WinOLS Mastery: Map Identification & Editing: Torque-Based ECU Operation
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Torque-Based ECU Operation
07.00
| 00:00 | - Understanding how to find and define maps inside a factory ECU, starts with an understanding of how the ECU functions and that's exactly what we intend to cover in this set of modules. |
| 00:11 | If we understand how the ECU functions then in turn we can understand what maps are likely to exist and which of these maps we're going to need to find and define in order to be able to adequately make tuning changes. |
| 00:24 | Given that most modern engine controllers operate on a torque based model, we're going to begin by learning what this means and how it works as this is quite a departure from what we experience with the majority of aftermarket standalone ECUs. |
| 00:39 | At its simplest, a torque based ECU uses a driver demand table that is derived from engine speed and accelerator pedal position in order to request a specific amount of engine torque. |
| 00:51 | From here, the ECU can then decide what is required in order to deliver the requested torque. |
| 00:57 | This may include the actual drive by wire throttle opening at the engine, remembering that the accelerator pedal is not directly connected to the throttle plate like in a conventional cable throttle arrangement. |
| 01:10 | In addition, the ECU can alter boost pressure in turbocharged gasoline engines or a combination of injection quantity and boost pressure on turbo diesel engines. |
| 01:19 | This of course is a very basic overview of what the ECU is doing and there are various inplementations of torque based control that depend on the specific ECU controller and vehicle that the ECU is fitted to. |
| 01:33 | A common question is why have OE manufacturers gone down this path and there are a number of reasons and advantages. |
| 01:41 | Really when we consider what the driver is doing with the throttle pedal, it is torque that we are requesting. |
| 01:48 | When we go to full throttle, we're simply asking for all of the torque the engine can deliver so this way it makes a lot of sense to model torque. |
| 01:55 | Another key advantage of a torque based ECU is that it makes for seamless integration with modern electronically controlled automatic transmissions and DCT or DSG gearboxes. |
| 02:07 | If we loom at the shift process for a DCT gearbox for example, when the driver requests an upshift, the transmission control module or TCM will send a request to the engine control module asking for a reduction in torque in order to allow the shift to progress. |
| 02:22 | The ECU then employs whatever means required to reduce the torque which may include a throttle closure, ignition cut, ignition retard or some combination of all of the above. |
| 02:33 | When the torque output channel from the engine control module to the TCM reaches the requested level, the TCM will then complete the shift and then increase the torque limit again. |
| 02:43 | This example is just scratching the surface of what torque control allows and why it's become the norm. |
| 02:49 | It's not an overly difficult model to understand but does require a bit of a different approach to your tuning. |
| 02:56 | Let's consider for a moment the operation of an older Bosch MED9 controller to gain an understanding of how Bosch implemented torque modelling. |
| 03:05 | In this ECU, we have a driver demand table that defines requested torque as a percentage of the available maximium engine torque. |
| 03:13 | From here the ECU uses a look up table to convert the requested torque percentage into a percentage of cylinder fill or relative cylinder fill as it's known. |
| 03:23 | This value is then used to define the cylinder charge, in other words how much boost do we need to achieve a specific amount of cylinder filling. |
| 03:32 | Lastly there will be a range of limiters that may work over and above these tables in order to ensure safety. |
| 03:39 | Obviously that's a very high level overview of the MED9 controller and we will be diving deeper into this in an upcoming module for those needing to calibrate this controller. |
| 03:49 | Of course not every implementation looks the same but I just want you to understand the principles for now. |
| 03:55 | There are some specific considerations with torque based ECUs that I also want you to keep in mind. |
| 04:00 | Firstly with turbocharged vehicles, you may not have a nice simple table that provides a boost target in psi, kPa or millibars that you'd normally expect in the standalone ECU world. |
| 04:12 | Instead, the boost target will be internally calculated by the engine control module based on the torque or percentage of cylinder fill that's being requested at any given time. |
| 04:23 | The tricky part is correlating a cylinder fill percentage to boost pressure values that we would be more familiar with working in and this is why datalogging is so important. |
| 04:34 | Particularly logging the stock calibration before you start making any calibration changes. |
| 04:38 | Another aspect we need to be mindful of are the various torque limiters that a controller will likely have. |
| 04:45 | These can be very frustrating if you aren't aware of them or can't find them as they can undo all of your hard work making tuning changes in the first place. |
| 04:53 | Often these will become obvious in a log because the ECU will simply close the throttle body partially in order to control and limit torque. |
| 05:02 | Lastly we need to be realistic with our expected torque values and what I mean by this is if we've made some hardware modifications to an engine, and we're expecting perhaps a 15% increase in torque, then we'd want to make a change of this magnitude to the torque target tables too. |
| 05:20 | Essentially matching the new torque capability of the engine. |
| 05:24 | Failing to do this can mean that we won't see the power and torque gains that we potentially should be achieving. |
| 05:29 | On the flipside, just going ahead and setting all the torque targets to unrealistically high values is not going to be the way and this can cause all sorts of issues from drivability through to DTCs that cause the engine to operate in limp home mode. |
| 05:43 | We also need to be careful with the changes we make to the likes of a driver demand or driver's wish table, particularly when we make changes to the part throttle torque request as this can have a big impact on throttle response or how the car drives and feels to throttle input. |
| 05:59 | Getting too greedy with your changes here can make your car tricky to drive smoothly. |
| 06:04 | This may all sound a little bit scary right now, however everything will become clearer once we move further through the course and particularly once we jump into the worked examples. |
| 06:14 | Let's quickly recap this module before we move on. |
| 06:17 | Remember, that the majority of current factory ECUs work on a torque based model where we're requesting a specific torque output for a given combination of RPM and accelerator pedal position. |
| 06:28 | Internally this is then converted into a boost pressure target on turbocharged engines, meaning that there often won't be a conventional boost target table that we may be more familiar with. |
| 06:38 | It's important to be realistic with our torque target tables and target the sort of torque increase that we expect the engine to be able to produce. |
| 06:47 | Also be mindful that there will likely be a number of torque limiters that are there to undo all of your hard work so these do need to be identified and raised accordingly. |
