Regenerative brake with slope / level dependence?

Discussion in 'Gen 2 Prius Technical Discussion' started by MickyMatter, May 11, 2020.

  1. MickyMatter

    MickyMatter Active Member

    Joined:
    Mar 2, 2015
    229
    146
    0
    Location:
    Germany
    Vehicle:
    2008 Prius
    Model:
    II
    While using the Hybrid Assistant App, I was wondering about the regenerative brake:
    In my surrounding area (Black Forest, Germany) are some very sloping roads, where the regenerative brake switches to friction-only brake.
    This happens with a cold or a already warm driven car, with 40% to 60% SoC.
    Even a slightly pressed brake pedal at 20 to 40 km/h (15 to 25 mph) results at the beginning of the slope in about 5 to 6 kW. (The indicator arrow says, the maximum of up to >20 kW would be possible.) And with the slope getting steeper the app doesn't show any regenerative charging power but friction-only braking.
    Even when braking until stop, releasing the brake and braking again the still very slow car will use the friction-only brake. But as soon as the road is flat again, I'm able to use the regenerative brake function again.

    So is there any inclination angle limit, from where the brake system is switching from regenerative to friction-only?

    SM-G950F ?
     
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    87,554
    38,973
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    what id the battery level? have you tried b mode?
     
  3. davecook89t

    davecook89t Senior Member

    Joined:
    May 10, 2016
    693
    513
    0
    Location:
    Washington State, Florida
    Vehicle:
    2017 Prius
    Model:
    Four Touring
    Interesting observation. I'm curious to see what explanations the more knowledgeable people on this site come up with. It seems as though you have seen this on many occasions at different levels of State of Charge, correct? Have you also been monitoring the battery temperatures as this has been happening?
     
  4. MickyMatter

    MickyMatter Active Member

    Joined:
    Mar 2, 2015
    229
    146
    0
    Location:
    Germany
    Vehicle:
    2008 Prius
    Model:
    II
    @bisco

    As mentioned above SOC is at ideal 60% or even below.

    I haven't tried B, because these steep slopes aren't this long (only a few hundred meters/ yards). But I'll do this next time. Maybe the behavior will change with the reduced recuperation in B.

    SM-G950F ?
     
    bisco likes this.
  5. MickyMatter

    MickyMatter Active Member

    Joined:
    Mar 2, 2015
    229
    146
    0
    Location:
    Germany
    Vehicle:
    2008 Prius
    Model:
    II
    Yes. The battery temperature was 23°C/ ?F (it's a common living room temperature.)

    As you can see in the map, with the road getting less steep the recuperation came back. 20200512_015915.jpg

    SM-G950F ?
     
    davecook89t likes this.
  6. dolj

    dolj Senior Member

    Joined:
    May 14, 2012
    4,344
    2,324
    0
    Location:
    Wellington, New Zealand
    Vehicle:
    2006 Prius
    What condition is your HV battery in?

    On those sections where it is (supposedly) using hydraulics only, what is shown on the Energy Monitor screen on the MFD?
     
  7. MickyMatter

    MickyMatter Active Member

    Joined:
    Mar 2, 2015
    229
    146
    0
    Location:
    Germany
    Vehicle:
    2008 Prius
    Model:
    II
    Yesterday I drove again this steep slope under the same circumstances. This time I saw a traffic sign warning of 15% of slope (= -8.5°).

    @dolj The MFD was showing all the time only blue arrows from the tires to the battery – even while the app was saying there's no recuperation.

    @bisco In fact B helped. After switching from D to B the hydraulic friction brake kept working. But there were also about 5 kW electric power regenerated, which they weren't there before in D.

    However it seems I'm not able to then slightly brake without the use of the hydraulic friction brake at some short but steep slopes. Immediately after this passage after the next corner there's a less steep road where I'm able to brake exclusively with recuperation and no hydraulic friction brake – slightly with 5 kW and even more with 10 or 15 kW.

    I'm wondering if there's any steepness limit (maybe around 15%) for a mandatory additional use of the hydraulic brake.
    Perhaps there are security purposes?
    I doubt it's a power/thermomanagement thing as my battery was well temperatured at 34°C/93°F (fan blowing at 1/6) and below 56% state of charge. The charging limit was shown at 25 kW.

    Anybody with the same behavior?

    SM-G950F ?
     
  8. davecook89t

    davecook89t Senior Member

    Joined:
    May 10, 2016
    693
    513
    0
    Location:
    Washington State, Florida
    Vehicle:
    2017 Prius
    Model:
    Four Touring
    I'm pretty sure I haven't seen anyone else discussing this behavior of the Gen 2 Prius on this forum. Perhaps you've made a discovery about this car that was not previously known. The only device on the car that I'm aware of that might come close to what would be required to measure the grade on which the car is traveling would be the headlight leveling sensor. It's unlikely that would be electronically connected to the HV ECU, but maybe there is a similar device that is. Is that what you are postulating?
     
  9. MickyMatter

    MickyMatter Active Member

    Joined:
    Mar 2, 2015
    229
    146
    0
    Location:
    Germany
    Vehicle:
    2008 Prius
    Model:
    II
    Yes, kind of. But my Prius has halogen lights only with a manual level correction dial wheel.
    There's a g-sensor for the airbags, which possibly can measure this too, but I doubt a double use of this delicate sensor.

    SM-G950F ?
     
    davecook89t likes this.
  10. R-P

    R-P Active Member

    Joined:
    Dec 6, 2011
    694
    184
    0
    Location:
    Netherlands
    Vehicle:
    2009 Prius
    Model:
    II
    Ony thing I ever noticed is when I drove over the Gotthardpass (MickyMatter will probably know it ;) ) and had deliberately emptied my HV battery to 2 bars, it was full again in a matter of minutes.
    Let's say I needed 50% to get it up to all green bars. The cells are 6.5Ah, so when charging with 3.25A, this (50%) would take me an hour. Or when charging with ten times more, so 32.5A, it would take me ten times less time, so 6 minutes.
    Assuming it can brake with 100A maximum (please correct me if I am wrong), this would take just under 2 minutes of sustained 100A charging of the batteries.

    Of course this is all from memory, but I remember being very disappointed at all energy I was throwing away with the (long) remainder of the trip downhill... So even if it took longer than those 2 minutes, I very much doubt it was over 4, so in my recollection, it must have been charging at at least 50% all the time.

    Quick google showed it average slope is (only) 7.2% (I was driving into Switzerland) so not sure if this corroborates os disproves your assumptions :ROFLMAO:
     
Loading...