Knock Control

The following is copied from PCLink help

Knock Control is a feature designed for reducing engine damage caused by detonation.  Detonation occurs due to sharp increases in cylinder pressure usually caused by the ignition event happening too early (too much advance), or excessive compression pressures (eg too much boost).. Other factors can cause detonation including excessive engine temperatures, low octane fuels and lean mixtures.

Detonation can cause irreparable damage to an engine, including burnt pistons and broken ring lands.  In almost all cases detonation can be avoided by reducing the amount of ignition advance for a given load.  The Knock Control function allows the ECU to detect detonation and automatically reduce ignition advance until detonation no longer occurs.

Timing removed by the Knock Control function remains removed until next time the ECU is shut down.  For safety reasons, the ECU will not attempt to put the timing back into the engine.  Timing removed will be reset when power is cycled to the ECU therefore timing changes are not permanently stored.

Warning:  Knock Control should be used as a safety feature only.

It is not design as a tuning aid to help determine optimum ignition timing!

Knock Mode

Knock Mode selects the operating mode of the Knock Control function.  The following modes are available:

• OFF - Knock Control is disabled. 4D ignition mapping can be used
  

• ON - Knock Control is active.  4D Ignition mapping will be disabled.

Knock Target Table

The 2D/3D Knock Target Table will become visible when Knock Control is activated.  This table sets the allowable engine noise for a given RPM/Load.  Each engine will have different noise characteristics.  Engine noise is generated by mechanical clearances, valve train noise and even valves closing against the seat!  Knock control will reduce ignition advance when the actual measured level of engine noise is above the value in the Knock Target Table.  This table must be manually filled out for a particular engine.  Knock Target values can range from 0 (minimum noise) to 1020 (maximum noise).  See the Knock Control setup procedure below for more info on entering values into this table.

The Load axis used for this table can be set under the Load Axis option.  Set Load Axis to None to use only a 2D table.  The RPM and Load centres of the tables rows and columns can be adjusted by setting the appropriate Table Start and Table Increment values.

Knock Retard Table (Ignition 4D Table)

Note:  This is read only table  (only the ECU can change its values).

Note:  Ignition 4D Mapping and Knock Control share the same ignition trim table therefore these functions can not both be used at the same time.

The Knock Retard Table (displayed as Ign 4D Table) shows the amount of ignition retard caused by the Knock Control system.  Each time the actual engine noise level exceeds the Knock Target value for that particular RPM/Load 0.5 degrees of retard will be added to a cell in this table.  The Knock Retard Table can be used to determine where excessive engine noise has been detected as each cell that has its retard value changed will turn blue.

The Knock Retard Table is cleared when the ECU is turned off.  Ignition changes made by the Knock Control function are NOT stored permanently.  The Knock Retard Table can also be cleared by setting Knock Mode to OFF, then back to ON.

Knock Retard Limit

The Knock Retard Limit sets the maximum amount of ignition timing in degrees that will be removed (or maximum amount of ignition retard).  This limit avoids the ECU removing too much timing if the value in the Knock Target Table is set too low.

Runtime Values

The following Runtime values can be observed under the Ignition Runtime Values tab to monitor the state of the Knock Control function:

• Knock Level - The current measured engine noise level.

• Knock Target - The current value as interpolated from the Knock Target Table.

• Ign 4D/Knk Trim - The current value as taken from the Knock Retard Table.  This shows the amount of retard caused by the Knock Control function at the current RPM/Load.

Knock Control Setup Procedure:

The following procedure is a guide to setting up Knock Control.  Unfortunately the amount of engine noise measured before and during detonation varies significantly from engine to engine, with sensor type and sensor location.  Experience is required to determine the best Knock Control setup.

At all times during setup, make sure that an audible knock detection device is used (such as a KnockBlock with headphones).  Avoid unnecessarily causing detonation as engine damage may result!

1.    Ensure the engine is tuned to its final optimum state, particularly ignition values.  Remember that Knock Control is used as a safety feature should  engine operating conditions change, not to determine the final ignition values.

2.    Ensure 4D Ignition Mapping is turned OFF.
3.    Set Knock Mode to ON.  This will activate the Knock Target Table and clear the Knock Retard Table (Ign 4D Table).
4.    Select the desired Load Axis.  This will typically be the same load axis as used for the ignition table.  Set Load Axis to OFF if only a 2D table is to be used (ie engine noise level vs RPM).
5.    Set up the Knock Target Table.  The following hints may be useful:
·    Use the Knock Level Runtime Value (under the ignition runtime values tab) to monitor the current engine noise level.
·    The engine must be run at various RPM and load values to determine the engines 'non-detonating' noise characteristics.
·    The value entered in the Knock Target Table will be the amount of engine noise that must be exceeded before ignition timing is decreased.  Therefore, this value should be the 'non-detonating' noise level plus some headroom.  Typically the value entered in the Knock Target Table will be about 10-20% higher than the 'non-detonating' noise level.
·    Enter high Knock Target Values in areas where Knock Control is not required such as idle, cruise and free revving.
6.    Set the Ignition Retard Limit to the maximum amount of ignition timing allowed to be removed by the Knock Control function.  This will typically be between 3 and 10 degrees.
7.    Perform power runs and operate the engine in all load/RPM areas where knock control is to be used.  Check the values in the Knock Retard Table (Ign 4D Table).  If these values are not zero (or have turned blue) then the Knock Control function became active in those areas.  It is up to the tuner to decide if this was due to the occurrence of detonation or if the Knock Target Table values are too low.  Remember the Knock Retard Table (Ign 4D Table) is cleared each time the ECU loses power.

Copyright 2006 Link ElectroSystems