MoTeC M1 Software Tutorial: Injector Configuration
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Injector Configuration
11.34
| 00:01 | One of the bigger changes with the M1 is the way the fuel injectors are dealt with. |
| 00:06 | Since the M1 uses a volumetric efficiency fuel model, when we are tuning the engine, we aren’t directly requesting a given fuel injector pulse width. |
| 00:15 | Instead, the efficiency table describes the mass of air entering the engine. |
| 00:20 | If the ECU knows the mass of air entering the engine it becomes relatively straight forward to calculate the required volume of fuel to achieve a target air fuel ratio or mixture. |
| 00:33 | In this case the ECU can now request a fuel volume. |
| 00:38 | The next step in the fuel model is for the ECU to calculate the injector pulse width required to deliver the requested fuel volume and this is achieved using the data entered into the Injector setup worksheet. |
| 00:51 | Obviously this data is quite critical as the whole fuel model relies on its accuracy. |
| 00:58 | In the past, when we thought about injector flow we may have considered the rated flow value of the injector in cc’s per minute or pounds per hour, and perhaps the injector dead time or latency value. |
| 01:11 | This only describes part of the injector’s flow though, and the M1 takes things further with full injector characterisation map. |
| 01:20 | Before we get into the setup, its important to understand what this means. |
| 01:27 | If we take an injector and measure the delivered flow over a range of pulse widths, we end up with a graph that looks something like this. |
| 01:36 | First of all we can see that when we start supplying a very small pulse width to the injector, nothing happens. |
| 01:42 | No fuel is supplied. This is due to the mechanical design of the injector as it takes some amount of time to respond to the signal from the ECU and actually overcome the inertia of the internal valve assembly before it can start flowing. |
| 01:58 | This time is known as the dead time or latency and in MoTeC’s hundred series ECUs this was called the ‘Injector Battery Compensation’. |
| 02:08 | If we now look at the top right corner of the graph we can see what we would end up with the injector was completely open 100% of the time. |
| 02:17 | These are the sort of numbers people commonly use when referring to injector size. |
| 02:23 | In general we will see a reasonably consistent relationship between injector pulse width and injector flow. |
| 02:30 | By this I mean that if we double the injector pulse width, we double the fuel flow. |
| 02:36 | This isn’t the case however at very small pulse widths where the injector is only just open and flowing fuel. |
| 02:44 | We can see that in this area the flow is quite non linear. |
| 02:50 | The majority of ECUs ignore this non linear area of injector flow and simply assume a straight line relationship between flow and pulse width. |
| 02:59 | The result is inaccuracies in the fuel mixture in the non linear area of injector flow as the fuel delivery calculated by the ECU doesn’t match reality. |
| 03:10 | While this might not seem too important for installations where the engine doesn’t operate in the non linear area of flow, particularly in performance applications with large injectors, the non linear area of flow may expand into a significant region of the low RPM and low load running of the engine. |
| 03:29 | The Injector characterisation tables in the M1 exist to remove these inaccuracies so the ECU always knows what pulse width to request to achieve a specific fuel volume. |
| 03:41 | Now that we’ve covered the theory, let’s look at what we need to do to set them up. |
| 03:47 | The first point to understand is that we aren’t going to be able to come up with these characterisation numbers by ourselves. |
| 03:53 | MoTeC or your MoTeC dealer will be able to provide characterisation data for many popular injectors, or if data isn’t available for your particular injector, you can send them in to MoTeC through an authorised dealer to have them characterised. |
| 04:08 | Alternatively some injector suppliers such as Injector Dynamics are now making this data available ready to load straight into an M1 calibration. |
| 04:18 | Since the fuel model relies heavily on this data, it needs to be correct for the ECU to do its job properly Let’s go through the worksheet in order, and we will start with the Fuel Injector Output setup. |
| 04:32 | The first parameter here is ‘Engine Charge Cooling Gain’ which describes the cooling effect of the injected fuel on the intake charge. |
| 04:40 | We are going to look at configuring this a little later in the course but its important to make sure there is a sensible number in here to start with, somewhere in the region of 13 to 25 is a good starting point. |
| 04:53 | Next we have ‘Engine Speed Reference Test Speed’ and ‘Test Output’. |
| 04:58 | These can be used to test outputs by making the ECU function as if the engine was operating at the chosen test speed. |
| 05:06 | Once the test speed is selected, we can then choose which output we want to test from the drop down menu here. |
| 05:13 | This is a good place to test the injector outputs are operating and wired to the correct cylinder. |
| 05:19 | The next parameter we have is “Fuel Timing Limit’ which the ECU uses to describe the last point before TDC on the compression stroke where fuel can be injected. |
| 05:30 | This can be timed to coincide with the intake valve closing angle to help ensure fuel isn’t being injected against a closed valve. |
