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Regenerative braking question

Discussion in 'Gen 4 Prius Main Forum' started by unigeezer, Jan 30, 2024.

  1. unigeezer

    unigeezer Member

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    Does regenerative braking only kick in when the charge light is a solid white?
     
  2. JC91006

    JC91006 Senior Member

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    Every time you brake, there is regenerative braking. Until you reach a really low speed of appox 5mph, then regular brakes will come on without regen
     
  3. unigeezer

    unigeezer Member

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    So, just to clarify, regen is fully engaged (no mechanical assistance) while braking, regardless of whether the charge indicator is fully filled in, as long as you speed exceeds about 5-10mph?
     
  4. sylvaing

    sylvaing Active Member

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    Or unless you're braking harder than what the regenerative braking can provide. Then the physical brakes are also applied. Using Hybrid Assistant, you can see a green a blue tick marks in the EV bar. The green one shows the maximum regenerative power that can be put into the battery and the blue one shows how much power can be sent to the motors. When the EV bar reaches the green tick, physical brakes start to be applied.
     
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  5. ChapmanF

    ChapmanF Senior Member

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    The regen and friction braking are under cooperative control the whole time. I'm not sure which Prius generation's manual these graphs came from, but they all look similar: (Edit: ok, it says right at the top, it's for 2017–2020 Prime, but again, the graphs are similar across the generations.)

    [​IMG]

    Your foot on the pedal is a computer input saying how much total braking you want. The brake ECU sends a message to the power management control ECU saying "want this much braking, how much can you do with regen?". The power management control ECU looks at the current state of charge and temperature of the battery, etc., and says "I can do this much". The brake ECU says "great, I'll do the rest with the friction brakes". They keep having this conversation many times a second the whole time you are braking, as the car is slowing down and the battery is filling up.

    If you're moving fast, when you first apply the brake, the regen part is going to be small (because at high speed, even a little regen is as much as the battery can take). As your speed comes down, regen moves up to be a bigger part of the mix, and the friction brakes do less. That holds until your speed is so low that regen can't do much, and then the blend shifts back to friction for those last few MPH.
     
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  6. unigeezer

    unigeezer Member

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    So, the bottom line is, brake pads will not last "forever". They just last longer than pads in cars without regen.
     
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  7. JC91006

    JC91006 Senior Member

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    150k miles is almost forever
     
  8. rjparker

    rjparker Tu Humilde Sirviente

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    300k miles on my fronts and counting. Regen does most of the work when you avoid hard slowing. Rotors stay smooth and original.
     
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  9. ColoradoBoo

    ColoradoBoo Senior Member

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    Yes the pads can last a very long time BUT there's also other things to maintain, like the brake fluid in the lines (which I change out every 3-years by bleeding all four ) and you also want to re-lube the slide pins inside the brake calibers at least every 4-years. (More often if you live in a hot area.) Else they can seize and it will wear down the pads very quickly. It's pretty cool to open up a caliper with 5-year old pads and see that's it's not even half worn, yet!!
     
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  10. sylvaing

    sylvaing Active Member

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    And even more often if you live in an area where they use salt on the road.
    I regrease my Model 3 brakes every spring when switching my winter tires for my summer one and will do the same for my Prius Prime.
     
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  11. ChapmanF

    ChapmanF Senior Member

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    In my experience, inspecting my brakes every time I rotate tires, the slide pins are among the parts least likely to need anything, other than sliding them inward and outward a few times to wake the grease back up, and checking that the rubber boots aren't damaged. They are also far from the only parts of the brakes that can cause dragging and accelerated wear. The "fitting kits" (springy clips that hold the ears of the pads) can lose their factory Teflon-like coating and become rusty and prevent free pad motion, or the notches in the bracket where those clips fit may rust and put a squeeze on the clips. If the piston dust boot gets damaged and lets water in, the piston itself can become seized, or the piston's square-cut rubber seal (a part you don't see except in a caliper rebuild) can become hardened and stop pulling the piston back when you release the brakes.

    All those are things worth checking in a brake inspection. My typical inspection either finds nothing needing work, or finds a new fitting kit called for (the kits are cheap). I can't remember the last time I found anything wrong with a slide pin after sliding it back and forth a few times.
     
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