BRZedit Drive By Wire Info
 

Greetings,

So I have been messing around with BRZedit since yesterday afternoon and I have some info I wanted to share with the group of BRZedit users. Mods, please feel free to move this post into an ECU Tuning sub forum as I am sure there will be many more threads like this in the months to come.

Anyway. After a little messing around I think i have a good grasp of how the Drive By Wire system works for the most part and I have a bit of info that will save some of you some head scratching and wasted time. :party0030:

First lets take a look at the stock maps:
http://i597.photobucket.com/albums/t...psfbac8630.jpg

As I was looking around at the maps I came across the Wide Open Throttle Torque Limits ... Thinking this was similar to the torque limit maps we have in Evo / Ralliart / 4B11T land I decided to smooth out the 2D and raise up the limits. After wards my logs showed some throttle closure right around the torque dip. So, I made another pass at increasing the limits and taking some more logs.... Throttle closure got worse...

Finally it dawned on my this is not a Limit table but a base table that is used to calculate where you fall on the Throttle Angle - Torque Request table. The result from this table lookup sets the throttle angle. Lets have a look at my logs and the tables that produced them:

http://i597.photobucket.com/albums/t...psab54710c.jpg

So, what it appears happens is this:

1. Mash the go pedal to the floor
2. ECU looks up the requested torque from Accel Pedal - Torque Request (Sport Mode)
3. ECU looks up value from Wide Open Throttle Torque Limit
4. AP-TR / WOTTL = Torque Ratio (%)
5. ECU looks up Throttle angle from Throttle Angle - Torque Request table

I have looked at the data over and over again, the only way the math works out is if the Torque ratio = AP-TR (sport mode) / WOTTL. This is only for WOT. I have not dug into the part throttle stuff yet. The Calculated Torque A and B tables must come into play somewhere, possibly for part throttle and not for WOT.

Long story short... Do not raise the Wide Open Throttle Torque Limit table beyond where your calculated torque values / Accel Pedal Torque Request lookups put you. If you do, you will end up with less than the desired throttle opening angle.

I just realized photobucket neutered all my images to 1024x768 ... derp... I'll pust up some better shots latter on

So to put this in geek-speak:
T_EST = f(N, LOAD) using either map "A" or "B"
T_WOT = f(N)
T_REQ = f(APP, N) using either map "Normal" or "Sport"

T_RATIO = T_REQ / T_WOT

TA_REQ = f(T_RATIO, N)
TA_CUR = current throttle angle

TA_DELTA = TA_REQ - TA_CUR
TA_TARGET= filter(TA_CUR, TA_DELTA, K) where K is the adaptive filter gain

Thanks for posting up screenshots! The more you post, the more we learn.

Edit: This is not dissimilar to the system brought to market by Porsche quite a few years back. Different manufacturers deal with pedal position in their own way. Supplemental reading: http://www.f1technical.net/features/17820

Yeah, that's what I ment to say lol..

I had it all worked out for the one example, but then realized it did not hold (the calculation that dropped me into the Throttle Angle - Torque Request table ) exactly... so I am sure there is a more complicated equation like what you posted.

What does hold true though is that the higher you set the Wide Open Throttle Torque Limit table the farther left you end up on the Throttle Angle - Torque Request table and the less throttle angle you get at WOT.

As with most of the DBW setups I have seen now, the key to adjusting the feel to your liking is adjusting the Throttle Requested Torque tables... Though in this case, I think the Throttle Angle - Torque Request table could use some smoothing.

BTW, I read your car log and you have good taste in both beer and car parts.

The wife is 1/2 Belgian, and Leffe is always welcome around our house... although any time you can find it, go for Duvel (s'il vous plaît).

Here are a couple of screen shots to illustrate a potential area of improvement with the stock DBW tables.

Firstly, in this graph of logged accelerator pedal position vs actual throttle position, you can see the relationship is fairly linear in most cases:
http://i597.photobucket.com/albums/t...psc29fae84.jpg

However, when you look at WOT.... notice how the Throttle Position trails off as RPM rises:
http://i597.photobucket.com/albums/t...ps43544969.jpg

This lines up perfectly with the stock .995 torque ratio % column from TA-TR table:
http://i597.photobucket.com/albums/t...psfaafed1d.jpg

Today I'm trying out a small tweak where I have flattened out the .995 column to 80%.

So you're telling me... slamming the pedal in an 86 will request 86 degrees of throttle angle for all engine speeds.

All Hail the Mighty 86!
:bow::bow::bow::bow::bow::bow::bow::bow:
:bow::bow::bow::bow::bow::bow::bow::bow:
:bow::bow::bow::bow::bow::bow::bow::bow:

So the throttle angle cuts down around the torque dip area no matter what speed you are at?

So, if I may ask: throttle plate closes around the dip RPMs at WOT, but it remains 100% open at partial throttle? If this is the case, I would like that behavior to switch places. WOT means I want to go right now, partial throttle (especially steady state partial throttle) means I just want to cruise. So one needs power, the other needs fuel economy.

Or am I seeing this all wrong?

