Traction control

[Jez]

How does traction control work on the S6? I see it can be configured to use a lateral g or steering wheel input - not really sure how this would work.

I'm familiar with Race Logic TC that monitors wheel speeds and can be configured to cut power when slip is detected.

[pat]

Jez,

The traction control strategy allows you to specify a spin target as a function of either steering wheel angle and road speed, or as a function of lateral G and road speed. Additionally if you have a lap beacon, you can tweak the spin target as a function of lap distance; if you already know that a track has a low grip section at a given point then you can adjust your spin targets for that section.

Spin is calculated by comparing individual wheel speeds to the road speed. A spin error is calculated by comparing the actual spin to the spin target, the result of this calculation multiplied by the gain, and that is used to generate a torque reduction value. This value is clamped as a function of RPM, before being used to index into the fuel cut severity and ignition retard lookup maps, that define the actual amount of fuel cut and actual ignition retard as a function of desired torque reduction and EGT.

You can use the EGT dimension to balance the torque reduction so as to prevent turbo or exhaust valve damage; imagine for a moment a situation with low EGT but too much wheelspin, you may be able to completely control the situation simply with ignition retard, it will be smoother (unless the resultant timing generates misfires) than using a fuel cut, but if the EGT was already high, the last thing you need is to dump even more heat into the exhaust, so a fuel cut would be better. Obviously if a situation starts with low EGTs but it's very slippy and the strategy has to run for a long time, you can configure the tables so that it "rides" up the EGT dimension with the bias shifting from retard to cut.

Hopefully this gives some insight into the way the traction control works,

Pat.

[Jez]

Thanks again Pat. How is road speed calculated?

[pat]

Jez,

Road speed can come from a multitude of sources!

It can be any individual wheel, maximum or average front, maximum or average rear, or indeed things like a radar ground speed sensor. The best choice will depend on the specific application, but using average front will probably work quite well on an RWD car. If the diff is fairly open and it is possible for one wheel to spin a lot, then it may be worth taking the signal from the gearbox that would feed the speedo and use that as radar speed, but on an LSD that may not work, it's relying on one wheel spinning much quicker than the radar speed, and with an LSD both rears could be spinning much quicker than the road speed, but because the road speed is coming from the 'box there would be no way to tell, hence average front might prove more useful. Of course in a four wheel drift, the only reliable way of detecting road speed is radar / laser measurement, GPS might be OK if a little slow.

Hope this helps,

Pat.

[Jez]

Got the Solaris installed and engine running now - Thanks Pat!

Today I wired in the wide band lambda sensor and ABS sensors

I'm having a bit of a problem getting the ECU to display speed. I've got the ABS inputs on the Unipolar inputs and I'm getting a signal when I spin the wheel. However the ECU doesn't show any speed. I've traced the AN06 voltage and get a voltage going from 0 to ~1v. So I've set the high and low thresholds to 0.3 and 0.7v.

Any idea what I'm doing wrong?

[pat]

Jez,

your problem lies with your choice of inputs. The Unipolar inputs have FIXED voltage thresholds at 1.25V and 3.75V, so your input signal, although large enough for the ADCs to pick up, is too low for the comparators. You have some options :

• Turn on the pull up to bias the signal. Do this by configuring the input type as Thermistor.
• Increase the output of the sensors by spinning the wheel faster!
• Re-pin the ECU so that the ABS sensors are on Bipolar inputs (AN01-AN04) and the crank and cam are on AN05&AN06, configured at Thermistor inputs

Hope this helps,

Pat.

[Jez]

Thanks Pat - I'll give those ideas a go. I think it'll be ok when the wheel spins fast - I've just been spinning it by hand at the moment.

[Jez]

Thats sorted now. Rewired to use bipolar inputs for the ABS

[Charlie]

Good work Jez!

[Wez]

Ryan got this working on my Supra yesterday, crazy indeed, very very impressed.