Traction Control Dangers and Engine Braking Savior

[hobbit]

I pointed out near the end of my rundown on B-mode that the "falls
on its face" behavior of letting up the pedal is favored by some
autocrossers, and is definitely useful in the slippery stuff.
.
_H*

[jayman]

Hobbit thanks for the writeup. I'll try B around the city and on the gravel road at the hobby farm to see if there is any difference.

[ncc74656m]

Oh boy, I hate ABS...

Not that I hate the concept or even application of ABS. I hate the fact that my Corolla's salesman lied to me and told me it had ABS (could've just been wrong, but saying that he lied makes me feel better), and I almost skidded right into an intersection one night when it was rainy and leaves were all over.

I distinctly remembered being told I had ABS, and so I squeezed the life outta those brakes. If I had known, I would've released and pumped.

On a funnier note (because I stopped in time), you should've seen the look on the guy's face in the next lane. He saw my sheepish "oops" grin and just kinda nodded and smiled.

Anyway, now that i know I don't have them, I haven't had a problem. Of course, I will be making sure I get them on the next car (still hoping for the Prius).

[statultra]

the ABS on the toyota prius is very sensitive, maybe too sensitive, my 01 prius almost got into a accident one day when there was a patch of ice near a 4 way intersection, the light was red, and i was trying to stop, but ABS kept kicking in making the brake pedal shake ( it was braking every second almost and on the ice it was braking every half second ) , to the point where i stepped really hard on the brakes and not much happened. I then used the handbrakes since i was down to about 15 mph.

Traction control doesnt bother me, its a good thing in some conditions ( in snow and ice, it actually helped me rather than held me back like other drivers ) up here in NJ well, last year snow was kinda on the bad side and the prius proved to be a good car, minus the ABS.

btw the ABS on the prius is very sensitive, i believe this is due to the interconnection of the ABS and the hybrid management system,

[Skeptic357]

<div class='quotetop'>QUOTE(narf @ Feb 9 2007, 03:10 PM) [snapback]387594[/snapback]</div>

It you have ZERO traction, the car will kill power to the drive wheels, but don't fool yourself into thinking you could somehow drive out if it if only the car would spin it's tires. Zero traction is still zero traction.
[/b]

That's not entirely true. I've seen my wife get through short patches of ice by furiously spinning the tire until friction generates enough heat to melt through to pavement. The downside is that there is a distinct odor of burning rubber--I wonder how many miles of wear the tire suffers in such an event.

I'm not suggesting that the above is a good idea, but it sure is frustrating to sit in my prius with the accelerator floored, unable to move because one tire is sitting on a patch of ice. Couldn't the car at least pretend to do something? My dad always said that having too much power available makes for bad drivers who try to power through every situation--maybe Toyota agrees, and traction control is their way of chiding, "Stop driving like an idiot, it's slippery out there."

[jayman]

<div class='quotetop'>QUOTE(hobbit @ Feb 9 2007, 03:22 PM) [snapback]387609[/snapback]</div>

rundown on B-mode
[/b]

Hobbit

I did try it out in city driving and it feels just like having a stick shift again, actually felt pretty good in city driving. No difference that I could tell on ice, with the studded tires I don't have a problem now.

I can tell though the city fuel economy would really suck if I drove in B all the time, so I won't use it anymore.

<div class='quotetop'>QUOTE(ncc74656m @ Feb 9 2007, 03:53 PM) [snapback]387633[/snapback]</div>

I hate the fact that my Corolla's salesman lied to me and told me it had ABS [/b]

They appear to lie for a living. Good training if they're seeking a future in politics!

<div class='quotetop'>QUOTE(Skeptic357 @ Feb 12 2007, 12:47 AM) [snapback]388737[/snapback]</div>

That's not entirely true. I've seen my wife get through short patches of ice by furiously spinning the tire until friction generates enough heat to melt through to pavement. [/b]

Or if you have studded tires like I do for winter driving, very *slight* wheelspin really helps as the studs can claw down into the ice and get you moving.

[slvr_phoenix]

For the record, only my first car didn't have ABS (also was my only manual transmission), so I've been driving with ABS all my life. And I'm not talking about a full on hard brake stop. I'm talking about a normal slow braking process on a slippery road.

<div class='quotetop'>QUOTE(Marlin @ Feb 9 2007, 12:07 PM) [snapback]387554[/snapback]</div>

During your rapid stops in snow, it was undoubtably the anti-lock brakes (ABS), not the Traction Control (TC) that engaged. I beleive they both use the same dashboard indicator.
[/b]

I have a feeling that we're arguing technical semantics. The TC is responsible for killing your power the instant there's a skid. That's what kills the generator brake. The ABS is responsible for pulsing your brake discs/pads so they don't lock up the wheel. It's the TC killing the generator that causes a bad situation to become worse. ABS in general I have no problems with. It's handy to have. Don't get your technical terms confused.

<div class='quotetop'>QUOTE(Marlin @ Feb 9 2007, 12:07 PM) [snapback]387554[/snapback]</div>

because the ABS does not engage until it detects that the wheels have locked up.
[/b]

You'll have to define 'locked up', as a minor temporary loss of traction during deceleration is not 'locked up' IMHO, yet that's what causes the situation. It's funny actually. When I'm accelerating the TC doesn't engage fast enough. I always beat it, causing the dreaded double-drop. In a deceleration however the TC drops your power before you can even flinch.

