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AWD in snow

Discussion in 'Gen 4 Prius Main Forum' started by Skewby, Jan 29, 2021.

  1. Skewby

    Skewby New Member

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    I started a profile literally for this reason only - I have snow tires and the e-AWD tech package. A few months ago we got a crazy snow storm in Calgary and I literally spent hours just driving in the worst areas TRYING to get stuck.

    I couldn’t. Every spot where I figured I would, where other cars had pulled over or were sliding backwards, this thing kept on going. It scraped snow almost everywhere I went, so I was worried about bottoming out, but it never happened.

    I drove through unploughed streets, and even up as many packed snow hills I could find. I finally found two instances where I put it in a worse enough spot:

    1) Driving up a steep hill, I stopped half way to help another guy get his car unstuck. I parked and got out and two of us were able to get him going. When I started again in a steep up hill, I had to get the guy to give me a small nudge - as in, he just needed to put a little more weight on the back wheels to get me going.

    2) In a snow Bank at the end of a driveway that had been shoveled. I wasn’t stuck going forward but when I tried to reverse back out, it wouldn’t go. So I pulled into the driveway, did a 23 point turn to get maneuvered forwards, and drove back into the streets.

    This comes from a guy that owned a Wrangler and an STI previously, so I can definitely say I’m very impressed.

    I recommend:
    - snow tires obviously
    - be gentle on the gas - let the electronics work itself out
    - extra weight in the hatch - I had my spare tires in the back and it got slower in the deep stuff as I took them out. The two times I got stuck the tires were in the hatch

    I’d love to know more about the AWD system. It truly feels like it’s as responsive as a 4-low or fixed axle AWD system, but I’m not sure what the electronics or mechanism is like.
    Anyways, very impressed!
     
    #1 Skewby, Jan 29, 2021
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  2. jdenenberg

    jdenenberg EE Professor

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    I have a 2020 AWDe LX with the poor OE Toyo tires. My previous 2016 Prius wit good tires (Nokian WRg3) had difficulty getting up my driveway when there was ice under a snow covering. My new Prius had no difficulty getting up my driveway at low speed. I fully agree that the AWDe system works well, but only at low speed. Having two driven axles together with, I believe, the use of controlled friction brakes to simulate "limited slip" differential functionality is quite effective.
     
    #2 jdenenberg, Jan 29, 2021
  3. ChapmanF

    ChapmanF Senior Member

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    I would venture that it's "limited slip" differential functionality that simulates individually controlled friction brakes. :) If engineers had had the means to build the latter back when the former was invented, they probably would have skipped "limited slip differentials" entirely.
     
    #3 ChapmanF, Jan 29, 2021
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  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Welcome and glad to hear some positive real world results!

    The rear motor has 7hp and 40.5lb-ft and it's in induction motor (vs. MG2's 71hp and 120lb-ft)

    For your perusal, if you're interested. (It's called E-Four in Japan).

    upload_2021-1-29_22-24-53.png
    upload_2021-1-29_22-25-7.png

    In North America, the rear motor is always active from 0-10km/h. Then "active when needed" from 10km/h-70km/h and then it's disengaged above 70km/h.

    You can switch to the AWD-e graphic on the MID if you want to see how the power is distributed.
    upload_2021-1-29_22-27-29.png
     
    #4 Tideland Prius, Jan 30, 2021
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  5. Elektroingenieur

    Elektroingenieur Senior Member

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    Indeed. Besides the coverage above and in New Car Features (more info), there are a few more construction details in a paper from the engineers at Aisin Seiki: Tahara, Y., Ogawa, K., Nonaka, N., Kimura, T. et al., “Development of Compact Electric Rear-Drive Unit,” SAE Technical Paper 2016-01-1104, 2016.
     
    #5 Elektroingenieur, Jan 30, 2021
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  6. Tideland Prius

    Tideland Prius Moderator of the North
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    Since I have you here, any idea what the lock-to-lock value is for the steering wheel for Gen 4? I can only find steering ratio but not number of turns lock-to-lock. The reason for this info is to reply to this member.

