engineermike
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- #1
Just another PSA...
I decided to work on the automatic downshifting of my Roush F150 and not only did I fix it, I uncovered some things along the way that some might find very interesting or useful.
The base drive downshifting was lethargic, slow to respond and usually made a couple of stops in gears on the way down to the final target gear. But I noticed that in Sport mode it would zap straight to the desired gear quickly and without making extra stops on the way down. Interestingly, copying the upshift, downshift, coastdown, pedal translation, torque converter schedules, etc. all from sport to base didn't fix the problem. It turns out there were 2 issues and I'll explain them separately:
1. The number of gears dropped per downshift: Apparently, Ford uses some insanely complex logic to determine how many gears to skip per downshift. It chooses the number of gears to drop as a function of weird stuff like road load, something called event lines, pedal position, pedal rate of change, drive mode, etc. and then looks up the ratios to drop in some sort of 4D matrix. There are something like 720 possible outcomes when downshifting from 10th gear. It's just nuts. The 4D matrix can be found in PCMTec by searching the navigator for "downshift event table". My understanding is that the outcome of all the calculations points it to a cell in these 144 tables. So, I copied the gear-specific column with the highest numbers to all columns for all tables for that gear (there are 16 per gear). This appears to allow it to skip straight to the gear you specify in the part-pedal downshift table.
2. The auto downshift delay: I logged these part-pedal downshifts in Sport and Base mode and found that upon tip-in, Sport mode would immediately (ok, milliseconds) send the signal to downshift. However, when doing the same thing in Base mode, it would delay 1-1.5 seconds. I searched and logged extensively to try to find this delay, to no avail. I did figure out another way to solve it, though. Table auF66752 basically takes the commanded drive mode and points it to a shift strategy. The column axis is the commanded drive mode, while the data in the table is the shift strategy it points at. 0 is base, 1 is sport, and they point to 0 and 1. Simple enough. This is the table that points drag mode to sand mode, for instance. Another example is in the F150, eco mode is pointed to the base shift strategy, which is why the F150 doesn't follow the eco shift schedules defined in hpt or pcmtec. Anyway, the simple answer here is to simply change base mode (0 column) to 1 (sport), and it then just defaults to the sport schedules and everything else shift related. I don't believe the pedal translation and stuff like burble mode follows; this table is just for shifting. The more complicated solution is what I did, where I pointed base mode (0 column) to sand mode (5) and then copied all my base schedules to sand. Now, I have my normal driving shift schedules when in base mode, but I get the very quick and responsive downshifts like sport does.
Between the above 2 changes, my truck now has millisecond-quick automatic downshifts right to the final target gear and it has transformed the driving experience. I wonder how many more people would love the 10R80 if it worked like this for all.
I decided to work on the automatic downshifting of my Roush F150 and not only did I fix it, I uncovered some things along the way that some might find very interesting or useful.
The base drive downshifting was lethargic, slow to respond and usually made a couple of stops in gears on the way down to the final target gear. But I noticed that in Sport mode it would zap straight to the desired gear quickly and without making extra stops on the way down. Interestingly, copying the upshift, downshift, coastdown, pedal translation, torque converter schedules, etc. all from sport to base didn't fix the problem. It turns out there were 2 issues and I'll explain them separately:
1. The number of gears dropped per downshift: Apparently, Ford uses some insanely complex logic to determine how many gears to skip per downshift. It chooses the number of gears to drop as a function of weird stuff like road load, something called event lines, pedal position, pedal rate of change, drive mode, etc. and then looks up the ratios to drop in some sort of 4D matrix. There are something like 720 possible outcomes when downshifting from 10th gear. It's just nuts. The 4D matrix can be found in PCMTec by searching the navigator for "downshift event table". My understanding is that the outcome of all the calculations points it to a cell in these 144 tables. So, I copied the gear-specific column with the highest numbers to all columns for all tables for that gear (there are 16 per gear). This appears to allow it to skip straight to the gear you specify in the part-pedal downshift table.
2. The auto downshift delay: I logged these part-pedal downshifts in Sport and Base mode and found that upon tip-in, Sport mode would immediately (ok, milliseconds) send the signal to downshift. However, when doing the same thing in Base mode, it would delay 1-1.5 seconds. I searched and logged extensively to try to find this delay, to no avail. I did figure out another way to solve it, though. Table auF66752 basically takes the commanded drive mode and points it to a shift strategy. The column axis is the commanded drive mode, while the data in the table is the shift strategy it points at. 0 is base, 1 is sport, and they point to 0 and 1. Simple enough. This is the table that points drag mode to sand mode, for instance. Another example is in the F150, eco mode is pointed to the base shift strategy, which is why the F150 doesn't follow the eco shift schedules defined in hpt or pcmtec. Anyway, the simple answer here is to simply change base mode (0 column) to 1 (sport), and it then just defaults to the sport schedules and everything else shift related. I don't believe the pedal translation and stuff like burble mode follows; this table is just for shifting. The more complicated solution is what I did, where I pointed base mode (0 column) to sand mode (5) and then copied all my base schedules to sand. Now, I have my normal driving shift schedules when in base mode, but I get the very quick and responsive downshifts like sport does.
Between the above 2 changes, my truck now has millisecond-quick automatic downshifts right to the final target gear and it has transformed the driving experience. I wonder how many more people would love the 10R80 if it worked like this for all.
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