Prius brake caliper spring?

Discussion in 'Gen 2 Prius Technical Discussion' started by sergbot, Jan 19, 2021.

  1. sergbot

    sergbot New Member

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    Hey, I have a prius I got from an auction and the brake rotor got damaged because the pad wore down to the metal, and carved the rotor. So now I can hear a rumble when the brakes are truly in use,

    and something I noticed from poking around the ecu, is that without hitting the brake pedal, the car is regenerating at like 15 percent capacity, but when hitting the brake padal, it engages the brake pads, they don't offer much braking at soft pressure, and engage more when you press harder, however, even when you Are pressing harder, the regeneration isn't at 100 percent, you have to be pressing hard to get it to be as high as It goes, and this is completely retarded and inefficient, because you'd want your regeneration At 100 percent before even touching the rotors with the brake pads.

    We can't really mess with this mechanic in anyway because it's built into the car, but I was thinking why happens if we put like 50 pound springs in the calipers? It won't effect braking because the abs motor and the brake caliper have like a thousand psi, so 100 pounds of pressure is absolutely nothing, however that might be enough to prevent the pads from begining to brake, and it might allow more room for regeneration before the pads start providing more stopping power.

    Thoughts?
     
  2. oldtechaa

    oldtechaa Active Member

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    Do the disc brakes on a Prius even have return springs? Even so, there are problems with the idea. One, some pad-rotor contact is necessary to keep both surfaces in good condition for when they are used. With light braking the pads are already used so rarely that the rotor can easily rust. Second, the Prius engineers likely tuned the regen rate to be best for battery charge rate and health and for regen to last as long as possible in normal driving, like down long hills, instead of filling the battery immediately. If you want an even higher regen rate you could just use "B" mode.
     
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  3. mr_guy_mann

    mr_guy_mann Senior Member

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    DON'T. Don't mess with your brakes- just fix them- now- and restore them to original function. Don't try and second guess what the engineers have designed as far as the braking and hybrid systems go. Don't worry about what the scantool shows you unless you are chasing an actual failure.

    The computers will use whatever combination of regeneration and hydraulic braking as needed to stop the car. How much regeneration will depend on vehicle speed, battery condition and state of charge, and how hard you press the pedal. The ecu will regen hard (80 to 90 amps) if you brake hard at higher speeds but will use the hydraulics sooner - because you are trying to stop as soon as possible.

    Posted via the PriusChat mobile app.
     
  4. ChapmanF

    ChapmanF Senior Member

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    No, you don't, because there can be moments when the car detects dodgy traction and needs to switch immediately to the four-wheel hydraulic brakes (the regen only acts on two wheels, so that risks loss of control at about twice the level of road traction where four-wheel braking is still safe).

    As the car is currently designed, there can already be a noticeable delay when the car does one of those forced switches from regen to hydraulic. It lasts for a tiny fraction of a second and feels a bit like the car got goosed from behind, though in reality it was only not-slowing-as-hard for an instant.

    People notice that mostly, not in situations where the traction is actually bad, but where one wheel hit some road irregularity and made the traction ECU think the traction was bad, which has the same effect of course. Lots of people already write repeated complaints on PriusChat about that and even repeated reports to NHTSA because it startles them and makes them think the brakes are unsafe.

    Your proposed "regeneration At 100 percent before even touching the rotors" rule would drive those complaints through the roof.
     
  5. sergbot

    sergbot New Member

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    They do not have springs. Thanks for your answer but I still don't see any good answers.

    The pad and rotor contact will happen anyway because any time you're going to come to a stop, they will be used. I think I disagree with the idea that the regeneration is intentionally weak for longer battery life. The Prius, instead of buying 10,000 gallons of gas in its life time, only buys 3000, getting every drop of power back is the highest importance. I think it's very ignorant and not very smart to always think the engineers are holier than God and their work is perfect. Most gasoline cars actually keep adding fuel to the cylinders WHILE GOING DOWN HILL. And most non toyota hybrids fight for their life to break 33 mpg even though that's broken by lots of european cars just on gasoline alone. Also, if high amperage regenerating would hurt the battery or longevity of the car, they would do it, period. The brake pads themselves can stop the car enough to lock the wheels, you don't need additional stopping power from mg.

    So in conclusion I think it's a complete oversight that brake pads engage rotors the second you touch the brake pads, they should have added an inch of free brake pedal movement to allow you to modulate mg braking before you'd hit the brake cylinder plunger

    The hydraulics are used immediately, you can modulate how hard they are engaged by pressing the brake really light, without pressure the brake pads can't do much work, however they shouldn't be engaged immediately because you're just turning energy into friction instead regenerating it.

    Sorry can you run that by me one more time, the axle creating drag irritates the abs system?
     
    #5 sergbot, Jan 20, 2021
    Last edited by a moderator: Jan 20, 2021
  6. ChapmanF

    ChapmanF Senior Member

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    You've heard the "can't outrun a bear" joke, right?

