NefMoto

When is each used?

So TABGBTS uses calculated EGT to decide when it is active.  What is the actual EGT from the sensor used for?

Rick

This has been pressing me for a while but I have finally worked it out.

I was looking into LambdaBTS and finally reached the conclusion that it only uses calculated EGT and not measured.  I did find the map for steady state EGT temp which is the most infuencial when it comes to high load.

In cars with EGT sensors there is another function active known as ATR - exhaust gas control.  It uses another parameter/threshold simialar to TABGBTS. Stock this is set to 980C.  Once this exceeded, the exhaust control kicks in.  It works using a PI controller to richen the mixture in order to bring it down below the threshold.  The hotter it gets, the more fuel is added.

This is great news for me. It means for requested torque above around 70 I use LAMFA to run lambda 0.85.  Lambda BTS will request the same lambda 0.85 at all high load/boost areas.  The EGT controller can then intervene  if things get too hot, by richening only as much as is needed to keep the temp in check.  It's effectively a closed loop EGT control system.

Rick

Does anyone know the name of the variable for actual EGT so that it can be logged instead of just tabgm_w? I was hoping to be able to log each sensors actual output individually but none of the variables under "GGATS 1.40 Gebergr

Can't remember exactly, but it's in one of the 13x blocks.  I

On an S4 it will sit at 945C until the temp goes above that.

Rick

The EGT from sensor is stored in variable tats_w (tats2_w).
The sensor delivers a pwm signal to port P_ats, the curve TABGTA maps
the sensor signal's duty cycle (taats_w) to temperature.
With VCDS the sensor temperature is contained in group 112 (for 2.7T).

Excellent, thanks guys, that'll work just fine.

Does anyone know what kind of sensor the EGT sensor is?  It delivers a PWM, so isn't a thermocouple.  Why did Audi use the PWM method?

Rick

Could be an active thermocouple sensor, with the electronic amplifier integrated. PWM is more immune to electric noise than millivolts out of a thermocouple

How many wires come from sensor?

The sensor has an electronics box at the interface connector that generates the pwm signal based on the sensor output.

So I wonder if the PWM vs Temp map can be edited so they read lower than 945C, or does the duty cycle drop to zero below this.

Rick

The Sensor is a Typ N Thermocouple. It doesn't make sense to modify the input map, as the S4/RS4 sensor electronics is only variing the PWM between 950-1025. For the full range you can use the RS6 sensor for example which can read from -40-1100°C.

Ok, so if you put the RS6 sensor in, then copy TABGTA from an RS6 map into your map.

I wonder if the RS6 uses the measured EGT in more functions than the  R/S4.  The R/S4 only uses measured EGT in the ATR function above 980C.  Perhaps the RS6 uses a lower threshold for ATR rather than using KFLBTS?

Rick

Hi Rick. I think you have worked it out. I eventually came up with the following words after pondering these for myself, thinking about what a professional tuner had told me and translating the various bits of the ME7.5 funktionsrahmen. The Audi TT 8N has an EGT sensor, but I think that there is still value in the ECU controlling to modelled temperatures for other temperature-critical components that aren't monitored by a sensor...

"The map KFLBTS which specifies lambda values as a function of engine speed and cylinder charge controls enrichment of target lambda. This only activates when several variables which represent modelled temperatures (a) at the exhaust manifold, (b) in the catalytic converter, (c) near the catalytic converter (d) at the cylinder head or (e) near the lambda probe, in a sub-function LAMBTSENABLE have exceeded their threshold and a start-up delay time has expired. Apart from the cylinder head temperature which is 200C, these values are typically 900-950C.

Enrichment can be deployed in desired areas, attenuated or eliminated by means of the map KFFDLBTS (Kennfeld fur Faktor Delta Lambdasoll fur Bauteileschutz, map for the multiplication factor for the change in target lambda for component protection) with units (x,y,z): RPM, % load, multiplication factor.

In addition to LAMBTS, the ATR module controls the general enrichment at high load and speed (full load enrichment). EGT control is applied only if the controlled enrichment is insufficient which improves fuel economy. Unlike LAMBTS which uses modeled temperatures, ATR takes an actual temperature input from the EGT sensor. The set point for EGT regulation in the ATR function is given by constant TABGSS (Sollwert Abgastemperatur fur Abgastemperaturregelung)."

I read what you wrote and it agrees with my research :)

Rick

Well at least we both came to the same conclusions independently.

Doug

Doug, would you mind if I integrated your content into s4wiki.com?

BTW outstanding summary...

LOL.

Feel free! But you might be interested to learn that I've just completed a draft of a 52 page technical article/FAQ for www.tt-forum.co.uk on remapping/tuning. The bulk of the technical content is based on the S4 wiki illustrated with BAM and BFV specific maps and supplemented, where appropriate, with translated sections of the ME7.5 funktionsrahmen recently posted by Tony.

A member of chiptuners.org is looking at it at the moment to give me a sanity check on the technical content. I'd happily pass it on but out of courtesy to the reviewer, to avoid losing control of my drafts and because I don't want material with  potentially silly errors floating around, I'd rather not distribute it until it has been knocked into shape.

If my current reviewer can't complete the task (bearing in mind that I've already had a professional tuner duck out after sitting on it for nearly a month), I'll happily post it up here for comment.

Regards.

Doug

I cleaned up the earlier posts. It seems as though the degree dot and umlauts are causing posts to be truncated. I will look into it.