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Why isn't regen integrated with the brake pedal?

Discussion in 'Model S: Driving Dynamics' started by dennis, Jan 24, 2013.

  1. dennis

    dennis P85D

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    When the Model S is going downhill and using regenerative braking, if you apply the brake pedal the amount of regen (as shown on the IP dial) is reduced, even though you are slowing down more. In the same situation in my Fisker Karma, when I apply the brake pedal the amount of regen increases. In fact, the first -.25g of deceleration is done through regen, and then it seamlessly adds friction braking if you decelerate harder. Is there some reason the Model S doesn't do this?
     
  2. smorgasbord

    smorgasbord Active Member

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    #2 smorgasbord, Jan 24, 2013
    Last edited: Jan 24, 2013
    You don't like one pedal driving? I love it. Heck, there's an argument to be made that in an emergency, regen braking will start a moment earlier - as soon as you take your foot off the accelerator, which happens before your foot moves to the brake and pushes down.

    Separating braking from regen makes things simpler engineering-wise since no blending needs to be performed. Just standard brakes.

    The amount of regen is naturally reduced because the friction brakes are slowing down the car. Same thing probably happens on your Karma, you just don't have a read-out. Same thing happens in Model S even if you don't use the brake pedal - regen decreases as speed decreases.
     
  3. Todd Burch

    Todd Burch Electron Pilot

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    Agree...and also agree that one-pedal driving is a gift from the Gods!
     
  4. montgom626

    montgom626 Active Member

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    Volt does as the Fisker does, step on the brake pedal = more regen.
     
  5. AnOutsider

    AnOutsider S532 # XS27

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    Not sure which is "better", but coming from sportier cars, I'm used to, and prefer, one-foot driving.
     
  6. steve841

    steve841 Active Member

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    I absolutely love the regen as is!

    Brakes only for a complete stop or those darn red lights.....
     
  7. dennis

    dennis P85D

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    I like one pedal driving, but I have found that heavy regen (3 levels available on the Karma) is not as efficient in freeway driving as lighter regen. As a result, I typically use a little brake pedal in those circumstances, but it results in regen, not in friction braking, so there is no "energy penalty" associated with 2 pedal driving.

    I DO have a read-out on the Karma, and applying the brake pedal increases the regen up to its maximum, and then it engages the friction brakes, while maintaining regen until it is no longer needed to slow the car. So removing your foot from the accelerator or applying the brake pedal has the same effect on regen. Since this is what I was used to, I was just surprised that the Model S did not exhibit the same behavior, hence my OP.
     
  8. Puyallup Bill

    Puyallup Bill Member

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    As does the LEAF.
     
  9. efusco

    efusco Moderator - Model S & X forums

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    You meet a lot of resistance on this site about the regen-on-the-brake issue. And despite 7 weeks in my Model S I still would have preferred a regen on the brake set up. I'm getting better at the one pedal driving thing. And while one pedal is nice for minor changes in acceleration and slowing it is NOT ideal for use of cruise control and other situations where you want to extend coasting distance or downhill.

    In the long haul/big picture I'll get used to the regen on the accelerator, and maybe I'll even come to like it. But I'm skeptical that I'll ever prefer it or consider it superior than regen on the brake. There are trade offs to both, I admit. But there's no way to claim that one is clearly superior over the other.
     
  10. Alpha

    Alpha Member

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    I see pros and cons to both ways. Having re-gen come on when braking (as well as other features such as creep mode) are artifacts of the way we are used to cars working, from the long history and precedent of ICE powered cars.

    Having friction brakes assigned to one pedal and only that pedal gives you more control really. Although I think it might be nice to have a high regen setting on the S rather than just standard and low.

    All those features and more could possibly be just a software update away, and then having the brake pedal use more regen at lower application and only inducing friction brakes at more aggressive braking could be a setting/preference.

    I'm sure it's a challenge to get a software algorithm to work perfectly like that (especially considering the various safety aspects involved) so maybe it's something they would add in later as a refinement after they get the basics down.
     
