Rolling in reverse (backing up slope)

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Visual

Well-known member
Joined
May 5, 2010
Messages
71
Location
El Dorado Hills
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?
 
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 :?
 
Visual said:
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.
 
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 ;)
 
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.
 
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.
 
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.
 
EVDRIVER said:
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:
 
planet4ever said:
EVDRIVER said:
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:


What do you propose is holding the motor in place or causing it to "creep", a double unity chip? If you are climbing a hill in a low powered EV and it stops still in place because it can no longer climb are you telling me it is not consuming significant power to hold that position? It's just a magic rubber band of non-energy that does it all:) One can replicate this feature in any EV but pressing the accel pedal on a hill to the point where the EV holds position. I don't know what grade you received in that class but you may have been better off in an electronics class with ohm's law. You could also pull your LEAF up to a concrete wall with the bumper on the wall and push the accel pedal and with the car static and the wheels just before the break-loose point let me know that the kw meter goes unchanged.
 
planet4ever said:
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:
There is no work being accomplished in that case, but there is power being used - although the motor isn't turning, the power being applied to the motor is still going somewhere - without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
 
Note that keeping the car still in a slope, no matter in which direction, by the mean of the electric motor (and not the mechanical brakes) is clearly stated in the manual as a "don't". It is awfully inefficient, obviously.
 
johnr said:
without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
OK, I can believe that.

EVDRIVER said:
Physics Grade D-
Electronics Grade F

Night classes opening soon....
I object! I still think I'm right on the mechanics. Shouldn't I at least get a B on the physics side? Now, as for electronics, I grew up in the dark ages. I don't think we even had transistor radios yet when I graduated from college. Sure, sure, I spent forty years programming computers, but I never pretended to understand the electronics in them. It was all just logic and math. So I'll accept the F in that course (which I never took).

Now, back to Visual's problem with his driveway ...
 
suresnoi said:
Note that keeping the car still in a slope, no matter in which direction, by the mean of the electric motor (and not the mechanical brakes) is clearly stated in the manual as a "don't". It is awfully inefficient, obviously.
Much the same way as holding a car with a manual transmission on a hill using the clutch is a "don't" :lol:

Worst part is, since the parking brake is electrically actuated you can't really use it as a temporary surrogate for the foot brake - which I guess would apply mostly for manual transmissions again, but from what I heard on these forums the LEAF's brake pedal preempts the accelerator pedal input, so you can't ease off one while pressing the other. A manual hand brake would be perfect for that situation.
=Smidge=
 
planet4ever said:
johnr said:
without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
OK, I can believe that.

EVDRIVER said:
Physics Grade D-
Electronics Grade F

Night classes opening soon....
I object! I still think I'm right on the mechanics. Shouldn't I at least get a B on the physics side? Now, as for electronics, I grew up in the dark ages. I don't think we even had transistor radios yet when I graduated from college. Sure, sure, I spent forty years programming computers, but I never pretended to understand the electronics in them. It was all just logic and math. So I'll accept the F in that course (which I never took).

Now, back to Visual's problem with his driveway ...


No, it always requires energy to counter an opposite force, how much more of a basic physics example could it be. If you don't agree, put your car on a slight hill and remove the brake, hold the car in place buy pushing the opposite direction on the back and let me know if you get tired. If not you are not using energy. Look up double unity devices, as much as some on U Tube want us to believe they exist, they don't.
 
Visual said:
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 ;)
I have the same challenge with my wife's Pontiac Vibe/Toyota Matrix automatic. It's downhill into the garage. The car will roll forward even when the transmission's shifted into reverse. I have to hold the brake and bring in some throttle.

The car will stay in place when in park, and with the parking brake set, but will roll downhill in either direction until there's enough hydraulic pressure in the transmission to counter gravity.

Her previous car was a Saturn Vue and it behaved the same.

I've never had an automatic transmission - I need to find the Leaf's clutch and learn how to down-shift. ;)
 
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