Practical Transmission Tuning: Step 3-1: Partial Throttle Upshifts & Low Gear Count TCMs

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Step 3-1: Partial Throttle Upshifts & Low Gear Count TCMs

19.43

00:00	Shift scheduling and drive mode tuning can be fairly straightforward or quite in-depth.
00:05	So, in this module, I'm going to go over some common use cases first.
00:08	And then if you want to take a deeper dive, you can stick with me all the way through.
00:13	To make it more manageable, we've broken this step up into three parts.
00:18	We'll start with partial throttle upshifts on more simple transmissions.
00:23	The second session continues into moderate upshifting and more advanced transmissions with more drive modes.
00:30	Lastly, we'll review downshifting.
00:32	At this stage of our process, our engine tune may not be complete yet.
00:37	So, for that reason, and in the interest of safety, we're going to start with partial throttle shifting first, and then wide open throttle shifting later.
00:46	In the earlier preparing to tune module, I asked you to consider what you like or don't like about the current transmission behavior.
00:54	If the vehicle has multiple drive modes, hopefully you've tried them all and taken notes.
01:01	With that info in hand, let's look at a transmission tune file and see how many shift schedule tables are present.
01:08	In this example, I'm using a 2006 Chevy Tahoe police package equipped vehicle with a four-speed automatic transmission.
01:17	In the HP Tuners VCM editor, I've clicked Trans and then the Shift Scheduling tab.
01:23	Now, if I hover over the button for the D1 table in the part throttle shift section, we can see the info states, this table is related to the shifter being manually placed in one rather than D for drive.
01:38	We can see this as an upshift schedule because the axis shows a lower gear number with an arrow indicating a change to a higher gear number.
01:46	Conversely, when we see a higher gear number with an arrow indicating a change to a lower number, we're looking at downshift scheduling.
01:54	When we look at the D1 table, we see the one to two upshift speed has been set to 255 miles per hour.
02:02	Since we'll never get to 200 plus miles per hour in first gear, we can infer that this mode is set up so if the driver manually selects first gear with the shifter, this table will never cause an upshift out of first gear.
02:16	This makes sense as the point of placing the shifter in the one position is to hold the vehicle in first gear within reason.
02:24	I say within reason because when we see something like this, it's important to be aware that there may be multiple systems at play.
02:31	We may encounter an application where a separate full throttle shift vehicle speed or engine speed based system causes an upshift even though the standard shift schedule tables are not requesting one.
02:44	Perhaps an upshift from first to second gear will occur if the engine reaches redline.
02:50	For now, let's leave this D1 behavior alone so we can close this table out.
02:56	Next, and similarly, there are three tables with D2 in the name.
03:00	The descriptions state they relate to the shifter being manually placed in the two position.
03:06	We can see this mode is set up so the vehicle starts out in second gear even from a stationary position based on the one to two upshift speed being zero miles per hour when the throttle is 62% or less.
03:21	However, if the throttle application is very high, perhaps this table is indicating we can launch the vehicle in first and it will upshift to second gear at 38 miles per hour.
03:33	If you want to know for sure, test safely while data logging and you'll either confirm your understanding or learn something new.
03:42	In this case, we could hold the brakes, shift into two, floor it, and observe which gear the TCM is in.
03:49	Then release the accelerator without launching.
03:52	The normal D2 third table has two to three upshift vehicle speed at 256 miles per hour.
03:59	So, much like the D1 behavior, this is going to hold the transmission in the gear we've manually selected with a shifter, gear two in this case, unless there's another system which will override this one and cause an upshift.
04:14	Again, we'll leave that behavior alone so we can close these three tables.
04:19	Now, we'll open the normal, performance, cruise, and hot tables.
04:24	I won't be adjusting the hot table because that's a shift schedule that's only used when the transmission gets overly hot.
04:31	Hopefully we'll never get the transmission hot enough for that table to do anything anyway.
04:37	And this will save you some time.
