BRZedit Drive By Wire Info

[mad_sb]

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.

First lets take a look at the stock maps:


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:



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.

[mad_sb]

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

[Shankenstein]

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

[mad_sb]

Originally Posted by Shankenstein

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_RAT, 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.

[Shankenstein]

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).

[mad_sb]

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:


However, when you look at WOT.... notice how the Throttle Position trails off as RPM rises:


This lines up perfectly with the stock .995 torque ratio % column from TA-TR table:


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

[Shankenstein]

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!

[Sargy]

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

[buditjoenawan]

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

[epifan]

Originally Posted by mad_sb

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:


However, when you look at WOT.... notice how the Throttle Position trails off as RPM rises:


This lines up perfectly with the stock .995 torque ratio % column from TA-TR table:


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

[mad_sb]

Originally Posted by buditjoenawan

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

LOL, So many questions

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.

[buditjoenawan]

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

[Shankenstein]

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).

[pozer]

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