Blending of VSS and RPM based shift tables

A forum for discussing applications and implementations of the MegaShift transmission controller code for the GPIO from B&G. This can control up to 8-speeds and 6 shift solenoids (plus a 16x9 table for controlling a PWM line pressure valve). It has manual and fully automatic modes (16x9 load x speed table), with under and over rev-limit protection, and full data logging of all inputs and outputs (among many other abilities). A TransStim to test your completed board is also available.
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mill3833
Posts: 72
Joined: Mon Jan 27, 2014 3:33 pm

Blending of VSS and RPM based shift tables

Post by mill3833 »

Lance,
I have a question that may be doable, but not sure...

My application is a drag car, that gets driven on the street a little. Street driving is mild, just trying to get to and from the track. Am not racing it on the street, not needing to optimize up-shifts and down-shifts. But once I get to the track, I'd like it to precisely make shifts based on RPM.

So basically what I'm describing is logic where below WOT setpoint (say 60% TP), use VSS table. Above WOT setpoint, use the RPM table.

The "Rev Limits" option almost gets me there. Problem is, this only provides one RPM shift point. I need the 1-2 to happen at 6000, 2-3 at 6000, and then let it over-rev to 6400-ish on the top end, if needed. So I need separate RPM thresholds for each gear.

Actually, on 2nd thought, I'm going to start racing it in the D3 manual position this year. Previously only did D4. But D3 is slightly stronger. So that would keep it from shifting into 4th, during the over-rev. Right? So I could use "Rev Limits" Upper rev limit = 6000, and set the VSS table for the 1-2 and 2-3 points at a mph higher than the 6000rpm point, forcing the 6000 Upper Rev to catch it.

What do you think?

Dave
Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: Blending of VSS and RPM based shift tables

Post by Bernard Fife »

So I could use "Rev Limits" Upper rev limit = 6000, and set the VSS table for the 1-2 and 2-3 points at a mph higher than the 6000rpm point, forcing the 6000 Upper Rev to catch it.
Dave,

I believe that should work. The 1-2 and 2-3 shifts will be at the set rpm (6000), and the shift table lookup value will be restricted to 3rd (by the lever position) so a shift to fourth shouldn't happen.

If we did want to expand this, though, perhaps a distinct rpm limit for each forward gear might work best?

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw
mill3833
Posts: 72
Joined: Mon Jan 27, 2014 3:33 pm

Re: Blending of VSS and RPM based shift tables

Post by mill3833 »

Lance wrote:


If we did want to expand this, though, perhaps a distinct rpm limit for each forward gear might work best?

Yes, something you can add at a later date. For now, I'll be fine having it shift at the same rpm for the 1-2 and 2-3 shifts.

Thanks,
Dave
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