Practical Transmission Tuning: TCM & ECM Integration

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TCM & ECM Integration

10.38

00:00	In order to understand why the engine and transmission controllers need to work together, first let's review what we're really trying to achieve with transmission tuning.
00:09	From a performance standpoint, we want to keep the engine package in its optimal rev range for horsepower and torque delivery within the physical limits of the drivetrain and the traction limits of the chassis, suspension, and tires.
00:22	We generally want to increase torque, but without creating more torque than the components can handle.
00:28	We can place torque limits at the end of our comfort level to get maximum reliable performance based on an investigation of what the drivetrain can handle.
00:38	We want to account for changes in gear ratio, tire size, and drivetrain swaps.
00:44	If our particular system allows for it, we can try to improve shift speed as well.
00:50	And while it may not seem as exciting as torque increase, improvements in shift scheduling for better drivability are sometimes the thing that puts the biggest smile on your face by resolving a stock behavior you aren't happy with.
01:03	While OE engineers are highly skilled and spend a great deal of time attempting to please all customers, sometimes they fall short of winning everyone over.
01:13	This is generally due to a combination of OE goals, constraints, and the simple reality that different drivers have their own personal preferences.
01:22	Perhaps you're mostly happy with the way the vehicle behaves, but in one or a few conditions, it does something that takes away from the driving experience.
01:30	There's a lot we can do to reduce or hopefully resolve those pain points and make driving more enjoyable.
01:37	The last goal is tailoring transmission behavior to specific use cases, such as towing, fuel economy, off-roading, or driving in low traction conditions like snow or ice.
01:48	In different scenarios, one size can't fit all, so there's an opportunity to create calibrations optimized for each purpose.
01:56	And we can balance that with compromises when it makes sense to avoid requiring excessive switching between calibrations on the road.
02:04	We achieve all these goals through a partnership between engine and transmission control.
02:10	As we're already aware, an engine can't stay in its ideal power band on its own.
02:15	It requires gearing changes from the transmission to keep the engine working efficiently at different vehicle speeds.
02:22	On the other hand, the transmission may not be able to shift without a little help from the engine in certain situations, so they need to work together, and like any good relationship, it starts with honesty.
02:34	What I mean by that is if our engine computer is lying to our transmission computer about the amount of torque the engine is making, the transmission won't prepare itself appropriately, and the results can be unpleasant.
02:46	Incorrect reporting of torque is one of, if not the biggest, cause of issues I see between tuned engine computers and transmissions in modern vehicles.
02:57	The level of integration expected is high, and both systems are designed to assume under normal conditions the information passed between them is trustworthy.
03:08	If your particular application doesn't have two separate physical devices for engine and transmission control, please don't let that give the impression that this doesn't relate to your vehicle.
03:18	Even when the engine and transmission control systems are housed in a single module, they're still distinct but codependent.
03:26	With that covered, let's take a deeper look at why accurate torque reporting is so critical.
03:32	Picture this scenario.
03:33	Our transmission is prepared for an upshift while the engine reports that it's making 150 foot-pounds, which is a modest amount on a vehicle that makes a maximum of 300 foot-pounds.
03:45	But what if the engine is really making all 300 foot-pounds of torque? And the torque is incorrectly reported because someone did the old half-the -injector-size, half-the-math scaling trick.
03:57	If you're not familiar, this is a procedure some use to run high-flow injectors on certain engine computers that only support entering up to 60 pounds a minute of injector flow.
04:07	And this can result in the ECU reporting airflow as being half of what it really is.
04:13	By having the calculated airflow, the ECU can end up calculating half the actual torque being produced and reporting that to the transmission.
04:21	When the transmission is expecting half as much torque as it receives, a number of choices are made incorrectly.
04:28	That can include target line pressure and clutch pressure, the profile the pressure ramps up at, the timing of off-going and oncoming clutches, total shift duration, potential torque reduction requests to the engine computer, and more.
04:45	Picture you're expecting a friend to pat you on the back and they give you a full -force shove instead.
04:50	If you were expecting a shove, you could plant your feet and brace yourself, but if you don't see it coming, you're probably going down.
04:57	The point is, knowing what's being delivered so you can respond accordingly can make all the difference.
