What does Toyota say about their stupid traction control?

Most traction control systems do not have electronically controlled differentials. Some selectively apply the brake on the spinning wheel, effectively transferring power to the other drive wheel. Sadly the Prius doesn't do this.

On the other hand, I just came back from a sixty mile drive through snow and ice, and our 2006 Prius did just fine. Along the way were several accidents, including a car that went over an embankment down to the lake, but no trouble with our Prius. Much of the road looked like it had been surfaced with a Zamboni. You could see the reflections of oncoming traffic. Still, even on the hills, our Prius did just fine. Perhaps it has something to do with good tires and winter driving technique?

Tom

 

Why do you not think that the Prius (at least in the Gen 3), does not selectively brake the slipping wheel?

Toyota describes TRAC here Traction Control – Truck Safety While the link is labeled "Truck Safety" it links from the Star Safety System page and is presumably a general description of how TRAC works in all of their current vehicles including the Gen 3 Prius.

"Toyota’s Traction Control sensors are activated when one of the wheels starts to slip. TRAC limits engine output and applies the brakes to the spinning wheel. (Figure 3) This transfers power to the wheels that still have traction to help you go safely on your way."

There is an earlier reference to "applying brake force to the spinning wheel(s)" which might be confusing but after reading the final paragraph I quoted above it seems clear that the reason the indicated the possibility of braking more than one wheel was just to cover what can happen with 4 WD.

 

Traction control on the Prius does not apply the brakes. It only cuts power.

VSC, on the other hand, does apply the brakes selectively. VSC does not always beep. Beeping occurs when VSC has reached its limit in applying corrective action.

Tom

 

Boy, now I am really confused. As the Toyota article points out, TRAC applies the brakes... which is contradiction to your statement?

 

Tom has a Gen 2 Prius, which does not apply the brake to the slipping wheel. The Gen 3 Prius (2010 on) does.

 

So this was an improvement in design for the 2010? Thanks.

 

Thanks for the clarification. I've read mixed things about the Gen 3 upgrade to TC. Some Toyota documentation states that it is just a software upgrade, but other information suggests that selective braking is used. I would like to see some definitive information about this.

Tom

 

Has Toyota stopped giving definitive answers on this site ?

 

Toyota marketing participates on this site. Sometimes they will forward a technical question to the engineers, but not often. We could make a direct request, but I don't like to play that card too often.

We had a chance to talk with the Prius chief engineer when the 2010 was unveiled. That was a great opportunity to get a lot of information in a short period of time. We talked about traction control, but unfortunately, various sources have subsequently released conflicting information. Even Toyota has said it both ways.

Someone with a 2010 needs to do some testing. All we need is a patch of ice: one tire on the ice, the other on dry pavement. That would answer the question in about two seconds.

Tom

 

I have had both my tires on ice, i rolled down my window and stuck my head out, i was trying to get stuck in a ice storm on a speed bump, once i got stuck there i could hear my car spinning the tire so i looked at the drivers side tire, it never moved but the other tire was spinning the whole time i could hear it.

 

Thanks for the information. That suggests that the Gen III Prius does *not* apply the brakes selectively during traction control. This is consistent with the information we were originally given by Toyota.

Tom

 

But if the traction control was more advanced it could apply brakes just to the spinning wheel, which would transfer drive to the other wheel.

 

LSDs are a brute force mechanical method of limiting slip, and they come with their own set of problems, especially when used on the front axle. Most advanced traction control systems avoid the "one slipping wheel" problem by selectively applying the brake on that wheel only, forcing power to the other wheel. This is the method used on the HMMWV, the Toyota FJ40, and many other advanced 4WD vehicles.

Tom

 

It does however seem to be inconsistent with what Toyota say on their web site.

If stuck on ice at a speed bump, presumably the wheel with no traction would rotate as the brakes pulsed whether they were just pulsed on the wheel with no traction or they were pulsed on both. I assume that this is what adamace 1 heard but it doesn't seem it would necessarily be an indicator that both are being pulsed?

 

Here is a video showing tire spin:

Here is a video posted some time ago that to me shows an alternating wheel engagement. http://priuschat.com/forums/gen-iii...3556-2010-traction-control-5.html#post1067714

Seems pretty clear to me.