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?
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?
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?
But I don't think cutting fuel on a WOT run is a good idea either.
RE: How does traction control work?
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?
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?
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?
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?
RE: How does traction control work?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
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?
RE: How does traction control work?
"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?
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?
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?
RE: How does traction control work?
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?
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?
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.