Deceleration “shifter” paddles inconsistent performance

Discussion in 'Clarity' started by Kyle’s Clarity, Feb 21, 2019.

  1. I’m wondering if anyone can shed some light on the inconsistency of the deceleration paddles. I understand “down shifting” increases the resistance created by the regenerative system but there are times where I’ll get it to 4 chevrons but the car doesn’t slow down as fast as usual/the charge indicator only shows minimal recharging (when it usually can go “off the chart”). Other times it won’t let me engage the 4th chevron (it’ll flash at me but stay at 3). On this latter point, I suspect that if the battery is near capacity then the regenerative system limits itself but I’ve had it on occasions where my battery is well below full and the 4th chevron won’t engage. Thoughts or knowledge anyone?


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  2. guinness10

    guinness10 New Member

    My experience is that the paddle/regent system doesn’t slow the car as much when the battery is near capacity. As for the 4th chevron not appearing, that tends to happen when going too fast. I haven’t nailed down the exact speed at which the 4th chevron doesn’t activate, but IMO it’s definitely tied to the speed the car is traveling.
     
  3. tterag

    tterag Member

    I've been trying to figure out if the car lights up the brake light when using the paddles. It definitely brakes hard enough on the 4th level to warrant it.
     
  4. Groves Cooke

    Groves Cooke Active Member

    "I've been trying to figure out if the car lights up the brake light when using the paddles. It definitely brakes hard enough on the 4th level to warrant it."

    If the battery is at a high SOC and you use the paddles the brake lights come on. If the SOC is less than 3/4s then the lights do not come on. I have observed this while driving at night. It is possible to see the brake lights light up reflectives sign in the rear view mirror.
     
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  5. PHEV Newbie

    PHEV Newbie Well-Known Member

    On another thread, a poster included information from Honda on how regen works on the Clarity. In normal braking, it's 100% regen until the last few feet. For a little while, my brakes were a little noisy and that's exactly what I observed. Of course, in emergency situations, it'll also apply friction braking. My point here is that it is unnecessary to use the paddles to get the maximum regen. They were kind of fun but I now only use them on mountain downgrades so I don't have to keep my foot in one position for so long.
     
  6. Ray B

    Ray B Active Member Subscriber

    The regen level is greatly dictated by the battery temperature and its state of charge (SoC). For a cold battery, say <30 F and with a high SoC, it will likely restrict the amount of regen power going to the battery. In some cases it will compensate by running the engine to manage the influx extra energy, or may just use more of the hydraulic (friction) brakes. As the battery gets depleted or warmer, it may begin to allow more regen power to be captured.

    The chart below on the right shows cold weather behavior of the battery. When SoC is high, it cannot accept a lot of power.

    Li-ion EV perf4.png

    Keep in mind that the brake pedal and regen paddles are not equivalent. Regen paddles only activate and regulate the capture of kinetic energy through the front wheels, while touching the brake pedal will do that along with applying friction to the rear brakes (and possibly some to the fronts as well; managed by the car's brain). In slippery conditions one should think about whether or not it is safe to employ aggressive regen, or rely more on the brakes to have a more stable deceleration.

    In cold weather when the 4 chevron regen only moves the needle slightly into the green and the car only mildly decelerates and I have to follow-up with the brake pedal, and the needle does not move any farther into regen, then I assume that it is mostly using friction brakes. This time of year that scenario is common, particularly when my SoC is above say 75%.

    And yes, I think when the regen power restricted, it may flash when 4 chevrons are requested, and bump it down to 3 or even 2.

    Looking forward to March...
     
    Last edited: Feb 21, 2019
  7. Mark W

    Mark W Active Member

    Thanks for those diagrams. Very interesting. I didn't know about the temperature influence on regen, it makes sense though. Where are those diagrams from?

    The part I left above doesn't make sense to me. It sounds like you are saying that whenever you press the brake pedal, rear friction braking is applied. Why would they make it work that way? Why apply friction brakes when it's not necessary? I have never read of any EV working that way.
     
  8. KentuckyKen

    KentuckyKen Well-Known Member

    I think the point @Ray B is making is that the paddles can NEVER call upon friction braking while the pedal MAY use friction braking. However IMHO, in normal use, ie moderate braking, there is no difference in regen.

    In the interests of full disclosure, I’m a paddle fan boy just because I’m too lazy to move my leg when just a finger will do.
     