05:02	Now, if you're one of the folks with a half-MAF setup like we touched on before, not to worry.
05:07	There are ways to correct torque estimation.
05:09	You just need to find tables related to torque estimation based on air mass and adjust them accordingly.
05:14	If you have any further questions on the subject, feel free to jump onto the community support forum and we can dive a little deeper.
05:21	Moving on.
05:23	It's important to note that not all ECU and TCM combinations use torque directly.
05:28	Some use a calculated load value, airflow, or some other measure that gives an impression of torque but isn't really relayed as a torque unit.
05:37	One way or another, the ECU still communicates the level of engine output that the transmission will receive, though.
05:44	Another type of issue that incorrect torque calculation and reporting can cause is unnecessary and unwanted torque reduction.
05:52	The last example we looked at involved under-reporting torque, but incorrect MAF scaling or speed density table settings can also cause over-reporting of air mass, resulting in over-reporting of torque.
06:06	If the torque limit is 500 foot-pounds and we're making 400 but reporting 600, we can run into limits causing throttle, boost, or timing reductions which are completely unnecessary and literally just slow us down.
06:20	Poor shift quality and feel, excessive clutch wear, and generally poor drivability are some other common results of incorrectly reporting torque from engine control to transmission control.
06:32	While some ECUs may not seem to use torque -based calculations for engine-related matters, the existence of torque-based tables and monitors may indicate that torque is being calculated and reported for TCM use.
06:46	Unless we're certain ECU torque calculation has no impact on transmission operation, it's best to err on the safe side and ensure reasonable torque values are being generated.
06:57	Here, the dyno is our friend since we can measure torque output and confirm it relates to the torque values the ECU is reporting.
07:06	While we can attempt to estimate torque based on engine displacement, compression ratio, air mass, fuel delivered, etc., there are many factors that can drastically impact actual torque output, like ignition timing.
07:21	Without a dyno to optimize it, that key factor alone would be a big question mark.
07:26	Rather than doing a great deal of work to ballpark potential torque output without a high level of accuracy, the dyno will just show us actual torque output, removing lots of guesswork in the critical process of accurately representing torque.
07:40	Another reason accurate torque reporting is so critical is that the transmission may, in some cases, need to request that the engine reduce torque so the transmission can complete a task.
07:54	For example, we talked about driven upshifts earlier, and if we're driving at full throttle, perhaps the transmission needs a brief reduction in engine torque output so it can cleanly and reliably shift into the next gear.
08:08	Much like shifting a manual transmission is kinder to the clutch and other drivetrain parts if we're not applying full power during the entire shift process, the same is true of an automatic.
08:20	Perhaps the clutches can't suddenly grab and hold that much torque without excessive wear or without shock-loading other drivetrain components.
08:28	In a partial throttle situation, grabbing a shift quickly might slightly reduce clutch wear by rapidly ramping up clutch pressure, and that would be acceptable for drivetrain parts, but could feel rough or jerky to vehicle occupants.
08:42	For various reasons such as those, it's desirable for the TCM to request a change in engine torque output from the engine controller to smooth a transition.
08:54	If the TCM requests a 100-foot-pound reduction for, say, 80 milliseconds while it completes a shift, ideally we want the engine to actually reduce torque by 100 foot -pounds, not only 50 and not 200 either.
09:09	We'll get into more details of torque reductions and torque increases later in the course, but I wanted to lay the groundwork for how the engine and transmission controllers work in partnership here and hopefully impress upon you the critical nature of accurate torque estimation, reporting, and requests between the engine and transmission.
09:29	Before that, though, let's review the main takeaways from this module.
09:34	The key goals in transmission tuning are improving performance, drivability, and tailoring the tune to specific use cases if needed.
09:42	Accurate torque reporting and communication between engine and transmission controllers is of paramount importance.
09:50	If the TCM is being given the wrong information from the ECU, it will often result in issues such as poor shift quality, excessive clutch wear, and poor drivability.
10:02	With this in mind, ECU tuning will sometimes require TCM tuning to avoid unwanted behavior.
10:09	Fixes for most drivability issues aren't super complicated.
10:13	Just be aware that like most things, more effort is required on your part as things get more heavily modified.
10:19	Lastly, while this is all very important for auto-manual valve body transmissions with TCMs expecting torque data, old-style transmissions or manual valve body systems which don't have TCMs don't need to know about engine torque.