A rant about regen

Discussion in 'Hyundai Kona Electric' started by hobbit, Sep 19, 2019.

  1. hobbit

    hobbit Member

    I read through several forum threads before actually joining up, and
    one thing that stood out for me was all the back-and-forth about
    optimal regen-level settings and their effect on efficiency. Here
    and in other similar forums, there's a lot of misinformation about
    how regeneration works in the Kona, and probably Hyundai/Kia's entire
    lineup of EVs and hybrids -- not to mention flat-out BS about
    optimizing energy use. In the 3-ish weeks I've been driving this
    I've played and learned quite a bit, and it wasn't hard to figure
    out what the real story is here.

    If you need a TL;dr for this, it amounts to "one-pedal driving is
    stupid". That may garner enough attention to want to read the
    rest of this and learn why.

    Driving the Prius for a decade and a half, especially with all of
    its added instrumentation, has given me a good "gut feel" for what's
    happening in a driveline. It was established long since that the
    second-generation Prius and everything that follows makes every
    effort to stay OFF the hydraulic brakes as much and as long as
    possible, duly proven out by my brake-line pressure monitors.
    I don't need to add such a thing to the Kona, however, to determine
    that its braking is FULLY INTEGRATED in much the same way, and that
    pressing the "service brake" pedal does not throw away energy as is
    so commonly feared. The Prius largely pioneered such well-integrated
    braking, and it's totally a known science among all the automakers
    at this point.

    I had already made some satisfactory tests around home, but today I
    finally got to drive a mountain-summit road up and down. [Wachusett,
    as a quick experiment after *hiking* up and down, before heading
    home.] On a weekday afternoon there weren't many people around, so
    I was running about 25 kW in a very leisurely tool up to the top.
    I was already at regen-level 0, which is my default, and on the way
    down used nothing but the brake pedal to control speed. That was
    showing around -20 to -30 kW as I expected, varying with the slope
    as I kept a fairly even descent speed. After a while of this I
    spotted a convenient pull-off and stopped, and got out to feel the
    front brake rotors through the wheel slots.

    Stone cold. In an ICE car, even in low gear, I would have burned
    my fingertip.

    Once back on the main road there was more downhill at higher speed,
    and near the end of that I pulled a pretty hard stop, about as hard
    as I dared with someone's pickup truck coming up behind me, to turn
    off into a parking area for another check. That peaked at -75 kW
    according to the yellow number on the energy display. And still,
    rotors stone cold. Oh, and I got two percent SoC back, heh.

    I never touched the regen paddles away from 0, and the results were
    exactly as I expected. You can do this experiment yourself; find
    a big downhill with a stopping place at the bottom and go to town.
    Braking is fully regenerative, exactly like in the Prius, and briefly
    falls back to hydraulics down around 5 or 6 mph where there isn't
    enough motor speed anymore and it doesn't matter. If your rotors are
    rusty after a wet night, you can feel that transition.

    The integration will kick out and fall back to hydraulics under a
    couple of rare situations. If you shift to N, you're completely
    on hydraulics, and you can use that to clean the rust off your
    rotors when needed. Heavy bumps in a strong stop will cause the
    drive system to give up on regen as too hard to control under
    wildly varying conditions, and some of you have probably felt that
    transition once in a while -- it's very quick but perceptible in
    the Kona, and probably due to today's faster processors and networks.
    Bad tuning of that and some lag in the early third-generation Priuses
    were one of the things that the ignorant masses were referring to as
    "unintended acceleration", more properly described as momentary
    braking-force fade, but they didn't learn to expect it and that the
    car was simply adjusting and was not about to let them down. Also,
    an outright panic stop with a fast swing of the pedal will likely go
    to hydraulics first, as there isn't time to coordinate negative motor
    torque between the brake controller and the power electronics. I
    don't know that 100% about the Kona but it was certainly true in
    the Prius, and the Kona has all the same sensors around the brake
    pedal to make that work the same.

    So there is no need or benefit from using any regen level other
    than 0. It's pointless, and only contributes to an *inefficient*
    driving style. I'm a little miffed that we can't set that as any of
    the drive-mode defaults, and the OM completely lies about that. But
    all I do is smack the right paddle once when taking off, and I'm set.
    The 0-regen glide is beautiful, a "float" that doesn't require any
    effort to lock one's foot at a particular position. In fact, there's
    a tiny bit of regen in that mode anyway, but at -2 or -3 kW you can't
    even feel the difference between that and Neutral. With any regen
    level above that, a driver is basically always pushing a lot of
    energy in and out of the pack, almost like bad ICE drivers who are
    gas, brake, gas, brake, and never just coasting. Maybe having regen
    recovers a little of that, but your *momentum* is the form of energy
    storage that requires no conversion to be utilized for what you
    want -- to jus' git on down the road! Why mess with that? Your
    motor, pack, inverter, and tires will appreciate having to work
    less hard overall.

