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Regen Braking

Discussion in 'Gen 2 Prius Main Forum' started by markabele, Apr 19, 2012.

  1. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    My whole life I have been taught to not "ride the brakes" but in some cases it seems like it is actually good on a Prius to ride the brakes via regen braking. So my question is, does regen braking wear on brake pads or anything else for that matter over time?

    fwiw I drive a 2012 but I figure the 2G community would be more likely to know this answer since you've driven a lot more miles.

    Thanks for any help!
     
  2. qbee42

    qbee42 My other car is a boat

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    No. Regen braking does not wear on any components, other than the drive train components that are always in play. There are two exceptions:

    1) Low speed - At speeds at or below about seven mph regeneration no longer works. At these speeds friction brakes are used.

    2) Heavy braking - In panic stops and other situations where regenerative braking is inadequate, friction braking comes into play.

    Riding the brakes on a Prius does not hurt the brakes, but it doesn't help your mileage. For best mileage, drive like you don't have brakes.

    Tom
     
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  3. puckdrop

    puckdrop Junior Member

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    You shouldn't touch the brakes unless you NEED to slow down. MOMENTUM is the key to good economy.. Regen is not free energy - you used fuel to get it !
     
  4. uart

    uart Senior Member

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    There are actually times when riding the (regen) brakes in a Prius can improve fuel economy. It can help to maximize regeneration in certain situations. Say you are descending a hill, and due to road conditions/laws there is a limited speed that you can reach at the bottom. You do actually regen more energy by limiting your speed the whole way down the hill rather than letting the speed build up and then doing all the breaking near the end. There are three main reasons for this.

    1. More steady speed means less overall windage losses.

    2. Spreading the regeneration over a longer period gives more efficient energy transfer to the battery.

    3. There is much less chance of exceeding the regen capacity and losing energy to friction brakes.

    On the negative side, try not to do it to the extent that you piss off other drivers too much.
     
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  5. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    I know how to regen brake and the benefits, just looking for specific info on whether it harms longterm the way friction brakes do. I think qbee42 answered it though.
     
  6. cnschult

    cnschult Active Member

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    the ultimate prius driver uses Pulse & Glide.
    on your consumption screen, you don't want arrows going into or out of the battery as little as possible as this is results in heat loss.
    you want to press the gas pedal fairly hard on acceleration so that the power goes to the wheels only (very hard to learn how)
    after that, lift your foot completely off the accelerator for a second and then pressing it back down ever so slightly to remove the arrows from going back into the battery. This only works below a certain speed (I think 38mph or so). When this happens energy is not sent back to the battery but you are just "gliding".

    in other words, there is no point to a hybrid. Transmissions are built well enough these days that Toyota could easily design the Corolla to shut the engine down as soon as you lift off the accelerator allowing you to coast for miles. In truth, you only need power for a few seconds and then a car with LRR tires could coast for close to a mile on that energy (much more if going downhill and much less if going uphill obviously). I'd like to see a Corolla built with this technology go up against a Prius and compare the FE, I bet the Corolla would beat the Prius in the city but lose on the expressway, but the Corolla would be many thousands of dollars cheaper than the Prius and you would never have to worry about replacing expensive HV batteries or Invertors.
     
  7. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    Highly disagree. The ICE is very inefficient at very low speeds. Hence, most "normal" cars have much lower in city MPG compared to highway.
     
  8. cnschult

    cnschult Active Member

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    Did you not read my post? conventional cars have bad city mileage because the engine is on all the time, if they ran for 5 seconds at high revs then shut down for a minute or two a toyota corolla would get over 120 mpg in the city. It would still get the same 40ish mpg on the expressway but cheaper to buy, cheaper to maintain, easier to maintain, and have lower insurance premiums. (prius has lower insurance due to more safety features, but more complicated cars such as AWD insurance companies do charge more for due to higher repair costs, so if the corolla & prius had equal safety features & crash results the corolla would have lower insurance)
     
  9. Britprius

    Britprius Senior Member

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    Many years ago Rover cars came as standard with a free wheel system to save fuel.

    To operate it you kept your foot on the accelerator and turned a knob under the dash, when you took your foot off the accelerator the car free wheeled, the same way you stop pedaling a bicycle.

    It also had the advantage that once you were rolling you could change into any forward gear without using the clutch.

    The last car I remember that used the same system that was available in Europe was the Vuatburge Knight "may not be correct spelling" this was a 999cc three cylinder two stroke powered medium sized car with oil mixed in the fuel. Went like stink using both meanings.
     
  10. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    Higher revs isn't the only variable in getting an ICE into it's sweet spot MPG-wise. Speed is also a factor.
    I get what you are saying, though. Those kind of cars would definitely get MUCH better mileage than a normal car. But I still believe having a battery powered drive at very low speeds is more efficient.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    Conventional cars also have an engine that is drivable in city conditions. Prius has a significantly more efficient engine, but without the hybrid system it would have awful drivability.