04:38	If you have a compelling reason to change the hot table to match another table by copying and pasting data over to it to avoid a change in behavior if the transmission briefly overheats, that's certainly something you can do at your own risk.
04:54	For now though, I'll close that one out.
04:57	And now we're down to three tables.
04:59	This process of walking through the tables, narrowing down which ones we actually want to change, really helps make the shift scheduling process less overwhelming.
05:10	Looking at these three table names, one is called normal, which leads me to believe it's used most often.
05:16	Then there's cruise, which likely means it's employed while cruise control is active.
05:22	And finally, performance.
05:24	The in-application help states this is actually a tow-haul mode on some vehicles, but on other vehicles that share this TCM, there may be a performance or sport drive mode that the drivers can select with a button or a switch.
05:39	At a glance, normal and cruise tables look similar.
05:42	So, let's copy all the data from the normal table and then paste it into the cruise table and see if we spot any changes.
05:52	Looks the same to me.
05:54	Had they been different, I would have looked over the changes to understand them and consider why the OEM made them different.
06:01	Then decide if I like the changes or not.
06:05	Next, we'll paste the same data into the performance table.
06:09	This time, we see some cells in the top right have changed color, indicating the values we've pasted do not match what was there.
06:18	Depending on the software you're using, there may not be a clear visual indication the changes have been made, so I'll give some alternate suggestions when we get into worked examples.
06:29	Here we see the rows related to upshifting have changed, and downshifts are identical.
06:34	We can also see that nothing has changed in the upshift scheduling until the driver requests a high throttle position.
06:43	So, under most driving conditions, this mode would behave the same as normal and cruise modes.
06:50	Looking deeper at what is different, we see the vehicle speeds the performance map upshifts at are lower than the normal map at those high throttle positions.
07:01	Since the vehicle speeds are lower, the engine speed the shift would occur at is also lower.
07:08	If we open the full throttle shift speed and RPM tables quickly for the normal and performance modes, we'll see the full throttle shift speeds are similar, but the shift RPM in the performance mode is much lower.
07:23	To understand when the full throttle systems are in control, there's an arming threshold and then a hysteresis value.
07:30	If you're not familiar with the term hysteresis, the short version is it's a buffer to help avoid systems cycling on and off erratically when they're on the cusp of a changeover.
07:42	In this case, the full throttle system takes over at 93% throttle and it will stay enabled until the throttle position drops below 90%.
07:52	Then to re-enable the system, throttle would have to go back over 93%.
07:58	Now, we happen to know this is one of the vehicles where the table labeled performance is actually used for tow-haul mode.
08:06	But even without knowing that, the data in the tables pretty much gives it away.
08:11	That type of inference really helps in situations where tables don't have explicit correct labels.
08:19	A true performance mode generally calls for shifting at higher RPM at high throttle to take advantage of the horsepower found there.
08:28	A tow-haul mode generally shifts a bit sooner to keep the engine operating in an area of higher torque.
08:36	From our mini investigation, we can infer that both the main shift schedule table and the full throttle shift RPM table labeled performance mode are set up for tow -haul purposes.
08:47	To recap, through using the in-application help and a bit of deductive reasoning, we've built a decent level of confidence that these three main shift schedule tables are for normal driving, cruise control, and tow-haul mode.
09:03	In some cases, there will be even more tables and sometimes they won't be as clearly labeled.
09:08	So, let's look at another example of how to narrow things down.
09:12	In all tables, we see the one to two upshift vehicle speed is down under 20 miles per hour at light throttle and up near 40 miles per hour at high throttle.
09:23	In order to confirm when a certain table is active, we can set the vehicle speed for upshift from first to second gear to 35 miles per hour across the entire range.
09:35	This is high enough that it'll be quite obvious when the table we've altered is active, but the vehicle will still be able to shift up to second gear safely.
09:44	To go from relative confidence to confirming that the performance table is active when the truck is switched into tow -haul mode, we'd make the 35 mile per hour change to that table only and store the changes.
