Cadillac ATS-V LF4 Driver Demand Table thoughts and an approach

Gone are the days of pressing the pedal down results in the throttle opening. Now the driver demand table is used to convert driver pedal input to a torque request. The engine management considers the torque request, the predicted torque output, and determines how much throttle is needed.

ATS-V driver demand table, graphs

Yes, the graphs look odd. Part of this oddity is the use of speed for the column values, but the graph also reflects the impact of GEARING across the speed range.

Driver Demand Table, tabular values

This is the same table with values shown. How do we read this table? The left axis is our pedal position, from 0-100%. So if we are at WOT, the bottom row is the row of interest. Note that not all cars have pedal position =100 at WOT. But to keep it simple, as on my ATS-V, WOT gives a 99.6% pedal position so we are operating near the 100 row.

Okay, so what is happening with the columns? The table can be RPM or VSS(speed) based. The axis here goes from 0 to 300, which suggests speed based. When you see huge numbers like these, the table is axle torque. If we saw 0-7200 numbers it would be a RPM table.

Also, conventional wisdom is this is VSS or vehicle speed in Kilometers per hour, not MPH. For an ATS-V with a max speed of 189 mph, the 300 kph table ties out to 186 mph. So that makes sense.

So far so good. Now let’s look at the same table in MPH

Driver Demand in MPH

So we can see we go from 10,113 ft lbs of axle torque requested at 0 mph down to 1,471 ft lbs of axle torque at 186 mph.

Okay, but what about engine torque demand? To get to engine torque, we need to consider the tire diameter, the final drive ratio, and each individual gear ratio.

Driver Demand by gear, RPM, and Engine Torque

So knowing the speed, and the tire diameter, we can calculate wheel RPM. Knowing the wheel RPM, and the transmission gearing (final drive x gear ratio) we can calculate the RPM for each gear. I have ignored torque converter interaction for this purpose.

Now this give us a table with engine torque requests (limits) by RPM range.

What we observe is that in 1st gear, the stock table request is for torque from 778 down to 448 ft lbs near the shift point. In 2nd gear, from 688 down to 502 ft lbs.

Why don’t we just max the whole table out from 0-300? That will result in huge torque delta requests; one oddity of the system is that it tends to respond less rapidly to huge requests, (perhaps fearing that they are in error?) So we want to request close to what we actually need.

It also suggests how the requested torque ends up being numbers we don’t find on individual tables — they are calculated from the driver demand and converted to engine torque.

Building down to minimum requests of 550 ft lbs of torque

In my case I would like my driver demand to be at least 550 ft lbs minimum at any point. So where I see the driver demand for a gear and RPM would fall under 550, I have inserted a 550 in my ‘desired’ area. The final driver demand table 100% row is then a calculated row showing (blue highlights) the cells that need to be increased, as compared to the original table in the row below (marked ‘Original’).

Not every cell needs to be changed. At higher speeds, where one could be in gear 4, 5, or higher, the RPM needs for the LOWEST numerical gear (highest ratio) assure that the resulting axle torque will also exceed the desired engine torque in each higher (lower ratio) gear at the same speed.

Driver Demand G

This is the tune G driver demand table I plan for the next test.

What do you think? Please share your experiences on what has worked well, what has not for ATS-V tuning.

Cadillac ATS-V Tune F

Changes: Overspeed limit max increased from .5 to 1. Waste gate open boost increased 2 pts. Peak torque and max torque redone as 1.2x stock tunes. Fast torque exit set to 50/25. Boost max limit added 1. Increased knock airmass. Further reduced main spark map, high octane to address KR. Transmission: increased TCC desired pressures, regulator gain, regulator offset, reset TCC desired slip to match Corvette, changed TCC adapt torque min. Disabled TCC in gears 2,3,4.

Conditions: 81F, engine Baro 12.235 inHg 74% humidity; correction 1.037 SAE J1439.
Output: Measured max 466.7 hp at 5315 rpm, 467.4 Ft lbs torque at 5198 rpm so
Corrected 484.0 hp at 5315 rpm and 484.7 ft-lbs torque at 5206 rpm.

Goals: Eliminate KR. Reduce TCC slip rpm. Reduce throttle opening.

Results: KR was reduced at WOT pressures to under 0.5 (but not eliminated); good progress. TCC still showed slip even though TCC was not applied in gears 1-4. Unclear if that helped or not; reset to stock for next tune. Still throttle closing; going to try Sam’s driver demand map which further increases driver demand, and makes more linear. Keeping an eye on misfires; going to go a bit richer next tune, from 12.7 to 12.5 AFR (14.113/12.5 = 1.12904 PE value). Fuel pressure holding fine so far. Boost rose to 19.2 PSI then fell to 18.5 before the throttle opened around 5800 rpm; not sure why. Still seeing a flat HP curve from 5300 rpm to 6200 RPM instead of a steady increase; not sure why.

Thoughts: reduction in spark to reduce KR at high pressures may be limiting hp at high rpm. Consider a richer PE and attempting to restore spark and still avoid KR or misfire.

Cadillac ATS-V Driver Demand & Torque – Tune E

Hp Tuners view of Hp, Torque, boost, TCC slip, and Throttle at RPM

The above chart is based on a layout file for HP Tuners to help with analysis.

The red line is HP, the light blue line is Torque, across two gears, 2 & 3, from 17 to 78 mph.

The dark blue line is throttle (versus pedal input), or how much the PCM commanded the throttle. The white line is RPM.

The yellow line is boost. There is a strong correlation between the boost curve and the Torque or HP curves before/after 5252 RPM where they cross by definition. Boost holds at 17.49 psi in second, and rises to 19.47 psi in 3rd gear.

At the highlighted snapshot moment, driver demand is at 109%. After this, driver deman falls off; I am not sure why. Later in the run at 5696 rpm in 3rd gear the commanded throttle opens due to boost pressure limits being exceeded, and boost falls off after that point, crushing the HP curve from there. Those boost limits will need further attention in the next tune.

The gold line is TCC Slip RPM. I note that here in my tune E TCC slip is actually well controlled in 3rd gear, and falls across 2nd gear rev range. I plan to increase the TCC pressures across 2nd gear parameters.

Overall this layout was helpful in analyzing individual tests, and comparing across scan files for these parameters.