MoTeC M1 Software Tutorial: Boost Control
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Boost Control
12.27
| 00:00 | If you are running a turbocharged engine, you can choose to use the M1 to control the turbo boost pressure using a waste-gate solenoid. |
| 00:08 | For those familiar with the older hundred series ECUs, the boost control system of the M1 shares some similarities but there are also some important differences. |
| 00:19 | The first key difference is that when discussing boost pressure in the M1, we are talking in ‘gauge’ pressure, not absolute. |
| 00:26 | This means that if we want to run one bar of boost pressure or 14.5 psi, in the M1 this is the equivalent of one hundred kPa. |
| 00:36 | It’s important to get this right otherwise your boost targets will be incorrect. |
| 00:41 | The other important difference is that the M1 gives you the option of incorporating a dedicated ‘Boost Pressure Sensor’ for the boost control subsystem. |
| 00:50 | If used, this should be mounted in the intercooler plumbing prior to the throttle body so it is only seeing positive pressure. |
| 00:57 | This sensor is optional and if it is not configured, the M1 will use the normal MAP sensor. |
| 01:04 | Let’s head to the ‘Boost Control’ worksheet and have a look at the settings. |
| 01:09 | The easiest way to look at the boost control settings is to split them up into four different sections. |
| 01:15 | These deal with configuring the boost sensor input, the waste-gate actuator output, the boost target or aim, and the actual control or feedback system. Let’s start with the boost pressure sensor. |
| 01:30 | You should be reasonably familiar with configuring a sensor by now and the boost pressure sensor is no different. |
| 01:36 | If used, we need to assign an input resource to it, choose a voltage reference, a filter value and a calibration to suit the particular sensor. |
| 01:46 | The filter value is worth discussing in a little more detail. |
| 01:50 | This filters the measured pressure signal and can be useful in stabilising the boost control system if you are seeing a lot of noise or spikes in the boost pressure signal. |
| 02:00 | Unfiltered, the boost control system will try and track these spikes and this can cause instability. |
| 02:07 | As with any filtering though, it does tend to slow the response of the system so we want to use as little as necessary. |
| 02:15 | A good starting point would be twenty milliseconds. |
| 02:19 | We also have the usual ‘Default’ value which should be filled in. |
| 02:24 | If the boost pressure sensor is not assigned, or it is deemed to be faulty, the M1 will revert to using the MAP sensor for boost control, and the system will function like a conventional boost control system. |
| 02:37 | Next we will look at the waste-gate actuator output and we can start by selecting an output resource for the actuator here. |
| 02:45 | We also need to set the output frequency which will depend on the particular solenoid we're using. |
| 02:51 | Normally a value of fifteen to twenty hertz is suitable for most common solenoids. |
| 02:57 | We also have a minimum and maximum duty cycle setting for the solenoid, which defines the useful control range of the solenoid. |
| 03:03 | Most solenoids won’t operate properly below about fifteen hertz or above about eighty five hertz. You can find the correct range by testing your solenoid. |
| 03:17 | We also need to set the polarity of the solenoid which defines if the solenoid will give maximum boost when at one hundred percent duty cycle or zero percent duty cycle. |
| 03:28 | This will depend on the waste-gate solenoid you are using. |
| 03:32 | If one hundred percent duty will result in maximum boost, the polarity should be set to ‘Normal’. |
| 03:38 | We also have the option to filter the battery voltage signal if desired. |
| 03:42 | Normally this isn’t necessary and can be left set at zero. |
| 03:47 | Now we will look at setting the actual boost target or boost aim and in the M1 this includes the ‘Boost Aim Main’ table as well as a number of limits that can affect the final boost target. |
| 03:59 | We will start here with ‘Boost Aim Main’ which by default is a single parameter for the boost target we want to run. |
| 04:06 | As usual you can set this up as a two dimensional or three dimensional table referenced to engine speed and throttle position if desired. |
| 04:14 | Again its important to remember that the values in this table are gauge pressure, not absolute. |
| 04:20 | I can’t stress how important it is to remember this as particularly if you are coming from MoTeC’s older hundred series ECUs, you may be used to thinking of boost targets in absolute numbers. |
| 04:32 | If you get this wrong, you can end up running more boost than you expected and this can also quickly result in serious engine damage. |
| 04:40 | We can see in the time graph here that the ‘Boost Aim’ channel has a ‘g’ beside it to show that it is gauge pressure. |
| 04:49 | The actual boost target will also depend on the various boost limit tables that you can see here. |
| 04:56 | These aren’t a limit in the conventional sense that you may be used to thinking of though. |
| 05:01 | by this I mean they don’t function a fuel or ignition cut to safeguard the engine. |
| 05:05 | That is done via the ‘Boost Maximum’ parameter we will discuss shortly. |
| 05:10 | These boost limit parameters can be used to alter the boost target based on various conditions. |
| 05:17 | The way any of the boost limits works is that it will target a percentage of the difference between the current ‘Boost Aim’ value, and the ‘Boost Activate’ value. |
| 05:28 | Let’s say for example that our ‘Boost Aim Main’ table is set to one hundred kPa, the ‘Boost Activate’ parameter is ten kPa and the ‘Boost Limit’ value for second gear in the ‘Gear Boost Limit’ table is sixty percent. |
| 05:43 | In this case the actual boost target will be sixty percent of the difference between the boost aim main and the activate parameters. |
| 05:52 | The difference is one hundred minus ten which is ninety kPa, and sixty percent of this is fifty four kPa, so the boost target in second gear would become fifty four kPa. |
| 06:05 | Various limit tables exist which can be used dependent on what you are trying to achieve. |
