Traction Control

[sparkymarvin]

Hi All,

I'm just curious about how other Prius owners feel about their car's traction control system.

The combination TCS, ABS, and VSC is very effective in the snow/ice and provides a bit of comfort that combats my feelings of paranoia during winter driving. I think it is a great system, but I do miss being able to spin my way up the iciest of hills in my old Saab.

Toyota says that the Prius has to limit its wheel slip in order to protect the electric motors. In my own opinion, I think that it is more an issue of battery loadings that could be damaging. If the Prius didn't have smart computers that make it the efficient machine that it is, it could be quite the little torque-monster. But burning up the tires could quickly lead to reaching un-kosher battery SOCs due to strong, hard discharge with little or no regeneration.

It seems that the computerized NiMH control and charging mechanism is a fine-tuned machine and shouldn't be tampered with.
But...
There is this side of me who wishes I could alter my car's programing to turn off rev-limiters, electrical load limiters, and most of all the TCS.

But then the mature, energy conscious, logical side of me takes over and I remind myself that I'm not really a motorhead. I drive a Prius because it is enjoyably calming, and I need to leave my electric motor tuning desires on the RC racetrack.

~Andrew

[V8Cobrakid]

the electric motors can only spin so fast. One of them.. i think mg1 has a limit that's pretty low. If the tires were to spin out of control, it could easily be destroyed.

[daniel]

I have no use for more power or acceleration than my Prius has. But traction control does have a down side.

On ice traction control is fantastic. I get going from a stop on ice much faster than most other cars, so I get through an icy intersection much faster than I otherwise would.

But traction control gave me a real scare once last spring, and I was only saved because I am relatively cautious:

I was waiting to cross a busy street. When I finally had an opening, I floored it, knowing that the car can accelerate very quickly. However, there was a very small amount of sand on the road, left over from the recently-melted snow, and the slippage caused tc to kick in, and I found myself moving very slowly across the heavily-trafficked street. It was not until I was well into the street that the wheels caught and I picked up speed. I made it only because I had waited for a much bigger opening than the car really would have needed on clean pavement. (My general defensive driving.) Without traction control the wheels would have spun one or two revolutions, kicked the sand away, and gripped the pavement.

Overall, I think tc is good. But it's not good 100% of the time.

[V8Cobrakid]

i learned if you jerk the wheel back and forth when it starts to slip.. it throws the spin speed off and traction control once again becomes your friend. also do this on gravel roads. Just enough to move the wheel to change where the turning pressure is comming from.

[jayman]

With all-season tires, Trac can become your worst enemy, especially on an icy parking ramp. The car will simply stop. I tested and the Trac also works in reverse.

I would imagine if you're stuck, the car simply won't move at all, not even to rock back and forth.

Good studless or studded winter tires really help here, but so would a momentary (Non latching) Trac disable button.

[V8Cobrakid]

what's kicking is in the basic trac.. it's designed so the motors don't exceed their limits and get destroyed. You would potentialy damage the car if you were able to turn it off.

behold.. the one flaw in a full hybrid ( so far ) that you can't just fix

[sparkymarvin]

Hey everyone,

Thanks for all the quick replies. I realize that any motor (even without fancy Toyota computers controlling it) has RPM limitations. I know that MG2 has a rev-limiter that is employed at top-end highway speeds, but...

I guess my question is...

Is the TCS safety-net really in place because of motor speed, or is it there because of some kind of electrical loading I just don't understand yet? Since motor speed already has a governor on it, why would that be the only issue with regards to the driver not having the ability to switch off the TCS like in "normal" cars?

I'm determined to get to the bottom of this.

~Andrew

P.S. If anyone from Toyota is reading this, I really hope the next generation of Prius has the following options:

-EV mode
-Traction Control disable switch
-Fewer dummy lights in the upper dash
-Fewer beeps
-RPM and load-meter options
-automatic back massage
-aroma therapy

P.P.S. Okay fine, I can live without the last two. I'll just settle for the first five then.

[mdacmeis]

The traction control in the Prius is really no different than most other vehicles, and many of those do not have disable switches either. The performance is a function of:

- Toyota Engineering desires
- Drive train protection requirements
- Motor protection requirements.

The Prius performance, as best as I can tell, is driven mainly by the latter two design requirements above. First, the drive train of the front wheel drive vehicle is susceptible to differential score if one driven wheel spins much faster than the other. Many other manufacturers incorporate a "poor man's" traction control which limits wheel spin even when traction control is not available or is disabled to protect the powertrain. Second, the motor requirements appear to have significant impact. The main concern appears to be a motor that rapidly accelerates, due to low load, then nearly instantaneously stops (as it would by gripping on dry pavement). This would result in a very large, instantaneous current change, a load dump in reality (same affect as when an alternator is running at high output and then the fuse blows or wire fails). This energy pulse is nearly impossible to control, and even with all the load dump protection in the electronics, I am sure the risk is significant. My experience to date suggests that Toyota is limiting large, instantaneous motor speed changes rather than primarily managing wheel slip.

As to the first requirement, it is clear to me that the equation used to restore torque when it has been reduced is too slow in it's recovery. Again, this is not unique to Toyota, but is an area where future improvement would be appreciated.

[tomdeimos]

I have had no problems with the traction control so far, on my steepest hill in the snow, but I do use snow tires.

If wheel spin is really needed there is no reason Toyota couldn't make it an option so the driver could disable the control partially. Instead of just allowing any spin they could allow a spin that is controlled to still protect the motor. but leave it to the driver to control the vehicle while disabled.

[jayman]

Yes, with good high-traction snow tires, Trac is your best friend. I had a chance to drive around Winnipeg today after our second blizzard in two days. The bumper was pushing snow but the car had no problem at all.

I tried a hard stop so the front would dig in. Instead of spinning on startup, the car just seemed sluggish. If I floored it, then the Trac would kick in to momentarily limit traction.

Keep in mind we had freezing rain again, so it was glare ice under all that snow. It's going to be a nightmare tomorrow morning!

The only disconcerting thing is hearing the snow and slush scraping under the car. And with the drifts here, any speed over 40 km/h and the snow flies over top of the hood and covers the windshield. I suppose if you regularly have to drive through snow a foot or more, either use chains or a 4WD.

I did have to drive around a 4WD Dodge pickup with a snowplow. He was plowing a parking lot and managed to bury the blade in a ditch, with the trucks butt sticking out into the street, and was shoveling the front end when I drove by. The driver just gawked at this tiny Prius chugging through the drifts.



I don't think he's going anywhere soon.