09:57	Then we gently accelerate to confirm the shift from first to second gear happens in accordance with the normal table values.
10:05	Next, we'd slow down, put the vehicle in tow-haul mode, usually by pressing a button in the vehicle or by selecting it via the infotainment system.
10:15	After getting the vehicle into tow-haul mode, we accelerate gently in first gear again and see if the vehicle gets all the way up to 35 miles per hour before shifting into second gear.
10:27	While this change isn't something we want long-term, it allows us to confirm when a certain table is active.
10:33	This ultimately helps us understand the TCM logic, and then we can make adjustments that will achieve our goals.
10:41	Now, that we've really confirmed the performance table is for tow-haul mode, we'll revert those changes.
10:47	At this point, we have a relatively high level of confidence in what each shift table does and when each table is active.
10:55	So, it's time to think about our goals.
10:58	As we test drove the vehicle and reviewed the existing behavior, what did we like and what didn't we like? In this case, let's say we don't like the truck going into overdrive at such a low speed while we're towing.
11:12	I'll highlight part of the three to four shift row here, and we can see if the vehicle is coasting or we're at real light throttle, it'll go into fourth gear at 24 to 26 miles per hour, causing the engine to turn rather low RPM, which we may not want.
11:28	By keeping the engine speed up where the converter isn't slipping heavily, we can improve efficiency and avoid creating heat unnecessarily.
11:37	Before we change these cells here, let's take a look at the four to three downshift cells because those also play a role here.
11:45	For example, with the existing settings, if we hit 24 miles per hour, we can shift up to fourth.
11:52	But as soon as we slow a few miles per hour, we'll be shifting right back into third.
11:58	That potentially overreactive shifting can be frustrating to the driver, especially in a situation where they happen to be driving at a speed where they're teetering between up and down shifting.
12:10	So, in this case, while we want to keep the engine speed up a bit higher, we're also going to leave a bit more room between the up and downshift.
12:19	This comes back to the concept of hysteresis that I mentioned earlier.
12:24	We're just making sure there are buffers built into our control strategies to avoid overactive switching.
12:30	If we grab these cells and make them 30, that means 30 miles per hour is now the minimum upshift speed from third to fourth gear.
12:40	And we're only going to bump these cells up from 22 to 26 miles per hour.
12:46	This will keep the minimum engine speed up more than it did before and gives us a spread of four miles per hour between the up and down shifts rather than only two miles per hour.
12:58	Now, I mentioned making this change just for tow mode, but let's say we put a higher stall torque converter in the vehicle and whether we're towing or not, we don't want the truck cruising below the stall speed of the converter.
13:10	If that's the case, then we really want to make that sort of change in all the shift schedule tables and possibly for multiple gears, not just between third and fourth gear.
13:19	Let's say our new converter has 300 RPM higher stall speed.
13:23	By looking at a data log of the vehicle cruising in various gears, we can see the vehicle speeds by which the stall speed has been achieved.
13:32	Then we can give ourselves a little extra margin if we want by adjusting up and downshift points accordingly.
13:38	So, for example, let's say we looked at the log and know we need to be over 17 miles per hour in second gear to stay 200 RPM over the new stall speed.
13:49	We go into the one to two upshift table and set all values, which are 20 and below, to 21 miles per hour and then set the two to one downshift speed to 15 miles per hour.
14:02	By doing so, we've allowed the vehicle to upshift and then slow a bit without going below the stall speed.
14:09	Then if the vehicle slows enough, it will still downshift to first gear as needed.
14:14	This process gets repeated for each gear.
14:18	Once you get your normal drive mode table updated, store the changes, and test drive.
14:23	You may find the downshift to first is a bit abrupt with it set to 15 miles per hour and decide to drop that to 12 miles per hour.
14:31	On the other hand, you may find you love having higher shift points and decide to increase them a bit further.