- budi

:thumbsup:

LOL, So many questions :bonk:

So, I have not looked into part throttle behavior much, will get to that latter.

It is not clear if the throttle plate is actually closing a little bit or if this is just something you see in one of the logged values.

There are two values i have been logging.. Throttle Angle % (the one shown in the graphs above) and Throttle Open Angle (sub)%. TOAs shows a flat 84.7% across the board for a WOT pull... it is TA% that shows the trail off.

For what it's worth my changes to the 0.995 column of TA-TR (making the whole column 80%) did not seem to make any difference in the logged values of TA% on the single wot pull i got to do on my way to work today.

I have to go through my logs from when I changed the WOTTL table and was getting reduced throttle angle to see how those look and if i was logging TOAs% then.

Thank you for your work for the community. These are invaluable information that has previously not been found/released. Reminds me of the 350Z where full throttle doesn't mean 100% throttle plate opening. The torque dip has always been a mystery right? This could (hopefully) shed some light on it.

- budi

Interesting that they left 4 degrees worth of safety in there. Most modern ECU's run a throttle sweep during key-on to recalibrate for accumulated grime.

Since it's hard-coded, I guess they feel certain that we won't accumulate any more than:
cake thickness = throttle radius * tan(4 degrees) = ~0.1" sounds good to me!

@Sargy, I wouldn't think too much over the dip. That's a datalog, not the code. The throttle command is being sent as 86 degrees, but it's only delivering ~75 degrees. That's a reduction in area of ~3% for an ideal throttle, and less than that for ours. It's probably a combination of motor holding torque vs aerodynamic torque... since it's a plate in high Reynolds number flow condition (10-20,000 most likely Source PDF).

This is exactly the type of posts we need. BRZedit opened an entirely new door to sharing information here. Love it.

So I have asked Epifan to rename the WOTTL Table to Requested Torque Base.

I have confirmed that these tables work the same way at the Legacy GT:

Throttle opening angle is set from the % value in the Throttle Angle Torque Request Table as such:
Requested Torque (from Accelerator Pedal Torque Request) / Base Torque (from Requested Torque Base) = Torque Ratio %


So a few examples:

4,000 RPM 75% APP = 179.2 RT / 186.6 BT = 0.96 Torque Ratio = 65.038 Degrees
4,000 RPM 85% APP = 186.6 RT / 186.6 BT = 1.00 Torque Ratio = 86.000 Degrees
4,000 rpm WOT APP = 196.0 RT / 186.6 BT = 1.05 Torque Ration = 86.000 Degrees

6,000 RPM 75% APP = 203.8 RT / 208.7 BT = 0.976 Torque Ratio = ~65 Degrees
6,000 RPM 85% APP = 208.7 RT / 208.7 BT = 1.00 Torque Ratio = 86.00 Degrees

The table data may look to be all over the place at first glance, but after you do a few tests you will see that values in the Throttle Angle Torque Request table are setup the way they are because of the way the Base Torque Request table is setup.. which actually mimics the stock torque output...

There are numerous posts on other forums that talk about re tuning subaru DBW setups and with the knowledge of how these tables work it should be fairly straight forward for someone to sit down and create some new tables (The will all need to be changed). This is one of the simpler implementations out there.. At least in comparison to an STi or Evo X anyway :)

Before people start complaining about how the throttle should be linear etc so that 75% app should be 75% throttle position etc.. Realize that would result in a lot of wasted throttle travel as you would get most of the power output at about 60% throttle... DBW allows you to fine tune the tables such that you can have 75% torque at 75% throttle and 25% torque at 25% throttle... Of course if you want 100% torque at 30% throttle you can do that too :)

Since we have alot of track nuts on here... if we want a throttle profile that allows for smooth modulation in a sweeper, what torque range should we accentuate?

Best guess:
For low powered applications (like a stock class 86), we know that any time we touch the accelerator there will be a request for significant torque. We want a long and smooth 50-90% range, with a big platform for 100%.

For high powered applications (400 hp turbo cars), the WOTTL would need to be accurately tuned. The throttle profile would want to spread out the turbo spool up range (30-75%) and make the top and bottom slopes more steep. You'd still want a platform at 100% for the rare occasion you can actually deliver full power to the ground.

This is great information, but makes me nostalgic for a mechanically connected throttle body. Drive by cable :wub:

True but, remember those cable throttles are the same ones that gave you 90% power at 60% throttle for NA applications anyway.

Honestly, the 86 in stock for seems fairly linear but i do feel it is low throttle biased... which makes it feel peppy but also feels to me like 1/2 throttle is as much power if not more than WOT.

As Shankenstein said, this give us the ability to tailor the throttle response to the specific application at hand... and of course to the drivers liking.

With turbo cars you also need boost control to have a throttle input parameter so your not making full boost at half throttle...

Id like to change my throttle mapping too, the stupid thing reads good until it gets up to 70% pedal throw then it starts to jump up and by 80% pedal the TB is fully open leaving 20% of motion uselss. That and the closing issue at high rpm is a head scratcher.

Hello Sorry for waking up this but none of the images are working :)))

I am more interested in a software or xl table for direct conversion to percentage