  11. apacheguy

    apacheguy Sig 255, VIN 320

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    I'm used to the LEAF so I initially expected regen to increase by applying the brakes. Having said that, I do enjoy one-foot driving, but I think it should be both. So yes, I like the aggressive regen when I lift my foot off the accelerator, but I think it should ALSO have the option to do an aggressive regen-on-brakes.

    Seems likely a relatively simple software adjustment and it should be offered as an option for those that have their preference.
     
  12. efusco

    efusco Moderator - Model S & X forums

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    No software update will get regen on the brake pedal, the car isn't built that way.
    The technology was mastered for regen on the brake over a decade ago by Toyota on the Prius, I'm confident that Tesla would have no problem replicating and improving upon that design if they chose to do so, but clearly chose a different direction intentionally.

    In the Prius design there is a small amount of regen on the accelerator that more accurately replicates the conventional ICE experience than the Tesla design which is WAY more aggressive than any ICE.
     
  13. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    I think you're conflating two different things: the amount of regen braking (as shown on the charge/discharge meter) feathers off as speed slows, but the rate of deceleration actually increases at the same time, until you're down under ten miles per hour, when regen feathers off completely. Try lifting off the go pedal at 60 mph, without touching the brake pedal, and watch what happens.
     
  14. dennis

    dennis P85D

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    #14 dennis, Jan 24, 2013
    Last edited: Jan 24, 2013
    The Karma allows 3 levels of regen to be chosen, although the 2 higher levels (Hill 1 and Hill 2) have to be selected each time you drive as they are not remembered.

    What I really like about the Karma regen on the brake pedal is how seamlessly it transitions from regen to friction braking. It is better than both the Lexus RX400h and LS600hL that we have owned, and as you stated it was Toyota who pioneered this technology.

    That said, when I drive the Model S I am adapting to a different style of using the accelerator and brake pedals, and really working at "keeping the needle at 3pm". :smile:

    I live at the top of a steep hill, with a 20 mph speed limit (which I exceed). When I am forced to apply the brake in the Model S to slow down more, the absolute amount of regen decreases. When I apply the brake in the Karma to slow down more, regen increases, up to a maximum. It was this situation where I noticed that the brake pedal was defeating regen in the Model S, which prompted the OP.
     
  15. Doug_G

    Doug_G Lead Moderator

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    Why doesn't it do this? Because regen on the accelerator pedal is awesome and way superior. Anyone who's ever driven a manual transmission will love it!
     
  16. efusco

    efusco Moderator - Model S & X forums

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    I've driven lots of manual transmission and I don't "love" it. I accept it, I can deal with it, but totally disagree that it is "way superior". It's an acceptable alternative, but far from perfect.
     
  17. ElSupreme

    ElSupreme Model S 03182

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    I am not good at gauging the regen yet. But I love that the brake pedal is only for brakes. Plus having it that way you can maximize the amount of regen possible. Only hitting friction brakes if necessary.
     
  18. mknox

    mknox Well-Known Member

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    I'll reserve final judgement until after I've had my car for a while, but I've raised concerns in other threads about cold weather issues such as unexpected loss of regen due to a cold battery and possible traction issues with the rear wheels on icy winter roads. I would like it to be switchable so that everyone could be happy.
     
  19. dennis

    dennis P85D

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    I think you missed the fact that when you press the brake pedal in the Volt/Leaf/Karma the car first maximizes regen and only engages the friction brakes if required based on the force you applied to the brake pedal.
     
  20. ElSupreme

    ElSupreme Model S 03182

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    But your regen is already maximized in a Tesla when you let off the accelerator. So maximized when you press the brakes.

    I think the brake pedal should work the brakes, not the motor with regen.

    With the Volt/LEAF/Karma you don't know when the friction brakes start to engage so it makes it harder to maximize. If you have enough stopping distance any energy scrubbed off in heat is energy that wasn't captured.
     

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