14:39	Ultimately, when we start making changes, we'll learn even more about what we like and don't like.
14:44	Another option we can throw in here is reverting the 0% throttle upshift points back to stock.
14:50	So, if the vehicle is coasting, we still let it upshift early.
14:54	Sometimes we won't know if we like it or not until we just try.
14:58	Once you're happy with the results, since the goal is to keep the engine from operating under your new converter stall speed, now you can take values you're happy with from the normal table used for testing and apply them to the other tables.
15:13	This way you avoid updating several tables over and over while you're figuring out what you like.
15:20	At this point, we've talked about a possible change for towing, some changes for higher stall converter, and changing the gap between up and downshift points to make situations where the transmission is going back and forth repeatedly less likely to happen.
15:36	Next, let's review repurposing a drive mode.
15:40	Perhaps you have a vehicle with a tow mode, but you never tow anything.
15:44	Let's make it a performance mode instead.
15:47	What would that actually look like? Typically, a performance mode will keep us in a lower gear under more conditions.
15:55	So, speeds for upshift and downshift are typically increased.
15:59	As you increase vehicle speeds for shifts, take care to avoid selecting upshift speeds that are very close to or higher than where the rev limiter can be achieved in each gear.
16:11	Otherwise, you can create a situation where the upshift will not occur.
16:17	Similarly, we want to avoid requesting a downshift at a speed high enough that it would cause the engine to mechanically overrev.
16:24	We'll start by pasting the normal table values into the performance table because we've already observed that they're more aggressive in terms of allowing higher vehicle speeds in gear.
16:34	Next, we'll grab this block of values from 0% throttle to 62% throttle across all gears, and we're going to add three miles per hour.
16:45	After doing so, we check to make sure we haven't caused a situation where within a row, the values aren't equal or rising as we progress from 6% throttle on upwards.
16:57	I say 6% on up because the first column will be used while coasting and sometimes we do actually want that value to be higher than the next column.
17:08	In first gear, now 62 to 69% throttle is set to upshift at 32 miles per hour.
17:15	We could leave that as is, but we'll interpolate between the 32 and the 34 so there's more of a blending of the new and old values.
17:23	We'll do the same in the next row.
17:26	And finally, in the three to four upshift row, we're going to leave this jump to 220 so it avoids an upshift.
17:33	At this point, we've only changed upshifting, but we can test drive the vehicle in tow mode and see what we think of our new performance mode before adjusting downshifting.
17:44	With upshift styled in, we'll move on to downshifts.
17:48	In this example, I'll start by making the same three mile per hour increase to downshift speeds.
17:54	That's going to make the TCM downshift into a lower gear and keep the engine speed up a bit higher.
18:00	Again, it's always a good idea to store changes and then test drive.
18:05	As we adjust downshifting further, I do suggest maintaining an increasing trend in speed with each row from left to right to avoid unexpected behavior.
18:16	We also need to make sure a gap is left between downshift speeds and upshift speeds with downshift speeds always being lower.
18:25	For example, we don't want to set up a fourth to third downshift at 30 miles per hour if our upshift from third to fourth gear is at 25 miles per hour.
18:34	The concern there is between 25 and 30 miles per hour, conditions would be met to both up and downshift.
18:43	Depending on the TCM, a calibration error like that may cause transmission damage, cause neutral to be selected, throw error codes, and other unpredictable behavior.
18:55	Before storing shift scheduling changes to the TCM, give them a second look to make sure you won't be creating overlapping up and downshift requests.
19:03	So, far we've covered how to repurpose a drive mode for something else and how to make a mode more sporty at partial throttle.
19:11	If the TCM you're working with only has a single shift schedule, the process remains the same and you simply have less work to do.
19:19	Just remember, our changes will apply to all driving since we won't have the option of switching between multiple behaviors without reflashing the vehicle with a different TCM tune.
19:30	On the other hand, if we have a newer vehicle with many drive modes, now we have the opportunity to save even more different settings to switch between on the fly.