Traction Control

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.

 

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.

 

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.

 

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.

 

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

 

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.

 

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.

 

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.

:lol:

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

 

Think we can make a snow plow for the prius? lol

 

I wonder, why couldn't a TC "controlled spin" button just change the allowed rate of tire spin?

So without this imaginary new mode, the drive wheels cannot have an average spin rate higher than the rear wheels. Suppose with this new mode, the drive wheels are allowed to spin, say, 15 MPH faster than the rear wheels? or 5 MPH?

Physics tells me there's a big difference between the coefficient of friction of two stationary surfaces (like tires in firm contact with ice, with no slippage) and the coefficient of friction of two surfaces in motion (like tires in contact with ice but slipping/skidding). There's also a big difference in change of rotation speed when tires are sticking or slipping: a large force applied to sticking tires will accelerate the entire vehicle, causing a small gain in speed; a large force applied to slipping tires will cause the tires to spin faster while still slipping, accelerating only the tires a great deal.

I assume the current TC behavior is so strict to prevent a dangerous condition. If the danger is the vehicle letting the wheel spin speed get away from it, the vehicle must be designed to detect and arrest this out-of-control spinning before it can result in dangerous speeds. (That is, they know how long slipping wheels take to develop dangerous spin speeds, and they know how quickly their system can detect and react to that condition.) How does this danger change if we allow the wheels to slip for a while longer before arresting the spin?

Maybe the difference is significant. If the system is set to arrest *any* difference in spin between the front and rear wheels (like the current TC behavior), maybe in some hypothetical situation it has 250 ms to catch and arrest the spin before a dangerous condition results. However, maybe if the system is set to arrest a spin difference of 15 MPH or higher, maybe it only has 30 ms to catch and arrest the spin. Maybe there's such a tiny time lag between 15 MPH of extra spin and large-dangerous-amounts of extra spin that what I'm proposing is impossible.

I don't know if that was coherent, but maybe some of the better engineering minds on here can help guess if the feature I'm proposing is even possible, so we know whether we should push Toyota for this.

--Michael Spencer

 

That seems like a lot of pondering for a simple questions. They have designed an advanced traction control system for the 400h. It will allow you to accelerate during tire slip. It will allow higher performance around corners, and so on.

They didn't go too much into depth with the prius because they were not sure if hybrids would catch on as they did. If they knew this beforehand, the prius would have speed sensitive volume control along with many other features in the U.S.

Traction control was designed to keep the electric motors from over spinning. With 295ft-lbs or torque (equivalent to my old HO 5.0L V8 engine) the tires would spin out of control too fast.

I've learned to not question the engineering of Toyota. Every decision was made for a certain purpose. We may not understand these yet but we will soon enough. ( or maybe not soon enough )

 

8) Michael Spencer,

I do not have an answer to your question. But, did the TC come in handy today with all your ice on HW 29 and I-80?

Ben

 

Hated that ice -- been waiting anxiously for an answer to the "ultimate ice scraper" question. But I have a 1994 Merc Sable GS Sedan. No Prius yet.

--Michael Spencer

 

I know when my Camry spun it's wheels light pressure on the brake helped, but the was an all mechanical set-up. I don't think it would work electronically.

 

as the Prius only has a 2 gear spider in the diffy I would assume that if you really had it floored and the spinning tire got good traction you'd probably rip the diffy apart. Bust the cross and probably the side gears as well as the spider gears. Normal, no spin, driving a 2 gear will probaby last forever.

 

8) All three of my Toyota's have TC now, with two having VSC as well. That being said, my only car without VSC is my Prius. TC did come in handy today here in Omaha. Ice, sleet and now snow on top of it. Glad I purchased new tires..

Ben

 

<div class='quotetop'>QUOTE(V8Cobrakid\";p=\"61003)</div>

HA! If this weather keeps up, I'll need one too.

The next morning, there was a small lake under my Prius in the heated underground parking. All that snow trapped under the car melted. What usually happens if you have to park outside, the snow freezes and the car is impossible to move.

 

<div class='quotetop'>QUOTE(Frank Hudon\";p=\"61288)</div>

Like a LD rear axle in a RWD car or pickup truck. One wheel is on glare ice and the other is on pavement. The driver floors it, the wheel is spinning like crazy, then it hits the dry pavement. BOOM!

I like mechanical locking axles in RWD pickup trucks, say Detroit Locker or PowerTrax LockRight, as they prevent the case destruction you can get from uncontrolled wheel spin. I have a LockRight in my old Ford F-150 and it works as advertised, it makes snow plowing much easier.

If you have a broadband connection, check out this URL:

http://www.richmondgear.com/PTRAX2.wmv