  9. tterag

    tterag Member

    Amen. Dittos here.


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  10. David Towle

    David Towle Active Member

    I just drive in sport with 4 chevrons (when allowed) and do 1 pedal driving 90% of the time.
     
  11. Edward Dries

    Edward Dries New Member

    Has anyone else noticed that when using the paddles to decelerate and then having to use the brake for additional stopping power that the brake is a lot firmer and takes more force than when just using the brake alone to stop?
     
  12. Ray B

    Ray B Active Member Subscriber

    It is hard to be dogmatic about very much in Honda Clarity engineering, because so very little is released to the public. I have kept at it by looking over their work published on previous generation of their cars, or similar cars, but one can never be sure what the heck they are doing. So all that I write on this and other topics can be easily set aside by reverse engineering or a glimpse of true information from Honda.

    Having said all that, I speculate that there are three strategies for 'cooperative braking' using the brake pedal - that is, regen braking + friction braking - and they come down to what this reference (https://www.mdpi.com/1996-1073/10/11/1875) describes as 1) Serial Braking, 2) ECO braking, and 3) Fuzzy logic :

    1) Serial Braking - Rear brakes are always engaged, the front divides the work between the regen and the friction brakes
    CoopBraking_Serial.png


    2) ECO - Regen is engaged to their maximum capability and any extra braking effort required is then split between the front and rear friction brakes.

    CoopBraking_ECON.png

    3) Fuzzy logic - a complex blend of regen and friction using numerous inputs to maximize regen, safety, stability, and feel. In the reference that these figures came from, they call it 'Racing mode control strategy'

    CoopBraking_Fuzzy.png

    Based on how complex Honda has made the Clarity, I would expect that the 'Fuzzy logic' approach is what they employ, and it would be impossible for general users to decipher exactly what is going on without investing serious time and resources. The end result is likely to be something as is described in this braking scenario (mild, followed by moderate, followed by heavy braking):

    CoopBraking_Fuzzy2.png

    In the paper, they explain how the ECO strategy is far superior in terms of efficiency, but you have to realize that all of the braking bias is in the front, and then it switches to a front/rear split which is quite destabilizing. Especially if you are at a slushy off-ramp and suddenly have to avoid something and brake. With a dramatic shift in brake bias, these kind of situations can be very difficult to manage for the driver and the driver assist systems. That is why I believe that Honda would prefer having a somewhat uniform brake bias and then maximize the efficiency only after safety and stability are looked after. It may not be the correct answer, but I would think most car makers are skittish about new technologies like cooperative braking by wire, and will err on the side of caution rather than simply maximizing efficiency.

    Just guessing...

    PS - keep in mind that this car, although front wheel drive, is a little less front biased in weight distribution than typical sedans due to the heavy battery under the floor and below the rear seat. So I think rear brakes may play a little more role than would be normally expected compared to a garden variety sedan.
     
    Last edited: Feb 21, 2019
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  13. Ray B

    Ray B Active Member Subscriber

    Hi Mark - just snooping around the web. It appears (though we can never be 100% certain) that the Clarity PHEV uses the EHW5 battery from Blue Energy - a joint venture between Honda and GS Yuasa. I found the chart on two different pages:

    https://www.blue-energy.co.jp/en/products/index.html

    https://www.gs-yuasa.com/jp/deepstory/vol5.html (right click and select 'Translate into English' if you are using Chrome).

    But I couldn't read the chart so I had to use Google Translate to convert all of the Japanese characters into English. Then I used ImageJ to strip out the red lines as they refer to a different battery.
     
  14. Mark W

    Mark W Active Member

    Good conversation.

    Ray, I appreciate you providing your analysis. I just want to make sure people here realize that you are trying to fill in the blanks as you explain above because Honda hasn't said how they implement their braking strategy in the Clarity. It's the only thing we can do, right?

    I can't imagine that this statement can be true though:
    "Regen paddles only activate and regulate the capture of kinetic energy through the front wheels, while touching the brake pedal will do that along with applying friction to the rear brakes". This doesn't make any sense to me. There is no logical reason to use friction brakes with a mild depressing of the brake pedal. I have read quite a bit about electric cars and braking, and have never read anything that says that friction brakes are used for mild to moderate braking.

    But, this is just based on my pea brained logic, and things I have read on the internet. I am far from an engineer. Much farther than most in fact :)

    Again Ray, thanks for your references, it was interesting reading.
     

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