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Coasting in neutral

Discussion in 'Prime Fuel Economy & EV Range' started by Crowmag Naman, Apr 13, 2017.

  1. priuscatprimeguy

    priuscatprimeguy Senior Member

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    cept for one of two things, if it's in "D" the car will bump into the car in front of you. If it's in "P" the roller in the tracking system will start bumping the tires each time it rotates through becoming a very annoying distraction and the car behind you will bump you in the rear
     
  2. fuzzy1

    fuzzy1 Senior Member

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    It should be in 'N', not 'D' or 'P'.

    The problem with 'N' in a Liftback is that the system is alive and drawing housekeeping power from the traction battery, but cannot recharge. If the car enters the wash with a low SOC, and AC is turned on for hot conditions, it can deplete the battery and start issuing warnings before the car reaches the end of the tunnel to safely re-engage D.

    A Plug-In with 1 EV mile remaining should not run into this problem.
     
    #22 fuzzy1, Apr 13, 2017
    Last edited: Apr 13, 2017
  3. eman08

    eman08 Active Member

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    You can coast in neutral in any state as long if you own a Prius because you are not changing gears manually. You are doing it with your foot. cops would never know about it, because you ain't got no green arrows and the transmission is still set to D but really you are putting it in neutral manipulating the transmission to coast and glide with the pedal.
     
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  4. fuzzy1

    fuzzy1 Senior Member

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    If it is in D or B, then it is legally in gear, no matter what your foot is doing to the gas pedal.
     
  5. Manjot Sandhu

    Manjot Sandhu Junior Member

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    Don't do it don't you get scary triangle sign?? ...don't do it Cz all the controls on prius are electric so don't mess with it

    Posted via the PriusChat mobile app.
     
  6. Crowmag Naman

    Crowmag Naman Junior Member

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    My observation is that the traction battery actually does charge in neutral according to the MPG and EV distance remaining. the numbers increase as you are coasting down the hill in neutral. In my prime premium anyway. and, by the way, thanks for letting me know its illegal to coast down a hill in neutral. Now im going to have to go to the police station (in drive) to turn myself in!
     
  7. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    I finally got around to looking at the car wash our dealership has, the only one our car has been through, see the car drives in and stops, then this massive frame of sprayers and brushes does the moving; was kinda relieved to see that.

    Other'n that, I never go through car washes; it's been decades. Every time you go through one is another time you've got a half-nice person cleaned car, with the wheel wells and various corners uncleaned, and scratches/dings gone unattended.
     
  8. iskey

    iskey New Member

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    Could the EV range calculation be going up because the computer is estimating the range based on current driving conditions assuming those conditions are going to continue? Like if you are going down hill it's projecting that you're going to be going down hill indefinitely, thereby increasing the range?
     
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  9. Crowmag Naman

    Crowmag Naman Junior Member

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  10. fuzzy1

    fuzzy1 Senior Member

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    As Iskey pointed out, this is the result of the calculations under improved conditions. My non-hybrid, non-electric Subaru does this too, on long downhills. But it isn't because any gasoline is being regenerated and put back into the fuel tank.

    My non-plug-in Prius has a formula that requires DTE to drop at least 1 mile for every 2 miles rolled, even when no fuel at all is consumed. DTE can never increase except when multiple gallons of fuel are added at once. I.e. when climbing a mountain, DTE can fall fast, then not recover on the down side. The Subaru DTE display does not have those constraints, so it does recover (even going over optimistic) on the downside. I suspect your EV distance remaining calculation is more similar to my Subaru DTE than to my Prius DTE.
     
    #30 fuzzy1, Apr 14, 2017
    Last edited: Apr 14, 2017
  11. Crowmag Naman

    Crowmag Naman Junior Member

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    Thanks for all the wisdom on this. I have adopted the pulse method going down hills and have found a compatible reward in battery charge vs overall distance using no power going down a hill. As recommended Ill let technology do the work. Its more fun and is what I paid for.
     
  12. Sandollars

    Sandollars Prius Maven

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    sheesh......
     
  13. vvillovv

    vvillovv Senior Member

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    See! one day driving EV will not be subject to going up hill .... ie: how many times have you seen coasting in neutral posts in NORMAL car forums? Somebody has to be really stingy about their fuel source to put the vehicle into neutral to go further DOWn the road......

    Quick glance around - nobodys watchin, right?, I just did it the other day to try an make it home in "all" EV, but the prime is smarter than I was and even with 3/10's EV left it switched on the ICE..... It was
    not easy knowing the ICE was on either, it was more of a gut feeling letting me know, the ICE is quieter than most of the road noise the car makes...... Than the prime further confused me by switching the ICE off and on 3 more times within a half mile. I finally ended up with 7/10/s EV miles left as I pulled into the driveway, less than a mile from where the ICE first started up.
    Prime also rewarded me the next day with 1 mile less EV range than the previous weeks average.;)