    More importantly in the safety context, you don't want to surprise
    drivers behind you. One of the first things I've installed is a
    "telltale" light for the brake lights, an LED right next to the
    power/regen bargraph on the left, and yes, while very heavy regen
    will cause the brake lights to come on [at whatever that NHTSA-
    mandated deceleration level is that I read about someplace], you
    can nonetheless regen at a level that basically makes the car fall
    on its face and *doesn't* warn the people behind you. That's just
    stupid, and could arguably be declared malicious if it was a factor
    in an incident. Unless you're trying to collect the insurance money
    from your rear-ended brandy-new EV, don't "one-pedal" in traffic.

    On the highway I might occasionally use a quick shot of level 1 to
    scrub off a couple of MPH and re-equalize my following distance,
    but only when it's clear to the rear and I don't have to slow any
    harder than that. If I slow in any significant way, I *want* the
    brake lights to come on to warn those behind [at least the ones
    that aren't buried in their phones].

    Credit where due: "Kiwime" and David Green, at least, have also
    extolled the benefits of regen-0 in other threads, and some of
    that coupled with my observations today is what prompted this.

    In the next post I will discuss how some of this relates to the ECO
    display, because I think I've worked out what that's about too.

    _H*
     
    Kamloops_KoNa, KiwiME, ehatch and 5 others like this.
  2. hobbit

    hobbit Member

    Part 2: The arc of ECO

    Drive mode "eco" is the only one that makes sense to me, because I
    love a "slow-bottom" pedal response for the fine control at low
    speeds I've come to appreciate in the Prius. All the power anybody
    wants is out at the far end of go-pedal travel, so it's not like
    staying in the smoother control scenario is going to have you making
    an annoyingly "stately entrance" onto the interstate. Both "Normal"
    and "Sport" are way too jumpy off the peg for me, and remind me of
    the typical fast-bottom throttle setups on most ICE iron. I hate
    that. Habitually *not* leaping headlong through intersections on
    the green has saved my butt on several occasions.

    So it's ECO and regen-0 for me, after trying out all the other
    setups. That feels almost exactly like the Prius, and in fact I
    noticed that on some of my early Kona test drives and sat there
    thinking "hey, I'm home". Regen 1, in fact, feels about like the
    Prius in "B" mode and even that's too much.

    There's been some conjecture about the "teal arc" over the center
    cluster circle, which one would guess indicates a soft limit which
    not exceeding too often gives you the most economical driving. I
    pay attention to such things, and have been running at or north of
    5 mi/kWh the whole time I've had the car so far. But sometimes on
    the highway it shrinks to a positively laughable sliver, and to
    maintain speed I need to go pretty far into the "red bars". Then
    it widens out again, seemingly at random, when conditions haven't
    appreciably changed.

    What I think it's based on is the car's *pitch* sensor. As in, tilt
    from front to back, trying to indicate to you that it's okay to push
    harder going uphill, but please rein it in on the downs. There are
    full G and acceleration sensors present for the stability control,
    so the drive system can easily get data on front-to-rear "G force".
    But that's not the only piece of input, as a sensor in a box can't
    tell if you're accelerating or just sitting pointing uphill ...
    but any *change* in wheel speed over time can complete that picture.
    As I watch terrain and the length of the arc, it seems closely tied
    with going up or down grades, and because the delta-speed calculation
    has to play into it that's the most likely reason its response has
    a bit of delay. It also seems to respond over a greater range at
    higher speeds.

    Now, here's where things get stupid. Any regen level greater than
    0 requires some bit of foot input to reach a "neutral float" level
    of power, as close to 0 kW as possible. The white arc underneath
    is clearly tied very simply to pedal position. In regen levels
    1 - 3 I have to push the pedal to simply glide, where in 0 I just
    let off and enjoy. The white arc nonetheless indicates that pedal
    push and holds there, and if I set regen 3 and am going slightly
    downhill on the highway, where I'd normally have nothing or a a tiny
    whisper of white, in regen 3 I'm way out tickling the "red bars" as
    though I was actively accelerating. Which makes that display even
    more misleading and useless.

