Living at the top of a hill... Disabling engine braking?

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Nougatti, Aug 20, 2016.

  1. Nougatti

    Nougatti Member

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    Why on earth would Toyota program the PiP - THE CAR WHO'S FUNCTION IS TO DRIVE ON ELECTRICITY AS MUCH AS POSSIBLE - so that the ICE starts when brakes are applied and the battery is full? Why in the everloving &%¤@ would the car first resort to engine braking and not the disc brakes instead? At least when going slower than 40 km/h (25 mph)?!

    Anyone know of some buried settings in maintenance mode or whatever that will prevent this from happening and tell the car to screw using engine braking while in EV mode?

    I now have to remember to set the damn thing in Neutral whenever I set off in the morning, which is a damn shame.
     
  2. JimboPalmer

    JimboPalmer Friend to those who want no friends

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    The car tries to protect the battery from over filling. I seriously doubt they have a 'destroy the battery' mode you can check.
    Perhaps a post-it note on the dash would remind you that you live on a hill?
     
  3. ChapmanF

    ChapmanF Senior Member

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    Spinning the engine for braking doesn't require fuel. Why would you object, or insist on using the friction brakes instead?

    -Chap
     
  4. CraigCSJ

    CraigCSJ Active Member

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    Try going slower than 19 MPH. At one time I thought the ICE would not turn on when I went down a hill with a full battery below 19 MPH. Since that was too slow most of the time, I just started putting the PIP in neutral.
     
  5. ChapmanF

    ChapmanF Senior Member

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    I can't recommend that ... remember that, in a Prius transaxle, there really is nothing like a mechanically disconnected, neutral selection. 'Neutral' in a Prius is just an electrical cutoff that is built in to satisfy regulatory requirements for a setting called neutral. By shifting into neutral while coasting, you don't prevent MG1 from spinning, and you don't prevent voltage from being generated (both MGs use permanent magnets, so if they move, they generate, no exceptions ... that's why all the towing warnings in the manual). But you do, to some extent, prevent the car from doing what it is programmed to do to keep the voltage and MG RPMs to safe levels.

    There was a note for Gen 2 (2004 New Car Features Manual, page TH-46) that if the MG speeds get excessive, the ECU will just decide you didn't mean neutral, rather than allowing destruction of an MG. (Sometimes, having Scotty down there in the engine room is comforting.) So probably, in a 2004 or later, you won't really hurt much by doing this, but won't really accomplish what you're after, either. Again, when the engine is spun for braking purposes, fuel isn't injected. What's the concern?

    -Chap
     
  6. bisco

    bisco cookie crumbler

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    once the pip uses the engine braking, it then goes through the full warm up procedure.

    pip was not designed to drive on ev as much as possible. however, toyota has been overruled by customers, and prime will be.
     
  7. markabele

    markabele Senior Member

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    Please only comment on stuff you know about.
     
  8. Topp Cat

    Topp Cat Member

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    Prius don't have ability to disengage the wheels from the drivetrain/ regenative brakes! The VW Jetta hybrid had that ability when battery full charged then coasting down hill man that car would pickup lot of speed I recall it coasting 90+ mph on a long decent.
     
  9. markabele

    markabele Senior Member

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    Attention.....this is a PiP forum. This is about the plug in prius. It handles things a little differently. I'm guessing several of you commenting on this aren't even familiar with the problem he is talking about.
     
  10. fotomoto

    fotomoto Senior Member

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    I have a CMax Energi that behaves the same way sometimes even on a level road. How? Fully charged battery and driving in L gear (for max regen and one pedal driving). Originally I thought the MG was simply spinning the ICE as work to burn off the excess charge but I changed my scangauge II display to monitor the ICE and sure enough it was burning fuel in its warmup routine. Grrrrr.

    I get around this by remembering to use D gear instead of L on my first trip. Once I dropped past 95% SOC, the issue goes away. Suggestion: pre-condition the cabin while unplugged to burn off some charge.
     
  11. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    Because once the engine spins it requires a full warm up. Really ruins the PIP mpg for a short trip to the store. The answer, unfortunately, is Neutral and brakes to the bottom of the hill.
     
  12. Nougatti

    Nougatti Member

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    >implying "free-wheeling it" with only using the friction brakes would destroy the battery...

    The issue is that as soon as the ICE starts spinning to aid in braking the car, it's not gonna shut off until after it's warmed up completely, burning precious fuel, thus "destroying" my small trip to the store that would be well within the EV range of the car.

    If I set the car in neutral, the car doesn't regenerate, and thus doesn't need to start the engine to avoid over-filling the battery. It will simply coast, leaving me to use the friction brakes to brake.
    What Toyota COULD have done was to shift the car into neutral (behind the scenes) as soon as I tried braking with the battery full.
     
    #12 Nougatti, Aug 23, 2016
    Last edited: Aug 23, 2016
  13. ChapmanF

    ChapmanF Senior Member

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    I think you might still be assuming there really is a mechanical neutral. There isn't; what ends up freewheeling is MG1. I don't think the issue was ever really destroying the battery, but MG1 does have its limits on high revving. When necessary, the car spins the ICE to hold MG1 revs down.

