Regen limited in cold temps or high SoC

Discussion in 'Clarity' started by Ray B, Jan 2, 2019.

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  1. Ray B

    Ray B Active Member

    I had noticed a limitation in the regen in the past when getting off the highway, that it wouldn't go to 4 chevrons above ~55 mph. It would blink and drop to 3 chevrons. Once I slowed below that speed the 4th chevron would stay.

    But I found a few days ago in ECON mode (no engine use, EV only) that the level of recharge I was getting from the paddles was pretty limited (maxing out at halfway to the first tick on the recharge spedometer thingy); even when applying the brakes a little more aggressively. Granted it was a winter day, but not overly cold outside (~36F/2C?) and the car is kept in a garage, so a little warmer than ambient temperatures overnight. There was ~10 miles used since the charge, so it was probably at ~75-80% SoC. And the car should have been fairly warm with the heater and general battery/motor use.

    I know there have been long discussions about triggering the engine when regenerating at very high SoC, but I am finding that the regen is limiting itself now in the winter (even in mild temperatures), and/or between 80 and 95% SoC. At lower SoC I didn't seem to have that regen limitation anymore and the paddles and brakes could bring the charge spedometer all the way to the bottom of the gauge.

    Not a complaint, but just something I had noticed for the first time after 4 months of driving it. Presumably, it uses more of the disk brakes when I hit the brakes when the level of regen is limited. Something to keep in mind over the colder months.

    I just read the relevant section of the manual:
    "In the following situations, the stage may not change and the stage number will blink even if you pull back the selector. The deceleration stage may decrease or cancel automatically:
    • The high voltage battery is fully charged or its temperature is too cold or too hot
    • The speed of the vehicle is beyond the deceleration range with SPORT mode off
    • Hybrid system protection is needed
    • The paddle selector is operated while your vehicle is stopped automatically by ACC with LSF
    If either paddle selector is operated, ACC with LSF will cancel automatically."

    Not sure if anyone else has noticed this regen limit in cold temps and/or at moderately high SoC.
    Dmiko likes this.
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  3. Atkinson

    Atkinson Active Member

    I have noticed this since cold weather began.
    Guessing the battery is too cold.
    Not sure what hybrid protection is.
    Vezz66 likes this.
  4. rodeknyt

    rodeknyt Active Member

    I, too, have noticed similar behavior. I live on a rather steep street and during the warmer months with a full charge I would trigger the ICE within about a tenth of a mile just using the brakes to moderate my speed. Now, with morning temps in the low-mid 50s, even with a full battery the exact same scenario hasn't triggered the ICE.
  5. ozy

    ozy Active Member

    I have noticed the exact same thing. In short, cannot use regen paddles when EV charge is full or the chevrons will tick down and the ICE will come on. I think that they use the term "Hybrid Protection" to indicate that you cannot safely supercharge a fully charged battery by employing regen. So HV kicks in to protect.
  6. KentuckyKen

    KentuckyKen Well-Known Member

    Exactly. @insightman first postulated that on the forum but so far no one knows for sure exactly how turning on the ICE accomplishes this.

    I did find this article from Jalopnik about brake pads in EVs

    that mentions this quote from Jaguar about this phenomenon:

    There isn’t an entirely short/straight forward answer here. The Reader’s Digest version of this is I can’t speak to other manufacturers requirements or the validity of Elon’s statement, but the brake pads on the I-PACE do indeed need to be replaced periodically. As you might imagine, the rate at which this is required varies widely owner to owner, based on his/her individual driving style

    The I-PACE offers two modes of selective regenerative braking; high and low.

    In low regen mode, the resistance of the electric motors is less obtrusive, allowing he or she to coast; similar to a normal internal combustion car. When an owner applies the brakes in this mode in normal braking conditions (i.e. not a panic stop) and when the battery is below approximately an 80% state of charge, the first bit of the pedal isn’t actually engaging the brake pads/rotors, instead it relies on using the resistance of the motors to provide regenerative braking; transferring braking energy into the battery to add charge. Of course in a panic situation the brake pads do engage the rotors to slow the car (causing wear).

    In high regen mode (single pedal driving) on the I-PACE, the vast majority (but not all) braking needs can be assumed with the resistance of the electric motors alone; in most cases the driver then will only use the accelerator pedal. This feature is especially helpful in urban traffic.

    There are exceptions of course. The battery must be below approximately 80% state of charge in order to receive the full benefit of the resistance of the electric motors. The idea here is that we can’t overcharge the battery and force additional electrons in, if it’s already full, so the resistance provided by the motors gradually does decrease the fuller the battery is requiring the use of the standard braking system.

    Emphasis added.
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  8. ralfalfa

    ralfalfa Member

    Very timely discussion. I noticed this behavior several times in the last few days here in NE Ohio when the temps are in the 20's F, and headed to this forum to see what other people noticed. Behavior as Ray B explained first- didn't matter what mode I was in, when I used the paddles to increase regen from low level to high (some lovely downhills) they'd just blink, and regen in general was low, and the ICE came on at the same time even in ECON mode. Always in the first 10 minutes of driving after fully charging overnight.

    I think the overcharging-protection explanation is entirely plausible here, since that behavior went away for me after 7-10 miles or so and the battery charge had dropped a bit (20-25%?). But I'll guess the algorithm isn't binary ( not "if temp < X and charge full, then regen= off" ); the accessible regen level seemed to change back and forth during the drive, lasted a different amount of time on different days, and sometimes I could push regen up to 2 but not higher, other times to 3 but not higher. That suggests some complex monitoring of battery temperature, charge, ICE output, etc. Would be very interesting to figure out what "temp X" is; and I'll try to note how it behaves when cold and in a lower charge state (if I can ever forget to plug the car in overnight).

    Not feeling any stress over this, the car just works and that makes me happy. But like a lot of folks on this forum, love the puzzles that living with a Honda Clarity throws at us all the time.
    MPower likes this.
  9. MNSteve

    MNSteve Well-Known Member

    Yes, us reverse-engineering guys mull over this kind of thing a lot. One of the things I've observed is that the algorithms that the engineers developed for all of the systems are either very complex or badly flawed. I hope it's the former, but it makes it difficult to predict what the car is going to do because it is apparently taking many factors into consideration. As another member mentioned recently, the behavior of the "gear icon" is not the same if you drive the same road at the same speed with the same battery charge when the temperature is the same, one day to the next. Maybe it's the relative humidity . . .
  10. insightman

    insightman Well-Known Member Subscriber

    The 2020 Clarity PHEV will probably get 100 mpg with a 100-mile EV range using the same hardware after the engineers get the algorithms straightened out. /s
    Johnhaydev likes this.
  11. KentuckyKen

    KentuckyKen Well-Known Member

    I wonder if after a long work day and a lot of karaoke and sake, a group of Japanese engineers decided that throwing in a little random number generator effect would drive those gaijin crazy?
    Last edited: Jan 11, 2019
    MNSteve likes this.
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