ASC and Neutral

Let me start off by saying that I consider the handling characteristics of the iMiEV to be very good and I have no problem tossing the car around while maintaining full control. The low CG of the battery and having it centered in the car certainly contributes to this solid and predictable feeling.

The following discussion is obliquely aimed at gathering more information for a future (and separate) discussion that Neutral plays in hypermiling. Bear with me…

I'm still driving a bunch of vehicles without even vacuum-assisted brakes, much less ABS and the brake-pedal-rate-detector in our iMiEV, and I am still trying to get used to the weird (to me) application of the Active Stability Control (ASC) system.

According to our manual, the "…(ASC) takes overall control of the anti-lock braking system, traction control function and skid control function to help maintain the vehicle's control."

When ABS is actively operating, I would perhaps describe the effect as a loud "juddering" and perhaps pulsating of the brake pedal (this I'm not sure of, as it's only kicked in once on me in a true panic-stop situation).

Traction control is described in the manual as "On slippery surfaces, the traction control function prevents the drive wheels from spinning excessively, thus helping the vehicle to start moving from a stopped condition. It also provides sufficient driving force and steering performance as the vehicle turns while pressing the acceleration pedal." This to me is interesting and perhaps a little scary, as that implies that both the drive motor and the steering are somehow being controlled.

Finally, Skid Control is described in the manual as follows: "The skid control function is designed to help the driver maintain control of the vehicle on slippery roads or during rapid steering maneuvers. It works by controlling the electric motor unit output and the brake on each wheel.", with a note stating that the skid control function operates at speeds of about 9mph (15km/h) or higher.

For those nervous about it, the good(?) news is that there is a convenient ASC OFF switch (have to hold it down for 3 seconds or more), which turns off both the skid control function and the traction control function. The manual suggests that ASC OFF can be activated when moving out of mud, sand, or fresh snow…

Now that we have the definitions, I had a disconcerting experience: I was going down a long sweeping high-speed curve (coming down out of the Santa Cruz mountains) going about 55mph with the iMiEV handling flawlessly under full control when I hit a rough patch on the road surface (not unusual with California's deteriorating infrastructure). No problem; however, the juddering ABS(?) and gawd-knows-what-else kicked in and noticeably forced the vehicle to slow down as I'm going around this curve in full control and gently accelerating. Have no idea if the ASC indicator turned on as I was concentrating on driving. Nothing untoward happened other than unnecessarily (in my opinion) slowing the car down and wasting energy. Now this bothered me, and even though Stirling Moss was one of the first race-car drivers to successfully apply braking on curves (you can look up "Trail Braking"), my own predilection with typically understeering conventional cars is to usually accelerate once I'm in the curve.

I'm relaying this as it is an unusual (to me) vehicle response and I guess it's a safety feature and I'm glad it is there for my wife. For myself, I need to take the iMiEV out on some deserted slippery roads or parking lots and play with it some more just to see what its limits are and how it responds both with and without ASC.

OK, so what does this have to do with Neutral and hypermiling? It's this: does anyone know how ASC is affected if the vehicle happens to be coasting in Neutral and hits a slippery patch on a bumpy curve?

JoeS said:

...How ASC is affected if the vehicle happens to be coasting in Neutral and hits a slippery patch on a bumpy curve?

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The short answer is no, but I would like to understand it. On a YouTube video a jounalist drove an iMiEV at 80 MPH on a Mitsubishi banked race track and said "wooo, the ASC must have kicked in. I won't do that again."

I just put a new ASC post on a new tread. I had it here before I realized how big it is.

FiddlerJohn, thanks for that ASC post. I think it answers my question.
It appears that the ASC system does, under certain conditions, decrease the power to the driving wheels, which implies that D must be engaged (and not Neutral) in order for it to do its magic. Have to wonder if that power decrease puts it into regen or merely cuts off power (which is what Neutral is, anyway). Notably, most of the balancing control is done by selectively applying individual-wheel braking, inducing over- or understeer as needed. Didn't see where they were making any direct corrections to the steering. Boy, sure wish I lived in snow country as taking the iMiEV for a spin (literally) would sure be a quick education in its ASC response. I'm quite impressed that manufacturers are venturing into this active stability control arena and it will be interesting to see what the various magazine road tests have to say about it.

JoeS said:

I lived in snow country

Click to expand...

How much sand and water would it take to make a parking lot slick?

Okay, this is crazy:
Put steel whiskey barrel rims on the outside of the tires and inflate to make slick LRR tires.
Or, wrap steel banding straps (for shipping crates) around the tires.

Sorry, I will be quiet now.

My daughter and I took our MiEV out in the snow a month or two ago. While I wasn't concentrating on HOW the stability control works, it did make it nearly impossible (at least at speeds under 30 mph) to get the car sideways. Although, applying the parking brake quickly "solved" that problem. Even with the stability control turned off, it still seemed to have very neutral cornering with little under- or oversteer. The car definitely did NOT try to take over the steering.

As the main purpose of our drive was to teach my daughter about driving in the snow, she did most of the driving. Thus, I didn't get a lot of time behind the wheel myself to discover all the subtleties of the stability control system.

