TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Model S Regenerative Braking is Different Than Hybrid Regen..Why?

Discussion in 'Model S: Driving Dynamics' started by Evbwcaer, Oct 5, 2014.

  1. Evbwcaer

    Evbwcaer Member

    Joined:
    Jun 21, 2014
    Messages:
    470
    Location:
    Minnesota
    I have had my Model S for a few days now and I have now had time to learn more about how the car drives.

    When I first got it, I had regen on low because I drive fairly efficient and wanted to utilize coasting....which is more efficient than regen.

    In all the hybrids I have driven, and I believe the Leaf too, when you lightly press the brake pedal, you get only regen braking. It is only once you press fairly hard on the pedal you get friction braking. The harder you push the pedal, the more regen you get, up to a certain point.

    On the Model S, there is no correlation between the brake pedal and regen. Regen starts when you are coasting or braking and coasting, but it does not increase regen as pressure is applied on the brake pedal and friction braking starts right when the pedal is pushed.

    Why the difference?

    The hybrid arrangement seems more intuitive for those that have been driving hybrids and ICE cars, so would be better if the approaches are otherwise equal.

    Thanks
     
  2. Bardlebee

    Bardlebee Member

    Joined:
    Apr 4, 2012
    Messages:
    599
    Location:
    San Antonio, TX
    I was thinking about this tonight. I think it is so aggressive in this sense because it attributes to a portion of the reason why the car goes so far long distances. I wondered why they didn't have an "off" setting and its likely because you would get reduced range if you did that.

    By taking your foot off the gas, regen kicks in. But, if you had it setup in the break, you wouldn't be getting any of that battery regen if you were coasting down a hill, which in Texas is all the time due to lots of hill country.

    In fact, in the hill country you will be going UP hills a lot, to not get that energy back going back down would be detrimental to range. This is probably the strongest reasoning to this design choice.
     
  3. ecarfan

    ecarfan Well-Known Member

    Joined:
    Sep 21, 2013
    Messages:
    10,373
    Location:
    San Mateo, CA
    The Model S regen function is simpler from the driver's point of view than the "hybrid regen" system you describe.

    In the S the right pedal allows you to easily and precisely modulate your speed, up and down.

    The left pedal is only used when abrupt breaking is required or when you need to come to a full stop more rapidly than the regen allows.

    I believe that if you drive carefully, allowing appropriate following distances, you will use the left pedal much less frequently than in an ICE or hybrid vehicle, resulting in less brake wear and a more relaxed driving experience.

    It just makes more sense to me. You have only had your S a few days, but I think that with a few more hours behind the wheel you will come to appreciate the Tesla approach to regen.

    Of course if you have to switch back and forth between the S and another car...you have my sympathies.
     
  4. bonnie

    bonnie Oil is for sissies.

    Joined:
    Feb 6, 2011
    Messages:
    14,241
    Location:
    Columbia River Gorge
    Eh, I switch back and forth between my Roadster (with regen) and a Jeep (with no regen) on a regular basis and it's no big deal. The way regen is implemented on a Tesla makes a lot of sense, but it doesn't mess up my driving on anything else. I just miss it when I don't have it.
     
  5. ecarfan

    ecarfan Well-Known Member

    Joined:
    Sep 21, 2013
    Messages:
    10,373
    Location:
    San Mateo, CA
    Bonnie I also switch back and forth between my Model S and an ICE, and since we all have a lifetime of experience driving "regular cars" it is certainly doable, but I really miss regen when driving a car that doesn't have it. And since I spend a majority of my driving time in the S, when I'm in an ICE the first time I lift my foot off the gas I think "It's like being in the last century driving this damn car."
     
  6. JohnQ

    JohnQ Active Member

    Joined:
    Jan 1, 2012
    Messages:
    1,585
    Location:
    Redding, CT
    In the end, the Tesla approach is a better UX/UI. I don't have to shift my foot position to get a moderate braking effect and can more effectively modulate my speed than moving back and forth to the brake. Like Bonnie, I can jump in a rental and within 2 minutes I'm readjusted to the brakes.

    Edit: Though like @ecarfan it does irritate me to go back to the old model.
     
