Attach your tune file (.hpt) and what you're trying to accomplish with the shift points and I'll take a quick look.Originally Posted by ryanallaire
Attach your tune file (.hpt) and what you're trying to accomplish with the shift points and I'll take a quick look.
Thank you I appreciate it, the issue I'm having is it seems to shift from 4th to 5th prematurely like it barely has 4th gear.
There are a couple things going on here.
First, by lowering the upshift RPM for 3-4 and 4-5, it's shifting at a much greater throttle angle.
Before:
ShiftScheduleStock.PNG
After:
ShiftScheduleModified.PNG
Even though there's a ~10% accelerator pedal margin between 3-4 and 4-5 in your file vs the ~5% in the stock, which seems like it would be less likely to upshift like it is, the modified file can shift at double the accelerator pedal position in theory, which is making it more likely to in practice. The core issue is that, when increasing throttle angle (accelerator pedal position) for a given shift, less torque retention (ratio of output shaft torque before/after the shift) across and torque reserve (how much additional torque can be commanded) after each shift decrease, both of which make the shifts much more pronounced and likely to occur in quick succession.
The other issue is throttle mapping and interaction with the shift schedule.
ThrottleAngleComparison.PNG
By softening the slope up to ~30% pedal position with a much steeper relationship from 30-40%, the truck will see a lot more operation closer to the 30% pedal position mark (as our torque demand hasn't changed) and the steeper ramp up towards 40% will make the transition much more pronounced - feels "spunkier", but creates some drivability challenges with the stock shift schedule headers.
When we're building our throttle mapping, we generally want to have them be as smooth as possible, and add a little bit more throttle angle from ~20% onwards with each successive gear to offset the increased load due to drag - makes for a less "squishy" pedal at higher speeds. An example from one of my files comparing 1st gear (left) to 6th gear (right), note the "bump" in the middle, which is calculated to offset rolling resistance and aerodynamic drag for this specific truck.
ThrottleAngleExample.PNG
Baseline Shift Schedule
When we're making a baseline shift schedule, the two metrics that we should focus on are output shaft torque retention for upshifts and input shaft (engine) torque reserve for downshifts.
For most of our "driving around" RPM band (idle - ~3000 RPM), we want to target 100% output shaft torque retention. 100% torque retention means that output shaft torque is constant across the shift, which is highly desirable because the truck will continue to accelerate as it did before the shift and shift shock is greatly reduced (there are quite a few academic papers on this concept, if you want to learn more).
Above that RPM band, we can blend input shaft torque reserve down towards zero for our upshift - still have to be a bit judicious in where to set those.
For downshifts, we do something similar with input shaft torque reserve. We will usually pick a pretty reasonable number for our "driving around" RPM band of 1600-2400 RPM, typically around 20-25% (lower holds a gear longer, higher drops a gear sooner), above that we will start to decrease torque reserve (we don't want to downshift so readily at, say, 3000 RPM) and below that we will start to increase torque reserve (to avoid lugging the engine). Again, have to use some judgement as you taper off in each direction. You'll also want to check for shift hysteresis, which means you want to make sure that there's
You can use the attached tool (Shift Scheduling Helper - V2.xlsx) to calculate those values above. It uses the Optimum Torque Trans table (Engine -> Torque Model -> General -> Torque Calculation -> Optimum Torque Trans) to do all the torque lookups. Cells in yellow are inputs, everything in green is calculated - I've done an example of how you might create an upshift schedule for a single gear on sheet 3b - Torque Lookup - Engine RPM. Note how I define fixed Engine RPM points and modify the TPS row to get to the desired Output Torque Retention per the above guidance. This makes it much easier to identify where to work, because it's far simpler to identify the RPM where you want to change a shift than the TPS. Keep in mind, I've used a factory map for TPS vs Throttle Angle in this example, so you'll have to input your desired mapping at the top.
Key thing to notice form that example is we're targeting a much lower throttle angle for a given RPM, which has the effect of holding a gear longer before upshift and preventing some of the stutter upshifts like you've encountered.
It's a very "dumb" calculator, but it's enough to get the job done, and it should be pretty obvious how to make useful revisions to the tool. There's a lot that can be added; to give you some ideas, the tool that I personally use includes torque converter characterization (K, STR, etc.), calculates load/drag throttle mapping offsets for towing and wheel/tire changes (like the above picture), adds a few more parameters and automatic checks for up/downshift and converter lock/unlock (hysteresis, for example), and builds torque management maps at the same time, but it's pretty overkill and not as user-friendly, so doesn't make much sense to share without a lot more instruction.
Bit long-winded and technical, but hope that helps give you an idea of where to work in your map.
All I have learned is that I really don't understand Automatic transmissions... I mean a torque convertor is just two box fans in a row, with one pushing on another.. right? . but they really allow for slippage between the two happening nearly all the time that would burn up a normal clutch in a manual rather quickly, right?
Gosh I wished I had a good map to cheat from...
Well i work on transmissions for a living, but I technically don't need to 'know' some of this stuff to do my job.. we're more on the engineering side of things here..
@SlowNStock call me a super noob but what numbers are supposed to be inputted? I've tried inputting the different throttle angles, TPS and output shaft rpm but I feel like I'm doing something wrong...
@SlowNStock could you post how/where to reset the alcohol density? Do you use VCM suite to do this? Sorry for the noob questions but trying to figure out if this is doable before spending $500 on the MPVI and credits.
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