Coasting and tranny ???

Discussion in 'Knowledge Base Articles Discussion' started by MR.K, Apr 7, 2008.

  1. MR.K

    MR.K New Member

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    When you shift back into Drive after coasting around 45-50 mph.....the motor ,if running, would be at an idle ..if not running ,stopped ....dose it jar the tranny or cause clutch wear ,Yea it's an automatic but it still has to have some type of clutch ? Has anyone did damage this way? ...Should you rev the motor a bit when shifting into D to keep the jarring down .....? I'd like to try this coasting thing ...just don't want to short"n the life of anything.....thanks.
     
  2. efusco

    efusco Moderator Emeritus
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    Nope, no clutch. no risk of damage. All that happens from neutral is a change in the power flow.
     
  3. Bill Merchant

    Bill Merchant absit invidia

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    The Prius has a Power Split Device, not a transmission like other cars. Although Toyota calls it an ECVT (Electronic Continuously Variable Transmission), it's a planetary gear set with MG1 driving the sun gear, MG2 driving the ring gear (coupled to the wheels), and the ICE driving the planetary carrier. The Prius is always in gear, even in N.
     
  4. patsparks

    patsparks An Aussie perspective

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    I'd be more concerned about over spinning MG1.
    If you accelerate from under 42mph to over 50 there is a posibility you will over spin MG1 ans damage it. This might happen going down hill.
    Then again the ICE may fire up to protect MG1 while in neutral, I haven't a clue.
     
  5. efusco

    efusco Moderator Emeritus
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    If you're in a ICE-off glide (under 41mph) and then go into a downhill acceleration you're safe from overspinning MG1 until you exceed 62mph....I do it every day on my commute.
     
  6. Danny Hamilton

    Danny Hamilton Active Member

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    No, it does not.

    Nope, If the Internal Combustion Engine (ICE) is idling while you are coasting in Neutral, then one of the the electric motor/generator (MG1) spins up to take the load off the engine. When you shift back into Drive, MG1 slows down as the ICE speeds up to create a nice gentle smooth transition.


    Not the type of damage you are asking about (shock to the drivetrain). There is some concern about MG1 spinning too fast if you switch into Neutral when the ICE is off and then coast downhill to exceed 62 mph. On the other hand, I'm not familiar with any reports of that damage yet either.

    First of all this would be entirely unnecessary. Additionally, I didn't think the car would "rev the engine" if you are in Neutral. I'll have to try this, but I thought that the ICE would continue at it's current rpm no matter how far you press the accelerator.
     
  7. qbee42

    qbee42 My other car is a boat

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    I don't think it will rev. As the driver of a Prius, you are just a voting member when it comes to engine speed. You push the pedal to register your vote to go faster, but the ECUs get to vote too. In this case I think the driver is overruled.

    Tom
     
  8. MR.K

    MR.K New Member

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    Thanks everyone....so to get it right ...#1 ..what speed can you go to N when driving? #2 ..what speed can you go back to D after coasting?...#3 ..is there below 42mph and above 42mph rules?.....thanks
     
  9. qbee42

    qbee42 My other car is a boat

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    62 mph is the magic figure which causes MG1 to hit 10,000 rpm. Below that you can shift in and out of N anytime you want. Some Prius drivers do it at higher speeds without reporting damage, but you take a risk when you do.

    Tom
     
  10. zeeman

    zeeman Member

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    interesting discussion and it sure makes sense to me

    one thing i cannot picture is how does engine engage so smoothly that you cannot feel even a small jerk?
    and, does the M2/generator ever spin in opposite direction while car is moving forward and ICE kicks in?

    i presume that M2/generator changes the speed really quick from say 5000 RPM to 3000 RPM and this causes the engine to start spinning from 0 RPM to say 1500 RPM if engine speed and load are under preset parameters.
    but, does M2 ever changes the spin direction while driving forward?

    I also noticed (via scan gauge) that above 42 MPH engine engages (spins) at lower RPM without fuel consumption.
    I presume this is so that M2 does not go in very high revs as that could potentially damage it at very high rotational speeds?!

    does anyone knows of any good animation that would show what happens with ICE, M1 and M2 at various loads and various vehicle speeds?
     
  11. Ichabod

    Ichabod Artist In Residence

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    You can play around with this flash toy that I made: Toyota Prius - Power Split Device

    MG2 has a fixed relationship to the wheels, so when they roll forward, MG2 does. When in reverse, MG2 spins the other way. MG1 can change direction during normal driving though.
     