  7. Saghost

    Saghost Active Member

    Joined:
    Oct 9, 2013
    Messages:
    3,024
    Location:
    Delaware
    In every car that uses the "regen on brake pedal" approach (including my Volt,) there are challenges with brake pedal feel. Some handle it better than others, but I've never seen a reviewer fail to comment on the odd pedal feel. I believe that this is the reason that Tesla and BMW have chosen not to take this route - it lets them deliver a typical tight responsive brake pedal.

    Not mixing the systems also makes the design far simpler - cars with regeneration on the brake pedal generally have force feedback actuators on the brake pedal and have to mix the regen and friction responses - lots of complicated programming that you don't need with the other approach.

    Of course, Tesla's approach means that if someone does switch to low regen and drive it like they used to drive their ICE car they are throwing a bunch of energy out the window that the other design would have recaptured - meaning it requires changes to the driver's habits for best results. So I'm not sure one solution is inherently better than the other.

    (As for me, I always drive my Volt in L, so I think I'm already more or less in Tesla's preferred driving style.)
    Walter
     
  8. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

    Joined:
    Jul 12, 2012
    Messages:
    4,502
    Location:
    Maine
    Two reasons:
    1 It's much easier to engineer
    2 Powerful regen allows 1 pedal driving. Hybrids can't allow enough regen to support 1 pedal driving so have to put regen on the brake to get real benefit from regen.

    I prefer to have the extra go pedal to control power rather than control regen and power so prefer regen on brake. But I hypermile so like to avoid brakes anyway if possible.
     
  9. HankLloydRight

    HankLloydRight Fluxing

    Joined:
    Jan 18, 2014
    Messages:
    5,785
    Location:
    Connecticut
    I'm pretty sure this is not true -- that regen is less efficient than coasting. Maybe that's true in a hybrid, but the MS is an entirely different beast.

    Since the Tesla engineers have worked very hard to minimize energy use (like "range mode"), and recapture as much energy as possible via aggressive regen, then I can only assume if "coasting" or "low regen" is more efficient, then they would have used those modes as a default, as opposed the high regen. Like a previous poster said, using low regen or coasting is just throwing all that potential energy out the window, or more accurately, converting it to heat in the brake pads instead of energy going back into the battery.

    I think you're just accustomed to the hybrid hypermileing paradigm. The Tesla requires an entirely different mode of thinking w/r/t regen and braking ("one pedal driving"). It's just going to take some time for you to switch your thinking on how EVs and hybrids work.
     
  10. Todd Burch

    Todd Burch Electron Pilot

    Joined:
    Nov 3, 2009
    Messages:
    4,734
    Location:
    Smithfield, VA
    Technically coasting is more efficient than regen in most cases. However, in real world driving it's not practical. Lights turn red at inopportune times and you have to stop quickly. People press on their brakes. Cars swerve. Coasting to a stop is virtually impossible.

    Fortunately, regen not only gives you efficiency benefits in 90% of driving, but you can still coast by "centering the needle" on Model S.

    Even though you may not be able to center it perfectly, you'll notice the power scale is logarithmic, so if you're close to zeroed out on the display you're consuming or regenning very little power.
     
  11. HankLloydRight

    HankLloydRight Fluxing

    Joined:
    Jan 18, 2014
    Messages:
    5,785
    Location:
    Connecticut
    Ok, I'm no expert, but in a Model S, how is coasting more efficient than regen if coasting is power neutral and regen, well, isn't?
     
  12. Zythryn

    Zythryn MS 70D, MX 90D

    Joined:
    Mar 18, 2009
    Messages:
    1,660
    Location:
    Minnesota
    Regen wastes 20-50% of your motive power. IF you can always stop by coasting, you waste none of that motive power.
    Most people find that they will need to stop more quickly than coasting to a stop. In such cases regenerative braking is your friend.

    So basically coasting is better than regen,
    regen is better than braking.
     
  13. Saghost

    Saghost Active Member

    Joined:
    Oct 9, 2013
    Messages:
    3,024
    Location:
    Delaware
    It's all about the result you're trying to achieve. Coasting means the car's kinetic energy is being used to overcome the rolling resistance and aerodynamic drag, and the car will eventually come to a stop.

    Getting the same distance without coasting would mean driving under power for some portion of the distance, and then regenerating to slow down faster toward the end of the journey. Under ideal conditions, the regeneration would put as much power back in the battery as the extra power you spent holding the car at speed for the first part of the drive.