    If engine-off is all it takes to get high city mileage, then a hypermiler should get astounding Pulse & Glide results in an original Chevy Malibu Hybrid, which has the engine-off BAS system. Did anyone try this before that version was discontinued?
     
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  12. NinnJinn

    NinnJinn Member

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    hmmm interesting!!! not sure if GEN 2 is different than GEN 1, but in a normal car with an actual transmission, the hills I "coast" down the normal cars pick up speed. start coasting at 52mph and start riding the breaks half way down due to going over 65.

    In my GEN 1, start going down the hills at 52-53mph and let off the gas with no breaks, and by the time I am at the BOTTOM of the hill, I might be going 55 or 56 if I am lucky. and the instant mpg is pegged at 100mpg all the way down and the flow is all going to the battery and is full by the time I am at the bottom of the hill. However, if I push the gas ever so slightly, where energy is going no where, thats when I hit about 65mph midway down the hill.

    I thought as long as you were going above 7mph, as long as you were "coasting" the car was regenerative braking?
     
  13. cnschult

    cnschult Active Member

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    you must be referring to the "Atkinson Cycle" which I admit I don't know anything about. yes I have tried this on a rental car (I would never do it on my own car because cars aren't "built" for this type of driving yet) when I got rear ended and the car was in the shop, I have car rental on my insurance and was given a free malibu non hybrid for a week or so.

    I filled it up and drove and recorded the mileage. I spent the day accelerating very hard and shutting down the car as soon as I got up to speed and coasted for a minute or two in neutral. There's this old notion that cars use a tremendous amount of fuel to start up, that may have been true decades ago but I doubt that's true with modern engines. I got 78mpg with a V6 malibu in the city. With a corolla built for this I could get 100+ mpg. This is not safe, when the car is off you lose abs, traction and stability control, power steering, radio, lights, wipers, etc. For this to work a car would need both a starter battery and an marine deep cycle battery to run accessories and safety features when the engine is off. The engine should shut off as soon as you release the accelerator. The engine would automatically restart if you pressed the accelerator (while you are still moving) or when you released the brakes (such as at a full stop at a light). There should be a button to maintain engine on if you know you'll need it in a second or two. There could still be a regen system to recharge the deep discharge battery.

    yes if you press nothing you are "coasting" which means you'll regenerate the brakes. That's great as you're pulling up to a stop sign or light.

    but what if you're very far from the light? regen will slow you down too quickly. press the accelerator very slightly and all arrows should disappear and you'll be in "glide" mode, the names are confusing because our glide mode is the same as coasting in a normal car.
     
  14. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    haha k, whatever dude

    I bet you have a system to beat the slot machines too right?
     
  15. daniel

    daniel Cat Lovers Against the Bomb

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    The availability of accessories like ABS is not the only reason it is unsafe to drive a car while in neutral. Lack of available power in an emergency is another. With the engine off or the transmission in neutral, you have to start it or put it in gear before you can accelerate. With a Prius, you have power available whether the ICE is on or off.

    Only in a situation such as uart described when you want or need to limit your speed. Slowing down or preventing gravitational acceleration are the only times when riding the brakes is useful.

    Not true. The principal advantage of a hybrid is that it can use a smaller engine, which cannot achieve the desired acceleration, and it can use an engine like the Atkinson cycle, which has higher efficiency but lacks torque. Both are possible because the electric motor is available to provide both power and torque when needed.

    While a conventional car could be designed that would allow pulse and glide operation, P&G is not suitable under all circumstances. There are many times when you must drive at a steady speed.

    It's a mistake to single out one feature alone, such as the ability to P&G, and claim that's the only advantage of hybrids.
     
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  16. justjeff

    justjeff Junior Member

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    Im curious.....how did you start the car while you were coasting? It was an automatic, right? Pretty sure it wouldn't be good to start an auto while the engine is still turning in neutral..or coasting any duration in neutral because the tranny needs the fluid to be pumped through it so you don't kill the tranny. I may be wrong though. Anybody?
     
  17. fuzzy1

    fuzzy1 Senior Member

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    Hypermilers have used similar methods to push a Prius to about 160 mpg.
     
  18. SteveDH

    SteveDH Junior Member

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    It would be interesting to compare the 2, presumably the Corolla would still need a largish battery to power the steering etc when the engine is off.
    However how well it would perform against a Prius driving through London in the rush hour.
    I don't do it often, but when I have, I have some steepish hills to go down, where I can coast down charging the battery so that the ice can remain off while I inch forward as the traffic lights at the bottom cycle 3 or 4 times, then there's lots of relatively unpredictable stop and start traffic where having a hybrid engine helps even out energy usage..
    hmm.