    Picked up a 2021 L Eco yesterday (Thoughts) | PriusChat
     
    #6 Tideland Prius, Jan 30, 2021
  7. Elektroingenieur

    Elektroingenieur Senior Member

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    Toyota has published that figure for other models, including the Prius c, but apparently not for the fourth-generation Prius. It wouldn’t be difficult to measure, at least to the accuracy of the steering angle sensor: just use a Toyota Techstream diagnostic system to read the Data List item while turning the wheel.
     
    #7 Elektroingenieur, Jan 30, 2021
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  8. 2020XLEAWD

    2020XLEAWD Member

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    Michelin Crossclimates did great on my AWD-e when I went snowboarding last month. Spent the extra $$ for AWD model because I hate putting chains on the side of the road.
     
    #8 2020XLEAWD, Feb 10, 2021
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  9. Skewby

    Skewby New Member

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    My question is how does it deal with slip of Right Rear and Left Rear? Does it torque multiply from right to left like your typical LSD, or does the electric motor attached to the axle allow it to apportion grip regardless of slippage on one tire? (I may not be understanding or describing properly but I hope you can make sense of what I’m asking)

    ie. the difference between a Jeep with fully locked 4WD low. Or is this just a motor that drives a traditional Axle?
    Thank you!
     
    #9 Skewby, Feb 11, 2021
  10. Tideland Prius

    Tideland Prius Moderator of the North
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    It doesn’t lol. My understanding is that it just divvies power front to rear and that there’s no means to distribute power left to right. Did you see power varying left to right on the AWD menu on the MID?
     
    #10 Tideland Prius, Feb 11, 2021
  11. jdenenberg

    jdenenberg EE Professor

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    That's the wrong question as power is applied equally to both sides. The question is, are the friction brakes applied to a wheel that is spinning.

    JeffD
     
    #11 jdenenberg, Feb 12, 2021
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  12. Mendel Leisk

    Mendel Leisk Senior Member

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    I’m often bemoaning Toyota’s blanket paywall policy for tech documents. Really think you get more bees with honey.

    Anyway, if they were to “ease into loosening up”, making that New Car Features section freely accessible would be a good first step.
     
    #12 Mendel Leisk, Feb 12, 2021
  13. jdenenberg

    jdenenberg EE Professor

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    The new Toyota Owner's app does provide access to some of this information as well as showing recent Odo and psi information uploaded from the Prius (until the "connected" trial times out).

    JeffD
     
    #13 jdenenberg, Feb 12, 2021
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  14. ChapmanF

    ChapmanF Senior Member

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    More carefully speaking, the game of a differential is it applies torque equally to both sides, exactly ½ of the torque coming in. Because power is torque ✕ rpm, whichever wheel is spinning faster is getting more of the power. If one wheel is spinning freely and the other is at 0 rpm, there's the classic open-differential complaint that the wheel at 0 rpm is getting ½ torque ✕ 0 rpm = zero power, and all the power is going to the wheel that's spinning.

    But it's probably true that the Prius has a simple existing solution for that, in the TRAC system it already has that is able to brake the wheel that is spinning.
     
    #14 ChapmanF, Feb 12, 2021
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  15. Skewby

    Skewby New Member

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    Yes this is exactly what I was asking and thank you for answering! I figured it was likely a brake system that would solve the problem (same thing I did manually on my old Jeep).

    Am I right in assuming this doesn’t transfer torque at all front-rear correct? It’s a separate motor in the rear so there’s only electronics connecting it, not an axle. So it *should* technically not be an issue in torque transfer if both of the front wheels were slipping, correct?

    It would be intriguing if it had a different motor at each wheel, driving them independently - that would’ve been an interesting system.
     
    #15 Skewby, Feb 14, 2021
  16. ChapmanF

    ChapmanF Senior Member

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    Correct.
     
    #16 ChapmanF, Feb 15, 2021
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