    However, no system is 100% efficient. Regeneration gives you back most of the extra power you spent - possibly as much as 80% of it. That still means you lost 20% of that additional power compared to just coasting. (Whereas using friction brakes would mean losing 100% of it.)

    As mentioned above, in the real world it is doubtful that you'll know when you need to slow down far enough ahead to just coast to a stop - and also unlikely that you and the people behind you will have the patience for it. In principle it would be more efficient if you could coast more.
    Walter
     
  14. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

    Joined:
    Jul 12, 2012
    Messages:
    4,502
    Location:
    Maine
    Nope. Regen is just more efficient braking than friction braking

    In a hybrid no pedal means very light regen. It's not ideal and hypermilers are used to a light touch in the go pedal to hit the glide point. But coasting no-pedal is easy. The adjustment required to one-pedal driving is that the glide point requires more go pedal pressure. But as I noted in a previous post, it also sacrifices precision on the go pedal, and that's a loss for hypermilers. I prefer the go and brake to be on continuous scale with the driver choosing where the glide point is and I like the idea of VW's system.
     
  15. SteveS0353

    SteveS0353 Member

    Joined:
    Aug 23, 2014
    Messages:
    357
    Location:
    San Diego, CA
    All good explanations. Coasting is not practical for much of real-world driving, but it's more efficient than keeping the speed on for a long time, then using regen, or worse, hard braking. I like the quote I saw earlier in this thread -- coasting is better than regen, and regen is better than braking. To maximize range requires a driving style that considers that.
     
  16. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    12,756
    Location:
    Texas
    The one thing that is sure is that you will do worse if you keep regen on the low setting. The reason is that you can glide on either setting (glide means to press on the accelerator enough so that you are not using energy or getting it back through regen), but when you have to stop more rapidly than the low setting allows, all the additional braking will come from friction braking rather than capturing the most you can from regen braking.

    In the "regen on brake pedal" system you never ever really get used to the transition from regen to no-regen when hitting a bump or washboard surface. You do get to know the situations where it's likely to happen, but it's always annoying when it does.
     
  17. brianman

    brianman Burrito Founder

    Joined:
    Nov 10, 2011
    Messages:
    15,487
    This.

    IMO standard is more real world efficient. Low is easier on your right foot for extended trips with light traffic; though CC helps even more.
     
  18. JohnQ

    JohnQ Active Member

    Joined:
    Jan 1, 2012
    Messages:
    1,585
    Location:
    Redding, CT
    Depends what you're after. If hypermiling, I get your point. For me, the goal is to be reasonably energy efficient but not to the point of radically changing the way I drive. For example, I'm not going to coast 1/2 a mile out from a red light, slowing well below the speed limit when I have traffic backed up behind me so I can avoid regen.

    It's a personal preference on where to put the regen and, at the end of the day, what Tesla did suits me. The question is whether it suits >50% of the population.
     
  19. Canuck

    Canuck Active Member

    Joined:
    Nov 30, 2013
    Messages:
    3,958
    Location:
    South Surrey, BC
    I don't even feel the regen on my Tahoe Hybrid or Leaf. I really feel, and like, the regen on my Tesla because it means that I can drive with mostly one foot. I wish the regen was like that in my other vehicles.
     
  20. Johann Koeber

    Johann Koeber Member

    Joined:
    May 1, 2012
    Messages:
    664
    Location:
    Nuremburg, Germany
    I definitely prefer the Tesla kind of regen, enabling one foot driving most of the time.

    Only improvement I could think of:

    In my opinion it gets too soft as the car slows down. It will not take you to a full stop. I think I would like that. I always have to use the friction brakes on the last foot or so.

    When I do use the friction brake, I would love to have it hold the car for a second (as in the hill assist), not just when it is on a ramp. Even on almost flat pavement the car easily moves. Actually I almost rolled in the car in back of me. Of course it is my fault. Maybe I should turn on creep.

    Porsche put a lot of work on the brake pedal UI to make it work like a 'regular' car (I refer to those as designed in the last century). The regen is activated by the applying the brake. The systems distributes the load to the regenerative braking system and the friction braking system to give you just the right feel of the brake. Works exactly as the brakes in the cars designed in the last century.
     

Share This Page