Aerowhatt
Gold Member
Posts: 446
Joined: Wed Jan 28, 2015 1:52 pm

Re: Winter Driving

Mon Jan 25, 2016 1:46 pm

tomrh wrote:
Aerowhatt wrote:When I was researching the car I read on some official Mitsu literature that the car has "positraction" rear wheel drive.

Do you remember where you found this?


I don't, but I will attempt to ferret it out again and post it here if I am successful.

Aerowhatt
(July) 2014 cool silver ES, acquired new 4/2015 (40.9ah at ~34K miles)
(Aug) 2014 Labrador Black Pearl ES, acquired new 3/2016 (39.7ah at ~20k miles)

Aerowhatt
Gold Member
Posts: 446
Joined: Wed Jan 28, 2015 1:52 pm

Re: Winter Driving

Mon Jan 25, 2016 2:27 pm

These specs under mechanical section of the document. So it's brake actuated limited slip. This was tipping point for me since I have driven just about every drive wheel combination up and down steep, curvy, mountain snow packed and icy roads. If it was a conventional differential I was going to pass on purchasing one. After some limited experience this first winter with some very slick conditions I'm completely satisfied with it's performance.


Motor: Electric AC SynchronousTransmission: Single Speed Fixed Reduction GearTransmission w/Driver Selectable ModeRear-Wheel Drive7.06 Axle Ratio80-Amp/Hr Maintenance-Free Battery w/Run Down Protection3329# GvwrGas-Pressurized Shock AbsorbersFront Anti-Roll BarElectric Power-Assist Speed-Sensing SteeringStrut Front Suspension w/Coil SpringsTorsion Beam Rear Suspension w/Coil SpringsRegenerative Front Disc/Rear Drum Brakes w/4-Wheel ABS, Front Vented Discs and Brake AssistBrake Actuated Limited Slip DifferentialLithium Ion Traction Battery w/22 Hrs Charge Time @ 110/120V and 6 Hrs Charge Time @ 220/240V

Aerowhatt
(July) 2014 cool silver ES, acquired new 4/2015 (40.9ah at ~34K miles)
(Aug) 2014 Labrador Black Pearl ES, acquired new 3/2016 (39.7ah at ~20k miles)

tomrh
Posts: 33
Joined: Tue Jun 18, 2013 12:27 pm
Location: Norway

Re: Winter Driving

Mon Jan 25, 2016 3:18 pm

Aerowhatt wrote:So it's brake actuated limited slip.

That is strange since I had the ASC switched off. Or maybe the ASC button doesn't disable all of the electronic braking? The car has far better traction with ASC off than those other rwd cars with open diffs that I have driven.
Black 2012 i-MiEV, 70k miles.
Black 2012 Leaf.

PV1
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Re: Winter Driving

Mon Jan 25, 2016 9:05 pm

I would have to say that the ASC off button doesn't completely disable the safety features. When trying to climb my driveway, the ABS was still making some noise even with ASC turned off. I believe this was mainly when holding the brake pedal while pushing on the accelerator. Also, with ASC off, my regen will still drop out if a rear tire slides.
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
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tomrh
Posts: 33
Joined: Tue Jun 18, 2013 12:27 pm
Location: Norway

Re: Winter Driving

Tue Jan 26, 2016 12:43 pm

I had to get to the bottom of this diff thing so I dug a snow ramp and backed the right side of the car on top of it so that the right back wheel was almost hanging more or less in free air with only a little snow under. Now the car was stuck with one wheel spinning and the other not moving at all. The conclusion is that i-MiEV has an open differential.

And I also demonstrated how bad the traction control really is, because when I re-engaged ASP it should have braked the spinning wheel letting the other get some traction. It did not, but choked any forward movement completely. What I think happened is that it did try, but the other wheel started spinning a little too and then both wheels were braked.
Black 2012 i-MiEV, 70k miles.
Black 2012 Leaf.

PV1
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Re: Winter Driving

Tue Jan 26, 2016 1:18 pm

tomrh wrote:The conclusion is that i-MiEV has an open differential.

Nice to know. Thanks for the investigative work.

And I also demonstrated how bad the traction control really is, because when I re-engaged ASP it should have braked the spinning wheel letting the other get some traction. It did not, but choked any forward movement completely.

So much for Brake Force Distribution :roll: .
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015
"Photon" - 2017 Bolt EV LT in Orange with QC - 7/31/2017

Solar-powered since 10/10/2013

kiev
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Re: Winter Driving

Tue Jan 26, 2016 1:54 pm

The yaw and g sensors also contribute to the ASC, so having the side of the car jacked up on a snow ramp might throw a signal that causes it to cut off the wheel torque, especially if the switch was thrown while the wheel was spinning.

The front and rear wheel speeds are also used in both ABS and ASC, so non-spinning front wheels while the rear was spinning may not fake it out either.
kiev = kenny's innovative electric vehicle

tomrh
Posts: 33
Joined: Tue Jun 18, 2013 12:27 pm
Location: Norway

Re: Winter Driving

Tue Jan 26, 2016 2:16 pm

It is possible to draw some conclusions on when to engage or disengage ASC. When the wheels have different friction, i.e. there are melted patches of bare asphalt or the ice has been sanded, then ASC works best, giving traction to the wheel having the most friction. If both rear wheels have equally low friction the ASC should be switched off. Two spinning wheels + ASC will only choke our precious speed. With ASC off, if one wheel spins it will still transfer all of its friction through the open diff to the other wheel (cf. my summer+spiked tire experiment).
Black 2012 i-MiEV, 70k miles.
Black 2012 Leaf.

Aerowhatt
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Re: Winter Driving

Tue Jan 26, 2016 2:50 pm

tomrh wrote:
Aerowhatt wrote:So it's brake actuated limited slip.

That is strange since I had the ASC switched off. Or maybe the ASC button doesn't disable all of the electronic braking? The car has far better traction with ASC off than those other rwd cars with open diffs that I have driven.


Spin differential is going to make a difference too. For instance you likely would have gotten better results if the "free" wheel spun slowly. ABS and traction control require wheels spinning within a range of the preferred spec to be effective. Remember we are talking about a computer software program which is making choices. A wheel (drive wheel) spinning outside of the parameters for brake action will get power reduction instead. So just like a non computerized drive system one must give it the right inputs to get the desired results. Unfortunately with a complex system it is harder to know just what those input are!

I know one thing for sure, it has far better traction on snow and ice (so far) than any open differential vehicle I have ever driven including my VW panel MicroBUS which had similar weight distribution. I believe it also has better traction than a positraction rear wheel drive Jeep pickup that I use to have. I'll need the rest of the winter to know how much better.

Interesting results in the wheel off the ground test. Raises more questions than providing answers (for me). I figured from the phrasing of the spec, that the differential itself was "open". Positraction provided by braking the wheel with less traction. Which from my experience with manually doing the same thing was preferable to a an actual limited slip differential both in possible available traction and free rolling resistance.

Aerowhatt
(July) 2014 cool silver ES, acquired new 4/2015 (40.9ah at ~34K miles)
(Aug) 2014 Labrador Black Pearl ES, acquired new 3/2016 (39.7ah at ~20k miles)

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