    None of that matters. What matters is that little yellow number on
    the electrical-usage screen, your kilowatts in and out. I've always
    had instantaneous-energy displays in the Prius -- battery current and
    an engine "horsepower" reading calibrated in kilowatts instead, so I
    know pretty well what it takes to push a vehicle around. This one
    is about a thousand pounds heavier than the Prius, but the way it
    drives in my preferred modes I can barely tell the difference. In
    fact the EV is less "engaging" than the Prius in a lot of ways, when
    I don't have to worry about bringing the engine into its sweet-spot
    or when to start and stop a burn. So I've had more leisure to play
    with things like the lane-keep nanny and figure out its many bugs.
    Stuff like that might become the subject of future rants.

    _H*
     
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  3. victor_2019

    victor_2019 Active Member

    Just because you are used to the Prius feeling doesn't make one pedal driving useless or stupid.

    I have eco mode set up to use regen 3 and i can control the vehicle speed completely using the acceleration pedal. I wish it had true one pedal driving like the leaf so i wouldn't need to take my foot of the accelerator at all.

    In terms of efficiency, there's no difference if you press the brake lightly in regen 0 or if you simply lift slightly the accelerator in level 3.
     
  4. Bugblndr

    Bugblndr Member

    Interesting testing and your findings are basically what I've assumed all along about the vehicle. That said, people buy EV's for different reasons and have different driving styles. For the first two weeks, I hated anything above regen level 1. Now I have regen level 3 set as the default for normal mode. When not using adaptive cruise control for no pedal driving, I'm pretty much always using one pedal driving.

    I tried eco mode for 1 day's worth of driving and wasn't a fan. I like the instant pedal feel, the ease of laying down the power when in normal or sport mode. I've driven a CMax for the past 4 1/2 years, 155,000km. While that car gets great fuel economy and has considerably more power than a Prius, that type of driving experience wasn't what I was looking for in an EV. With the hybrid, I was trying to drive efficiently and get great mileage per tank. With the Kona, I don't really care as charging costs are so cheap.

    That's the great thing about the car, you can adjust it to fit the way you want to drive.
     
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  5. electriceddy

    electriceddy Well-Known Member

    Now if it could just "stay" that way :rolleyes:
     
  6. hobbit

    hobbit Member

    For reference, here's one of the other in-depth regen discussions that
    helped lead me to research and report:

    http://www.mykonaev.com/forum/viewtopic.php?f=11&t=21

    Perhaps someone who's also a member over there could drop a link
    back to this? There are only so many forums that one has time to
    usefully join...

    _H*
     
  7. SeanH

    SeanH Member

    I also moved from a Prius to the Kona EV, but have driven a bunch of miles in Teslas (company cars).
    I keep my regen at "1" because I like the slight decrease from pure coast when I let off the accelerator -- this is how the Prius felt and this is actually how my other car (a Subaru Forester) feels.
    I have driven many, many miles with 1 pedal driving in Teslas. I hate it. The primary reason is that for normal driving it is fine, but for dense traffic and/or pedestrians, I really like the ability to "hover" over the brake pedal. This is the best and fastest way to stop quickly. I can't do this with 1 pedal -- it doesn't slow down fast enough even with it set to "3" and even pulling on the paddle. I can suddenly "lift off" the accelerator, but that doesn't generate as much braking as mashing the brake pedal. I've had too many close calls where the extra time to switch pedals nearly caused an accident.
    YMMV of course :) I like that the Kona gives us the option.
     
  8. robxb

    robxb Active Member

    Great tip, thanks!

    I really dislike how regen doesn't light up the brakes.. in 16 years of driving (mostly in Toronto), I have never been involved in an accident in stop-and-go traffic (knock on wood), as I generally read the road ahead, looking for brake lights, etc, but I tell ya, I came close when changing lanes behind a leaf and it slowed right down without the brake lights coming on. For safety's sake, EVs REALLY need to have those lights coming on even when there's slight deceleration.
     
    ehatch likes this.
  9. SkookumPete

    SkookumPete Active Member

    Right. The Eco mode gauge is bogus, as I pointed out in another thread.

    As for the rest, I just can't see that there's a right or wrong way to use regen. I personally favour automatic regen as it largely eliminates the need to touch the brake or paddles except when coming to a stop.

    We've had this discussion before about the supposed benefits of freewheeling, but in the final analysis it's a big-endian vs. little-endian sort of thing.
     
    Last edited: Sep 20, 2019
  10. FlbrkMike

    FlbrkMike Member

    Thanks for the useful information, but I have to disagree with your basic premise and your conclusions.

