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How does traction control work?

How does traction control work?

How does traction control work?

(OP)
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?  

RE: How does traction control work?


Many systems control loss of traction while accelerating, by quickly applying brake pressure to slow down the spinning wheel. Similar to ABS, but backwards.

RE: How does traction control work?

Retarding (or even cutting ) the spark is faster than controlling the throttle.

Cheers

Greg Locock

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

RE: How does traction control work?

(OP)
I've heard cutting the spark is bad on the engine/cat/muffler... especially if it backfires when the raw fuel hits the exhaust.

But I don't think cutting fuel on a WOT run is a good idea either.

RE: How does traction control work?

Well I guess that's why calibrators get the big bucks (haha), they tune the response so as to minimise the damage and maximise the  benefit. The brakes are neat and fast, but down the track I think you'll see more done in the diffs themselves.

Bear in mind that they are way out of any concerns about fuel consumption and emissions when calibrating this stuff, and also bear in mind that at WOT they are probably running very rich to cool the cat and valves anyway, so running the cat feedgas even richer is no great disaster.

Cheers

Greg Locock

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

RE: How does traction control work?

One thing that using the brakes provides is some sort of troque transfer across the diff (open).

 In fact I think that mercedes uses a sort of logic to braking across the three open diffs to provide an active torque control in their awd (?4-matic?) system.

Nick
I love materials science!

RE: How does traction control work?

Yes, there's a sort of battle going on between those who want to fit open diffs throughout the driveline, and then control the torque split via the brakes, and those who want to make the diffs more complex and keep the brakes for braking.

A cynic might argue that the second proposal would be better for a real off roader, and all the soft roaders would be happy enough with the first.

When you add in a vehicle stability system the argument gets even more complex. Personally I like the idea of steering the car via left to right torque split, rather than the brakes.

Cheers

Greg Locock

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

RE: How does traction control work?

I agree with the second camp, but I'm more of a performance and technology type of guy.

As far as hardware cost I can easily see why open diffs and a brake controlling system to modulate torque at each wheel is better for the sales guys.

But I also think that the really awesome electro hydraulic diffs that the WRC uses are the cats pyjamas...

Imagine a car that can accelerate as fast as an F1 car, on dirt, snow, and tarmac.

RE: How does traction control work?

The brake solution also sells lots of replacement pads and rotors if you abuse the system.  Ignition retard and cylinder cutout are quite effective at controlling power.  In some racing series you can hear the engines popping and rasping as the power is cut in low traction situations.

RE: How does traction control work?

Another effective way to reduce engine torque is to place a second throttle body in the induction path in series with the main throttle body.

That can then be operated quite independently from a stepper motor, very smooth, and with a very wide range of control.

RE: How does traction control work?

NickE says: "Imagine a car that can accelerate as fast as an F1 car, on dirt, snow, and tarmac."

Sorry - no I can't. Not if propulsive forces go through tyres anyway. Rubber on snow just won't do it, however much traction control you've got.

RE: How does traction control work?

Traction control- another system designed for idiots who really don't know how to drive properly.

I've never been a fan of 'drive by wire' and am constantly amazed how some peeps survive their daily commute whilst glued to the cell phone, or tinkering with their radio or nav system. I'm absolutely floored by the new Lexus coming out soon that will parellel park ITSELF.

No freekin wonder todays techs need a degree in computers just to fix the brakes. The cars price goes up- the drivers I.Q. goes down. Thankfully my car still has a throttle cable and not a computer network controlling my throttle plate, brakes, ignition timing, and fuel mixture. So what if I can vaporize the tires at 50MPH and only get 17 MPG. At least when an alternator diode dies, my car doesn't immediately shut down.

RE: How does traction control work?

LordMalak,

Ha, Ha, Ha - your starting to sound a bit like a luddite there!

Surely progress is the name of the game: fuel economy, safety, customer satisfaction etc etc....

MS

RE: How does traction control work?

(OP)
LordMalak -

Well at least I don't have to change points! hahaha!

So without sophisticated brake actuators, or extra parts (i.e. electronic throttle) is the timing retard the best way?

How much can you safely retard the timing at WOT?  What are the dangers of doing so?  (Burnt valves? Overheating exhaust?)

RE: How does traction control work?

I would think a large drop off in power might be the biggest problem with pulling out to much spark advance.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: How does traction control work?

Modern EMS systems use a 'torque down' system; as opposed to just cutting the spark x number of degrees the EMS will reduce the torque by x %. There is a big difference because the torque management system will have been calibrated so that the correct amount of spark (fast path torque) is safely removed before the throttle (slow path torque) must be moved - with out burning valves etc. Infact there will probably be an exhaust temp limit function that works all that out as well - if it has been calibrated correctly.

The thing that can often get overlooked is that during large spark retards the boost increases and the ECU starts to worry that something is going wrong causing all sorts of problems.

MS

RE: How does traction control work?

Read .......  (search for ["traction control" "generic manual" site:uk] in google, and download that PDF file. I am not allowed to promote according to the rules)to understand how these systems work, including selective injector cutting or selective ignition cutting..

Since almost all race and rally cars work with multiple throttle bodies controlled by cable still this will apply for those cases.

Of course with almost all road cars in Europe now with ETC you may as well close the throttle a bit as already explained above. Stability control uses the selective brake method..

Hope that answers your question and that you may install many traction controls..

RE: How does traction control work?

gijim-

Quote:

Well at least I don't have to change points! hahaha!

No, no points- but the first thing I did when I bought my car was rip out the fuel management computer and replace the distributer with a stock GM HEI unit with a vacuum advance unit, and I recurved the mechanical advance to match that of the 72 vette (which is where I got the engine).

Anyhow, I'm not familiar with the traction controls that apply brakes to slow the 'gripless' wheels to regain traction, but I've worked on countless others whose engine management system momenterily changes the 'performance map' to lower engine output until traction is regained.

But as the markets work, applying brakes to control traction makes absolutely NO sense, so thats probable where the market is heading (so you buy more pads/rotors). I still chuckle when I remember a certain mercedes that came into our shop with a trac light on, ABS light on, and the trans/engine in 'limp mode' because a brake lamp bulb burned out. About a 200 dollar repair bill to clear all the computer codes, and replace a 2 dollar bulb.

RE: How does traction control work?

Well, it does make sense if you are using an open differential which will transfer torque to the wheel with less traction.
Applying the brakes on the slipping wheel will make it look like it has traction & the differential will transfer torque back to the wheel with traction.

If you are doing it on both/all wheels though it seems like it would just be easier to reduce torque at the engine by closing the throttle, retarding timing, cutting fuel or cutting boost.   

RE: How does traction control work?

Makes sense to me as well, where the car has 4WD and three open diffs, especially if the car already has ABS fitted.  

Just about all of the brake control hardware and wheel speed sensors would already there, so all it needs is additional software to make the system work.

I don't see that increased pad and disk wear is really going to be a serious issue either. At least not on an ordinary road car.

RE: How does traction control work?

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.

RE: How does traction control work?

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.

RE: How does traction control work?

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.

RE: How does traction control work?

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.

RE: How does traction control work?

(OP)
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

RE: How does traction control work?

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

RE: How does traction control work?

(OP)
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.

RE: How does traction control work?

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.

RE: How does traction control work?

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



RE: How does traction control work?

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.

RE: How does traction control work?

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

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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