Regen Braking With Cruise Control?

Discussion in 'Clarity' started by M.M., May 21, 2018.

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  1. M.M.

    M.M. Active Member

    Couple of questions maybe someone can comment on:

    I've noticed that with the paddles the max regeneration (at least as shown on the power gauge on the instrument cluster) is not as great as the regeneration you get if you apply some brakes. That is, if the gauge shows about halfway through the green with four chevrons of regeneration selected, then you put your foot on the brake, the gauge will increase to three quarters or more of the way through the green.

    Unlike my previous car, the feathering of the regenerative braking and mechanical brakes is so good that I really can't tell when the mechanical brakes kick in.

    So, first question: Is the gauge accurate when it shows higher regeneration while braking? That is, does the brake pedal do more regeneration than the paddles allow?

    Separately, in experimenting briefly going down a steep hill, I noticed that while four chevrons of regeneration was not sufficient to keep the car from accelerating, if I turned on cruise control and set it to, say, 25mph, the car would show more aggressive regeneration and would more or less maintain that speed, even without my using the brakes.

    Which leads to my second question: When the cruise control slows you down, will it only use regenerative braking, or will it resort to the mechanical brakes if that's not sufficient?

    I tried feeling the discs at the bottom of the hill; they were quite hot but not scorching, which was inconclusive since I did have to brake a bit very near the bottom, although I really have no sense of how quickly discs heat up or how quickly they cool.

    I'm curious about this because, if the cruise control does indeed do more aggressive regeneration than the paddles without resorting to calipers, that would be an easy way to descend a steep hill without touching the brakes.
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  3. Wall-e

    Wall-e Member

    I have been finding the regeneration applied with the paddels to be very simular to the regeneration with the brakes. The only difference I can find is you can create a much larger braking force with the brakes which causes greater regen.

    Driving down the street with the brake pedal pressed I will press the paddles and watch the regen graph. Typically I see no benefit from a regenerstion standpoint to use the paddles. I use the paddles when I dont want to take my foot off of the go pedal going around a turn or coming to a light.
    KentuckyKen likes this.
  4. KentuckyKen

    KentuckyKen Well-Known Member

    Thanks M.M.,you’ve given me the excuse to get a non contact IR thermometer (which I’ve always wanted) and check brake rotor temp before and after a hill descent with regen only vs regen w brake pedal effort (enough to add more regen but not bottom out on the gauge). And regen vs ACC. Will try to get to this week if I can find a sale on it.

    PS: just got a borescope with a 20 ft reach cheap since it has no screen and WiFi’s to my phone. So I can snake it in all those places we can’t see. Trying to find horn emitter now. If you need to see an inaccessible area on the car let me know.
  5. rodeknyt

    rodeknyt Active Member

    The ACC is all cars will use the mechanical brakes if needed to maintain the set speed. That's why your discs were hot at the bottom.
  6. Tahuna

    Tahuna Member

    I don't know for sure, but this is my guess as to how it works:

    Think of the braking system as a black box. It gets some input asking it for braking, and it does what it needs to do. If it can use regen it will. If it needs more braking than regen can provide or can't use regen for some reason then it applies physical brakes.

    There are several inputs to this system - the brake pedal, the regen paddles, the cruise control, the collision avoidance system. The paddles have a few clicks of preset braking levels, the cruise control applies braking as required, the pedal may call for braking, etc. The braking system adds up all these inputs and figures out how to apply the braking.

    So a couple of clicks of regen paddles is probably exactly the same as a light touch on the brake pedal, and exactly the same as mild deceleration from the cruise control. Once the maximum regen level is reached and more braking is required, either because you're pushing the pedal harder or the cruise controls wants to slow down faster, then the braking system will apply physical brakes.

    Again, just my guess, but that's the way I'd do it if I were designing it.
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  8. DVoran

    DVoran Member

    Test drove the 2018 Volt and a Tesla and found their regenerative braking (and one-pedal driving) much stronger than that in my Clarity. Would like to have the one-pedal driving option of the other cars combined with the much lighter paddle driven regenerative braking.

    Sent from my iPad using Inside EVs
  9. KentuckyKen

    KentuckyKen Well-Known Member

    The Clarity may not be a true one pedal car, but it comes very close. I can one pedal most of the time except for the last few mph when I have to come to a full stop.
    What really sets it apart is the seemless transition between regeneration and friction braking. Nobody does it better; you can’t tell by pedal effort or feel whether it’s regen or friction!
  10. M.M.

    M.M. Active Member

    Based on simple observation, the first half of that is almost certainly what it does--2 chevrons on the regen paddles is equivalent to a light touch on the brakes or cruise control hold-back on a shallow slope, four chevrons on the regen paddles is equivalent to light-moderate pressure on the brakes or a somewhat steeper hill with cruise control.

    Thing is, though, if (and this is not a given) the green area on the energy gauge is not lying, then moderate or moderate-strong pressure on the brake pedal or cruise control on a steeper hill will give you more regen than four chevrons on the regen paddles will. That is, if I put it in four chevrons, then apply some brake pressure, the line will go deeper in the green than where it was. Likewise for ACC on a steeper hill--the line will go deeper into the green than it will with the regen paddles. It's also possible the green area could be lying, and/or that the feathering starts (but you do indeed get more regen) at deceleration greater than four chevrons.

    Assuming rodeknyt is correct, and ACC will make use of the brakes for hill deceleration and not just while following another vehicle, then there's no real difference between using the brakes when the paddles aren't sufficient and setting cruise control.
    I agree completely that the mixture between regeneration and friction braking is impressive; unlike the Volt, which has a very noticeable breakover point, I really have never been able to tell the difference.

    That said, coming from a Volt the weak regen even with four chevrons is what I am most disappointed in with the Clarity. If I'm driving really gently and/or on very mild slopes, I can get pretty close to one-pedal driving, but the number of kW of regen is way less than I had gotten used to in L in the Volt (which was strong without being violent), and I have to spend way more time with my foot on the brakes than in that car, especially on moderate downhills (plus, since the Volt definitely wasn't feathering the mechanical brakes in L, you could be confident you weren't relying on the brake pads). Likewise in the Volt, it didn't have adaptive cruise control, but if you put it in L with cruise control on it would aggressively maintain speed on downhills without ever touching the brakes, which I was hoping was the same in the Clarity but looks like otherwise.

    There's a lot to love in the Clarity, and it's certainly a good car, but if both cars had the same interior, the mushy regen would have had me buying a new Volt instead.
  11. LAF

    LAF Active Member

    you mean size or quality of interior, because both are not comparable between cars, not to mention the visibility.
    Johnhaydev likes this.
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