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Visual
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Rolling in reverse (backing up slope)

Thu Jan 13, 2011 4:51 pm

My driveway slopes down into the garage, so I have to back up the slope, and I found the Leaf rolls forward if I take my foot off the accelerator (almost said gas pedal :oops: ) - haven't had this happen in automatic transmissions in decades - does the transmission disengage as soon as you lift your foot off the accelerator?
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Gonewild
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Re: Rolling in reverse (backing up slope)

Thu Jan 13, 2011 5:09 pm

Have you tried to backup then put the brake on and push the had brake?
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johnr
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Re: Rolling in reverse (backing up slope)

Thu Jan 13, 2011 7:42 pm

The Leaf is supposed to have creep built in, and I would assume that's supposed to work in both directions. So it should continue rolling up the driveway, not the other way. Hmmm :?
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Re: Rolling in reverse (backing up slope)

Thu Jan 13, 2011 7:46 pm

Visual wrote:My driveway slopes down into the garage...........................................
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I have the same situation. I plan on backing into the garage. Have you tried backing in?

We do this procedure with our Prius.

When we used to back out of the garage: I didn't like the feeling of not being able to see the street very well with the combination of backing out of the garage and up hill at the same time.
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Visual
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Re: Rolling in reverse (backing up slope)

Thu Jan 13, 2011 8:04 pm

I haven't used the "hand brake", which is actually electronic, and it would help since it disengages automatically when you hit the accelerator (our Audi has the same setup), but the real question is most automatics don't roll in the opposite direction, even when you're on a slope, so it caught me by surprise.

I checked again tonight when I got back home, and it rolls about 2-3 feet then stops. Still a bit strange - its the kind of thing I'd expect on a manual (when you take your foot off the brake and your clutch is still in, it starts rolling until you let the clutch out).

Nothing I can't handle, just a little unexpected - will probably bother my wife more ;)
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blorg
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Re: Rolling in reverse (backing up slope)

Thu Jan 13, 2011 11:39 pm

On a steep enough hill most automatics will roll back a bit. In my Murano (has a CVT) it seems to do it more than traditional automatics, and it takes some owners by surprise.

Just like a manual tranny, you just learn how to deal with it. Doesn't bother me at all now in my Murano, and I assume it's very similar in the Leaf. It would be NICE to have it not do this, but I don't think it's an actual problem with your vehicle.

Very interesting that it does stop after a couple feet, though.
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planet4ever
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 1:52 am

Well, in an ICE, reverse works by changing the gears so that the car goes backward while the engine is still rotating the same direction as always. The bias to creep forward, caused by the fact that the engine is still spinning, automatically becomes a bias to creep backward.

Someone who knows more about electric motors than I do should jump in here, but AFAIK, reverse works by changing the phase of the AC current being supplied to the motor so that it spins backward. There is no implicit creep, so one has to be added artificially if you are going to have it. I assume that would be done by biasing the phase so that pedal-off still has a slight forward force. To get the result you might expect in reverse it would seem that the sign of the bias would also have to be reversed. Perhaps someone forgot about that or decided it wasn't a good idea.
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garygid
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 9:34 am

The 2010 Prius has Fwd and Rev "creep" programmed in.

If the LEAF does not have a little R-mode creep programmed, it might be an unintended oversight?
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 9:59 am

There is no transmission in a Leaf, it is a directly coupled transfer case, a fixed gear reduction and torque converter that goes to half shafts to the wheels. Forward and reverse are controlled electronically and the motor spins backward. The creep control is electronic and it uses extra power to do so, I never have this on other EVs but for those that don't drive a stick it is a smart idea, also because of the electronic park brake.

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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:01 pm

EVDRIVER wrote:The creep control is electronic and it uses extra power to do so
Are you sure about the second part of that statement? What I remember from my physics classes is that power is the rate of expending energy, and energy is force times displacement. I was careful to say in my statement earlier that the phase bias applies a force to the motor. But if the motor isn't turning, then there is no displacement, hence no energy, hence no power. It's been more than 50 years since I took my last physics class. Maybe I've forgotten, :? or maybe they've changed the laws. :shock:
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