How does traction control work?

[gijim]

Okay, wheel sensor detects rear wheels are slipping on acceleration. (You floored it from a stop in slick conditions) On the newer engines with electronic throttles, they can just close the throttle a little bit... but if you have a mechanical throttle, how do you reduce engine torque enough to regain traction?

The common answer seems to be "retard the timing", but can that reduce the torque enough?

 

[LordMalaK]

not all cars have a pressure pump and accumulator system in the ABS system, at least they didn't when I retired 2 years ago. Sure with the current flashable controllers you can update the software (via satellite now) but unless your driving a 50,000 dollar car your not piloting a fully traction controlled vehicle.

So the question that started this thread is 'loaded', i.e. 'how does a watch work'.

perhaps gijim can tell us a bit more details as to what system he's referring to.

Basically traction control works like this:
1. wheel slips
2. computer senses the slip via ABS sensor
3. computer stop wheel from slipping.

 

[GregLocock]

That's one way of doing it, but it certainly isn't the only way. You can implement TC using just vehicle speed and engine speed as inputs. It's not as good, but it is hard to detect.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Lou Scannon]

Greg wrote "You can implement TC using just vehicle speed and engine speed as inputs. It's not as good, but it is hard to detect."
This approach, it seems to me, would be limited to vehicles on which vehicle speed is being sensed from a non-driven wheel/axle.
The existence of a torque converter in non-lockup mode would tend to muddy the waters a bit, too. A driver slipping the clutch in a manual trans car would likewise confuse the issue.

 

[jbthiel]

There was quite a bit a rumor going around in NASCAR many years ago that some drivers were using TC. The "inside man" who talked to a magazine said it was done by comparing a front wheel speed and the diff speed, then pull out timing to lower engine output. I believe that there were even some "black box" systems available to the saturday night racers to interface with their MSD boxes.

 

[gijim]

After some googling, I found a sentence that sums up what I understood:

"FACT: Timing controls can only reduce 15% of the engine horsepower and are very hard on your engine."

That's exactly what I thought, you couldn't get enough control on the engine with just a timing retard.

HLC, thanks for the link. Cutting the injectors seems to be the way to do it.... I'd imagine that one (or more) cylinders would go lean for a cycle as the fuel on the intake walls gets drawn in, but I can't imagine that being as much of a problem as gasoline burning in your exhaust with a timing retard

 

[mattsooty]

Gijim

I wouldnt believe everything that you read on Google. That FACT is utter rubbish.

Modern EMS systemes use spark timing to effect torque downs, it is not 'hard' on the engine (how can it be seeing as the cylinder pressure is reduced?)

If there is still a requirement to reduce torque even further (almost never in a TC torque down) then the throttle will be closed.

The injectors are not cut because doing so would burn you catalyst out in a very short time. Retard will increase port temps but this will have been calibrated so as not to be a problem.

MS

 

[gijim]

It's hard on the engine in that you can burn up a valve if it hasn't been "calibrated".

I'm assuming a race vehicle which does not have a catalyst, has a mechanical throttle, and the installer doesn't want to "calibrate" anything (or is inexperienced). The fuel cut seems to be the best of everything.

The only down side is that you can't vary the power cut as infinitely as a timing retard.

 

[LordMalaK]

you can cut fuel and retard spart simultaniously and still keep your stiochiometric ratio (somewhat) so you don't damage the convertor. Thats exactly what the earlier GM systems did, RABS it think it was called.

 

[mattsooty]

LordMalak,

Are you sure.....?

It must be a pretty incredible system if you can remove fuel by way of fuel cut yet continue pumping the same amount air through the cylinders AND still keep the same AFR at the catalyst?!?!

MS

 

[LordMalaK]

It doesn't cut fuel completely, but changes the injector pulse width and timing as well as ignition timing to lower engine output.

By creatively changing these two parameters they can decrease the output power and still maintain a proper exhause gas output at the converter. Not very sophisticated but it did work.

 

[patprimmer]

Garbage.

If you reduce fuel and maintain air you must go lean.

If you do not change fuel you will not loose power.

If you reduce fuel you must also throttle air supply.

If you cut fuel and ignition simultaneously so the lean charge does not fire and less unburnt fuel is sent to the exhaust, you still run a serious risk of torching a piston.

Regards

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