| 06:11 | The M1 will look at all the limit tables and choose the lowest value to be applied at any particular time. |
| 06:18 | For this reason before you start tuning the boost control, its important to make sure that all the tables are set to one hundred which effectively eliminates them and the boost target will be equal to the ‘Boost Aim Main’ table value. |
| 06:31 | If you are unsure which limit is active, you can look at the ‘Boost Aim State’ to find out which table has control at any time. |
| 06:40 | Lastly we are going to discuss the boost control system which includes the parameters for when the boost control system will be active as well as the PID parameters for the tuning how the system responds to an error between the actual boost and the boost aim. |
| 06:55 | First up I will move up to the ‘Boost Control Mode’ and enable the boost control sub system. |
| 07:01 | If this is left disabled, the boost control system won’t do anything. |
| 07:06 | If we move up a little further, we have some parameters to control when the boost control system will function. |
| 07:12 | First we have ‘Boost Filter’ can be used to smooth the boost pressure signal due to noise or fluctuations in manifold pressure. |
| 07:20 | This is similar to the ‘Boost Pressure Sensor Voltage Filter’ we already discussed. |
| 07:25 | A small amount of filtering can help improve control if you the boost signal is quite noisy. |
| 07:32 | Next we have ‘Boost Activate’ which defines when the boost control system will become active. |
| 07:38 | This prevents the boost control system operating continuously and it needs to be set at a pressure below where the waste-gate actuator is effective. |
| 07:47 | The ‘Activate’ parameter also plays a part in the various boost limits as we have already discussed. |
| 07:53 | This should be set relatively close to the minimum waste-gate spring pressure. |
| 07:58 | If it is set too low, the boost control system can suffer from integral windup where the integral component of the PID algorithm increases the waste-gate duty cycle to try and achieve the aim boost. |
| 08:11 | The result can be boost overshooting the target and generally poor control. |
| 08:17 | ‘Boost Margin’ provides a control region both above and below the boost aim. |
| 08:23 | Let’s say the Margin is set to twenty kPa and the Boost Aim is one hundred kPa. |
| 08:28 | When the boost pressure is less than ‘Boost Aim’ minus ‘Boost Margin’, which in this case is eighty kPa, the boost control will be one hundred percent which will help us to quickly bring up the boost towards the target. |
| 08:42 | If the boost pressure exceeds ‘Boost Aim’ plus ‘Boost Margin’ which in this case is one hundred and twenty kPa, the boost control will be reduced to zero to help reduce over-boost. |
| 08:53 | Between these two bounds, the boost control system will operate normally. |
| 08:59 | ‘Boost Margin’ is a useful parameter to help get you out of trouble however while you are tuning the system you should make the margin a large number, say sixty kPa. |
| 09:09 | The reason for this is that when the margin is hit it ceases all control which makes it hard to see what you should do next. |
| 09:16 | Once the system is tuned and running reliably set the margin a little outside normal boost fluctuation errors. |
| 09:24 | Next we have ‘Boost Maximum’, which is the point at which the boost control system will be deactivated completely and a fuel cut can be applied. |
| 09:33 | This setting can be used as an over-boost setting to safeguard the engine in case of a failure in the waste-gate system. |
| 09:40 | The last parameter in this section is the ‘Hysteresis’ setting, which applies a hysteresis to both the ‘Activate’ and ‘Maximum’ parameters. |
| 09:50 | Tuning the boost control system should be achieved first by calibrating the ‘Boost Control Feed Forward’ table which is the starting point for the waste-gate actuator duty cycle before any closed loop control is applied. |
| 10:04 | If this table is properly tuned, it will mean that any error between the boost aim and the actual boost pressure is small. |
| 10:10 | This will give fast boost response and also means the closed loop control system doesn’t have much work to do. |
| 10:18 | The ‘Feed Forward’ table can be set up as a two dimensional or three dimensional table with ‘Boost Aim’ and ‘Engine Speed’ reference. |
| 10:26 | You should adjust these axis so that the feed forward table can cover the expected range of your boost aims. |
| 10:33 | If you find that the waste-gate duty cycle needs significant adjustment to maintain good control as the engine speed increases, this can be handled by enabling the engine speed axis too. |
| 10:45 | At this point the boost control system will be running in open loop mode as the PID control parameters are set to zero by default. |
| 10:53 | This means that if the actual boost pressure is higher or lower than your target, the M1 won’t adjust the waste-gate duty cycle to try and correct the error. |
| 11:02 | You can still achieve exceptional results in open loop mode but if you want to use closed loop control that can be done via the proportional, integral and derivative gains here. |
| 11:14 | Tuning the proportional, integral and derivative gains correctly is beyond the scope of this course. |
| 11:21 | To help set up the feedforward table a simple integral control can be used though. |
| 11:27 | A number of zero point five will give a five percent change in duty cycle for every ten kpa of error between the boost aim and the actual boost pressure. |
| 11:38 | Using this configuration, the M1 will be able to make small changes to the duty cycle to achieve the correct boost. |
| 11:45 | This will enable you to find accurate feed forward numbers to enter into the table. |
| 11:51 | When entering numbers in the feedforward table you need to use the “Boost control” Channel and not the Boost Actuator Output duty cycle. |
| 11:59 | This is because on an external waste-gate the solenoid will likely be set up as an inverted output in which case the Boost Actuator Output duty will be the inverted number of the Boost Control duty. |
| 12:12 | Once the main configuration of the boost control system is carried out, you can access the more common parameters such as the boost aim and limits from the ‘Boost Control’ worksheet in the ‘Tuning’ workbook too if you prefer. |
