Pressure Drop Across Throttle Body - Anybody know how this table works?

[RobCat030]

I guess technically isn't an HPT question since this is a user defined table, but you guys are pretty smart so I thought I'd ask. I'm not 100% sure that this table is active, but I think it is. It's somewhat similar to table 19621 on Ecoboost stuff, although different because it's related to WGDC on those cars, whereas barometric pressure is a fixed dependency.

Screenshot 2021-12-01 180904.png


I think that this is used to create TIP/ETC Vacuum assumptions for throttle area calculation. X axis is either throttle angle or position %, my guess is angle. Y axis I'm even less certain on, but I believe it is equal to MAF in Lb/min (either measured or desired, not sure) divided by BARO. Cell values are in inHg and seem like they should be pressure drop, or TIP-Inferred MAP.

Why do I care? Well, I think if I could understand this better I could nudge the ETC model away from its dependence on BARO (although I'm not sure if I would still be lying about the physics to the PCM)

Here's the thing, none of these tables reflect any reasonable pressure drop at barometric pressure with the engine running. For example, pressure drop at 15% throttle would be something near 10inHg on my car, nothing in this table comes close to that. So I'm kind of stumped. I tried haphazardly looking through patents, haven't found much. Here's my current guesses

1) Cell values are actually some sort of percentage or ratio of pressure drop

2) These are flow bench measurements using some odd standardized conditions where the airmass is the independent variable, not pressure

3) It's a compensation applied to another calculation, possibly just Baro - inferred MAP

[murfie]

Y axis looks like RPM to me. *10^5

X axis could be manifold vaccum, probably in a unit like KPA. The interpolation between the values is kind of odd. Makes me think its actually reversed and its throttle angles.

table is populated with VE or load.


There's clearly a bump in the upper right corner (.07, 50/62) that looks like an idle plateau to me. Then the peak around .5 (5000 RPM) is typical for VE/load/ torque.

3d table.jpg

[RobCat030]

Interesting, I'll try testing that today. The info I put forward was from SCT, but I'm not opposed to considering that they're wrong. Throttle angle definitely seems the most plausible to me, I think that the table itself is meant to determine manifold vacuum to feed to the predictive area tables.

I'd need to think for a bit on how best to derive pressure drop from VE. I guess that VE goes to inferred MAP and then is subtracted from BARO? That would be a bummer..

Also, 0% VE at 700RPM and 15 degrees throttle?

[murfie]

The 0's are in the .4 row. If its vaccum and not reversed, the engine is stalling so yeah 0 VE. If its throttle angle, its just the inverse.

VE to MAP is easy with known cylinder airmass. Its what Fords SD model does.