
     
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  7. Prius42

    Prius42 New Member

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    Thanks for the excellent explanation!
     
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