| 05:39 | This works closely with the Fuel Injection Timing table that we are going to look at a little later. |
| 05:46 | The important part to note is that if the end of injection angle is later than the Fuel Timing Limit, the injection pulse will be reduced and the engine will run leaner than expected so entering the minimum value of 120 is a good starting point. |
| 06:03 | The Peak and Hold current settings are used to define the operating current supplied to the injector drives. |
| 06:10 | If you are using low impedance peak & hold injectors, these parameters describe the peak current used to initially open the injector, and the holding current that is used to keep the injector open. |
| 06:22 | For high impedance or ‘Saturated Drive’ injectors, the peak current is used for error checking as this will trigger a diagnostic error if the peak current value is reached. |
| 06:33 | We also have ‘Fuel Injector Peak Time’ which again is a diagnostic check on the operation of the injectors. |
| 06:41 | The values we have just talked about will be supplied for your particular injector type by MoTeC so you don’t need to worry about coming up with the correct values on your own. |
| 06:53 | The last parameter here we need to configure is the ‘Fuel Injector Type’ which describes how the injector will be driven. |
| 07:01 | Injectors are broken up broadly into High Impedance, where the resistance across the injector measures between approximately 8 and 16 ohms, and low impedance where the resistance measures between approximately 0.5 and 6 ohms. |
| 07:16 | High impedance injectors use what is called a saturated drive, while low impedance injectors use a peak & hold drive. |
| 07:25 | The M1 also offers a special ‘Extended Peak then Hold’ mode which can be used for some low impedance injectors which are particularly slow to respond. |
| 07:35 | This setting extends the peak current until the ‘Fuel Injector Peak Time’ parameter has been reached. |
| 07:42 | The last job here is to assign a fuel injector output resource to each cylinder. |
| 07:48 | This can simply be done from the drop down menu here for each cylinder. |
| 07:53 | Since the firing order is already programmed into the M1, we can assign the resources in numerical order. |
| 07:59 | i.e. Cylinder 1 would be configured to ‘Injector 1’ resource, and cylinder 2 to ‘Injector 2’ and so on. |
| 08:07 | Now we can look at the actual injector characterisation tables. |
| 08:12 | We have a separate adjustment available for each of the injector drives on a particular ECU and they are listed here. |
| 08:20 | If we click on a cylinder, the relevant tables are shown here to the right. |
| 08:25 | These injector characterisation tables are a four dimensional table, and include a number of tables at different battery voltages. |
| 08:34 | This is how the ECU accounts for fluctuations in battery voltage. |
| 08:39 | At each point on the battery voltage axis, we have a conventional 3D table that defines the requested fuel injector output volume in micro litres versus the differential fuel pressure. |
| 08:51 | With differential fuel pressure effecting where in the table the ECU is taking the value from, this is one reason including a fuel pressure sensor can improve the accuracy of the ECU. |
| 09:03 | Again remember that we aren’t required to come up with these numbers so don’t get put off by these tables. |
| 09:11 | he injector linearisation tables are only used to describe the area of non linear flow which usually extends to a pulse width of perhaps 2 to 3 milliseconds depending on the injector. |
| 09:24 | Beyond this the ECU can consider the injector flow to be linear and it can use the ‘Reference Flow’ value for the injector which we enter here. |
| 09:33 | The reference flow will be measured at a specific ‘Reference Pressure’ so it’s important to enter this correctly too. |
| 09:41 | Lastly we have the ‘Injector Minimum Volume’ setting which basically describes the minimum volume of fuel that it’s possible for the injector to deliver. |
| 09:50 | If the result of the fuel calculation ends up with a requested fuel volume smaller than this volume, the injector will not be operated. |
| 09:59 | As you can see, there is a lot of data that we need to enter into this worksheet, but fortunately there are a few ways of speeding up this process. |
| 10:08 | We have already looked at how we can use the compare function to copy injector data from one calibration to another, and this is a good way to set up a calibration up if you already have another calibration running the required set of injectors. |
| 10:23 | We can also use the import function which we have also discussed previously, however this is only useful for the actual characterisation tables, and ignores the current settings as well as the reference flow and pressure. |
| 10:38 | If you want to import an entire injector calibration into your package, the simplest method is to use the ‘Import Configuration’ option from the ‘File’ menu. |
| 10:49 | To use this you will need a valid injector calibration file from MoTeC to suit your particular injector. |
| 10:56 | We can then simply click on ‘Import Configuration’, select the required calibration file and the injector calibration data will be imported. |
| 11:07 | A results box will confirm the import was successful and you can scroll through to see exactly what parameters have changed. |
| 11:16 | If we now close the results box, we can see that the injector data has changed. |
| 11:22 | This concludes the main input setup into the M1, but there are still a couple more worksheets to go through to cover the ECU outputs and we will deal with these next. |