    I don't know that I could make it clearer by just writing it out a second time, but if there were any specific parts of it that you found unclear, I might be able to help. I don't know what to say about axle/drag/irritates since none of that was in there to begin with.

    If you search these forums for terms like brake, bump, manhole, failure, whoopee, etc., and read some of the many reported complaints, you'll start to realize that many drivers already don't like how long the (tiny fraction of second) delay is at times when the car needs to quickly replace regen with friction. Your proposal to keep the friction brakes even further out of action during regen would worsen an effect that many people already dislike.
     
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    If you want the braking system to work differently, then design your own car. Just test it as much as Toyota did. The engineers ain't perfect, but I think that if they could have tweaked regeneration to pick up more mpg's then they would have. Unless doing so might have compromised safety.

    AFAIK, the brake pads "pre-stage" by lightly applying so that there is minimal time to switch from regenerative braking to hydraulic- such as when you go from slowing a bit to sudden panic stop. Yes we are talking fractions of a second here, but that can be the difference between having a collison or not.

    The potentially greatest difficulty is when the driver is braking and the car is primarily regenerating (drag is produced on the front axle only) - if during this the wheels lose traction (skid or slip) then the car must cease regeneration then apply the hydraulic brakes so that the ABS can modulate wheel speeds. This takes time. Increasing pad clearance increases the time before the hydraulics can work so that increases braking distance.

    Posted via the PriusChat mobile app.
     
  8. sergbot

    sergbot New Member

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    Okay sorry but that doesn't make sense, there isn't a delay between regeneration and caliper braking, both are used at the same time.

    Whatever people are experiencing happens when the driver backs off the brake pedal a little amount, even if you move it a quarter inch, the regeneration will go from 20 kw to 6kw, and the car will lunge forward because it's not being stopped as hard anymore, then the driver panics and slams the brake pedal, and the calipers lock the rotors.

    I don't know why the regeneration is so botched either. I guess it's because it's too responsive with no delay? With brake pads, after applying force to stop, you have to take off the pressure, then the pressure has to dissapate, then the piston has to retract a hair length, and only then can the rotors push past and start moving again. I guess that sort of creates a capacitive effect that makes the ride smooth.

    I guess also there isn't enough range of motion for the brake pedal sensor for regenerative braking, the braking is like half a parabola, with 6kw constant braking and then it goes from 20 to 40 kw in like a quarter inch, they should have made it linear and they should have given you more room to brake the pedal . Also I think regular brake pads are linear, you get the stopping force you push with
     
  9. sergbot

    sergbot New Member

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    Well actually I'm arguing for increasing the pressure, not the distance. The pads would still be touching the rotors, its just it wouldn't apply stopping force until later in the pedal press.

    And generally the way they should have done it was with a one inch range of motion for Variable regenerative braking before the pedal touching hydraulic hardware, and this too wouldn't add time or distance to the calipers.
     
    #9 sergbot, Jan 21, 2021
    Last edited by a moderator: Jan 23, 2021
  10. oldtechaa

    oldtechaa Active Member

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    Wrong. I'm surprised you've never experienced the effect of loss of traction while braking. It happens often on some Prii, especially in certain conditions. It has nothing to do with the force on the brake pedal or the position of the brake pedal. It's the decision of the car's braking computer to release regen and engage hydraulic brakes, and it can feel like you're no longer braking for a second.
     
  11. ChapmanF

    ChapmanF Senior Member

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    With a profile that says "Joined: Tuesday", you might not yet have positioned yourself to establish a new explanation of what long-time members of PriusChat have learned over twenty years about their cars. That isn't to say that can't happen, only that you haven't yet.

    Usually the way you would do that would be to review what the many existing PriusChat posts already say about the regen-to-friction transition effect, think up some sort of experiment procedure that would expose a difference between the existing explanations on PriusChat and your new preferred explanation, conduct that experiment reproducibly, and post about your materials, method, and results.

    Sometimes members want to go by the "well, I am an XXX with YYY years of experience" method instead, only that doesn't work as well, because of course on an anonymous Internet forum, saying "I am an XXX with YYY" is precisely as convincing as saying "I am a beagle".

    [​IMG]

    Hence, the members who most successfully establish their chops on a forum like this one generally do it by consistently bringing the goods.
     
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  12. jerrymildred

    jerrymildred Senior Member

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    You and several others have been bringing the goods for longer than I've even known there was such a thing as a Prius. (y)

    I don't linger long trying to straighten out people who won't let themselves be confused by facts. I see a lot of this silliness on the Prius Prime group on Facebook. But it's rare to see such firm belief in stuff that's so far from facts that are so public and easily verifiable. :whistle:
    ;)
     
  13. ChapmanF

    ChapmanF Senior Member

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    Everybody's new to a community once, and trying to figure out what the prevailing expectations are.

    PriusChat is awesome because it's not the same as X Facebook group, and that means it asks a little more of everybody.
     
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  14. jerrymildred

    jerrymildred Senior Member

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    Very true.
     
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