  12. richard schumacher

    richard schumacher shortbus driver

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    It's better to learn how to "glide", that is, modulate the gas pedal so that there are no arrows into or out of the battery on the "Energy" display. This avoids fiddling with the shift lever, allows the battery to charge normally when you do want to slow down, and eliminates any possibility of damage to the electric motors at high speed.
     
  13. Danny Hamilton

    Danny Hamilton Active Member

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    I'm not certain but this seems a bit confused. I don't think there is a limit at 62mph that prevents you from shifting in and out of N. Additionally, I don't think MG1 exceeds its rated RPM at 62mph unless the ICE is not spinning. As long as you are traveling faster than 42 mph when you switch into N (which leaves the ICE spinning), I don't think MG1 will exceed its RPM rating at 62 mph.

    The concern isn't switching in or out of N at any particular speed. The concern is switching into N when the ICE is not spinning (which can only happen at speeds less than 42 mph), and then leaving it in N while accelerating down a long steep hill until the vehicle exceeds 62 mph.
     
  14. Danny Hamilton

    Danny Hamilton Active Member

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    Technically, at any speed you like. Legally in many jurisdictions, never. There is no technical limit that I am aware of that prevents switching into N, nor is there any speed at which switching into N is physically damaging to the the vehicle.


    The vehicle should not prevent you from switching back into D at any speed. As long as the ICE is running, there is no risk of physical damage to the car from the act of switching in and out of Neutral no matter what the speed you switch into or out of Neutral.


    Not exactly. There are different rules for a spinning ICE versus a non-spinning ICE. If the ICE is spinning you can switch into and out of Neutral without risk of damaging the car. If the ICE is not spinning then you will exceed the rated RPM of the motor/generator, MG1, at 62mph. If you want to avoid exceeding this rating, and you switched into Neutral when the ICE was not spinning, then you should switch out of Neutral before you exceed 62mph.

    Note that as long as you are traveling faster than 42 in D, the ICE will be spinning when you switch to N, so there will be no risk of exceeding MG1's rated RPM. If you are traveling slower than 42mph in D, then the ICE may or may not be spinning. If you are traveling slower than 42 mph in D and the ICE is spinning when you switch to N, then you will not exceed MG1's rated RPM at 62mph.
     
  15. efusco

    efusco Moderator Emeritus
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    We're not saying you can't shift into N above 62mph only that if you're in an ICE-off/ICE-not spinning condition and exceed 62mph that MG1 will exceed 10k rpm. So, I'm gliding at 39mph, the ICE is at 0 rpm. No I shift into N just as I crest a hill. At this point the ICE is not able to start no matter what. So I glide down this hill and my speed passes 62mph MG1's rpm will now exceed 10k rpm and apparently the apocolypse will result. Noone's yet commented that they've tried this. I've hit 62mph with MG1 at about 9960rpm but just didn't really want to risk the fates.
     
  16. qbee42

    qbee42 My other car is a boat

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    Correct. The concern is keeping MG1 under 10,000 RPM. If the engine is spinning, its speed reduces the speed of MG1, and presumably the ECU is smart enough to keep the RPMs under control. The problem comes from the ICE staying off if you switch to N when it is off, then accelerating until MG1 goes too fast. Admittedly it takes a pretty specific set of circumstances to make this happen, and a darned steep hill.

    Tom
     
  17. Oddest_raindrop

    Oddest_raindrop New Member

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    As far as something good to play with and explain the prius I found this to be pretty good Prius driving simulator
    not sure on the acuraccy but apear some what realistic
     
  18. zeeman

    zeeman Member

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    excellent find!
    thanks
     
  19. hobbit

    hobbit Senior Member

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    There's also Graham Davies' nomograph, for that one-page
    at-a-glace overview.
    .
    _H*
     
  20. edthefox5

    edthefox5 Senior Member

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    Hi Danny,
    Just got my CHiltons 2001-2008 Prius edition and have read it cover to cover and they talk many times about the "damper" . Its used in place of a clutch with a detailed description of removing it to remove trans from motor. I found alot of errors in the book so far. Is this another one? BTW, your doing an excellent moderator job. You and MR Efusco. This is an excellent site. A pleasure to use and have bought many things from the "Shop" and always happy.Thanks alot!
     
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