<div class='quotetop'>QUOTE(Marlin @ Feb 9 2007, 12:07 PM) [snapback]387554[/snapback]</div>

And in any case, whether it was ABS or TC that you encountered, neither one caused you to lose traction
[/b]

Sorry, but you're extremely wrong. That's exactly what I'm trying to point out so people are aware of it. You're happily driving along on a snowy road. You're braking normally (even extremely safely) with the generator braking conveniently providing a more secure braking mechanism than the real brakes. Then oops a minor slip. Because gosh, that never happens on snow or anything. Most cars wouldn't have a problem. They'll at most anti-lock while you're braking and keep your traction the same or better.

But the Prius instantly drops out of generator-braking and kicks in the real brakes the milisecond a single wheel (of all four) slips. The resulting jerk caused by switching from one brake system to another at the drop of a hat when the other three wheels could all have perfectly reasonable traction turns a minor slip for one wheel into an actual skid for all four. It's this switch that causes a loss of traction. (If you ever fully lost it to begin with, which is debatable as the other wheels could have still had it.) And letting off the brake (even accelerating) doesn't regain you any traction at all either because the TC has grounded you. And if it happens while steering/turning you can't even seem to turn into the skid for that matter, because again, the car seems to think that it's a better driver than you are.

In the Prius, an incredibly minor slip of a single wheel while braking turns your car into a useless cage where all you can do is grab on tight and hope for the best. No driving skill can save you because the car prevents you from being able to use any of your skills. Where as other cars won't switch brakes like that on you to catapult you into a skid at the slightest hint of lost traction.

As much as I love my Prius, I'm also beginning to hate it. I drive well. I have good instincts and reflexes. I could make even a '98 Mercury Sable for all its weight look like a rally master. I've grown up driving in snow, ice, and gravel. But in a Prius I'm at the mercy of some very badly designed 'safety' features that turn emergency situations into nightmares.

The last thing that the Prius should do is drop the generator-braking in a skid. Besides the chunk when it switches causing a minor skid to suddenly become a major one, the generator-braking is also a much more stabilizing braking force than the real brakes. What you want if anything is for the overall braking force to remain identical, which it doesn't do. But if you're going to change the quantity of braking force, at least do so by kicking in more on the transmission, not grabbing the tires harder. If it has to change anything it should not only kick in generator-braking during a skid, but should even automate engine-braking during a skid. Instead you get is the worst option of all, a sudden switch over to pure use of the least effective braking mechanism in the whole car out of all three braking forces that it has available.

In other words, it's an extremely bad design. TC shouldn't drop the generator-braking if ABS kicks in. The only way to mitigate it is to use the engine-braking in conditions when you could expect a loss of traction, and to put some actual tires on the car. The stock ones just plain suck.

[slvr_phoenix]

<div class='quotetop'>QUOTE(narf @ Feb 9 2007, 01:10 PM) [snapback]387594[/snapback]</div>

The problem isn't the ABS or traction control, it's the crappy tires that come stock on the prius.
[/b]

No flirking schiznit! I'm very much growing to hate the stock tires. Because I want to avoid these TC problems with the Prius I'm even contemplating wider wheels as well as new tires. Unfortunately at this exact moment I just bought a new car, so I don't exactly have money for new tires let alone new wheels. The Prius is the first 'normal' driving car I've ever owned where I've even considered seperate summer and winter tires instead of all-weathers. I abhor the Prius TC and it's awful that the stock tires ask the TC to come out and play so often. The only worse tires possible would be those infernal low-energy tires. So far I'm not convinced that the Prius tires aren't low-energy tires for the traction they get...

<div class='quotetop'>QUOTE(narf @ Feb 9 2007, 01:10 PM) [snapback]387594[/snapback]</div>

It you have ZERO traction, the car will kill power to the drive wheels, but don't fool yourself into thinking you could somehow drive out if it if only the car would spin it's tires. Zero traction is still zero traction.
[/b]

Zero traction, sure. However zero is exceedingly rare. Zero is statisticly theoretically possible, but highly improbable. So zero power is not a good solution to almost-zero traction. Chances are if you can spin the tires slow enough, you can get out. (And then there's rocking.) But if you can't spin the tires at all...

The TC as implemented is just awful. The drop of power is such a horrible solution. It should at most limit the RPMs so that if you've already dropped the power by beating it to the punch then it effectively does nothing. Protect the system from damage without trying to kill the driver. And the TC should most definately not kill generator-braking when ABS kicks in. The absolute last thing that you want if you lose traction on a single wheel is a change in braking force. The only time I could remotely consider dropping the generator-braking would be if all four wheels had sustained zero traction for more than 500 miliseconds. (And even then I'm still not for it.)

I can understand why from a technical perspective they do this, to protect sudden changes in traction from causing damage to the car. However there are solutions to this that would be safer for the driver and keep the parts all within spec. They'd just cost a tiny bit more.

[jayman]

<div class='quotetop'>QUOTE(Silver Phoenix @ Feb 13 2007, 01:57 PM) [snapback]389553[/snapback]</div>

The TC as implemented is just awful. The drop of power is such a horrible solution. It should at most limit the RPMs so that if you've already dropped the power by beating it to the punch then it effectively does nothing. Protect the system from damage without trying to kill the driver. And the TC should most definately not kill generator-braking when ABS kicks in. The absolute last thing that you want if you lose traction on a single wheel is a change in braking force. The only time I could remotely consider dropping the generator-braking would be if all four wheels had sustained zero traction for more than 500 miliseconds. (And even then I'm still not for it.)[/b]

I agree. I'm sure most Prius drivers have felt the "lurch" of losing regen braking when a wheel has very briefly slipped. It really gets your attention!

[richard schumacher]

SP, sorry if I missed a description of it above, but exactly what are you doing to make this behavior appear?