    "What matters is that little yellow number on the electrical-usage screen, your kilowatts in and out."
    Actually that's not what matters, at least to me. I love the fact that I'm saving probably 75% or more on fuel costs, but I really don't GARA about saving a kWh here or there. That's nibbling around the edges and, in the long run, just noise in the data. If it makes you feel good to constantly monitor your performance then good for you. I adjust the regen based on how I like to drive. In the area around my home there are lots of up- and down-hill roads with many twists and turns. I like being able to drive with one pedal most of the time and regen 2 does this perfectly. On my way to work, I encounter more of the same kind of roads but also some 55 mph expressways with stoplights. I'll go back and forth between 1 and 2 (sometimes even 0 or 3). I use the left paddle probably 75% of the time to come to a complete stop.

    Always ready to use the brake pedal, of needed, but I prefer to one-foot it as much as possible. This car reminds me of driving slot cars when I was a kid.
     
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  11. SkookumPete

    SkookumPete Active Member

    So you ease the throttle to keep your distance from the car in front, or to slow gradually for a light far ahead, and your brake lights come on? That would make you more annoying and dangerous than the two-footed drivers whose brake lights give no meaningful information.
     
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  12. FlbrkMike

    FlbrkMike Member

    Exactly. Brake lights don't come on when you downshift a manual transmission either. Most drivers in general just need to be more observant of what's going on around them.
     
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  13. ehatch

    ehatch Active Member

    Safety,people need to stop hugging the bumper ahead, regen/no regen. I do prefer one pedal driving,and do slow down ahead of time,similar to using ACC. WHY the brake light doesn't turn on using regen. shouldn't be acceptable to the NHTSA, need the brake light.

    @hobbit bit thanks for the thoughtful "essay" on regenerating braking,and actually taking the time to test the brake rotor heat,finding it's absent after steep downhill driving. So,our EV brakes will still wear less outside high speed/emergency braking.
     
  14. Esprit1st

    Esprit1st Well-Known Member

    Why would you be observant? That's what insurance is for, right?
    The car is the safe place for texting, reading, putting on makeup, smoking and eating!

    Sent from my moto x4 using Tapatalk
     
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  15. SkookumPete

    SkookumPete Active Member

    Do you mean "doesn't always"? Because it's been settled here and elsewhere that regen does trigger the brake lights at a rate of deceleration where an ICEr would have their foot on the pedal.
     
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  16. DelRider

    DelRider New Member

    Wow, two walls of text. Not gonna read them; really enjoying the Kona and just not the hand-wringing sorta guy. But kudos on the fortitude my man! Carry on all.
     
    Kitsilano likes this.
  17. KiwiME

    KiwiME Active Member

    Thanks for your write up. I forgot about that forum as it didn't get updated often.
    If you are interested in further engineering-level technical analysis (having the time to spare, a familiarity with Excel and using a newish Android phone/tablet) you will find Torque Pro more fun than a barrel of monkeys.

    You can log the data over time then analyse that using Excel in the relative 'safety' of your home or office. It's practical to use the app's logging feature up to about 1/2 hour (e.g. to create DC charging power profiles) or log the data by hand at waypoints to come up with longer-term averages.

    On the subject of your thread I've had a crack at measuring maximum regen efficiency and that turned out to be 83%, but as I did that ages ago it could need correcting. Essentially, that means entering the regen region of the power envelope inadvertently loses 17% of energy you've paid for.

    On a 670 km round trip, I was able to determine that regen returned 17.5% on the first more-hilly half and 13.1% on the second flat half.
     
    Last edited: Sep 20, 2019
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  18. KiwiME

    KiwiME Active Member

    Funny, that's how I feel about watching sports... It's not really hand-wringing by any means, just curious minds want to know. I don't care about the Kona's economy, if I did I would have stuck with my previous ICE car and saved myself 75k.
     
  19. ehatch

    ehatch Active Member

    I got confused with Hobbit's "essay?" Well then , why did an ICE SUV nearly run into my cargo the other day :( Thanks for clarifying,haven't had a chance to "test" the brake light during regen.stopping.
     
  20. electriceddy

    electriceddy Well-Known Member

    https://insideevsforum.com/community/index.php?threads/small-issues-quirks.5006/page-15#post-69503
    I mostly drive ECCO level 3 regen and take my foot completely off accelerator in order to insure the driver behind is aware of my deceleration or touch the brake petal while in SCC
     
    Last edited: Sep 21, 2019

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