I don't know for sure what the car does in neutral, but note that the owners' manual says the following regarding towing the car with the rear wheels up but with the front wheels on the ground:

"Place the selector lever in the "N" position. Turn the electric motor switch to the "ACC" position..."

It follows this with the caution:

"... If the electric motor switch is in the "ON" position, the Active Stability Control (ACS) system may operate, resulting in an accident. ..."

This implies the ACS system operates in neutral, which is what I would expect. Note that they make you hold the ACS button for 3 seconds to deactivate it. And, there is a warning light when you do this. I don't think they would want the ACS system to be deactivated so easily - by simply shifting into neutral - with no indication to the driver.

PS - Here's me driving my other Mitsubishi in a little snow 3 years ago.

http://www.youtube.com/watch?feature=player_detailpage&v=qQcXs4DORYE

Quixotix, cool video of you plowing your Mitsu SUV through the snow … whenever I'd try that with my old ('67) Saab (a wonderful car in the snow), with its full-length underpan it would simple rise up onto the snow like a toboggan and suspend its four wheels up in the air. Had to be moving fast to negotiate snow depth like that.

Anyway, back to ACS: after playing around some more and taking bumpy curves at speed I find that ACS does its thing and selectively applies individual wheel braking irrespective of whether one is in D or Neutral. My specific concern was whether ACS also adds power to the drive wheels when in D, which would be 'safety' feature missing if one were coasting in N. As best I can tell it only reduces/cuts power to the drive wheels.

Nevertheless, this a something to consider for anyone who attempts coasting the iMiEV in Neutral.

Joe, besides that '67 Saab, do I detect an aircooled VW driver? I missed the '3 second rule' and did not achieve satisfaction when I tried to disable the ASC for some i-ice skating...
John, no need to silence your craziness, or break out the banding- ever experience what happens when an amateur detailer applies tire dressing to the tread? Slippery City! A quick wipe of armor all or baby oil should slick up the tread for all the experimentation you desire.... And then of course the responsible thing to do afterwards would be a brief burnout to remove the remaining oil and prevent it from degrading your tread compound...

JoeS said:

... after playing around some more and taking bumpy curves at speed I find that ACS does its thing and selectively applies individual wheel braking irrespective of whether one is in D or Neutral.

Click to expand...

You beat me to the punchline.

We got just enough snow this morning for me to "test" out my i-MiEV some more. First, to hopefully avoid confusion (or maybe create it ) I'll start with my definitions:

ABS (Anti-lock Brake System) - Keeps the wheels from locking-up (skidding) when you apply the brakes.

Traction Control - Keeps the drive wheels (the rear wheels on our cars) from spinning when you step on the "gas".

Stability Control - Tries to keep the car from spinning out.

Obviously these functions are integrated to work together as they all use the same brakes and may need to operate at the same time.

As JoeS found, I agree that stability control works in neutral as well as "D", "ECO", and "B". But I also tested reverse. It does NOT seem to work in reverse. I could easily make the front of the car slid out causing a spin. It hadn't even occurred to me that stability control could apply power. I think this would be rather unlikely for legal reason if not for any other reason. Would you want to try to convince an average jury that it was a good thing that the car self-applied power just before it crashed?

ABS and Traction Control seem to work in "D", "ECO", "B", and reverse. ABS works in neutral as well (Traction Control, of course, can't as without power applied to the wheels, they can't spin).

As many of you recall, I utilize N very often while driving my iMiEV if I'm trying to extend my range. Works like a charm, and I do it on even a slight downhill and with no perceptible change in speed; i.e., I keep up with traffic and no one is the wiser. Reminder: the iMiEV manual says NOT to do this!

ASC on the iMiEV is particularly sensitive on curves with a bumpy road surface. For example, when on a highway at speed "in gear" and taking a sweeping downhill curve with regen providing just a little retardation and when hitting a rough spot on the road then all of a sudden the ASC turns off the motor regen and selectively applies the brakes, all accompanied by the ABS clattering. Most disconcerting with the car jerking quite a bit - not at all a smooth response. I don't like this and often turn off ASC if I'm driving on known bumpy winding backroads.

A couple of days ago on a particular stretch of highway that I know has a bumpy curve I decided to try taking that curve in Neutral with ASC normally engaged. Speed maybe 50mph. It all happened too fast but ASC/ABS did kick in (dashboard light lit) but the effect was rather mild because there was no regen to kick out. Here's what's interesting: with the car still at speed and when subsequently shifting back into D, nothing happened! It took a few attempts over a period of maybe 5 seconds before shifting into D (from N) resulted in the motor re-engaging. I had even begun having visions of pulling over to the side of the road with a dead car.. :shock:

After re-engaging, all was perfectly normal. Seems there's a long time delay for the iMiEV's computer to gather its wits after such an untoward event.

Just another data point, that's all.

My favorite i-MiEV-in-the-snow video:

http://www.youtube.com/watch?v=m2Tt3bmy9mE

I had a little fun in the rain the other day, turning off the traction control and putting the i-MiEV sideways around a corner. I was amazed at how neutral the car feels when hanging the rear-end out. It took less than 0.5 seconds to "snap" the car back in line. The electric motor is wonderful because of its linear power delivery. No problems keeping the rear-end sideways.