    In Gen 1, it was actually up to you to be careful about that; if you shifted to neutral below about 45mph (Gen 1 MG1 had lower rev limits) and let the car coast above that speed, you'd have blocked the car from bringing the ICE into play, and you'd end up over-revving MG1.

    As I posted above from the Gen 2 NCF, they added an override in Gen 2 so that it will ignore your selection of neutral and spin the ICE anyway if needed to protect MG1. I assume this is still the case in Gen 3, PiP, and later, though at the moment my techinfo days are used up so I can't just go check.

    I'm not sure what part of that made markabele think I didn't know what I was commenting on, but I thought I did. Mark, if you point to specific parts you think I had wrong, I'll be sure to check the next time I feed the techinfo meter.

    -Chap
     
  14. Nougatti

    Nougatti Member

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    Ah, so it's not gonna hurt the MG1 by neutraling it down the hill (approximately 1 km (0.6 miles)) at each fully charged start, since it will ignore me and enable engine braking anyway, as soon as anything is nearing damage?
    However, you mentioned that it will still produce electricity, even in neutral coasting. Where does this electricity go, exactly? Because while coasting down hill in Neutral, the A/C, vacuum pump etc are draining the battery slightly I guess, so I loose about 100 m off my range at the bottom of the hill. FYI, with a non-fully charged battery, I will gain approximately 500 m or so of EV range from my 1 km downhill coast.
     
  15. QuantumFireball

    QuantumFireball Active Member

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    If you're always starting your journey going downhill, maybe you should try having it so your battery is not fully charged when you leave? Maybe try setting the timer to only charge for 70-80 minutes (assuming 230V)?
     
  16. Nougatti

    Nougatti Member

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    Yeah, that would be best, but the car as varying range remaining when I park it at home.
    I therefore have no way of knowing how long the charge actually takes unless I do an extensive series of experiments where I literally go out to check the car every other minute to figure out the exact time for how long it takes to charge at that and that percentage. 220-240V, yeah.

    Has anyone tried attaching some sort of small raspberry pi-connected sensor/transmitter thing to the little light by the charge port which shuts off at the end of charging? That sensor could let my phone know when it's done charging through bluetooth or something. Or even just a signal inside the house in the form of a diode or beeper.
    Alternatively, I could hook a recording amp-meter to the outlet I use, if those exist?
     
  17. ChapmanF

    ChapmanF Senior Member

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    To be most careful, remember I read that in the 2004, Gen 2 New Car Features Manual. I assume they wouldn't have added that feature in 2004, then taken it out later, but if you want to be sure, don't take my word for it on the internet, look it up in your PiP NCF manual.

    Well, nowhere, because Prius "neutral" is a cutting off of the semiconductor switches that allow it to go anywhere. The MG rotors are built with permanent magnets, so there is no way to stop them making voltage whenever they turn, but with all the switches off there is no current. In that case there is also nothing loading the generated voltage down to below the breakdown limits of the winding insulation, semiconductors, etc., which is why one of the reasons the owner's manual warns against towing with the wheels down. (Edit: the oil pump could be another reason.)

    Again, probably not something you have to worry about as long as your model does have the "ok, you didn't really mean neutral" function, but could be worth checking.

    -Chap
     
  18. QuantumFireball

    QuantumFireball Active Member

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    Yes that is a more difficult problem if your state of charge is inconsistent before charging. There are OBDII scanners (Bluetooth or wifi if you want wireless) which will give you a lot more information - so you could potentially get the SOC from that and stop the charger when it gets to a certain level (maybe by some sort of relay controlling the mains socket?) - but I suspect implementing a solution for this would be a DIY job...
     
  19. Redpoint5

    Redpoint5 Senior Member

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    Perhaps the part about damaging the motor by running them too fast? The PiP is good at least up to 82 MPH.

    It's absurd the things that trigger the ICE to run, especially using brakes when the battery is full. There is no need, and no reasonable explanation for it. The same thing happens when I do heavy regen while in EV mode for extended periods of time. For no reason, the engine comes on.
     
    #19 Redpoint5, Sep 3, 2016
    Last edited: Sep 3, 2016
  20. roflwaffle

    roflwaffle Member

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    It looks like the boost circuit in N (and under heavy load) keeps MG voltage in the ~200-500V range when the car is on. Some (most?) states don't allow a car to be on when it's towed, and in that situation I can see how there might be problems with unregulated open circuit voltage, lubrication, and so on.

    VH boost

    But yeah, the Pip kicking the engine on the force drain/balance the pack after it's fully charged in annoying. N gets around that, but it's kind of a waste too. I've been thinking about throwing together an arduino controlled receptacle/current sensor to cut off power when the Pip's charger starts tapering current near the end of charge, but that's pretty far down on my todo list.
     
    #20 roflwaffle, Sep 3, 2016
    Last edited: Sep 3, 2016
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