    By the way ----- my favorite Hanks is BIG not to be outdone by TOY which Hanks wasn't in....:rolleyes:

    tide - edit What kinda car wash only gets 3 cars in at a time? On sunny weekend days in the winter one local wash vendor stuffs 10 cars in at time. They have it timed down to the mini second. They also just ope
    ned a brand new expansion 2 lane wash in one location. Soon to be expanded to the other busiest locations most likely, Now they can get twently cars through every 2 minutes. Here let me do da mafhs

    It takes a minute for one car to go through the wash
    10 cars can be washed at the same time
    How many cars can the washer wash in 2 minutes?

    answer 20
    (they have two lanes now....)
    Moral of the story is Don't post anything bout N or B in here unless you're ready for a lots o TORment
    I'm out of here ......
    If driving EV, does the computer remove electrons from the Battery when in neutral?:LOL:
     
    #33 vvillovv, Feb 2, 2018
    Last edited: Feb 2, 2018
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  14. Paul Gregory

    Paul Gregory Active Member

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    I don't see how mileage can improve by coasting in neutral. The powertrain of Priuses has no neutral, only a simulated neutral, which it does by running both motors in reverse rotation to each other. Both motors are connected to the drive wheels at all times; there is no clutch of any kind. When you switch to neutral, the electric motor needs to run backwards, to counteract the torque on the wheels.

    So no, I don't believe you are improving your MPG by coasting in neutral.
     
  15. ChapmanF

    ChapmanF Senior Member

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    The car doesn't have to use any power to do that; it simply open-circuits the motors so no power is being sent to or coming from them, and they spin with the directions and speeds the nomograph says they will, because there isn't any alternative.

    This neutral isn't much more or less 'simulated' than any other car's neutral: with the motors open-circuited, only negligible torque makes it from the engine to the drive shafts or vice versa. There's typically a certain negligible torque making it through other transmissions in neutral too, just because of viscosity of the oil between synchronizers or whatever.

    In the end, whatever way you might have built a transmission, you look at it and ask "under what conditions does this thing effectively transmit no torque", and you arrange for N to be those conditions, and there you are.
     
  16. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Wayne Gerdes has a video, tutoring someone on hypermilimg a 3rd Gen, and he has them shift it to Neutral.
     
  17. Paul Gregory

    Paul Gregory Active Member

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    Well, the claim is that coasting in neutral increases gas mileage. But that simply can't be true. Think of the Prius drive train as a rear differential axle, having a gas engine on one wheel, and an electric motor on the other. The drive shaft would drive the wheels. That's not how it's laid out, but that's how it works. There is no actual "neutral" because there is no disengagement of the motors from the drive wheels.

    Whenever the car moves, it has to spin either the gas motor or the main electric motor (the smaller motor only sets the ratio of the CVT). So, when you shift it into "neutral," what's really happening, is that the wheel sensors cause the computers to match the rolling speed of the car to the speed of the drive train. The electric drive motor has to run in reverse to do that, and if the gas motor is running, the electric one has to run even faster to prevent torque going to the wheels.
    So there is no actual neutral, only a mode where the drive speed is matched to the rolling speed via the computer and the velocity of the electric drive motor.
     
  18. ChapmanF

    ChapmanF Senior Member

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    No, that isn't what happens. I explained what happens in #35.
     
  19. Paul Gregory

    Paul Gregory Active Member

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    The problem with that theory, is that should the gas engine kick on, either to maintain charge or for interior heat, the only way to prevent it bolting off in neutral, is for the electric drive motor to rotate in the opposite direction.
    You see the problem with your explanation?
     
  20. ChapmanF

    ChapmanF Senior Member

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    You seem to think we're both competing in a game of made-up explanations. One of us isn't.

    It will probably help for you to use the established names for the two motor generators: MG1 and MG2.

    In neutral, both MG1 and MG2 are electrically cut off. They are neither generating nor consuming power.

    MG2 (the main "drive" motor) always rotates whenever the wheels do, and always in the same direction relative to the wheels. Nothing else can happen. The gearing between MG2 and the wheels is fixed.

    The car does not need to do anything special to make MG2's rotation match the wheels. When the wheels move, MG2 moves. Nothing else can happen.

    Between MG2 and MG1 is the power-split device, what you refer to in #37 as being like a differential. It enforces that MG2, MG1, and the combustion engine all must rotate with speeds and directions that make a straight line across the nomograph. Again, the car does not need to do anything special to make that happen. Nothing else can happen.

    In this part of your post, a bit of a trick question appears: how does the gas engine kick on, when neutral is selected, given that no torque reaches the engine to crank it without current flowing in MG1, and neutral electrically disconnects both MGs?

    The key to the trick question is that the HV control ECU has its fingers behind its back when neutral is selected, and there are a few situations where it will temporarily bend the rules long enough to do something it needs to do, and then resume the both-MGs-unpowered, neutral behavior.

    The cases where it will bend the rules are limited, and spelled out in the manual. That's been discussed, for example, in this post on gen 2.

    You should double-check whether "to maintain charge" or "for interior heat" even are reasons your car will bend the rules and start the engine. At least in earlier generations they have not been. You will get a warning message about discharging your traction battery if you stay in neutral too long. If that is different in your Prime, that's a change from their previous practice.