HV Battry Charging While Gliding in N

Discussion in 'Toyota Prius Family' started by diamondlarry, Jul 31, 2008.

  1. diamondlarry

    diamondlarry Super MPG Man/god :D

    Has anyone else noticed that at speeds between 33 and 36-37mph that if you are gliding in N that the pack is actually being charged? I have seen it several times but today was finally paying attention when entering a glide and noticed that as I started a glide at 30mph at the top of a hill that the HV battery current was reading +1.0. When my speed reached 33mph, the current went to ~-5 or so amps. When the speed reached the 37mph area I felt what seemed like a drag being released and the current went back to +1.0
  2. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Larry:

    ___That is something I have not heard of before? Sounds like a nice tool so as to keep your top glide speed below 33 mph in a P&G segment whenever you can? Can you control it to reduce any regen when running a glide manually like we used to?

    ___Good Luck

  3. diamondlarry

    diamondlarry Super MPG Man/god :D

    It is definitely something I'm going to keep an eye on over the next few days. There are a few places where it's nice to go just a smidge faster so I don't end up coming to a pulse point at the bottom of a hill. This will definitely change how I decide to handle those situations if this theory holds up.
  4. JimboK

    JimboK One owner, low mileage

    Yep, see this. It doesn't last long and seems largely unpredictable, as the scatter chart entitled "Neutral Glide Current Flow and Relationship to Speed" shows. The only clear pattern I've consistently seen is documented on the chart following that one -- a downhill glide steep enough to accelerate, where I see a transient spike of positive current flow often exceeding 10A along with that same "drag release" sensation.

    I have some more 30+ MPH data from other trips that I want to plug into another scatter chart. Admittedly the one that's there doesn't have many data points in that speed range.

    Overall, my tests show neutral glides to have slightly greater drag, a lower battery draw, and (possibly) slightly better fuel economy than pedal-controlled glides.
    Last edited: Jul 31, 2008
  5. shifty35

    shifty35 Well-Known Member

    Interesting then, that the Prius has no "true" neutral - the electric side is still free to pull / push current from the wheels.

    That seems to have ramifications as to what the real meaning of "neutral" really is... in the Prius case, I suppose it means the ICE is not connected to the wheels. While the MG sets are always connected.

    Can you brake w/ regen while in N?
  6. JimboK

    JimboK One owner, low mileage

    Actually, the ICE, MG1, and MG2 are always interconnected via the planetary gear set. It might be said that N simulates neutral in a conventional car by allowing the drive train to freely spin. What is disconnected from all that in N is pedal control.

    Which means, to answer your question, braking in N provides no regen. It is for that reason that I always shift back into D before braking. It also gives the operator a handy way to clean the brake rotors of accumulated rust (a byproduct of regenerative braking) by braking hard at speed while in neutral.

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