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Link G4 Plus Software Tutorial: Knock Control

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Knock Control


00:00 - Knock control is an advanced option that can be used to combat detonation or knocking by automatically retarding ignition timing when knock is detected.
00:09 Setting up knock control is complicated and time consuming and needs to be approached carefully to achieve an effective result.
00:17 It's also important to understand that knock control is not a fix for a poorly tuned engine and should not be relied on to keep your engine safe.
00:25 It's designed as a safeguard in case poor fuel quality or excessive temperature results in detonation.
00:33 The knock control system can be accessed through the knock control menu and the ECU settings menu.
00:39 Click on knock control to get started.
00:42 First we need to configure the type of knock control system being used.
00:46 This will depend on your ECU as some contain built in knock control and others will interface with the external G4 knock block.
00:53 Choose the relevant setting based on your application.
00:57 If you are using an external knock block for knock control, you will need to set up a digital input configured as digital knock feedback and an auxiliary output configured as knock window.
01:07 You can find more information about setting these in the knock block manual.
01:12 The next job we have to do is set up the knock frequency channel.
01:16 This is used to tell the ECU what frequency knock is occurring at and this makes the knock control system more accurate.
01:23 There are two ways to set the knock frequency, we can calculate it using the calculation contained in the knock audio section of the help file here.
01:32 All we need is the piston diameter and this is proven to be very effective.
01:37 Alternatively if you have a knock block you can sample the engine noise during knock and use the knock audio function to analyse the actual knock frequency.
01:46 This needs to be done with care as you need to induce knock in the engine and this can potentially damage the engine.
01:53 In this example, we're going to select 7 kHz narrowband.
01:57 Gain channel selects the gain to be applied to the knock input.
02:02 This is used to ensure we have good resolution on the knock signal.
02:06 We will start with this set to one.
02:10 This may need to be adjusted later if our knock levels are too low to distinguish knock.
02:15 As the knock control system functions it will apply ignition trims any time knock is detected.
02:22 We can choose to keep these trims or clear the trim tables any time the ECU power is cycled.
02:27 Now we need to set the knock window which is the window of crankshaft position that the knock detection system will look for knock.
02:35 Window start is the degrees of crankshaft rotation after the ignition event occurs and window length is how long the window will be.
02:44 We're going to select 10° as our start point and a window length of 50°.
02:50 There are some tips in the help file to help you adjust these numbers.
02:55 Ignition retard limit defines the maximum retard that the ECU can apply to cope with knock events.
03:01 Remember that we shouldn't be relying on the knock control as a replacement for proper tuning so normally a small amount of retard should be adequate.
03:09 We're going to select 4°.
03:13 Retard gain defines how quickly the ignition will be retarded.
03:16 Larger numbers will retard the timing faster and we're going to enter a gain of 0.5 here.
03:24 One great feature of the knock control system is that once knock is removed, the ECU can then start adding timing back in to restore engine power.
03:32 The advance delay defines how long the ECU must see no knock events before advancing the timing.
03:39 This works in conjunction with the knock advance which defines how fast the timing will be added.
03:45 We're going to set the delay to one second and the advance rate to 0.5° per second.
03:50 Lastly we have some lock outs for both RPM and throttle position so we can control where we want the knock control to be active.
03:58 We're going to allow knock control anywhere above 1000 RPM and 10% throttle.
04:04 Once the initial setup is complete, we need to allocate tables for the ignition trims on each cylinder.
04:10 These tables can be allocated through the knock control menu by clicking on table allocation.
04:16 Normally we would allocate each cylinder to its own table so we have individual cylinder knock control.
04:23 Once configured, these tables can be reached through the knock control menu and we can view them to see if any trims have been applied in the knock control system.
04:32 It's advisable to configure the axis on the ignition retard tables to match the main ignition table.
04:39 If you are seeing different knock levels from some cylinders, you can adjust the gain for each individual cylinder until the background noise levels are matched.
04:47 This will give the most accurate control.
04:50 These adjustments can be made through the cylinder setup option in the knock control menu.
04:55 Now let's take a look at our knock target table.
04:58 This table can be accessed through the ECU settings menu under the knock control heading.
05:04 This is a 3D table that normally would be set to have the same axis as our ignition table.
05:10 This table sets the threshold that the ECU will consider as knock.
05:14 This table needs to be tuned to account for the level of background noise from the knock sensor input and for this reason the knock threshold will increase at higher RPM.
05:24 Tuning the knock target table needs to be done in conjunction with input from an audio knock sensor so that you can validate if the engine is actually experiencing knock.
05:35 Once the target table is tuned, you can test the system by purposefully advancing the timing enough to cause some light detonation.